Producing more neutrons

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Johnny
Posts: 2
Joined: Mon Feb 27, 2023 7:03 pm
Real name: John Cobble

Producing more neutrons

Post by Johnny »

I was wondering if you were to add multiple inner grids to a Fusor how many more neutrons would be produced for every cage you added? This Fusor would be running with Deuterium gas.
William Turner
Posts: 31
Joined: Sun Nov 27, 2022 10:09 am
Real name: William Turner

Re: Producing more neutrons

Post by William Turner »

Assuming you are talking about:

- spatially separated cathode grids and not concentric
- all cathode grids have at least a path through the vacuum to the anode and are not completely obstructed by other grids

Then if they have paths on all clear apertures to the anode the current would increase and fusion scales directly proportional to the ion current (this is the ideal case, assuming that all the cathodes can operate at exactly the same voltage or each cathode is supplied with a different power supply because likey the voltages will be different and one will probably limit the operation of the others).

Alternately if they have few paths, then they probably would act like a larger single cathode.

Voltage is the best scaling you will get in an electrostatic fusion device.

Will

P.S. Update your user name to your full name (forum rules)
Johnny
Posts: 2
Joined: Mon Feb 27, 2023 7:03 pm
Real name: John Cobble

Re: Producing more neutrons

Post by Johnny »

Thank you and I will
User avatar
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Producing more neutrons

Post by Liam David »

These experiments have already been done in academia (both concentric cathodes and multiple non-concentric cathodes in the same device). Although some of the published papers are less than spectacular, they illustrate some of the basics. The bottom line is that in a glow-discharge fusor, multiple concentric grids are unhelpful and multiple non-concentric grids don't perform better than a single grid run at the same total current.
User avatar
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

Johnny,
Increasing current or voltage on an IEC fusor will increase the fusion reaction rate. Here's why. Higher voltage increases the fusion cross section. Actually the typical fusor running deuterium at around 30 - 50 kV is only operating at the low end of the fusion cross section curve. The peak for DD reaction, if memory serves, is around 1000kV (a million volts). So the higher the voltage the better for neutron production. The DT reaction peaks at a much lower < 80kV.
Increasing current means that you are increasing the density of ions at the center of the cathode grid and I believe the fusion rate goes as the square of the density. There are a number of IEC researchers out there that run fusor like devices in a pulsed mode where a capacitor bank is charged up and discharged into the fusor. Pulses only last for a few milli-seconds but the discharge current can easily go into the amps. Some papers have claimed 10^9 - 10^10 neutrons per pulse.

Hope that helps,
Rich G.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

Due to the slope of the D-D cross section there is almost nothing to be gained after 200kv applied. You are just making the fusor an impossible thing to construct and control, in addition to an extreme health hazard.

The best slope ends around 150kv with the ideal being under 100kv. The best amateur effort would strain to reach 100kv due to nearly insuperable insulation and x-radiation issues. Special issues, not imagined, await any who would work over 100kv.

We see a 1000 fold increase in fusion cross section between 8kv and 150kv. After that no real viable gain in fusion is seen

Richard Hull
Attachments
crossSections.jpg
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
Bob Reite
Posts: 576
Joined: Sun Aug 25, 2013 9:03 pm
Real name: Bob Reite
Location: Wilkes Barre/Scranton area

Re: Producing more neutrons

Post by Bob Reite »

Most of us work around 40KV to 50KV At those voltages things are manageable. Going above 60 KV, everything starts becoming a big deal. Corona, X-rays, you name it.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
User avatar
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Producing more neutrons

Post by Liam David »

While totally irrelevant for most people here working at lower voltages, the dominant species in a fusor is (D2)+. Each nucleus has half the total energy gained from the potential well and so the rate calculation becomes 2 * n * crosssection(E/2) * v(E,m_D2) instead of n * crosssection(E) * v(E,m_D). You're lower on the cross-section curve than you think, even ignoring things like the abundant molecular processes that reduce the ion energies.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

Yet we do fusion. Sufficient for many here. The simple fusor remains the most inelegant method of doing fusion. It is cheap, it works. Elegance costs money and is just not to be found in the simple fusor.

