#3 FAQ - Operating a Fusor - startup - run - shutdown

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Richard Hull
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#3 FAQ - Operating a Fusor - startup - run - shutdown

Post by Richard Hull » Wed Dec 09, 2009 7:28 pm

The vacuum part of a fusor is its life blood just as deuterium is its food.

This FAQ will begin assuming you have a fully assembled fusor system with.....
1. A standard two stage mechanical pump with good oil in it capable of a 10 micron vacuum at the inlet head.
2. A thermocouple gauge in the foreline between the mechanical pump and high vacuum pump
3. A good vacuum valve at the end of the foreline located near the outlet or low vacuum side of the high vacuum pump.
4. A diffusion, (diff), or turbo high vacuum pump, fully isolated with valving on each side of it (noted in points 3 and 5 here)
5. A gate or control bellows valve between the high vacuum pump's inlet, (diff pump), and the fusor. (We will call this the fusor valve)
6. A high vacuum gauge on the fusion chamber, itself.
7. A source of deuterium gas with a line leak valve, (needle valve), connected to the fusor. (We will call this the gas control valve)
8. A high voltage power supply that is fully and correctly metered
9. A protected viewing port or video camera/monitor combination to observe the inner grid area.

Question: With all of the above, how do I start and run a fusor to make fusion?

Take the following steps to obtain the proper vacuum and operational regime.

1. Make sure all high voltage power is off.
2. Make sure all vacuum valves are closed and that all vacuum gear and pump related power is off.
3. Turn on the camera/monitor system, if you have one. Turn on all radiation monitoring gear.
4. Turn on all vacuum gauges and metering.
5. Turn on the mechanical pump only.
6. Open the pump's gas ballast. The pump will be more noisey when this is done. Leave this ballast open until told to shut it again.
7. Let the pump run for a few minutes until the foreline is pumped down to well under 50 microns by reading the thermocouple, (TC), gauge. If it will not fall below 50 microns, you have a bad leak in the foreline or a bad mechanical pump. (It is best to allow this line to drop as low as practical.
8. Open the foreline to high vacuum pump valve. We will call this the "foreline valve". Open it all the way and leave it there until told to close it. The pump will load up and the pressure on the TC gauge will rise. This is normal. It will begin to fall again as the diff pump or turbo pump volume is pumped down. Hold at this point until the pressure on the TC gauge is again at its lowest point, but it has to be well under 50 microns. If not, you have a bad valve or seal at the inlet or outlet of the High vacuum pump. Once well below 50 microns, or as low as you can get the volume, proceed to the next step.
9. Open the gate or control valve (fusor valve) to the fusor. We will call this the "fusor valve". Again, the pressure will rise and the pump will load down as the entire fusor volume is pumped down.
10. Now look at both the foreline TC and high vacuum gauge on the fusor's readings. They should track somewhat alike. Again, you must acquire a vacuum with just the mechanical pump, on both gauges, indicating a pressure well below 50 microns before going to the next step. If not, you have a serious leak at the fusor chamber somewhere among its many ports and seals.
11. Close the gas ballast on the mechanical pump. The pressure might drop another 2-5 microns and the pump will get much quieter.
12. You now may start the high vacuum pump, turning on the turbo motor or, if you have a diff pump, turning on its boiler heater and cooling fan or cooling water flow.
13. If you have a turbo pump, the high vacuum gauge on the fusor will plummet rather quickly to some base pressure in the 10e-5 to 10e-7 torr range. If you have a diff pump, you will have to wait a few minutes for the boiler temperature to come up to operational temperatures. Ultimately, the high vacuum gauge will drop in pressure to well below 10e-5 torr or lower using the diff pump. You are now fully operational, vacuum wise.

Setting the deuterium gas flow for fusion********************************************

This is tricky and if you aren't careful you will waste your deterium and use it up at a prodigious rate. Follow these instructions carefully and monitor your high vacuum gauge constantly.

