Question on quick voltage ramp-up

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Anze A Ursic
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Question on quick voltage ramp-up

Post by Anze A Ursic »

Hello,

I've posted before in the HV section of this forum about the Spellman DF3 power supply I have, but this pertains to something else. The supply in question requires a minimum voltage setting of about 15-16kV to which it ramps up in about 10 seconds. There doesn't seem to be a setting that changes this. I am curious how bad this is in practice for a fusor. I've only ever ran my device to 5kV at about 15mTorr. We have a better HV input now, a much better 18" long ballast resistor, etc, but I am still worried that this quick ramp-up may cause instabilities in the plasma or something else.

Would one way of countering this effect be to pump down the chamber to very low pressures (<1mTorr), have the supply ramp up but not form plasma, and then slowly increase the pressure, letting the plasma form? Then stabilize the pressure at 15mTorr or so and actually continue slowly increasing voltage? We do have a really nice pressure controller so we can just set it to 15mTorr and it'll go there quick and stabilize.

Maybe I'm overthinking this, but again, I've only ever done 5kV and I ramped up to that slowly (probably 1-2 minutes or more), but I may be overly cautious, in which case, let me know! Any info is appreciated!

AAU
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

You have the right idea. If you are forced to a minimum HV at 15kv, do not admit any gas at all! bring the gas in very slowly and bring the voltage up from there while jockeying the gas at the same time. It is how the fusor is run regardless of initial voltage. Tune for minimum smoke.

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Anze A Ursic
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Richard, thank you! When you say "bring the gas in very slowly" are we talking about air or Deuterium?

My understanding is that fusors are operated by going to about 10-15mTorr vacuum, sparking a plasma and then increasing the voltage to the typical 30-35kV ranges. Then the turbopump is turned on, which evacuates all the remaining air and the pressure drops to below mTorr, the plasma extinguishes and then Deuterium is slowly added, which brings up the pressure back to the 10-15mTorr range and you (hopefully) get fusion.

In my case, should I evacuate the chamber to below the mTorr range, let the power supply ramp up to 15kV then reintroduce some air to raise the pressure to 15mTorr wherein I'll already get a plasma and then continue raising the voltage to 30-35kV, then pump down again to below mTorr and introduce deuterium? Or should I evacuate the chamber to below mTorr, get to 15kV and just continue raising the voltage to 30-35kV with no plasma formation (because of the very low pressure) and then directly introduce Deuterium, skipping the air plasma formation?

This may be overly pedantic, but I am trying to hone down every single fine detail for this run to be successful. Again, any feedback is much appreciated!

Anze
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

Hi Anze,

You’ll want to get your pressure down via turbo before letting in deuterium. Don’t let any air into the chamber, it’ll mess up operations.

Once you’ve dropped below 1 micron, you should start adjusting your chamber valve in preparation for deuterium flow.

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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

Richard does mean add deuterium gas. One does it slowly via a leak type valve so the current does not run away as the high voltage starts to really create a plasma. Just as Matt is asking about having a low enough starting vacuum (i.e. 10^-4 torr or lower) the voltage at 14/15 kV is still too low to create any real conductive path under those very low vacuum conditions. This allows one to use deuterium gas to control the fusor; in fact, this is exactly how I control my fusor - it really helps to prevent as many runaways - of course, one has to have a 'leak valve' that releases the high pressure behind it extremely slowly into the chamber. Hence, normal valves are unsuitable for fusor work. Some people use a pin hole cap with a more normal valve to better enable gas flow control.

For instance, once you ignite a plasma at 15 kV (make sure the current is in a safe range), you'd never want to 'ramp' up the voltage at that fixed pressure because otherwise, a massive current surge would occur (and one could damage/destroy the power supply!) So, with chamber at 10^-4 torr and the power supply at 15 kV, slowly start raising the chamber's pressure. At some pressure the plasma will ignite - make sure your current isn't exceeding your systems safe operating conditions. Then under these conditions, one has to decrease the pressure in order to raise the voltage for an active plasma already at 15 kV.

So, the plasma is ignited with deuterium gas at 15 kV; then as you lower the gas inflow rate, you closely watch your current and add more deuterium gas to keep the current up in a safe range. Keep following this procedure until you reach the max voltage you plan on using. Do note a runaway condition with the current is likely to occur and you must lower the voltage to protect your power supply. As the system 'cleans', this will occur less often.

Critical point to note: Always keep the current in the safe known operating range for the transformer and diodes! Burning out a diode is a pain - destroying your transformer will ruin your day (or many weeks till you decide what to do about a new one.)

For a fusor run, using air as the trace gas to create a 'first' light plasma for the run would be rather counter productive - one always uses deuterium for any real fusor run. I only use air when I 1) just checking the power supply system 2) want to burn out the chamber to help reduce known trace contaminates and don't want to waste deuterium gas. Bottom-line: best not to use air to establish a plasma. Start with deuterium.

Also, no where did you mention throttling the chamber to reduce the turbo's performance. Otherwise, you will waste a vast amount of deuterium gas trying to reach the operating pressure.

