2016 SRC Presentation
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This document contains two graphs showing the relationship between central density and rotation frequency. The first graph shows how central density increases as central rotation frequency increases from 0 to 30 kHz. The second graph shows a similar relationship between central density and wall rotation frequency from 0 to 6 kHz. Both graphs demonstrate that increasing rotation frequency is correlated with higher central density.
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2016 SRC Presentation
Editor's Notes
- Axial magnetic field that provides confinement in the radial direction. The rings have an electric voltage of about 150 V to confine the ion as the ion moves along the magnetic field line. ExB field drift Omega can be either the diocotron rotation or the plasma rotation which is driven by the ExB drift and the diocotron rotation occurs when the plasma is off-center.
- The Fourier Mass spectrometry is done by driving a plasma at or near the cyclotron frequency (which is mass dependent) and then, as the frequency of the driving is lowered, we find the resonant frequencies of the plasma, which we can then use to determine the elemental composition of the source.
- Non-neutral electron or ion plasmas confined in Penning-Malmberg traps have inherent confinement times which are long, but finite. In practice, background neutral gas and small confinement field asymmetries exert a drag on the rotating plasma, causing slow radial expansion and eventual particle loss. The rotating wall uses torque to recompress the plasma so that it can be trapped in the Penning-Malmberg traps and increase the density. The rotation is based upon the 8 segments of the ring that are driven by a electrical sine wave. Each segment of the ring is at 45 degrees out of phase with its neighbor, which results in an rotating electric field inside the plasma. Confinement is bad since the longer the confinement is, the more probable it will be that there will be collisions with neutral gas. (Gas density is about 1/10th of our plasma density). If the rotating wall frequency is too high in comparison to the central rotating frequency, the plasma will not couple and it will act like there is no rotating wall. If the frequency of the rotating wall is too low in comparison to the rotation frequency, the plasma will be forced to expand radially since we are slowing it down. EQUILSOR does a numerical calculation of the rotating wall frequency because in order to calculate the rotating wall frequency, we need to know the total electric field of the system at that point. EQUILSOR is taken after we dump the ions we collect from the plasma. We cannot predict what are parameters will be until after the experiment. We have also worked to increase the number of ions in the plasma.
- Ring operating voltage- After we trapped the plasma at 153 V, we then dropped the confinement rings to around 40 V. This is important because at 153 V, the plasma doesn’t reach the rotating wall. Increasing the ring operating voltage causes the plasma to extend longitudinally and reach the rotating wall. Dump delay- This helps us seek the lifetime of a plasma by dumping the positive ions that are collected. This will help us determine how well confined our plasma is. Frequency of the rotating wall- must be set to be slightly faster than the central frequency of the plasma. Catch delay- improve the amount of ions that we trapped
- No fit, but it is definitely linear.
- Very scattered, there is a trend upwards that as the central density increases, the wall rotation frequency increases too. However, this graph is obviously nonlinear. Variation is caused by the variation in the plasma radius, poor consistency in the source generating ions, and the length of the plasma.
- Our central density is about 10^11~10^12 m^-3 where the maximum is at 4*10^13 m^-3. We want to get to about 4*10^12 m^-3 (10% of the maximum) central density for a good analysis. Frequency of the rotating wall must be set to be slightly faster than the central frequency of the plasma. Most of our future efforts that we will focus on will be ensuring that the rotating wall will behave so that we can obtain a plasma with sufficient density More fine tuning on the catch delay Ring operating voltage