FAQ - Gas flow rates in a fusor

[Richard Hull]

In operating a fusing, deuterium fusor, it is very important to assure yourself of a healthy volumetric flow rate of the reaction gas (deuterium). The balance is between your continuously operating pumps and the gas admission metering rate

I only recently discovered I was running too "lean" for all these years.

What follows is a posted response to a question of why my fusor did so well at the 2005 HEAS conference, based on my disclosing that I had learned a secret of increased performance from Carl Willis and Brian Mc Dermott.

****************************************************************

I have always operated my fusor with a slight leak of gas and a nearly shutoff vacuum valve. As such, I ran at pressures of 4-8 microns and did OK.

I was goadded by both Carl and Brain to open up the vacuum valve a good bit over my normal operating point and crack open the deuterium valve even more to boost the overall pressure to 10-15 microns! This is indeed a terrible waste of D2, but works incredibly well as the gas load and flow through the fusor is rather tremendous and is pure D2, which is what is desired.

A heavy flow of D2 is needed, not just a flow. The gas load on the diff pump needs to be significant. I actually metered the gas up to close to 20 microns in the best moments of run. This allowed a whole bunch of fusion to occur at much lower voltages. My neutron counter sang at a measured rate near the end of the "money run" at a rate of >2000 CPM. The ten minute total was 16,338 but the best part of the activation run was attained in the last 5 minutes of the run as the pressure and voltage were constantly edged upward.

Carl claims his best results were with a flow rate of up to a few sccm/min which almost lets you see your dollar bills being blown out the exhaust of the pumps. With these flow rates, I can actually connect up one of many mass flow controllers!

It is a good thing that fusor runs are, first of all, infrequent and, secondly, of very limited duration. At this rate, I don't know if a heavy water electrolysis system could keep up without a large reservoir and a head start. (Of course, I use only pure bottled gas.... read, $$$)

Bottom line is.... thanks go to Carl and Brian for kicking me in the ass to goose my system good. It made a world of difference and explains why I did fusion just fine for all these many years, but never hit 250,000 n/s while others were activating and getting higher numbers at lower voltages and at pressures I thought might have been artificially high due to faulty instrumentation at their end.

Even old farts learn pretty good if beaten on the head smartly. I am glad they persisted in their insistence on using my gas up at a rate about 10 times that to which I was used to. It paid off very well, indeed.

It seems the fusor works mostly off of fuel, fuel, fuel and lets cross sectional potentials fall where they will. The "Lawson criteria" can be handled in a lopsided many and still let you do fusion.

Even though I was the host at HEAS I was not the only teacher or student there. Most of us there served in a full dual role capacity. We served up our bits of knowledge, hard learned and yet also absorbed the wisdom and empirical experiences of others.

****************************************************************

The secret is get a good pressure gauge and proper valving in your system that will allow you to adjust for a real 15-20 microns of run pressure. Do not nearly completely "choke off" the vacuum pump, but instead increase gas flow to load up the pump a bit.

This is still a delicate adjustment and needs a well sealed fusor that has a stable pump and gas metering system.

Richard Hull

[Roberto Ferrari]

Richard,
Thanks for the details.
What about the load to the diff pump? Can afford that flows?
Did you run the sistem closing the shutoff vacuum valve, with 15-20 microns into the fusor?
My point is to learn if you need really the high flow or just the high pressure.
I am starting to imagine a closed and well pre-degassed glass vessel with the classic inner grid and outer electrode, with 20 microns of deuterium, the electrodes out through glass-to-metal seals and the whole bulb under transformer oil. In that way could apply more HV into the fusor.
Kind of "fusor bulb" as mentioned before in this forum.
What do you think?
Roberto

[Richard Hull]

Roberto, I never shut off the vacuum valve,as the fusor demands a volume flow of D2 for the best results.

As regards a bulb fusor. I don't believe in it doing fusion to any measurable degree, nor would I dream of recommending it to anyone as an operational modality. This would be far more dangeous than a bell jar fusor and I warn strongy against their use as well!

Fusion to a measurable or significant degree demands only a metal vessel be used.