1. Close your, (fusor valve), gate or high vacuum pump control valve to the fusor. Unless you have a plus ultra system, the pressure will rise. As it rises, notice its rate of rise. It must be under 0.1 micron per second or 1X10e-4 torr per second. ( 1 micron every 10 seconds) If more than this, you are awfully leaky and will waste a bit of D2 gas.
2. Now that you have a feel for you leak rate, barely crack the (fusor) gate or bellows control valve to cause the pressure to start to drop again. Allow it to reach a stasis point where the pump is just keeping up with your leak rate.
3. Now barely cock open the gas control valve. This is a super fine adjustment. Let the gas in at a rate where you hit about 10 microns on the high vacuum gauge. ***note*** look at the TC gauge. It should still be in its low range of 10-50 microns. If it climbs and continues to do so, you have too much opening on the fusor valve. Turn off the gas control valve and close the fusor valve a tiny bit more. Repeat the gas admission process until you get a stable flowing gas pressure of at least 10 microns in the fusor that is stable against the high vacuum pump's pinched off fusor valve. This is an art that must be mastered.
4. Turn on the high voltage power supply and adjust it upward until a glow just lights. If the current draw is over 10ma, turn the power back or off. You must back off the gas pressure by ever so slightly reducing gas flow rate or opening the high vacuum valve to drop back to maybe 6 microns. This is a constant battle at startup but will stabilize. Try again to bring the voltage up until you get a glow.
5. Assuming you have a glow, that is stable at some voltage, V, and at a current under 10ma without the grid heating red hot, you have arrived at a point where real opeartion and fusion can begin. If the voltage is below 15kv you will need to nurse the system to higher voltages to do much fusion. To do this, try reducing the operating pressure. At 15kv, you will be be making x-rays and they will be pouring out of the viewing port. If you are well above 15kv, you should be detecting neutrons via whatever instrumentation you have and, thus, doing fusion. From this point on, it is a matter of controlling the fusor valve, the gas control valve and the power supply in such a manner that you can achieve a higher applied voltage at the highest gas pressure within the limits of overheating and damaging the grid. You are on your own.

Warning*** always glance at the TC gauge from time to time when running a fusor. It MUST remain, forever, below 50 microns and preferably below 40 microns. What is happening is that the flowing D2 gas is loading up the Diff pump and thus causing a rise in the foreline pressure. Normal, yes, but it needs to be monitored. More than about 50 microns on the TC gauge and you are just throwing away valuable D2 gas.

Shutting down after a run**********************************************

This is far more important to you than the startup procedure!! Mess up here and you will regret it later. You can now destroy your turbo pump or create a horrible mess in your fusor and all vacuum lines by burned diff pump oil with just one slip in the shutdown process.

1. Shut off all high voltage to the fusor.
2. Shut the deuterium gas control valve tight and shut off the D2 gas bottle valve as well.
3. Open the fusor valve, all the way. The pressure on the high vacuum gauge will now plunge as the high vacuum pump is no longer choked off or throttled back.
4. After a couple of minutes, close the fusor valve tightly. The fusor is now isolated from the vacuum system. and the pressure will start to rise on the high vacuum gauge. This is normal. Ignore it. If you wish, you can now shut off the high vacuum gauge electronics.
5. You may now shut off the turbo pump. Once it has wound down and stopped, go to the next step. If you have a diffusion pump, turn off the power to the heater on the boiler, but leave the cooling fan on or water flowing. Leave this cooling cycle running for at least 10-15 minutes. I let my boiler temperature fall below 50 deg C before turning off the fan or stopping the cooling water. proceed to the next step after turning off the cooling at the approriate time.
6. Close the foreline valve tightly
7. The TC gauge should now read well below 30 microns or your low, base, foreline pressure seen earlier in step #7.
8. You may now turn off the mechanical pump. It is important to let the mechanical pump's foreline up to air and not leave a vacuum in this small volume or it might lift oil up out of the pump, fouling the foreline. Do this now! It is assumed you can open the foreline to air by some artifice already in place, (valve, quick release coupling, whatever).

This completes the startup-run-shutdown cycle for a basic fusor outfitted as noted above.

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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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Tyler Christensen » Wed Dec 09, 2009 8:17 pm

Here's one operational tip regarding getting the right operation pressure in the fusor with diffusion pumps that I haven't seen mentioned before...

I couldn't get my diffusion pump throttled down enough even with the valve cracked as low as I could get it, so I put the diff pump on a variac. At 80V it is very low pumping power and with the gate valve wide open it is perfect for 1sccm deuterium flow. This probably isn't "proper" to run a diff pump at lower voltage, but it sure is working great for me right now.

