Producing more neutrons

[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]

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]

Thank you and I will

[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.

[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.

[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

[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.

[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.

[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

[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.

[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.

[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.

[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

[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.

[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