Richard Hull

[Todd Massure]

This is really interesting. I'd like to dig a bit deeper as to why this happens. I'm reluctant to chalk it up to more fuel, as I can't imagine the fusor starving itself for fuel at the rate that it's doing fusion, I apologize if I'm not understanding.
Could it be that the flow allows cooler, denser fuel to be constantly introduced? Maybe this has an effect on poissor density or the mean free path?
Or maybe it's introducing new fuel that is not ionized, allowing higher potentials with less current?
At any rate, it's very interesting

-Todd

[Richard Hull]

This has been discussed before and is actually seen in hydrogen thyratrons and planned for in same.

Hydrogen and metals are like water and sponge for the most part. Metal lattices suck up hydrogen to a point and then aspirate it back out. However, varying pressure, temperature and ion bombardment screw with the normally gentle absorption and desorption.

Those intimately familiar with every aspect of the hydrogen thyratron realize the hellish nightmare involved in manufacture of one of this specialty tubes and can easily see why a medium sized tube like the 5C22 costs over $1300.00 new.

In order to even get the thing to work, only the most pure 9999 or better metals are used. They are degassed to levels that would amaze even a class A vacuum expert. they are pulled to extremely hard vacuum levels and left their for days and weeks and then back filled to the micron range with ultra-pure, ultra clean and ultra dry hydrogen. Only after all of this is the tube even half way reliable and repeatable in its operation.

For those in doubt, details of this hellish nightmare story are told in the Rad-Lab series on radar in the volume "Pulse Generators". it focuses on how the early H2 thyratrons lasted 16 hours MAX and had to be yanked and replaced after each bombing mission in planes equipped with radars. It was so bad that they kept the much more reliable, but bulky and heavy, spark gap in the mightiest airborne radars until very late in WWII as the new tube was just not reliable.

The hydrogen thyratron has a built in heater to re-gas the cold tube which tends to absorb the H2 gas contained in it when cold or inoperative for a period of time. All of this demands a separate 100-500 watt heater supply just to work the cold tube back into a usable range. this normally takes 5 to 10 minutes of warm up time before voltage can be applied to the plate and grid system.

This bears to the fusor argument for volumetric flow in that not one of us here has the money or the time or the stones to seek out, pay for and assemble a fusor from pure tatalum, beryllium oxide, pure paladium and or gold and other metals needed to have a sealed off reliable unit. We would still need the ultrapure 99999 D2 and not the cheapo $400.00 a bottle rot gut 995 stuff we use now.

So we avoid all these issues by using crappy materials like stainless and other metals. We avoid the week long 10e-9 pump down, we avoid the separate paladium reservoir and 200 watt auxiliary heater system.

We only need to keep the metals fully loaded with heavy gas loaded deuterium and let it reach stasis with its bombardment, pressure and potential so that in the guts of the fusor we have a pure and stable environment in the reaction zone. We literally equalize the constant loss and desorption of D2 from the device with an equivalent input flow that lets the device see a stable 15-20 microns without a single belch of gas. This takes a healthy setup time and a large gas flow and waste of relatively cheap D2.

So, yes, it is possible to make a zero flow, pinched off constant pressure D-D fusor. It is just not possible for YOU to make one unless you spend the long buck and go the long mile.

Remember..........what one hand gives, the other takes away.......there are no free lunches in nature........... it's the only game in town and it is rigged.

You pays yer money and you takes yer chances.

Every real fusor operator sees this and knows it viscerally in every fiber of his being. I just figured that my fusor worked well at lesser flows. I just learned it will work better at lower voltages with greater flows. The waste still hurts but is offset by the joy of bigger neutron numbers.

Richard Hull

[DaveC]

I have a question about the need for flowing Deuterium gas in operation of the fusor. The answer may be obvious. But here's where I am viewing things.

The systems usually are well sealed and degassed. So... the majority of gas molecules in a Deuterium fill to 10 -20 microns pressure or so... is just.... Deuterium.

The quantity of deuterium atoms in the fusor is on the order of 0.1 mole times the pressure ratio to atmospheric pressure... or about 1/50 x 1/760x 0.10 or about 2.6 micro-moles of Deuterium gas.

That's about 1.6E+18 molecules, give or take. So at about 1E5 neutrons/sec, we should have enough D2 in the system to run for about a decade or so, before a fall-off occurs.