A few asides FYI: pressure for a fusor isn't absolute so the pressure you are saying may or may not work for your fusor - it can vary depending on many parameters of your system. Also, measurable fusion gets going near/above 20 kV but as one approaches/exceeds 30 kV it is far greater.
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

As noted above in the responses.....
You have a vacuum system to take the air out!
Why re-introduce it?
You are struggling to get a pure deuterium atmosphere into the chamber.
Whenever fusion folks are talking about introducing gas into the chamber it is only deuterium.
Operating a fusor is an art and not a science. Like all art, technique is needed and is developed in the hands-on experience from the doing.
I have written extensively on this in the FAQs.

viewtopic.php?t=9174

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Ah, ok, so I think I get it. A true fusor run is no air any time and it's pressure controlled, not voltage controlled. So I can go up to 30-35kV at extremely low pressures, then control the pressure via Deuterium flow to get plasma and (hopefully!) fusion. I see.

Two notes: I have an MKS mass flow controller that can be remotely operated, so you can set different flow rates rather quickly to increase pressure. It's in SCCM which is good because I know a lot of people here talk about flow rate in ml/min, so that's a 1:1 conversion factor. The chamber we have is pretty big for fusor applications, so I may need more flow than the typical run.

Further, I have an MKS T3B gate valve controller just before the turbo pump so turbo is easily throttled. We actually use it in pressure control, so you set the pressure and it reads the voltage from the pressure gauge to get to the proper pressure. It is kind of slow in terms of reaction time, so I may not rely on it solely to get to the 10-15mTorr range for fusion but it's very good at stabilizing the pressure at a specific point, so that's excellent. Once fusion starts I'll just tell it to do 14mTorr (at this range, it jumps +/- 1mTorr every few seconds), so the run should be steady.

Thank you!

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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Voltage determines the pure probability of quantum tunneling. (fusion) Low voltage-low fusion probability (cross section)
Pressure determines how much fusion fuel is present per unit volume in the reactor that can be turned into fusion ready deuterons.
Current determines how many deuterons, (ionizations of the gas), that might be present at a maximum to do the fusion probability dice throw.

All three are critical to doing fusion never think one is better than the other, though voltage sets a detectability limit for the amateur.

viewtopic.php?p=86189#p86189

viewtopic.php?p=89829#p89829

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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

Maybe I wasn't clear but it is a bad idea to have the power ramped all the way up to full on the variac (setting 35 kV) and then try and add deuterium to 'strike' the plasma. Such a situation would very likely create a runaway current that could damage or even burn out your transformer. Certainly it will be hard on the diodes - of course, that is what the ballast resister is supposed to help prevent but it is best not to depend on that to prevent damage as you frankly lower the voltage to lower the current. Besides, you'll likely then end up below 15 kV and have to start over. So, get a low vacuum, set your system to 15 kv and slowly ramp up the pressure to create a plasma (likely the current will runaway and you'll need to lower voltage/pressure to control the situation.) Then when all is stable, then adjust pressure and voltage to achieve the 35 kV or so. Since your supply automatically starts at 15 kV, that should be your starting point, not 35 kV.

Controlling flow also requires adjusting the throttling valve for the chamber to the turbo - so that can make controlling chamber pressure a bit more difficult.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Ok, that make sense (again!). Wish I could try this a few times myself but since even with the initial 15kV voltage we are technically producing X-rays, we cannot do it without an agent present measuring exposure... kind of sucks, but is what it is.

And I do have a nice 125W, 18" long 100kOhm resistor in series with all of this to hopefully prevent any damage in case of a runaway.

Anze
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Also, Dennis, while I now understand balancing the pressure and voltage/current, the final pressure at fusion voltages (~30-35kV) should be around 10-15mTorr right? Or should I not care about being in that range and just focus on maintaining a nice plasma at those voltages?

Anze
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

Good question - as I mentioned, the exact pressure your chamber requires will depends on your system design and equipment (to some extent.) Generally, it is, as you suggested, between 5 to 15 microns pressure and most people do operate their fusor in this range (smaller chambers have higher operating pressure.) Of course, it is possible your detector is off in calibration and the reading might then be somewhat different.

However, the issue, as you pointed out, is your power supply is unique: it has to start at 15 kV (mime starts at "0" using a variac.) This makes the process more difficult. So, what you need to do first is get the supply to turn on without a 'runaway' of current. To do this I'd suggest that you get the fusor below 1 micron, and this should enable you to get the power supply to turn on (it reaches 15 kV) without striking a plasma - yet. Then carefully raise the deuterium pressure in the chamber so your fusor becomes conductive - i.e an electrical plasma/glow occurs.

One must watch both the chamber and the current very closely - as the pressure in the chamber rises - using the leak control rate of deuterium entering the fusor - at some point the plasma will ignite (and the current will rise rapidly/spike.) As long as the current doesn't exceed your supplies allowed value, you have an acceptable pressure to start with. If the current jumps too high, lower the pressure and/or voltage to control the current (however, your supply can't be lower than 15 kV so that is then problematic.)

If the current is acceptable and you have a stable plasma at 15 kV your ready to begin raising the system's voltage. To raise the voltage without a current run away you need to lower the chamber pressure first (current will drop.) To compensate for the current drop (i.e. keep the current at an acceptable value) you slowly raise the voltage (say 17 - 18 kV). Keep up this iteration process until you 1) get to the desired operating voltage or 2) get a high enough rate of counts on your neutron detector that enables you to test for real fusion.

As you attempt these steps, the current is likely to 'runaway' requiring you to lower the voltage to get the current back to the desired range. Hopefully, this doesn't extinguish your plasma or shut the supply down.

Your power supply information should enable you to determine the max allowed current. Obviously, try not to exceed that value - that is why fusors need ballast resisters - they prevent damage to the transformer or diodes from a sudden current 'spike/runaway' giving you time to lower the voltage before supply damage occurs.