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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Doug Coulter » Wed Dec 09, 2009 8:48 pm

Richard,
great FAQ and right on the money, it's what we do here and it works great. With our particular turbo, at high vacuum it takes too long to spin down, so we use the Pfeiffer recommended procedure of letting a little air in behind it (into the roughing pump line) if we're in a hurry to get in there and try something new, that's about the only difference. We can just turn off our roughing pump on that system as it has no oil to suck back. On our diff pump system (with oil type rough pump) we do it just as you said except that for rapid cycling we'll leave the diff pump hot and valved off at both ends while we access the tank innards, then re-rough pump the tank before putting the diff pump back into the game, which means we don't have to wait for it to cool and re heat. This lets us try 10 things a day or more when we are plotting all the other variables (like grid geometries) against things like Q. So that's why we have the 3 valve system on that -- so we can leave the diff pump hot and ready.

Tyler,
we do that too, only since it's a mere heater, we just use a lamp dimmer. It's a little touchy and takes awhile for any adjustment to take full effect (thermal mass in the pump) so we labeled the dial of our dimmer and now know where to set it for running. We use full power for the first 10 min (our pump takes around 15 to get to full temp at full power) and then set it back, and after a few more minutes it is stable. I really doubt it hurts anything. You are still keeping the oil at its boiling point, just not boiling it as hard as full power does. Using the lamp dimmer means freeing up a variac for something that needs a better waveform than what comes out of a lamp dimmer (almost everything else there is).

It works great, and now we can use the gate valve for fine adjustments at all -- as you say, at full power these pump too fast for this use. I note Richard has a pretty small pump, so maybe doesn't have that problem at his place. But we did here as we had a larger diff pump on a pretty small chamber.
Why guess when you can know? Measure!

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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Chris Bradley » Wed Dec 09, 2009 9:38 pm

Richard, you say to raise the foreline to atm but I'm not sure if you're indicating that you need a vent valve to air to do that with.

In any case, I have a suggestion for this final step: I guess we are creatures of our original training, and my first vacuum experience was with a plasma cleaner in a clean room. So naturally the procedure I tend to stick with (perhaps unnecessarily) is to vent the intake port to atmosphere *before* actually turning off the pump. This guarantees that any volatiles sucked up into the port and the oil (which is usually the cleaning solvents, in a plasma cleaner!), or any fractions thereof, stay positively in the mechanical pump if not sucked through and exhausted.

A problem that always faces this scenario is how to conveniently add yet more valves and bits-and-bobs to the setup. My solution is very low-tech, but still very effective. Drill a 2mm hole in a vacuum interconnection, or blanking piece, and just stick a bit of kapton tape over it! As shown.

The procedure is then, simply, once all valves are closed and *with the pump still running*, just lift up the kapton tape. This vents the port (quicker than the pump pumps) and then you can turn off the mechanical pump without any fear of the remotest back pressure. My E2M2 pulls 3 microns total pressure almost immediately in its intake port and the addition of this 2mm diameter area of kapton tape exposed to the vacuum makes no difference at all to that. So the effect overall in a bigger system is surely essentially zero.

Sticking with this as the procedure also has one other redeeming beneficial effect. Ordinarily, never shut off a mechanical pump with the gas ballast open, as you risk it cranking backwards and not only back-displacing vapour but possibly liquid oil. But if you've forgotten the gas ballast, after venting the port to air this doesn't happen anyway so becomes a somewhat 'forgettable' risk.
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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Richard Hull » Wed Dec 09, 2009 9:45 pm

My diff pump is a two inch pump and is air cooled. The best of all worlds.

I have an ignorant friend, ( actually many such). He is about to leap into the fusor arena and had called a while back bragging about picking up a nice a diff pump with a 12" throat! He was proud that he got such a massive pump compared to mine. (Guess he figured he would one up me here). He got it for $6.00 at a scrap yard. A rather stupid economy. I said nothing, of course, but did congratulate him on his coup.

He has only seen one diff pump in his life and that is mine that has been bolted into my system for the past 5 years.

I thought, "Wait until he needs to buy 2 quarts of diff pump oil" or has to hand craft a cover plate and seal with a 2.75 conflat choke point to mate to his system. It is water cooled, naturally, and it sounded like 1/2" copper coiled piping. Nice water bill or forced pump/radiator recirculating system to make it go. I hate to think of the electricity bill to operate what might be a kilowatt heater.

