ICP input gas flow calculation

[steve_rb]

Suppose we want to have 10^9 neutrons per second. what should be the amount of D2 gas going inside ICP? Has anyone done a similar calculations?

[Chris Bradley]

steve robinson wrote:
> Suppose we want to have 10^9 neutrons per second. what should be the amount of D2 gas going inside ICP? Has anyone done a similar calculations?

The question is meaningless and poorly researched.

You've not indicated any process for fusion, nor ion energies/distributions, nor density, &c., &c., &c., by which such a calculation can be made. Fusion doesn't just happen when you put deuterium in one place. You need high specific energy in fusible ions (for one thing) and ions in an 'ICP' are very cold. Might aswell be at absolute zero, on the scale needed for fusion.

Your question is a bit like asking 'how many dollars do I have to stuff into my bank account before a car appears for me'. Sure, stuffing money into your bank account is one step to getting a car, but you're missing quite a few steps there.

[Carl Willis]

The gas flow rate in an ion source is usually determined by two things: the pressure needed to obtain a sustained discharge, and the conductance of the extraction aperture through which waste gas is differentially pumped. It is almost never a fixed design quantity because it is easy to control and necessary to control to get good operation. 1 sccm is a quantity that works well on the proton sources my company builds and on the deuterium ion sources I have used at home. Numbers too much higher than that probably reflect unnecessary waste, and numbers a couple orders smaller are impractical to achieve.

The required pressure depends on many things. If the RF discharge is magnetically enhanced with helicon or ECR modes, the pressure can be quite low (<1e-4 torr) and the plasma density high. Without magnetic enhancement, I don't see getting below about 1e-2 torr.

The size of the extraction aperture (hence its conductance) is determined by the Child-Langmuir law, a function of extraction voltage and beam current and the species being extracted. The application probably dictates the beam current, and the extraction voltage is probably constrained for practical reasons to a few dozen kV, tops.

You're the only one who knows sufficiently well what your objectives are and what your design is right now to calculate any numbers, but maybe this will steer you in the right direction. I think you should be heavily relying on published experience rather than designing an ion source from scratch.

-Carl

[steve_rb]

let me put it this way. if inside ICP pressure is 1 millitor and outside pressure is 10^-2 militorr and aperture dameter is about 1.5 mm how much H2 gas is flowing through aperture?

[John Futter]

Steve

Its time you did your own work and find out about differential pumping

there are very good texts for free on the net about vacuum technology where this is covered in depth and the maths is no more than a 4th grader would be comfortable with.

[steve_rb]

Not that easy mate. I looked at a few of these links but still too complicated for me.

http://www.therebreathersite.nl/01_Info ... rifice.htm
http://www.pipeflowcalculations.com/orifice/theory.htm
http://www.flowmeterdirectory.com/flowm ... _calc.html

[Carl Willis]

Nobody's going to do the problem for you. If you can't find this problem set up online, you haven't checked some pretty obvious references. Keep looking.

-Carl

[John Futter]

One from this site

viewtopic.php?f=10&t=3649#p21057

[steve_rb]

using Daniel orifice flow calculator software I have got about 500 ccm which seems too high. I don't know what mistake I have done.

[Carl Willis]

Hi Steven,

You should probably change the operating pressure from "gauge" to "absolute." Right now you are effectively working at atmospheric pressure, and so the calculator is using the wrong (viscous or turbulent flow) equations. You want it to use molecular-flow equations.

I didn't check the specific gravity at STP of D2 gas (what you need to be using to get a correct answer for D2 flow), but that's another thing you need to have correct in order to get a meaningful answer. You might read the help file to be sure that the calculator will in fact do a valid calculation under the circumstances.

-Carl