The process requires experience and depends on a host of parameters so the only way to determine how your system performs is to try it. As your system is run and 'cleaned' you'll find it gets easier to start up and maintain a steady plasma with no runaways.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Thanks again, Dennis. I guess now having the T3B pressure controller is more useful than ever. I do understand what you are saying and I'll adjust my plan accordingly, but out of pure curiosity, why couldn't one go to the final voltage (~35kV) at 10^-4 Torr and then slowly add Deuterium? It seems to me as though if one had an incredibly precise way of inputting deuterium where he could vary the flowrate pedantically and slowly, the runaway current effect wouldn't take place, or am I wrong?

Again, just curious. The closer I get to a true fusion run, the more fine details I learn. Shame I can't practice with air plasma but the second we expect to get X-rays, we're under the purview of the health and safety office, which is completely understandable, just limits my experimental experience before going into the real thing.
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

One certain can do as you suggest; just that the danger of a drastic runaway that damages your supply increases with increased voltage. If it is computer controlled (the power supply) and it can react in fractions of a second, and with your ballast, likely all would be ok when trying that method. However, that might take a long time before the fusor started to behave and create a stable plasma on first light up (load the walls, remove trace contaminates.) Meaning you might struggle to get stable operation started. Still, up to you to try what you want and see what is what. As long as you are confident the supply will survive, then I guess why not? Can learn from the experience no matter the outcome.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Somewhat unrelated, but I just noticed whenever I opened up the main gas inlet valve the pressure immediately rises. At first I thought my swagelock tubing system was bad, so I redid it and tested it, and noticed the MKS mass flow controller we use (179a11cr38m) is not actually rated for such low pressures and it seems to leak badly. To a point where we can't get past 20mTorr with the turbopump. So now I'm curious how other people control flow of D2 remotely. I know several people who have manual valves next to them, but I'll be about 7m removed from my device in another room, so how would I go about controlling the pressure remotely? Are there any inexpensive ways this could be done or am I gonna have to cut 7 meters worth of tubing to get the bottle next to me?

Anze
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

I have been following this and Dennis has given great advice. You have a special limitation that none of us have as we are private, self-funded and private property owners with our fusors in our homes, private labs, garages or outbuildings. We get to police ourselves. We are the purse holders, machinists, electronics builders, instrumentational specialists, the vacuum system experts and technicians. We are the rad-safe officers as well in our situation. As such we, have all gained a lot of experience over these many years in this type of system and, as noted, know what to expect in the way of radiation emissions from the fusor at all levels of voltages via our own measurement taken and recorded

I have held out of this discussion due to your special situation and need to please many masters who seem to have little understanding related to fusion or the amateur fusion effort related to operation of this type of device. Hopefully, once you radiation department actually measures around the operating device, they will come to realize the fusor's rather benign nature. At 7 meters distant, I am sure they will find any radiation, be it neutron or X-ray, to be immeasurable.

If you are forced to operate at this distance the cheapest solution would be the 7meters of gas line to the device. Operating, flowing deuterium, (differential pumping in-effect is what is needed), and controlling it is critical.

All the best of luck on solving this issue.

Richard Hull
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Re: Question on quick voltage ramp-up

Post by Liam David »

I would advise against a 7m gas line for deuterium purity reasons relating to conductance. You should be able to find a suitable MFC on Ebay for <$200, and probably <$100 if you look long enough. Something in the 10-20 SCCM range should work fine.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Thank you Richard for your response!

Liam, we actually have a bunch of MKS MFCs here but the issue is they're not rated for such high pressure differentials. I'm struggling to find one on Ebay that would suit my needs or maybe we could use the ones we have and I'm missing something?

Not sure how much money we can still spend, but worst case scenario I could attach a gear to a manual valve there and get a stepper motor with a gear to open / close it. If I make a large enough gear size differential it could be pretty sensitive too I suppose, for minute adjustments.

Either way, I'll try and find a solution with something we already have.

Anze
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

I assume here the dual gauge step down regulator has been tried to near atmospheric pressure and has already failed.

One could make a work-a-round. Use an empty small gas cylinder and evacuate it (turbo); then back fill with anywhere from a 50 torr
to ? of deuterium gas; then use your flow controller - now the differential pressure is significantly smaller - to control inflow to your chamber. Obviously, it requires testing to determine the max. pressure that the unit can withstand - easy to determine.
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

I got a near perfect condition MKS MFC for $71 on eBay. It’s a 10sscm type and works great and has a web interface that makes setup and zeroing a snap. Keep watching eBay and be prepared to snipe! I see this being sold new for over $4k still. Deals are out there if you look.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Matt,

Any chance you could provide the model number? Mine is a MKS 179a11cr38m. But we have a metric ton of these things in the lab so I'll go check now to see what we have and if we have anything close to what you have.

Anze
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Re: Question on quick voltage ramp-up

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Hi Anze,

It’s a GM50A013101RMM020.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Interesting, the maximum pressure differential seems to be 10-40 psid for your model, which is also outside the fusor pressures right? Honestly, I'm not quite familiar with mass flow controllers, so I'm wondering if mine just has a bad seal or something. Also, yours seems to have a maximum inlet pressure of 150 psig. But I assume you're using a lecture bottle or something similar of D2, which is often 1500-2000 psig, so how do you account for that?