Why is it that the gas flow seems to be necessary? I could see a pressure, (but not a gas density) increase as the unit heats up, but it doesn't seem necessary to actually flow the gas...

Thoughts?

Dave Cooper

[Frank Sanns]

When Richard fired up his fusor, it dropped right down to a vacuum of a couple of microns or less. He added back a small amount of deuterium and tried to balance the voltage, current and pressure with not much sucess. The fusor was not well behaved as the voltage and current were varying widely and there were only a very few neutrons being produced. I too have seen this. A suggestion was made to put in enough deuterium to take it to half to one torr and to let it glow clean, embed deuterium, flush, whatever you would choose to say is happening. Richard did this and the voltage dropped down from 30KV+ to 3-5KV. Slowly the pressure fell through the well throttled vacuum valve and at around 7 kv, neutrons started to fly. As all of you lucky fusioneers know, this is a very low voltage for measurable fusion to occur but it does and did none the less. Continuing with the pressure drop, the neutron numbers contiued to increase and Richard and Carl and Brian arm wrestled over the vacuum and deuterium controls. In the end a greater flow of deuterium gave the highest number of neutrons that Richard has produced in his fusor.

Before my thoughts on why this occurs, I need to say that I have observed this behavior on my fusor and also can SEE LIVE with the unaided eye what is going on inside the fusor. My viewport has a 4 inch (10 cm) actual viewing area so many hours have been spent running my fusor below 12 kv so I can observe and correlate. What I have seen is that even though my fusor will hold vacuum very well with leak rate in the one microns per 10 minutes or better region, I still see differences in visual apperance and neutron production with flow rates.

Condition #1: A clean chamber pulled down to 10-15 microns and lit. Appearance is blue plasma with a star that reaches somewhat outside of the inner grid but not to the outer grid. Voltages are high and stability is not great.

Condition #2: Pull chamber down to 1 micron or better and admit in enough deuterium to raise the the pressure to 500 microns then let the vacuum pull down slowly (10 microns per second) to 10-15 microns. Huge red star that reaches through into the chamber and even through the outer grid. Voltages drop and neutrons start a little above the pressure for star mode. After a couple of minutes the color slowly starts to fades to ruddy brown and neutrons slow down or nearly cease. Electrical control is still good until pressure falls to near extinction and then gets touchy and neutrons fall off even though the voltage is high.

Condition #3: Pull chamber down to 1 micron or better and admit in enough deuterium to raise the the pressure to 500 microns then let the vacuum pull down (10 microns per second) slowly to 10-15 microns. Big red star again and neutrons again. This time balance the dropping pressure with deuterium. Leave the deuterium at or near this flow and adjust the vacuum valve to hold this setting or open it a bit more to drop the pressure and get to higher voltages. Result is sustained bright red full star and great neutron numbers.

My thoughts of why this happens:

Deuterium is much smaller than air and has a much longer free path. It is cranking around in the chamber and into the walls and the grid and will knock off metal and gasses and water like air can't. This contaminates the gas in the chamber quickly even though the measured pressure does not change much. This would probably wane as the fusor would be operated over many hours or days but not many of us run that long. The impurities compete for collisional energy and quench the fusor.

Deuterium has much higher thermal and electrical conductivity than air. The fusor is much better behaved when the fusor is run on deuterium and not the junk from the grids and the walls. Also the vacuum gauge is calibrated for air. Deuterium cools the thermocouple better so the pressure is actually higher than you would think. Operating parameters then are much more even and easy to control because of the increased mobility and electrical carrying capacity of all the deuterium.

I have more thoughts on the matter but I will end this post and comment more as the argument starts! lol

Frank Sanns

[DaveC]

Frank - Thanks - very informative.... and no argument here. What your experience appears to indicate is that there is a lot of plasma -- surfaces interaction that has to be considered to maintain the desired gas density.

I am assuming the high Vac pump is running all the time... (throttled or otherwise) so that a pressure drop would be consistent with either an adsorption of fill gas (a gettering action by clean surfaces in the fusor) or a plasma induced desorption of surface trapped gases and water which had been slowly desorbing at the original pressure of the chamber and are now pumped off quickly. (Usually the later process results in a rapid pressure rise first , then a drop off.)

