Question on quick voltage ramp-up

For posts specifically relating to fusor design, construction, and operation.
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

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

Anze
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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.

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
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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.
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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 ... .
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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 )
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

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.

-Matt
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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.

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
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

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
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

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.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
User avatar
Anze A Ursic
Posts: 157
Joined: Thu Mar 10, 2022 9:28 pm
Real name: Anze A Ursic

Re: Question on quick voltage ramp-up

Post by Anze A Ursic »

Sorry! Will be more pendatic going forward!
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”