Any help appreciated, thanks!
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

I’m using a syringe with deuterium in it. To be fair, it gets touchy under 1sccm of flow.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

In my infinite wisdom, I just realized the thing I attached onto my chamber is a mass flow METER, not CONTROLLER.... brilliant.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Hello again, everyone!

So after taking your advice, I was able to start igniting some pretty cool plasmas with Nitrogen (saving Deuterium for the actual tests, once I'm familiarized with this procedure). However, I keep getting a problem; I set my power supply voltage to its minimum value of 8.5kV (not 15-16kV as previously thought), strike a plasma and it's great, it's stable and it stays like that for a while. However, soon after raising the voltage above 10kV, there are massive fluctuations in current and they're nearly impossible to control with the pressure control. Even if I leave the fusor alone at, say 12kV and 4mA, current starts shooting one way or another. Sometimes you can see these quick bursts of light like in this video of my run today (check the very end, just after 50 seconds): https://www.youtube.com/watch?v=Iqbn_KJtKco

Or, on the other hand, sometimes the plasma just extinguishes without warning. We have thus not been able to get a stable plasma past around 11-12kV... I am using a Spellman DF3 power supply with a remote control system, a 18" 100kOhm 125W resistor and an MKS MFC for pressure regulation to our gas (Nitrogen now, Deuterium later).

Any help appreciated. I am really looking to push this thing to 30-35kV for fusion voltages.

Anze
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

Sounds like you’re burning off “junk”. I see this whenever I’ve opened my chamber and messed around inside (swapping cathodes for example).

This is why I keep my voltage low and work my way up over several days/weeks.

Does your pressure swing up and down a lot while this is going on?

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Hard to say about pressure swings, I monitor it in my Labview gui but the refresh rate is not that high so large, quick spikes often go unnoticed. I will say though, the current spikes up a lot, so I assume the pressure does too. Do I just keep burning plasma until all the smut is disintegrated then? And why does it happen at higher voltages but not really at 8.5kV?
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

This is a combination of issues; as Matt say's, you are burning off contaminates AND most likely metal from the cathode (as vapor.) These can cause havoc with current/voltage control. It takes time to learn how to quickly adjust voltage, vacuum flow rate (via the main butterfly/bellows/gate valve) and/or gas flow (via leak valve) to control these swings. All new fusors tend to have these issues. But as the chamber seasons, and you gain experience these issues tend to get very easy to control.

At higher voltages, water vapor more readily breaks down and your cathode more readily sputters (lower vapor components.) These take awhile to burn off in a manner that the fusor is more stable. Once my fusor has been closed and contaminates burned away, I have next to no issues striking and controlling the plasma for long time periods. But hic-ups do occur even then.
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

So how long (hours/day and days) should I leave a plasma ignited to burn it all off? Or I assume this is not a one size fits all scenario. Also does running it hotter, so that the electrodes start glowing, help this process?
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

Hard to say. It takes me around a week of running for around 30 minutes a day to get “clean”. You’ll notice that as you run, you’re able to push voltage higher and higher. Don’t rush it, those arcs can be damaging.

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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Matt has rediscovered my old saw about daily improvement in fusor action. I have posted such continuous improvements in a running, updated listing each day. This is most normally the case just before my early October hosting of the HEAS event. Many travel from afar for the fun, flea market, camaraderie, and to see a good fusor in operation. I must not disappoint and, therefore, need to get the fusor in peak performance mode.

My fusor lay dormant for the vast portion of the year. As such it rises to atmosphere within about 1 week after shutdown from a super run and sits unused for months at a time. Now, I can demonstrate fusion to anyone on the spot in an impromptu run at any moment in time. Unfortunately, it will be a weak one in spite of being definitive. I might after 1/2 half-hour of running be able to show 1000 cpm on a neutron counter continuous fusion output.

However, give me 6-8 consecutive days to load the walls over a period of 30 minute runs each day and I can, on that 6th or 8th day, give you over 100,000 CPM on the neutron counter within 10 minutes of startup. It is a "conditioning period" or "wall loading" period as I have termed it.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Well like I said, below 10kV we're pretty stable. Should I just leave it there for a while and try running it as much as possible every day? Also does it matter what gas we're burning? I don't wanna waste the lab's Nitrogen supplies and I can't burn Deuterium for this because we only have one lecture bottle, so can air plasma do the trick?
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

In my experience, no! You must load the walls with deuterium. I have fully explained my reasoning over these many years in over many posts. many of the better fusioneers, such as Matt, hang in there and pick up on this process.

The art of running fusor is gained over time. With the obtaining of this carefully developed artifice comes the conservation of deuterium in preparatory run periods. This artifice can be different for different fusors. The science is limited here, but well understood....Crash deuterons together and you get fusion. All the rest is mechanical, electronic assemblage coupled with artifice in the amateur fusor. Give me $100,000 and I can, with the proper mechanical assembly, the proper electronics, assemble a small fusion system that is a turn-key, instant performer that needs no more artifice than turning on the power.

A good, starving fusion artist can, with less than ideal mechanics, relatively poor electronics and marginal entry skills do fusion! A boat load of them over the last 23 years have done it here. I will add the vast majority did it so marginally poorly that the moment they registered a "win", they left the field....It was a lark for them. They forced the science with just enough art to do fusion.

As regards the need to conserve deuterium, I am on my second 50 liter cylinder of deuterium after 20 years of doing fusion. It is an art.

