Deuterium ion speed at 30kv.

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Retric
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Deuterium ion speed at 30kv.

Post by Retric »

There seems to be a lot of misunderstanding of the physics involved
with this these fusers so I am going to try and post some clear
theoretical post’s on this stuff.

I am going to ignore relativity for now but feel free to correct any other
mistakes.

See http://www-istp.gsfc.nasa.gov/Education/wenpart1.html for a
clear but long definition of Energy particles.

Basically an electron volt represents the energy an electron gains or
loses when going though a field of X volts to X+1 volts. For example
in a TV an electron is accelerated though a 30,000 volt (30kv) field to
~1/3 the speed of light or ~100,000 kilometers / second.

Anyway we want to know how fast the Deuterium is going as it enters
the center of a fussier. Assuming it’s accelerated though the same
field strength say 10,000kv to 40,000kv we know the energy gain is
the same but its mass is different.

Kinetic energy = 1/2 Mass * (velocity) ^2

Deuterium = 1 proton + 1 neutron.

Electron mass = 9.10938188 * 10 ^ -31 kilograms
Proton mass = 1.67262158 * 10 ^ -27 kilograms
Neutron mass = 1.6749286 * 10 ^ -27 kilograms

So 1 deuterium nucleus weighs ~ (1 proton mass + 1 neutron mass )
/ (1 electron mass) ~= (1.6726158 * 10 ^-27+ 1.6749286 *10 ^-27) /
(9.10938188 * 10 ^ -31) ~= 3700 times the mass.

So ((100,000km/s) ^2 / 3700)^.5 ~= Deuterium velocity. Thus 30kv
Deuterium ions have a velocity of ~1,600,000 m / s.

Which means that to last for a full second the ion would need to travel
though the chamber well over 1 million times. So even in a 99.9%
clear cage the ion only last well under ~1/1000th of a second. (The
time for a full path is longer than distance / max velocity; you have to
add in the time it takes to change direction at each end but that's
more math than I want to get into in this post.)
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Javier Lopez
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Re: Deuterium ion speed at 30kv.

Post by Javier Lopez »

This excel table calculates it. I hear that D+D fusion greater area is at 1MeV, but I see in lots of posts speaking of about 30kV
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Richard Hull
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Re: Deuterium ion speed at 30kv.

Post by Richard Hull »

We recognize the optimum part of the curve exists at 1mev, but very nice, easily measured fusion is done at 30kv in our fusors.

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
Wilfried Heil
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Re: Deuterium ion speed at 30kv.

Post by Wilfried Heil »

Maybe these numbers come in handy, for cm sizes and MHz oscillations:

Deuteron speed at [keV]:

1 keV : 0.033 cm/ns
10 keV : 0.10 cm/ns
25 keV : 0.17 cm/ns
50 keV : 0.23 cm/ns
100 keV : 0.33 cm/ns

On a ns timescale, Deuterons look quite sluggish.
The speed of light is 30 cm/ns.
RealBorg
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Re: Deuterium ion speed at 30kv.

Post by RealBorg »

According to Wikipedia the optimal temperature for deuterium fusion is 15keV.

Does this mean I have to accelerate the deuterons with 15kV? Or would I need 55.5MV?

From my understanding of thermodynamics (mass/impulse), deuterons in an equilibrium with electrons at 15keV would still be 3700 times slower than the electrons or about as fast as beeing accelerated by 15kV.

Tom
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Richard Hull
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Re: Deuterium ion speed at 30kv.

Post by Richard Hull »

It is all about cross section and a look at the cross section for D-D fusion we see a steep initial probability of fusion up to about 100kev kinetic energy, then it rather lazily rolls off to a maximum just above 1mev energy.

The greatest gain in fusion per unit energy is from 0kev to about 100kev and thus fusion is possible over this lower range with rapidly increasing probability. Far less is gained, per unit kev increase, especially going from say 200kev to 1 mev.