When I do a glow discharge in the bell jar system, I generally see a substantial pressure rise... for quite a while, until the system scrubs itself clean. I think metal systems clean more quickly. I usually need to do it several times before there is a only minimal rise in pressure. But have not done it with either H2 or D2 as yet.

Actually I have also thought higher pressures should give more output. Your experience there at Richard's has shown that quite well. I think that was a nice piece of work all around.

Dave Cooper

[Richard Hull]

The key is that higher pressures WORK and that a flow WORKS and a pinch off at constant D pressure does not in the average dirty or rarely fired amateur system. I have tried for years to get fusion with fixed pressure and no flow, which would seem ideal. All attempts fail.

I have always observed flow works and static pressures with zero flow fails, as have other fusioneers here with working systems.

Part of the issue revolves around infrequent use, constant disassembly/re-assembly, re-pumping, failure to retain full pressures indefinitely between runs, indifference to obtaining pure materials in construction, etc.

As I noted in the H2 thyratron posting, I am certain a static pressure fusor, sealed off, COULD BE MADE.

The big thing I learned is that the flow rate needs to be rather massive compared to all my prior activity where a highly throttled back pump sucked microscopiocally at a niggardly flow of D2. The flood gates need to opened at both the gas and vacuum end. Compared to being a miser on D2, you need to be a Diamond Jim, big spender.

Of course, you will not drain a cylinder fast even in this new regime as you are still talking microns of gas and a few sccm/min of gas. I doubt if I have two hours total heavy fusion time making neutrons in my 5-6 years in this operation.

Pump and glow cleaning time is another matter. I know for a fact that the pump ran on the fusor in 2000 for 51 hours. In 2004 it was similar. This last weekend we ran for 3 hours straight with less than 15 minutes of neutron production and less than 5 minutes of super "activation" level running. My D2 cylinder on fusor IV is the same cylinder I used one Fusor II and III. Going into this past weekend, it was nearly empty (less than 20 psig at the head). I might still have a few more runs in it, yet, but I will be going to my second cylinder soon. So, I suppose that with ealry activity mistakes and such, I might find that I got 2-3 hours of fusion time out of that first 25 liter cylinder.

So, the upshot is that flow works and heavy flow works better. The reasons may be many and varied in actuality, but given the amateur nature of this effort and inspite of even high end systems in operation, ..........."flow makes it go".

Remember what mom said when we were growing up, "Starve a fever.....Feed a fusor.

Richard Hull

[Todd Massure]

This has alread got me thinking about some kind of "scrubber" for the fusor. No good ideas yet.

-Todd

[Donald McKinley]

Regarding the Deuterium flow producing a stable high neutron count:

Since the D2 gas entering the system is "cold," it makes me wonder whether this is a thermal gradient effect. Has anyone tried recirculating a small portion of the plasma through a heat exchanger so that instead of a fresh supply of D2, there is just a cold supply. Alternatively there could be a large cooling reservoir connected with two small tubes on either hemisphere, say 4 or 5 times the volume of the actual fuser with some means of circulation. One method would be to put a small overall voltage gradient across the fuser with the pos potential near an exit port to an exchanger reservoir and the neg near the return tube from the reservoir. Gas would come in at one potential and be forced out by pressure at the other potential, the circulation being caused by the ions crowding near one port due to the gradient?
?
?
?

[Richard Hull]

Pardon me but ...WHAT!?. Not meant to be a slam, but humorous.

The actual temp of the inlet gas is absolutely unimportant in any manner whatsoever. Once again, I think the confusion is one of verbage in the fusion biz versus the lay understanding of temperature of fusion being in the hundreds of millions of degree range. A gas at fusor pressures in the million degree range would not char toilet paper left in the fusor, let alone ignite it.

This has been told and retold many times in past posts.

Temperature in fusion relates to gas molecule kinetic energy. If the particle density is low then the concept you and I have of what is hot and what is not becomes invalid. (as relates to burning our pinkies).

When I do fusion in my Fusor IV at 31kv, the fusion performed by the fastest deuterons is occuring at over 350 million degrees kelvin, yet the shell of the fusor never warms to more than 150 degrees F in a short run. The verbage is fusion physics verbage and not weatherman verbage.