Richard Hull
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

If you use air, you’ll pull in moisture with it. Sort of like drinking salt water to quench thirst :-) You need to get moisture out of your chamber.

Like Richard said, you shouldn’t be using up much gas if you have your turbo/diff throttled back. I’d switch over to deuterium so you can clean and load at the same time in anticipation of getting the green light to go for fusion.

-Matt
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Read this FAQ and the PDF. It is there for a purpose. The cooling issue is not critical to doing fusion, but only to doing it better. The theory of wall loading is the important point.

viewtopic.php?t=13736

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

I guess my main point of concern is that mine and Matt's MFC is leaking air into it, and so I am wondering if the plasma I'll be getting will be pure Deuterium or contaminated with air.

Also by throttling the turbo, doesn't that inherently bring air into the system? So the plasma doesn't have to be perfectly clean?
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

Running the plasma longer certainly helps; ditto allowing the electrode to heat up and glow (but only for short times; don't want to sputter away the cathode!) I burn my system with deuterium because it is highly reactive but I do have a lot of deuterium. Argon works very well, but nitrogen isn't very good since it combines with any available oxygen to form undesirable contaminates (Nitric-oxide family.)

As for throttling a turbo, all that should mean is lowering the rate gas is removed from the fusor. In that way, one uses less deuterium for the same system pressure. Since the fusor should be leak tight, this does not allow more air to build up in a fusor chamber.
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Re: Question on quick voltage ramp-up

Post by John Futter »

Lets get back to the original Question

Quick voltage ramp up

At work we have several accelerators.
upon starting these they are ramped up slowly (conditioning) to the operating voltage dejour with a brief spell at some point above the operating point.

This allows the insulators within the system to come to field equilibrium which takes time for the electrons to redistribute.

If this is not done or not done long enough then terminal flashovers take place (doing damge to insulating surfaces).
So how long does this take
For our 3MeV accelerator about 0.5 to one hour from cold start ie we start at about 0.8MeV and work up to 2.7MeV over that time to drop back to 2.5MeV for a PIXE run.
So
for fusors starting at around 15-20KeV would be wise to start lowish and work your way up from there to 30-60KeV.
this assumes that you are not putting gas into the system
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

A fusor and an accelerator is a lot like comparing a Model T ford and a Hypersonic SR-71; not a lot in common relative to running.

So all I can only say is what I know on these fusor power supplies and my experience in operating a few. Others here like Richard have far greater knowledge both on the technical side of power supplies(PS) in general and operating fusors.

So, from my limited knowledge, the fusor has a ballast resister to prevent the PS from being damaged when the plasma arc's in such a way that the PS "see's" an essentially direct short. So certainly a sudden start up at higher voltages (say 28 kV) is not really different then this situation. That is, you set the an acceptable voltage your supply likes (but is not too near its cut off voltage), slowly increase the deuterium flow control valve so the fusor chamber's pressure starts to rise to the normal operating pressure; suddenly, the plasma ignites and you have a momentary short - the ballast resister handles this and you then you lower the voltage (but do not extinguish the plasma or you have to start over.) Lower the voltage will, of course, lower the current to an acceptable range. Once you have the plasma you can also control current via chamber pressure (for me, this is fast but depends on the system design.) You now have your plasma and the PS is running at an acceptable voltage. Raise the voltage as needed to get the neutron rate up to readable levels.

I do not know your system or its unique properties and only you by experiment can determine its exact operating parameters/best start up or control methods. These are suggestions for ideas to consider. This may not work or you could possibly fry your PS (assuming your ballast fails or is not sufficient.) So you and only you can decide the best and safest approach.
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

John,

Could you go into a little more detail about field equilibrium and how you suggest we startup operation?

Do you suggest that we start out at say, 20kV and leave it for a bit before we strike the plasma? Or do you mean to strike at 20kV and then leave it there for awhile before we ramp up voltage to operating voltage?

-Matt
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

A lot of messages here with info pertaining to different aspects of operation, so thanks to each person taking the time to help out!

John, same question as Matt here. Should I just turn up the voltage at low pressures where no plasma ignites and leave it for a while or does your advice mean burning plasma too?

Richard, the thing I'd stil like to clarify before wasting Deuterium and getting in trouble for it is with regard to how much I should throttle the turbo. I have read your FAQ about gas flow rates. You mention only a few SCCM is good, so should my plan be to throttle the turbo to a point where only a few SCCM (2-3) brings the pressure up to plasma ignition? Currently I am hitting about 1.5-2.0E-5 Torr with the MKS T3B Butterfly valve to the turbo fully open (maximum flow rate). Should I throttle it to the high E-4 range to where that, opening my MKS MFC to only a few SCCM, would get me to the 5-15mTorr range where my Deuterium plasma will ignite?

Thanks!
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

I don't do SCCM as I shun all MFC operations. To start, all gas and HV are turned off. My capacitive manometer reading pressure is bottomed out with the turbo throttle valve to the fusor wide open. Start here.........

Now throttle the turbo until you strangle it off to the point that the pressure just barely starts to rise due to leaks real or virtual. This should almost be totally closed! (turbo barely even pumping at all). Next, I just barely crack the throttle valve back open a micro amount. This operation saves deuterium gas!!!!

Now I raise the voltage to what I want as a starting point 10kv...15kv...20kv... whatever.... No glow should be seen as you are at deep vacuum.

