Question on quick voltage ramp-up

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Anze A Ursic
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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
Matt_Gibson
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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?

-Matt
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Anze A Ursic
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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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Dennis P Brown
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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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Anze A Ursic
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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.

-Matt
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Richard Hull
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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.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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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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Richard Hull
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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
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
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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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Richard Hull
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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

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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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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Dennis P Brown
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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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Anze A Ursic
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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.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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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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Richard Hull
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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.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Anze A Ursic
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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.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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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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Anze A Ursic
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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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