The 1mev level is merely a desideratum, a limit beyond which you are throwing input energy in a toilet. For the amateur fusioneer, anything over 100kev is throwing money and energy in the toilet as costs, dangers, and epic fails await.

This is why we can do rather impressive fusion levels at only 40-60kv applied in a fusor. (2 to 4 million fusions per second)

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
John Fenley
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Re: Deuterium ion speed at 30kv.

Post by John Fenley »

Richard Hull wrote:The 1mev level is merely a desideratum, a limit beyond which you are throwing input energy in a toilet.
If you raise the energy far, far above this, it seems like you could use the accelerated ions to heat the "cold" ion cloud that forms inside the center electrode to keep the average energy there above 30kev. I'm thinking now of using a cyclotron or electron beam to add energy to a regular system rather than needing extra high voltage on the inner grid. I'll poke around some more to see what others have done.
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Richard Hull
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Re: Deuterium ion speed at 30kv.

Post by Richard Hull »

If you look at the entire D-D fusion cross section you see the desired fusion above 3 mev nose dives to near zero at extreme energies. Why? Well if you study the entire neutron physics and fusion physics of things, you will discover the Oppenheimer-Philips reaction for D-D. This reaction is often refered to as "stripping".

Above 3mev, fusion in D-D rolls off as this reaction fuses nothing but is so energetic it shears neutrons from the deuterons with no fusion at all. It gets much worse at higher mev, which explains the droop in the D-D cross sectional diagram at higher energies.

Many studied but stupid folks originally poo-poo'd our fusion efforts as not being fusion at all, but claimed our neutron counting detection results were due to the Oppenheimer-Philips reaction, the problem is they remembered the reaction and what it did (nice little students), but they forgot the tremndous energies required to make it happen and mindlessly refused to believe you could do D-D fusion at only 30kv. This old saw about why we aren't really doing fusion is now just a relic of our early internet efforts by the naysayers who have all gone on to other things once we showed them up on the matter.

Going to higher energies will truly be throwing energy in the toilet on a vast scale where the fusion disappears and we are talking the purest form of net energy loss that one might imagine.

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
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Rich Feldman
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Re: Deuterium ion speed at 30kv.

Post by Rich Feldman »

Been meaning to correct a couple of minutiae noticed in this thread.
RealBorg wrote:...From my understanding of thermodynamics (mass/impulse), deuterons in an equilibrium with electrons at 15keV would still be 3700 times slower than the electrons or about as fast as beeing accelerated by 15kV.
Tom, you missed a square rooting. In thermal equilbrium, when all particle types have the same average energy, the D+ ions are only about 60 times slower than the electrons. At 15 keV the velocities are 0.4% of c and 24% of c minus a bit ('cause the electron velocity is sort of relativisitic).

Back in 2006, W. Heil posted a table with velocities that are about 7% too high. Probably from a few too many rough approximations, or adopting a deuteron mass 13% lower than that in the literature. Corrected values of sqrt(2E/m) to the same precisions are:
1 keV: 0.031 cm/ns ( 310 km/s or 0.1% c)
10 keV: 0.10 cm/ns (1000 km/s or 0.3% c)
25 keV: 0.15 cm/ns (1500 km/s or 0.5% c)
50 keV: 0.22 cm/ns (2200 km/s or 0.7% c)
100 keV: 0.31 cm/ns (3100 km/s or 1.0% c)

Accelerating a deuteron to precisely c/100 takes rest_mass/20,000 = 93.8 keV. For c/1000 it's just 938 electron volts.

A solar wind deuteron at 400 km/s, a few solar radii out, would have 1.7 keV and could reach Earth in 4.3 days.
But at the Sun's surface that speed is not enough to escape solar gravity.

This thread's nominal case is 30 keV, for which I figured deuteron v to be 1696 km/s. As a mnemonic, that's 1.0 AU per day. :-)
All models are wrong; some models are useful. -- George Box
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