Only now do I start to admit deuterium gas very, very slowly. Usually you see a very dim glow start. (this assumes you do actually have hyper fine gas flow control.) A bit more gas will see this glow develop into a brighter glow. stop short of a very intense glow.

Now your are working. you may note the current pressure on your vacuum gauge and slowly raise the voltage. The glow will get brighter. As the voltage is raised higher, the grid may start to glow red hot.

This is the moment you learn control of pressure, voltage and current in a complex spider monkey twisting of gas flow and voltage controls to go ever higher in voltage toward fusion. good luck.

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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

I like to think of all the adjusting as a slow motion tango…
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Nice analogy.

I have long sought to bring this fusor operation under Arduino control, but the motorized and electronic controls do not match the artifice of a trained operator. Even with great controls driven by a microcontroller, some hysteresis needs to be built it. Finally, can you think of every possible situation and program the perfect response that will not cause power supply destruction or the melting of a grid?? What about the intelligent micro controller opening, full wide, the turbo throttle valve and the thing trying to maintain gas pressure by opening the gas flow valve so much it drains your deuterium bottle/syringe?

Yes, there are work around safe guards to the above, but can you cover every single instance and issue that might pop up? I say yes, but I feel much better with my hands on the controls.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Richard, I am trying your advice of throttling the turbo but I have a question. I have a T3B Butterfly valve that can throttle the turbo. I am doing a systematic test to see how much I can throttle it to get back down to the pressure I pumped to initially. I got down to 2.3E-5 today, so I tried putting the T3B to 75% open, 50% open, 45% open etc. Every time I close it more, the pressure increases from about 2.3E-5 to 2.4E-5 or more if the jump is drastic, and then it slowly goes back down to the starting point of 2.3E-5. This is what should happen until I get to a point that the pressure rises and fails to start going down again, or worse, rises and keeps rising, correct?
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Yes! I actually note my wide open pressure and then slam the throttle closed. when the pressure starts to rise I only then crack the valve. If it still rises I crack it open a little more. I keep cracking it in micro steps until I see it start to fall like the turbo is struggling to vacuum it out. Only then do I stop and raise the voltage to where I want to start and only then start to admit gas. Once a glow is seen I jockey the gas and voltage from there.

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Re: Question on quick voltage ramp-up

Post by John Futter »

Sorry have been off line for a while
voltages below 16-20kV are probaly fine to go to for a starting point
You will find out otherwise if you have sharp edges and this figure will go down dramatically.
Corona starts at aroud 20kV disrupting the fields outside your vacuum, and for very good insulators within the vacuum it will take time for surfaces to leak to the applied field.
doing things before this equilirium will mean a flashover across your insulator usually leaving eidence of where it has been --in most cases a carbonised track so now your insulator is compromised.
I take exception to Dennis's comments-- this is just good high voltage technique for fusors ion sputter systems, mass spectrometers or accelerators.
Flash over a glass accelerator tube too much and you are in for a mega dollar fix with lots of downtime. Ion implanters of which i work with daily run voltages similar to fusors and voltage breakdown under operation is to be avoided ie contaminated films and insulator damage. This with ion source running at 0.1torr and beam line running 10^-6 torr with ion source differentially pumped to get the pressure gradient.

hell lots of time and lots of money why not go to max voltage and see what happens
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

John,

Any indicators that we can look for during conditioning? Or, is there a point (5 mins for example) where things should be good to go?

Let’s say that I ramp up to 60kV over a 5-10min period, and nothing flashes over, would it be safe to then ramp down to my starting point (10kV) and then “go for broke”?

-Matt
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Richard, that's interesting. If I even go from 100% open to 50% open, the pressure rises, so I think if I "slammed it shut", the pressure would increase dramatically. But I did notice if the butterfly valve is set to 38% open, it slowly trickles down to the lowest pressure as before. This is a butterfly valve so fully (100%) open equals 90 degrees open and closed (0%) equals 0 degrees so using the 38% open. I was able to calculate that the actual available surface area is only 15% of the original. I calculated this by assuming fully open means that the full surface area (100% of the area) of the T3B butterfly valve (ISO100) is available to extract air, while at 36% open, only 15% is. Not really sure why I'm writing this, as I have no follow up questions, maybe I'm just curious if, based on your experience, I should be getting the same pressure with the T3B butterfly more closed than just 38%. Pic below shows what I'm talking about.

Anze
butterfly valve open clse.png
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Also, Matt, great questions! I'm also interested to know that.

Anze
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

My throttle valve is run almost completely shut during my fusion operations. Probably 99.6% dead shut! Wide open I can hit in the 10e-5 torr. The turbo is very efficient. I usually have to shut the valve 100% closed and in just a few seconds my chamber has a real micro leak and pressure starts to climb. I then crack the valve just off shut. Usually the pressure still rises but slower. I then barely turn the knob again and the pressure may stabilize. I then crack it just enough more to see the pressure start to fall back. This tells me I have really strangled the turbo action, but it is still just barely pumping to somewhere in the 10e-5 range. This is where I can take the voltage to 15kv and start hyper slowly allowing gas in until I get glow.

With a butterfly valve, a good sealed fusor chamber and a great turbo, I would think 1% closure or even less would be the norm! I am not a fan of butterfly valves.

I use a 2.75" CF bellows valve to throttle the turbo and it runs barely off the closure seat!!!