If obtaining fusion is likened to mining coal, we are mining it by going at the coal face with our heads from a running start and scrabbling it up with our bare hands. Yet we get coal. Who knows, some clever fellow will figure to bring a large rock and throw it at the coal face to save his head. We can't afford more useful mechanical methods. We need just enough to keep warm by. We aren't looking to benefit mankind by supplying them with heat or energy. Let them get theirs, we have sufficient to our needs.

You must ask yourself..."How many neutrons are enough?".... "Am I willing to pour in the money needed to get them?"...."Do I come to the game willing and capable of doing this?"

Many arrive here with big dreams and ideas. Few make the grade of even doing fusion, much less producing huge neutron output levels.

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
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

In response to Liam’s post of a few days ago,

So, what your saying is that most of the fusion interactions are due to the molecular species of deuterium (D2+) rather than the mono-atomic species…and also that most of the fusion reactions are due to the accelerated D2+ ion slamming into a more or less stationary target D2 neutral molecule at the core (rate ~ 2n* σ(E/2)*v(E,m_D2). The maximum available energy for the reaction is E/2 due to conservation of momentum (i.e. at E = 50kV the max energy available for reaction is 25keV).

There is also the possibility of D2+ reaction with D2+ ions from the opposite side of the grid. Beam to beam collision. These would have a max center of mass energy = 2E available for the reaction since the total momentum is zero and all the energy is available for the reaction. These reactions are 4X higher on the fusion cross section curve (i.e. at E = 50kV the max energy available for reaction is 100keV).
I guess the reaction rate for these are ~ 2n*2n*σ(2E)*v(E,m_D2) = 4n^2*σ(2E)*v(E,m_D2). Does this sound right?

Another question… In the IEC device which process dominates in terms of fusion neutrons?

Rich G.
User avatar
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

In response to Johnny's question of Feb27,

I can see an advantage in using two cages (outer bigger cage at anode (ground) and a smaller cathode inner cage at -HV) to create a more symmetric electric field situation. This could help in the case of a spherical cathode grid inside of a cylindrical metal vacuum chamber and you would certainly need both if using a glass bell jar chamber (which I don't recommend).

Rich G.
User avatar
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Producing more neutrons

Post by Liam David »

Rich, you're mostly correct. I'd suggest you read my high-level explanation for the various fusion mechanisms in a fusor here: viewtopic.php?p=96483#p96483. It might answer some of your questions, although I kept it light on details and math. In summary, beam-beam fusion is negligible.

In most fusors D2+ is the primary species and most experimental papers I've read, as well as simulations done by myself and others, indicate it causes most of the fusions (with background D2). There are some caveats and technicalities but I won't go into them here.

You have to be careful about your cross-section definitions (center-of-mass vs. beam-target). Your beam-beam reactivity should be 2n*2n*σ(2E)*2*v(E,m_D2) since the v in <σv> is the relative velocity (here I assume 1D). All the cross-sections σ(E), σ(E/2), etc... that you and I have written use the beam-target cross-section function.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

It is all about explaining a mess in the simple fusor. Laudable effort in explaining a mess filled with wrong species and chance fusions, but it works.
BOT is shown to work a bit better.
Multi-grid systems with filaments boiling off electrons might be better.
Well made ion guns are known to do better.
You pay your money and build better stuff, you'll do better. You will only do what D-D fusion allows in any assemblage. With an expenditure of $150,000 you can approach some limited degree of purity of species in play and leave the amateur mess behind.

More neutrons are out there awaiting the expenditure. Energy production is not out there at any level of expenditure.

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
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

Thanks Liam, yes 2*v in the beam to beam situation. My bad.

Its hard to believe, given the above discussion we get any neutrons at all especially at such low kVs as 30.

