Plasma Density of a Non Neutral Plasma

Bryce Spencer

What will be discussed today• Our intention in our experiment and our motivation for

exploring the parameters of plasma density• What we did in our experiment• What our results were in our experiment • What we concluded and what would change in future

experiments

What is a non neutral plasma?

Motivation• We initially began our experiment by attempting mass

spectrometry of our plasma using a Fourier Transform Ion cyclotron resonance to determine the composition.

• However, it became evident that as we began to run our experiment, our plasma was not reaching a high enough density to make a spectral analysis.

• We then concluded that we needed to determine the best way to get a plasma with high enough density so that we could take an accurate Fourier Transform of the ion motions.

Relevant Background information

• A rotating wall confinement system was introduced by Anderegg, Hollmann, and Driscoll in 1998 as a way to better confine the plasma in a short, finite area. (Phys. Rev. Lett. 81, 4875 30 November 1998)

• Key to having a proper rotating wall is finding the correct rotating wall frequency.

• In order to calculate the frequency, we use a program called EQUILSOR

Experimental Methods we used

• We varied the ring operating voltage• We varied the dump delay• We also varied the frequency of the rotating wall• We changed the catch delay• We then ran these parameters into our Equilsor

program that then calculated the central rotating frequency, the wall rotating frequency and the central plasma density.

Results

0.00E+00 2.00E+12 4.00E+12 6.00E+12 8.00E+12 1.00E+130.00E+00

5.00E+00

1.00E+01

1.50E+01

2.00E+01

2.50E+01

3.00E+01

Central Density (/m^3)

Cen

tral R

otat

ion

Freq

uenc

y (k

Hz)

• After analyzing our shots with varying conditions, this graph is comparing the central density to the central rotating frequency.

Results continued• We then measured the

frequency at which a particle at the wall will rotate and the central density of the plasma.

0.00E+00 2.00E+12 4.00E+12 6.00E+12 8.00E+12 1.00E+130.00E+00

1.00E+00

2.00E+00

3.00E+00

4.00E+00

5.00E+00

6.00E+00

Central Density (/m^3)

Wal

l Rot

atio

n Fr

eque

ncy

(kH

z)

Conclusions• The density of our plasma is too low for a good

analysis using Fourier-based mass spectrometry.• In future experiments, our main focus will be to vary

the frequency of the rotating wall and the amplitude of the rotating wall.

• Other changes will be made to help fine-tune our system.