The math

1 ev of energy = ~11,000 degrees kelvin
31,000 ev of deuteron energy = 31,000 x 11,000 = 341,000,000 degrees K. Most fusion in a fusor is done at much colder temps as not all or even a lot of fusions occur at full energy, so a great amateur fusor is probably working of a central, fusion core, gas temperature at a rather chilly 100 million degrees.

To be effective at the gas inlet for fusion, we would need a 100 million degree heat exchanger. So we let electrical acceleration heat the gas to hundreds of millions of degrees once in the chamber. However, at the pressure we are using to do fusion (very low), the core of the reaction zone is really quite cool in our mental concept of the terms hot or cold at full atmospheric pressure.

Physicists use temperature and electron volts freely among one another, but use only temperatures for the public in an attempt to blow the usual quantity of smoke up their skirts to shake out a little more cash to piddle at fusion. It does sound damned impressive though, don't it?

Why do they do this? It is awfully misleading to the common Joe. Well again, that is the point. Physicists are looking for cash and an attempt to give the public viable data with a full treatise on what the electron volt is and how this seeming electrical unit relates through the thermodynamics of particles in motion given by Boltzman would be a fools errand and forgotten after they watched only one episode of Survivor or Crossing Jordan which is more at their level fo understanding anyway. ...... So, they (the physicists) figure the money will flow far more freely by telling the public they need the cash to achieve those fearsome 500 million degree fusion temperatures and open up the fusion utopia of tomorrow for all.

The average automotive ignition system or TV picture tube voltage is quite capable of elevating gas temps in a fusor to about 200 million degrees.

Thus, it is not tough to get fusion fuel gas up to fusion temperatures. It is not difficult to do fusion even!! It is impossible, at the current time, to produce any useful energy via fusion.

Richard Hull

[Donald McKinley]

Thank you Richard for your response,
No offence taken.

Greetings from So Cal. I think I understand what you mean in your reply post. Your comment that "Temperature in

fusion relates to gas molecule kinetic energy" is precisely what I meant. Sorry for my unfortunate choice of words.

The reason that I mention this idea of cooling is because I know that there are hysteresis issues even with free

particles, and wonder if in this case sudden and vigerous kinetic energy gradients can overcome a possible problem

that I wonder about. I imagine that these plasmas take some time to acheive equilibrium even after they seem to be

uniform.

I think that in Frank's three conditions post several posts ago, I would want to verify the contaminants hypothesis.

Frank, in condition #2 in your post above, after achieving the ruddy brown and the "slowing or nearly ceasing" of

the neutrons, will a quick rise of D2 pressure refresh the neutron output immediately, or does the rise in neutron

output fit a profile of decreasing contamination in the reactor gas? Have you tried contaminating the reactor gas

intentionally with Hydrogen1 gas during burn. If H1 will displace the contaminants without materially affecting the

fusion rate, it may be cheaper to run a continuous low percentage Hydrogen flush to carry away the crud and preserve

the Deuterium supply. Also the Hydrogen may flush much faster than the Deuterium because of its much smaller mass.

If this post is too elementary Richard, please let me know. I am doing a lot of reading. I won't mind remaining mute

as long as necessary until my knowledge is a little less ragged. I suspect that others will want to know the answer

to the last paragraph though.

Again Richard thanks for your good information, it is a pleasure to find a group of people who are interested in

truly interesting things.

Don

[Frank Sanns]

Don,

Good questions but tough to get at the answers.

First of all, neutron counts are not a one or two second procedure. You can hear and see a difference in counts but even with a sensitive He3 detector you need time to statistically know that there is a change. I think that time is on the order of 5 seconds for a drastic change in neutron output and more like 15 seconds for moderate change. This means that you can not instantly see a change in neutron production. In 5 seconds quite a bit of concentration changes can go on in a fusor especially with the pressure change that comes along with rapidly increasing the D2 flow while you try to balance the vacuum throttle valve to maintain fusion conditions.