1. Only 1/2 the energy from the high potential goes into most of the reactions...

2. Speaking classically we would need something like a million volts to breach the coulomb barrier. So in the simple fusor its quantum tunneling that allows fusion reactions to happen at all... as Richard put it " Yet we do fusion" and with the simple fusor. I like the coal mining analogy.

Thanks all,
Rich G.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

Rich, yes, we do fusion at a net energy loss ratio of 1:10e-9. Like the original query you put forward, it is about the neutrons for me. Fusion means nothing beyond the gateway to legal neutrons in my lab to do amateur activation experiments. Fusion, scientifically, and even technically, is easy to do, as we have always noted.

I am glad you liked the coal face analogy. It sounds stupid to go at a coal face with your head, (hopefully with a helmet on), to win what tiny amount of coal you can get off the mine floor after each run at it. However, that is what the simplest original spherical fusor of 1999 does in its effort to make fusion and neutrons!

Many improvements in the amateur fusion effort has managed to place a sledgehammer in the hands of our best fusioneers here. (They get more coal/neutrons for their efforts) . Still there is no one with a pneumatic jack hammer yet for any number of reasons. (mostly money, but often they have reached a point with the sledgehammer where their take of neutrons and fusion is satisfactory to their purpose.

The effort to understand what is wrong with the simple effort and why it is so inefficient has always been a quest and many have laudably contributed to this understanding over the years. The great thing is we are at the quantum crap table trying to magically slip past that potential barrier. Unable to obtain the purity of the single shot sniper rifle that gets a win every single shot. We, in the simple fusor, are effectively blindfolded behind a machine gun blasting away, wasting bullets insanely to get what we get via shear volume. We just overpower the the quantum probabilities consuming mass quantities of joule energy for our pitiable returns. Wasted energy and effort is of no concern if it is neutrons you want.
...... and that is OK for many here. You just need to determine how many neutrons and how much fusion is satisfactory in your effort.

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

Re: Producing more neutrons

Post by Dennis P Brown »

As for Rich Gorski's suggestion of a 'two cage' system inside a given fusor (outer ground screen and inner cathode), I did that experiment some years ago in a large volume fusor. I wanted to address the issue of increasing fusion rate via simple increased D2 pressure via decreasing the available volume for the plasma - so the fusor's remaining unused volume had no plasma.

In this experiment, I used a smaller ground cage (compared to the fusor chamber volume) while keeping the absolute fusor volume constant. This enabled a significantly higher operating pressure of D2 for identical constant current/voltage used w/o the cage. The fusion rate increased with increased pressure and the increased pressure supplied more D2 ions.

While the experiment was done to demonstrate that decreasing the active plasma volume inversely increases optimized fusion chamber pressure for any given fusor, any effect by a separate ground cage was not apparent nor really something I could determine. This experiment also demonstrated that a outer ground cage does work to enhance total neutron production regardless.

So, I can't say a grounding cage had much effect on total fusion rate (due to better plasma symmetry) over and above the increased gas pressure - the pressure tracked nicely with fusion rate as the fusor volume was decreased (so the 'effective' ion volume was lowered) permitting higher D2 pressure. By creating a half effective plasma volume (@ 32 kV, 24 ma)I was able to increase fusion rate by 50% due to the D2 pressure going from 12-15 microns to 28-30 microns (measure via a Bubble dosimeter.)