It is important to remember that at any pressure below 20 microns you are and have been in molecular flow regime. The only way a single molecule of gas gets to the turbo is to chance bounce through the tiny orifice of a nearly shut valve's opening via Brownian motion. Our old buddy Carl Willis used a custom, laser drilled orifice in his gas line! Even wide open in his gas line and unthrottled turbo he could never get a 20 micron D2 gas flow. He strangled his gas line!

The above procedures saves deuterium gas.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Ok I think I understand now. When you close the valve, your pressure is higher than when it is fully open, but at the same time, pressure does not continue rising. You're just hitting the spot where pressure stabilizes (no rising), but that spot is higher than when the valve is fully open.
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

I never fully close any valve when operating my fusor Anze- the main throttle valve for the chamber is always slightly open to remove deuterium gas (keep the system flowing.) The inlet valve for deuterium is always open to allow gas to enter to maintain the desired pressure. In theory it is possible to have a closed system but very unlikely to remain static so continuous but slow flow of gas is the ideal methodology to keep a fusor stable.

As for my butterfly valve for my running fusor, it is barely cracked (certainly not over a few degrees and likely much less.) If 38 degree's, with no inlet flow of gas into the fusor (i.e. deuterium) then that means you have a huge source of contaminate gas coming from somewhere and that isn't good.

Multiple people asking questions in a thread - ok, well, if one raises a fusor to 60 kV (chamber is obviously below 1 micron - why raise it so hig but that isn't the question) and no break down occurs, certainly one can lower the voltage (to 10 kV, or 20 kV or what ever you want) and slowly increase the inlet flow of deuterium (assuming one has nearly closed the high vac/fusor throttling valve) and allow the pressure in the chamber to slowly rise to the proper fusor range ( 5 - 25 microns depending on chamber size) and get the deuterium to ionize. Depending on ballast, and power supply as well as voltage, one gets a plasma to ignite. Then watching current, takes steps to prevent over current (damage the P. S in some way) or lose the plasma (extinguishes. ) That's the fun of first light in a fusor - a complex balancing act between gas pressure, voltage, flow rate (inlet and exhaust) and operator response rate ... .
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Dennis - thanks for the response but I have to apologize here for my ignorance. I'm somewhat new to vacuums and I thought that by throttling the turbo, you are inherently introducing outside air back into the system. Basically, I viewed pressure in the chamber as a ratio between air coming in through leaks and what not and the air being pumped out. That obviously isn't the case, which is why I kept hammering on a dead end question. My bad.

As far as throttling the turbo now, the 38 degrees was the angle at which I would still maintain the same low base pressure of 2.0E-5. Of course, I now understand that the point of throttling the turbo is to raise the base pressure a bit. At least I have to. My system is massive and if I don't raise the pressure to about 3-5E-4 Torr, I need close to 7-9 SCCM of Deuterium to strike a plasma. Way too much. Right now I'm doing the following: I pump down at the beginning of the day, reach 2.0E-5, throttle the turbo with the manual gate valve (we have it in series with the T3B Butterfly valve and the turbo) and I reach around 5E-5 at almost fully closed. It stabilizes then and roughly 4-5 SCCM is enough to raise pressure to 20mTorr to ignite the Deuterium. But I noticed an issue. When I strike a plasma, because I'm in the ~10kV range minimum voltage with my weird power supply, the initial ignition is very chaotic and current rises above 10mA. Usually, when the valve to the turbo was cracked open, by throttling the MKS MFC delivering the gas, the pressure would plummet down to a value at which current was around ~5mA. Now, because the turbo is throttled, even by closing off the MFC, the pressure goes down very very slowly. So what I have been doing is applying 11-12kV, striking a plasma, current goes to >10mA, so I just quickly slam the voltage down to the lowest setting of 8.5kV and that stabilizes the current. Not ideal, but if it preserves D2, I'm good with it.

Still getting some instabilities in my plasmas past 9kV or so, but we will continue burning deuterium for the next few days about 30 min a day to get rid of all the smut. Is there a current range I should be burning at? I assume the cathode should just not glow bright orange, correct?

I am attaching a pic from today's Deuterium run at 9-10kV! The colors are slightly off due to the camera's exposure settings, but I'm happy for today nonetheless. First deuterium plasma ever!

Thanks for the help, everyone!
deuterium plasma!.jpg
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Re: Question on quick voltage ramp-up

Post by Dennis P Brown »

Running for 30 minutes to burn off contaminates seems excessive. I only need a few minutes. Also, when your system is clean, I'd think that closing your gate valve (or butterfly) to the turbo would only cause a very slow rise in chamber pressure. If not, you could have a leak; I'd think keeping it under vacuum, even a very large system would keep it rather clean. Once my system is set up, I rarely ever open it to the air.

I take my system to mid 10^-5 torr with the turbo but then nearly gate it off at that point and start to open my deuterium inlet valve to get that gas into the system. This brings my deuterium pressure up to 5 microns or so. With my power supply set to achieve roughly 8 - 12 kV to start the process. I carefully increase the deuterium pressure to ignite the plasma. Once the plasma ignites, the current surges - I lower the voltage to get the current in a safe range. During this process the plasma easily cleans my system as I raise the voltage in steps to 33 kV while holding current under 30 ma or so. I do get surges from time to time during this process and these, for my system, can reach over 100 ma. Such swings are normal.