With that said, I do not think the neutron production is instant when the deuteium is added but rather a displacement of SPECIFIC contaminants. I do not think all contaminants are the same and I do not think it is just simple dillution of the deuterium. There are differences in electronic configurations of all of the different atoms. Some have the potential to interfere with fusion more than others. Consider for example, a CO2 laser. The laser will not work with only CO2. Other gases need to be mixed in to transfer the energy through intermediate steps to the proper CO2 energy level for lasing. One of those gases is Nitrogen. Nitrogen has a rather simple energy structure so if you happen to have another atom like deuterium in an excited state, the nitrogen can sap the energy out of the system rather quickly. If the ionized deuterium looses its energy because it has inadvertantly transfered its energy to nitrogen impurities, then fusion will slow or stop. There will be drastically increased neutral deuteriums in the plasma so there will not be many deuterons left to be accelerated by the electric field and to go on to do fusion.

Frank S.

[longstreet]

I don't know if you can immediatly dismiss the impact of your neutral gas's temperature. But I think to really analyze the affects would be really hard. Perhaps a cooler gas has a smaller mean free path and so is more redily ionized. Decreasing the temperature also causes an increase in the number of molecules in the chamber for a given pressure.

Thanks,
Carter

[Starfire]

It could be interesting to recirculate the exhaust D2 - this would enable scrubber or other external gas process's to be applied - cyclone temperature balance, de-ionised, what ever and perhaps indentify the relevent flow property which promotes fusion. Is the residual Nuclear ash gas a factor? refiltering via a palladium membrane to accept only D2 as the return?
This might also help reduce running costs if sucessful, to the point where perhaps a D2 reservoir can be used internally - similar to a thyratron and the system sealed once pumped down.

There is potential for good science here, if only from observation of the negative aspects of low flow hi-voltage.

Also, does this mean a MOT is adequate for an effective fusor? A whole new ball game here!

[Richard Hull]

1. <"Decreasing the temperature also causes an increase in the number of molecules in the chamber for a given pressure.">

Gas temperature change will not change the number of gas molecules in the chamber, only their velocity. Only the leak-in and vacuum-out flow settings will determine the number of gas molecules in a chamber.

2. Neutrals, even high speed ones, may or may not be going the way we need them to go to fuse and as such are not a real fusion force below 40kev as even off center collsions would not do well. Above 40kev neutrals might start entering the picture as the cross section even for glancing hits will improve. A rare and lucky 30kev deuteron in a 35kv powered fusor hitting a 10kev neutral at 45 degrees is pretty much a non-fusion event. Fast neutrals will not become important, I would think, until one is actively working above 60kv applied or higher. Most low end fusion, 20 to 35kv, should be hot, head-on or near head-on deuterons.

Richard Hull

[longstreet]

1. If you are maintaining a constant volume and pressure then any change in temperature mandates a change in the density of the molecules. If you are maintaining a constant density then you must allow increased pressure at increased temperature.

All I'm saying is temperature shouldn't be quickly thrown away. Contamination is probably a bigger factor here, but unless someone has done enough experiment to show that you can't really be stating it as fact.

Carter

[Richard Hull]

You mentioned an increase in the number of molecules with decreasing temp. If you are talking about wall locked additions as contaminants, then that is backwards. The colder a wall or environment, the more likely the number of molecules of any gas will stick on the walls or within the molecular structure. reducing the number of gas atoms drifting about and reducing the density and dropping the pressure.

We cook or heat the walls via bombardment or thermal blankets to CHASE out of the molecular structure of the inner wall surface or release the molecules into the chamber for removal via pump out.

This is why with bombardment, the pressure rises as more atoms appear from the walls and, conversely, why we use a cold trap to freeze out and hold nasties in the trap, thus further reducing the pressure and gas molecule count in a chamber.

The same number of molecules are always there in the chamber they are just stuck to the walls at low temps or on their way to the pumps at high temps.

Richard Hull

[longstreet]

No, I'm just talking about basic introductory thermodynamics here. Go look at a PV diagram. If you hold pressure as constant and increase the temperature then your volume increases. Obveously the size of the chamber doesn't change. But since density is just molecules divided by volume, this changes the relation so that increased temperature means a decrease in density (inversly proportional). You can obfuscate this by including other processes which depend on temperature, but that doesn't really accomplish anything now does it?