If the ground cage enhanced fusion rate in of itself, I can't say but certainly increased total pressure appears to achieve this for any given fusor.
User avatar
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

Dennis,

Yeah, I agree with your conclusion that symmetry between cathode and anode has little to do with the neutron yield. This is due to the short MFP were dealing with at typical fusor pressure of ~10-20 microns. This means fusion events are between neutral D2 molecules and high energy D2 molecules as well as high energy impacts on the cathode grid. The main thing is that there are almost no beam to beam fusion events at this pressure. From that point of view just sticking any cathode geometry inside a chamber filled with D2 at the 10 microns should generate fusion events when its brought to > 20kV. Maybe even just the feedthrough stalk without a spherical cathode grid or a flat plate. How about an ion source accelerating a beam to >20kV and just letting the beam into a chamber filled with D2 gas? All these should show some level of fusion events taking place.
Symmetry might become more important if we can get a fusor to operate at a pressure of 1 micron or less where beam to beam reactions become more probable and then beam focus and symmetry could become important. Take a look at the free path distribution plot I created below. I think its quite informative. It shows the probability in percent of a particle traveling a distance l at various pressures.
freepathdist.jpg
.

Based on the values I used for temperature (400K) and D2 diameter (2.89^-10m) the MFP at 10 microns is just 1 or 2 cm. The direction I'm going is to use ion sources (circumferential) that can operate at 1 micron pressure where the MFP is near 10cm and as many as 10% can reach a distance of 25cm before the first collision. These circumferential sources can operate at 1 micron and produce tens of mA of beam current. Then there should be some level of beam to beam interactions at the center of a 7cm radius chamber. So far in my experience using these ion sources I'm finding that at 1 micron pressure there is almost no ionization present in the chamber (and no current registering on the HV supply) even at 30kV when the ion sources are not energized. With the sources switched on I can reach 20 mA of current on the HV supply. So I'm thinking given the mean free path at 1 micron of 10cm I might be seeing beam to beam interactions as well. I'm just at the start of this adventure and so far all I know is that fusion neutrons are present.

I'll report on this as things progress.

Rich G.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

I take issue with the 400kelvin assumed ion energy under full voltage with collisions and acceleratory urgings this is a much more a velocity space consideration. Assuming some mean temperature is a very big stretch. A one cm acceleratory path at 10 microns in a 20kv system of a 6" sphere of an ideal 5cm wall to grid field would amount to 4kv max average ion energy at collision or even less for D2+ This is not fusion conducive.

Blanket assumptions in the torrent of particles in a plasma, thin or thick is a folly.

None of us here figure that every deuterium atom becomes a deuteron. (long understood here)
Likewise, none of us here really believe that every deuteron that is created in the fusor is accelerated in a 20kv field reaches an energy of 20,000 X 11,400 = 228 million Kelvins. If we believed any of this, that would be folly as well.

We do not believe the particle velocity space in the plasma is 400 kelvins for the sake of any calculations. There are no averages or means within the fusor when in operation.

Nice chart but it doesn't describe the interior of a working fusor. Many have tried to figure out the fusor as to why it works and what holds it back. We are positive only of the fact that it is something that cannot be quantized along any idealized lines that tell the whole story. It is too simple a device with too much going on in it to say, " I know just how it works."

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

Re: Producing more neutrons

Post by Dennis P Brown »

No surprise that you are not seeing an active plasma at 1 micron; certainly my fusor system flashes out below 5 micron (32 kV.)

I will say this after talking to experts in the field of ion fusion. No one has bothered to build any serious fusion devices to really test/exploit particle beams in a serious manner. While efficiency of the accelerators is large (about 25% wall outlet to multi-MeV deuterium ions for the pro's) the low density (read, no significant interaction) has been the issue that prevented anyone from trying to use this process for plasma machines.

If you think about it, hitting a solid D2 target with high MeV deuterons would create a much improved probability of fusion. Yet the yield in energy would be rather small considering even a few milliamps isn't a lot of ions compared to what a power plant would require. So, from what I understand, that is why this hasn't been attempted for inertial fusion; however, no one is certain if such a device could or couldn't achieve viable fusion via 'flash over' ignition. That is, a powerful D2 ionized beam (many MeV) is used to create a tiny fusion event in a solid target of D/T fuel to start fusion (local burn) and get all the fuel to burn.
User avatar
Rich Gorski
Posts: 133
Joined: Mon Aug 01, 2022 4:34 pm
Real name: Rich Gorski
Location: Illinois