There is no magic starting voltage - if 18 kV works, that is fine. Ditto for 10 kV or 25 kV, or 10 kV, etc; however, too low a starting voltage makes getting a plasma going more difficult to occur. That is, when the current surges too high, then one needs to lower the voltage and this extinguishes the plasma. So I aim for a start voltage that gives enough leeway to lower the value some without causing the plasma to fail. Be aware that for most power supplies its max. allowed current issues that matter during this process - not to exceed the safe range for the power supply. Starting at the lowest acceptable voltage reduces the stress your P.S. when the plasma first ignites. Mine is very tolerant and accepts surges well over 100 ma for a few seconds; allowable current depends on your system but that is why a ballast resister on the main supply output is important. My x-former can only tolerate 28 - 30 ma max for continuous operation. Surges of 100 ma or so can be tolerate for short periods. The ballast resister keeps current issues in check during those short runaways periods.

Any plasma will do the job of cleaning a reasonably clean system in a few minutes; longer isn't necessary unless one has a great deal of organics in their system (in which case then using solvents to clean would be the better method to do first) or physical water (trouble - should never occur.) Vacuum systems should generally be kept under vacuum (fore line closed, of course when that pump is turned off.) This will keep the system very clean even after weeks of sitting - as long as one has no real physical leaks (rather then just virtual leaks - aka out gassing.)

The plasma color looks fine - it appears you have a good current density )
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Dennis, thanks for the response again. I am assuming ny chamber is still a bit dirty solely due to the fact that there are still some flashes / current spikes in my system every so often and now when we increase the voltage, sometimes the plasma just dies. Or even if we leave it alone to run at 8 5kV, it just dies after 5-10 min. But we run it very low current, around 4mA. No cathode glow. I was told I should keep the cathodes glowing just a little bit to maintain a plasma without extinguishing it.

Anze
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Another run today, taking advice from a few people to run hotter and we were able to make it to 11.6kV before it shut off today. I tried keeping it around 6mA at this voltage, since it's where plasma continued to glow. I think past around 11.5kV, I need to keep it above 6mA, but we're going up...

The only concern I have is that the wire feeding the electrodes is thinner in gauge, but also made of Tungsten, so I'm worried about melting it. But from what I gather, the glow in the fusor electrodes is due to ion bombardment, not current, correct? So, since that wire is out of the way, it should be ok, correct?
DSC_0035.jpg
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

I’ve gotten my tungsten wire bright orange with 600watts without any damage to it. I’ve got a stainless mesh filter/trap below the cathode that should block any shards from leaving the chamber, just in case I do melt mine down.

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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Please in future when you do a run and want to convey the facts, always state the average run voltage, current supplied over the run and the deuterium pressure over the run...

These details tell us where you are in your operational regime.

Whatever your run pressure was, (unstated), I suggest you reduce it so that higher voltages can be reached. Easily detected fusion can begin at 15-20 kilovolts. (Assumes a moderately sensitive neutron detection system.)

The grid is part of a closed, series electrical circuit and carries the full electrical current in the wire. However the gas is the real load and of much higher resistance that the wire. Thus, the ion bombardment is due to the full current in the device spent over a much lower resistance and thereby, a lower dissipative component of the circuit.

While the load is a conductive, yet a resistive gas plasma, (not a true thermalized plasma), almost all the energy input to the device is spent in heating the shell by electron bombardment and fast neutral bombardment. Effectively, 0.0000001% of the energy input results in successful fusion.

How much energy is expended the the glowing grid? Only dropping the device in a bomb calorimeter to determine the time ordered delivery of thermal energy to the shell compared to the electrical input energy to run the fusor would produce a small wattage differential that would be the grid dissipation in joules or watts. With the high voltage this would be tough to do. A far more doable possibility is to use the viewport to have an optical radiometer look at the glowing grid to determine the energy needed to raise the temperature of the mass of tungsten read by the radiometer.

I suspect a few tens of watts would be the grid dissipation. This represents lost deuterons and some small amount of fast neutrals. An orange hot grid is a poor electron emitter as well and this is part of the current dissipation figure within the grid.

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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Ok, so today pushing more current and voltage resulted in the top cathode getting disconnected from the HV input. I knew it was a weak point when I built the thing but I hoped it would've just worked. There were small arcs / sparks there before it disconnected so definitely not good. I'm going to open the chamber, take it out, rebuild it and retry. I know how I can make this thing way more sturdy in terms of handling power. Will update once I restart experimentation.

I'll apply for the plasma club for now, fusion coming soon...

Thanks for the help everyone! Be back soon
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Re: Question on quick voltage ramp-up

Post by Matt_Gibson »

How much current and at what voltage? I had my cathode fall off the feed through stem when the SS tubing (holding the tungsten wire loops in place) became orange hot and expanded. I had to crimp it on much harder…

-Matt
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Anze A Ursic
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Around 11kV and 6mA. My cathodes were badly connected to the wires carrying power. Again, didn't think it would be a problem but I guess it was. I should he back to running by end of next week.
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Richard Hull
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

Matt had to ask for voltage and current..............

Voltage, Current, Pressure!!!! .....always!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Anze A Ursic
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Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Sorry! Will be more pendatic going forward!
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Richard Hull
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Re: Question on quick voltage ramp-up

Post by Richard Hull »

When a new operator does a run and either has a problem or a question related to his results of said operational run.
We long time fusioneers can be of little to no help without complete stated conditional knowledge related to the run in question.
Yes we can make a wild haired guess, but can you rely on it? We can't rely that we can help you if we are given only partial information.
A good scientist will try to expound on and supply all useful data from any experiment.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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