[Richard Hull]

Again the fusor volume is fixed and can never change. Assuming no absorption or desorption, the number of particles will not change. Increasing temperature will increase pressure not through a density change which is the number of particles per UNIT volume, but through a change of velocity or KE of the particles. Lowering the temp will reduce pressure not through a change in density, (no particle number change or volume change possible in a closed system), but through a reduction of their KE (velocity related only via temp). This is what is actually seen to occur on a capacitive manometer during normal fusor operation.

Richard Hull

[longstreet]

How many times must I restate that this is for CONSTANT FRIGGING PRESSURE? You have two holes in the chamber leaking gas in and out to maintain the pressure. If the chamber was completely sealed up then NO, the density wouldn't change. But that is exactly the opposite of what we're talking about.

[Richard Hull]

I think we are talking about something that probably is a given and unavoadable in the operation of a fusor. One seeks a constant flow rate. This is impacted by far more than the leak in rate of gas and pump out rate. One can never attain a perfect flow rate in an amateur system. The best one might hope for is some operational stasis regime that is quite literary balanced on the head of a pin and affected by more variables than are readily controlable over a period of time or operating voltages and currents.

This is why, from start to finish, even on a long sealed system, 1-3 hours of prep time is needed to get the average system up from cold to its MAX fusing condition.

In the best D-D systems, you might detect fusion in under 30 minutes, but putting the system on the head of that pin is an art form and takes a while. The trickiness of going from first detection to maximum output for a given system and voltage is a supreme balancing act.

No one has reported or operated a "turn-on and go" fusor system. This is mostly because they are always taking it apart, modifying grids, changing valves, pumps etc. Most failure to ease into fusion is a residual water and wall gas related problem which tends to make a lot of folks think it is a D2 feed issue. Contaminants and water are just burned out of the system or deposited in the walls or pumped out over a very long period. (montrhs if no bake out and infrequent fusor use.)

A lot of fusor operators never take this to heart and often look for the quick fix. A quick fix would be a heat taped bakeout for 24 hours with all pumps running and ion bombarding during this time. Few, if any ever do this, so, ALL have issues with chamber gas flows, odd ball pressure puffs and what appears to be balky valving in the gas lines, etc. When all of this is really failure to prep the system to a high standard of vacuum readiness and seal.

Fusors work OK whether in this state of "vacuumist grace" or not, but if not preped and held at a high state of vacuum purity, they are balky.

Few fusioneers have $1000 micrometer thimbled sapphire needled gas leaks to warrant an asbolute inlet gas leak rate. The norm is an e-bay needle valve. Likewise, only a couple of us have formal feedback looped $3000.00 gate valve systems coupled to capacitive manometers. Most often it is just a 2.75" conflat hand operated bellows valve. So, instead of a smooth gas pressure we see variations until we get the our two crude valved system balanced on the head of that pin.

Richard Hull

[AnGuy]

>No, I'm just talking about basic introductory thermodynamics here. Go look at a PV diagram. If you hold pressure as constant and increase the temperature then your volume increases.

This doesn't really apply at the sub-micron pressure levels because the majority of volume is vacuum. In order for the pressure to rise, the density of gas atom must be high enough that they press against each other (or at least frequently collide enough). Consider this. if you have a single hydrogen atom in a vacuum chamber and heat the hydrogen atom, does the pressure increase?

In the context of a fusor, usually a vacuum pump is keep running to remove any containments released by the bombardment of gas molecules as well as metal vapors released by the hot inner grid. By far the major increase of pressure is cause by the release of these containments than the rise in temperatures of D2 gas. Pressure in a fusor is largely caused the amount of gas atoms present, not the temperature.

[AnGuy]

>Few fusioneers have $1000 micrometer thimbled sapphire needled gas leaks to warrant an asbolute inlet gas leak rate. The norm is an e-bay needle valve. Likewise, only a couple of us have formal feedback looped $3000.00 gate valve systems coupled to capacitive manometers. Most often it is just a 2.75" conflat hand operated bellows valve. So, instead of a smooth gas pressure we see variations until we get the our two crude valved system balanced on the head of that pin.

Speaking of Leaks, has anyone looked at using calibrated helium leaks for feeding D2? I assume that the leak flow is too low to use realistically in a Fusor (usually around 4 to 5 X 10 -8)