Measuring the plasma specs?

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Werner Engel
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Measuring the plasma specs?

Post by Werner Engel » Thu Apr 24, 2014 5:51 pm

Hello "fusor" world!

I searched through this forum and a lot of literature and did not find a complete list of measuring methods to describe the quality of the plasma within a fusor. We can measure neutron production, bremsstrahlung, vacuum pressure, voltage, current and that’s almost it.

What about plasma density? Wouldn’t it be useful to also track this parameter – and not only at a certain point but over the whole crossection of the plasma focus?

The JET-Tokamak uses Thomsons Scattering which seems quite complicated and is not very well described in literature in a precise way. Andrew Seltzman has published some words regarding his TS - apparatus – but it also seems to be quite difficult to build – not to mention to interpret the results.

My question: Anyone tried to use ordinary laser absorption methods? Or laser – spectroscopy with a lambda-tuned laser?
My idea: Use a laser to shine through the plasma and measure the absorption value on the other side of the plasma. By changing the wavelength (eg. dye laser in littrow configuration) and intensity you should be able to detect changes in optical permeability – and by calculating the plasma frequency (reflection/absorption border) out of these values it should be possible to get an idea of the plasma density using the SAHA equation. Using a scanning mirror construction with a moving focus, this could be used to get a 3D image of the plasma – or am I wrong?

Greetings from Austria,
Werner

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Richard Hull
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Re: Measuring the plasma specs?

Post by Richard Hull » Thu Apr 24, 2014 6:16 pm

This laser methodology for examining the plasma was supposedly done in the late 60's for the ITT Farnsworth project when the new laser technology was looking for things to do to justify itself by a couple of universities. There was a general concensus that the center was more dense, but specific numbers were varied and vague. Importantly, this is not a compression device, but functions in this mode only as one of many modes that does fusion in many ways, by many processes. The plasma is but one way to and end of many co-jointly acting ways. The fusor's mult-modal fusioning is its success! The fusor doesn't really strive for one method of doing fusion. Yes, it originally did, theoretcially. To those who know its real modus operandi, it is an elegant entanglement of many situational games of chance that are favored to one degree or another within its volume.

Oddly, this original post should have gone in the theory forum just as I have scolded another for posting a neutron counting methodolgy in that forum rather than here where it belonged. Oh well.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Werner Engel
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Re: Measuring the plasma specs?

Post by Werner Engel » Thu Apr 24, 2014 6:43 pm

Thank you very much for the Feedback.
Anyway - I will give these ideas a try with my fusor over the next few months and post the results - if there will be any usefull ones ;-)
I will start with an ordinary 445 nm laser and my thorlabs ccd spectrometer and will keep you in touch (posted in the theory forum).

BR,
Werner

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Chris Bradley
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Re: Measuring the plasma specs?

Post by Chris Bradley » Thu Apr 24, 2014 6:55 pm

There's almost no plasma in a fusor. It's mostly neutral gas, and what there is, especially the 'important' stuff, is non-Maxwellian so values from many 'advanced' plasma measurement techniques that assume high ionisation ratios and Maxwellian distributions will likely confuse you.

You should have found examples of Lamgmuir probe and Faraday cup measurements, though, although you also appear to have missed the very simple and non-arduous registration instructions. I look forward to reading about your laser experiment results. I'll be surprised if you measure anything, but go and surprise me!

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Richard Hull
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Re: Measuring the plasma specs?

Post by Richard Hull » Fri Apr 25, 2014 6:28 am

Yes, by all means, post any results that you obtain along with you methodolgy. It is results and interesting experiment that we are interested in. As Benjamin Franklin noted...."Let the experiment be done!"

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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