Re: Producing more neutrons

Post by Rich Gorski »

Richard,
Boy what a thrashing (LOL). My post was in no way an attempt to explain the complex plasma environment of the typical fusor. I’m sorry you took it that way. The discussion began with grid symmetry and that I was moving in a different direction with my device, into a pressure point where the typical fusor cannot operate and where symmetry might matter. The chart was only there to illustrate the point about pressure and interaction probabilities in the case of simple billiard ball interaction… and of course the temperature I used of 400K is meaningless but it served to get my point across. My claim is that beam to beam fusion interactions are indeed possible in a system like the one I am building. Here the particle interaction is not so strongly dependent on pressure. Instead it might also depend on the interaction cross section, density and interaction time and as Dennis stated it will be exceeding small in my case. The question is can it be better than the typical fusor.

Dennis,
Your right. At 1 micron there is no active plasma in most of the my chamber. However there is active bright plasma in the confines of the sheet beam emitted from each of the dual ion sources that is visible all the way to the center of the chamber and well into the space on the opposite side. So, I would be tempted to say there is some level (obviously small because of density) of beam to beam interactions that goes as the square of the particle density in that region. My interest is to experiment in this region of pressure with a 360 degree ion beam that is focused in the vertical plane increasing density. Could it exceed the fusion rate of the typical fusor? Maybe, we’ll see. It also allows the possibility of experiment to look at effects of beam current to fusion rate and beam energy to fusion rate independently. This is possible in my system because I have independent control over beam current and beam energy. Something you cannot achieve in the standard fusor since the ionization current is dependent on the power supply voltage.

Work on colliding beam fusion for power generation started in the 1960s and has not stopped. The latest being Helionenergy (www.helionenergy.com heavily funded thru private entities) which uses a dual colliding system of intense plasma pulses, accelerated and coupled with some kind of pulsed millisecond magnetic confinement. I just barely understand the concept.

Rich G.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

Helion is doomed to fail like all the rest of past and present fusion efforts. Just another throwaway of lots of money.
The winner will be 10X++ output over input energy running 24-7-365. All other efforts get to join the rubble pile of 75 year old fusion attempts.
Gimme a coal fired or gas fired or a fission power station any day of the week. They've be doing it 24-7-365 for many years. Fusion has been doing nothing for almost as long.

There has never been even one break even fusion event since the last H bomb was tested and even it produced real power for under a few 10s of microseconds.

Fusion will remain the energy of a very distant future.

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

Re: Producing more neutrons

Post by Dennis P Brown »

Serious attempts using ions to achieve real fusion energy outputs has never been tried to my knowledge (maybe a Black program but that must have failed.) Certainly ion collision fusion has been around since the 1930's! As for any startup, well, they are always producing many orders of more power than consumed ... on paper. I'll just say that it is worthwhile to look into but not expecting too much.

Well, here at the Fusor Forum there are a number of clubs - the Plasma Club, the Neutron Club, and Activation Club (i.e. Advance fusor users - the one I'd like to get into!); however, the one unofficial club that has no list is the one where poor Richard must once again, patently explain and often in some detail, exactly why the person posting is in error (and I've joined that club a few times already!)

I consider it an honor to get into that unofficial club since no guts, no glory and everyone should try and exceed their limits. That is and always will be praise worthy* but runs the risk of getting a 'thrashing' from those that are both wise and well learned in various subjects ;)


* for those that base their concepts on fairly reasoned and thought out physics; and if really 'out there' - have at least built it to determine if worthwhile (again, been there done that unsuccessfully with a new type of neutron detector material/design - that build crashed and burned - lol.)
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Producing more neutrons

Post by Richard Hull »

Got an idea? Sure it will work? Think it is gonna' be easy because it is "at the undergrad level"? Got th' bucks to see it through? Got th' skills to make it all happen as planned?

Get busy. Build it. Test it. Get back to us with full info and details. We appreciate all the doers who put forth the effort.

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)”