I finally got to see the monster last weekend. It must have come out of a CRT manufacturing facility! As I peered into the open maw, .......oops....what's this?.......
"Where is the Christmas tree", I said. "What Christmas tree", he responded. Apparently in the mass shipping of it and 6 tons of other lab refuse to the salvage yard, it fell out and was lost forever.

Well that was that. He is only out 6 bucks, but I did tell him that it would make a nice space heater/door stop....Maybe even a space age stew pot.

I educated him on the spot. He is out looking for a replica of mine now.

Bigger, is not necessarally better. Often, it is just more stupid.

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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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Richard Hull » Wed Dec 09, 2009 9:56 pm

I have a fast disconnect KF16 on my short rubber hose to the mechanical pump that I just spin the wing nut loose, unclamp, and lift the flange connector of 1 second, then reclamp. No valves needed. It is assumed that any such foreline "up to air" effort by the user is covered in some suitable fashion. My foreline is a small SS manifold that allows a port for technical vacuum access outside the fusor use. It can be seen in images of my fusor. One pump, dual use.

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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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Chris Bradley » Wed Dec 09, 2009 10:07 pm

I guess that may not necessarily be obvious to some, then. Some pumps have anti-suckback capabilties that would mean you wouldn't be able to just lift off the connection, as you do, without a long wait and I would suggest the facility to positively vent the foreline to air should be considered before designing one's system.

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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Doug Coulter » Thu Dec 10, 2009 3:27 pm

Another funny one Richard! My keyboard may not live though too many of these.

Yes, you have the best diff pump setup for a fusor that can exist, we weren't as lucky with our Varian being water cooled and larger 3.5" (400w heater). That one is backed by a 1 hp(!) direct drive pump.
Talk about overkill for a 6" Tee chamber! But those small air cooled ones are kind of rare surplus, your friend found something much more common, evidently a lot of places that used those big guys either went out of business or switched to turbos, and they are all over the place out there.
I got offered one about the size of an automobile for real cheap. Would make an interesting decoration if I had room for silly things like that.

We handle water cooling ours with a 5 gal bucket and a submersible fountain pump from Lowes.
We sometimes have to add some "blue ice" to that for long runs, even when using the dimmer on the heater to throttle it. BillF recently found a little system from a leak detector for hardline coax or something similar that looks a lot better, and in that case the forepump is only a couple hundred watts. I'm going to strip that all down and rebuild his system to use that stuff -- much more appropriate for this use.

In our diff pump system, we've been using the cheap diffoil 20, no santovac, no serious cold trap (water cooled) and it's been working OK. I did go down the "ultra high vac, extra purity" route on another system to see if those things that weren't being controlled for were the source of some strange results we were getting -- but nope. Still see the strange (good!) results intermittently on either system, so there's another variable we're missing that needs control. I am resisting reporting those good results until I can get them every time, so far, nope.
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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Quantum » Thu Dec 10, 2009 8:40 pm

Would I be correct in assuming that a smaller diff pump will be less likely to contaminate the system, due to there being less 'surface area' of oil exposed to the system?

EDIT: ie, less oil exposed to the system.

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Re: FAQ - Operating a Fusor - startup - run - shutdown

Post by Richard Hull » Fri Dec 11, 2009 3:58 pm

No. Not really. The size of the pump should be related to the pumped volume and your needs. There has never been a neutron producing fusor constructed here that a 2" or 3" diff pump would not plunge from a mechanically pumped 10 microns to .01 microns, (10e-5 torr) in under one minute, once the oil boiled at proper temp.

My system takes about 5-7 minutes of mechanical pumping to hit 10 microns in the chamber. The diff pump oil takes another 5-10 minutes to hit pumping temp. I see the baratron's reading plunge rapidly in under 30 seconds from ~8 microns to 10e-5 torr in my system and it is not perfectly sealed. I have a rather constant 1micron pressure rise in 30 seconds on my sealed off fusor chamber. It fuses flawlessly. I have no need, whatsoever, for sealing it any better than this. So, the sleeping dog is left in repose.

The key here is that your mechanical pump must get a bottomed vacuum in the system very fast to well below 20 microns. Below 10 is preferred. If you can't do this, you have a crappy mechanical pump, fouled oil or system, or a horrid leak. No need to start the diff or turbo until this issue is fully resolved. Once this mechanical vacuum is achieved, almost any diff or turbo will yank any normal sized amateur fusor system to a deep vacuum 3 or 4 orders of magnitude below operating pressure with great ease and fast, too.

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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