Effects of high energy alpha on materials

[MSimon]

Anyone got any better ideas ?

Boron 11. Then the sputtered material is a reactant and not a poison.

[Keegan]

^ I wish i could find some good data on alphas and diamond. I am really interested to know how much sputtering would really happen. The SP3 bond is pretty special. Also remember 12C is one step in the p + 11B reaction.

Boron is nice. Im yet to look up the cross sections, but as posted earlier

11B + α → 14N + n + 157 keV.

[MSimon]

I am really interested to know how much sputtering would really happen.

It doesn't matter how special the bond is. Hit it with 2 MeV alphas and it will crack and the pieces will be sent flying.

[93143]

Doesn't the surface of the magrid have to be conductive?

[tombo]

Why?

[TallDave]

To hold the positive charge.

[tombo]

Why not an insulating outer layer over the conductive electrode?
I can't see how it would hurt anything, especially if thin.
A thin high breakdown voltage insulating layer could mitigate the Paschen arcing problem.
But, we would need to work out exactly what happens to the electrons that impact it.
The electrode should not see much current if the magnetic field is doing its job.
So it could be made of a poor conductor such as graphite which is a good high-temp vacuum-stable material & much cheaper to deposit than diamond.
The coils obviously have to be very good conductors.

Another thought:
The high current coils if well insulated from the electrode layer would not have to be at that same high potential.
They could be at near earth-ground potentials.
This would greatly simplify the power supplies.
Most good thermal insulators are good electrical insulators too.
This also applies to the water cooling layer and would alleviate some of my safety concerns.
It would also greatly simplify the coolant piping.
(i.e. Water must be treated as somewhat conductive. Does anyone know about LN2?)

[hanelyp]

If you wrapped the magrid in an insulator, electrons making it through the magnetic insulation would pile up on the outside of the insulator layer until enough charge/voltage built up to break through or the voltage drive on the magrid could no longer compensate. The magrid casing needs to be conductive, though not necessarially a good conductor.

[drmike]

From a circuit design perspective, an insulator on the MaGrid looks like a capacitor. Instead of a direct connection between the field and the plasma, you are capacitively coupled. Not exactly accurate, but gives an idea.

Putting a dielectric material on the outside of a conductor reduces the E field, and we don't really want that. We need as strong a field as possible, so having a conductive surface is important.

[domoarrigato]

Maybe I'm missing something, but if the alpha's are +2 charged, won't they tend to escape the magrid in an orderly fashion through coils? After all, they should follow the magnetic field lines in the opposite direction of the recirculating electrons to some degree. Seems like there will be six beams of alpha's (in a truncated dodecahedron arrangement).

[blaisepascal]

Maybe I'm missing something, but if the alpha's are +2 charged, won't they tend to escape the magrid in an orderly fashion through coils? After all, they should follow the magnetic field lines in the opposite direction of the recirculating electrons to some degree. Seems like there will be six beams of alpha's (in a truncated dodecahedron arrangement).

The acceleration caused by the fields is proportional to the charge, but inversely proportional to the mass. The alphas are about 3600 times as massive as the electrons, so the forces on them are about 1800 times weaker than on the electrons.

So the alphas won't be affected much by the magrid.

[MSimon]

The high current coils if well insulated from the electrode layer would not have to be at that same high potential.
They could be at near earth-ground potentials.
This would greatly simplify the power supplies.

Yep. Great idea. Except that suitable insulators would increase the coil size significantly and thus increase alpha impingement and heat loads.

[eros]

The acceleration caused by the fields is proportional to the charge, but inversely proportional to the mass. The alphas are about 3600 times as massive as the electrons, so the forces on them are about 1800 times weaker than on the electrons.

So the alphas won't be affected much by the magrid.

You mean that force depends at charge and alphas charge is two times electron. So force is double, but mass 3600x so accelration comes 1800 times weeker than electrons.

Thanks! I just asked same thing in other thread. If electrons have 8mm circulation radius, then a=v² /r, hmm, what is electron and alphas speed? electrons are light so they travel fast compared alphas, there is maybe some effect..? E=½mv² so speed come v=sqrt(2E/m)
electrons are 70kev? alphas ~2Mev
r1=8mm r2=?

r2=(8mm*2Mev *3600mu)/(0.07Mev*1mu *1800)
=8mm*2*2/0.07 = 457mm

Seems no problem at small coils, but max 50kv/cm, 1Mv grid => min 20cm. Somewhere talk at max 25kv/cm -> 40cm it may effect..

Where come 8mm radius, I take it somewhere. It must depend B field. More calculations are needed..
My skills are quite limited I am only ~engineer.

[blaisepascal]

The acceleration caused by the fields is proportional to the charge, but inversely proportional to the mass. The alphas are about 3600 times as massive as the electrons, so the forces on them are about 1800 times weaker than on the electrons.

So the alphas won't be affected much by the magrid.

You mean that force depends at charge and alphas charge is two times electron. So force is double, but mass 3600x so accelration comes 1800 times weeker than electrons.

I mean't acceleration all around, since it's acceleration which is directly related to the kinematics. a=F/m, and F is proportional to charge q.

I did make a mistake, however. An alpha is 4amu, and an electron is about 1/1800 amu, so an alpha isn't 3600 times as massive as an electron, it's 7200 times as massive. So the acceleration on the electron is 3600 greater, not 1800 times greater, than the acceleration on the alpha.

Thanks! I just asked same thing in other thread. If electrons have 8mm circulation radius, then a=v² /r, hmm, what is electron and alphas speed? electrons are light so they travel fast compared alphas, there is maybe some effect..? E=½mv² so speed come v=sqrt(2E/m)
electrons are 70kev? alphas ~2Mev
r1=8mm r2=?

r2=(8mm*2Mev *3600mu)/(0.07Mev*1mu *1800)
=8mm*2*2/0.07 = 457mm

Seems no problem at small coils, but max 50kv/cm, 1Mv grid => min 20cm. Somewhere talk at max 25kv/cm -> 40cm it may effect..

Where come 8mm radius, I take it somewhere. It must depend B field. More calculations are needed..
My skills are quite limited I am only ~engineer.

The radius is (as far as I know) the gyroradius, which is related to the magnetic field. It's inversely proportional to the magnetic field strength and charge, and proportional to the particle momentum perpendicular to the magnetic field. Under otherwise identical situations, the same calculations as above apply, and the alphas have a gyroradius 3600 times as large as the gyroradius of the electrons. The only changes left to affect it are the velocity and direction of the particles. But unless the alphas are significantly slower than the electrons, their gyroradius is going to be significantly larger.

[rcain]

nasa, semiconductor (+self-annealing) - circa 2000 - GaAs or SiC :: http://findarticles.com/p/articles/mi_q ... 19757/pg_1

us nano bucky+gold - march 2008 :: http://technology.newscientist.com/arti ... icity.html::

(same) nano - http://nextbigfuture.com/2008/03/direct ... -into.html

interesting?