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Irvine Field Reversed Configuration Ion Density and Flow. T. Roche, F. Brandi, E. P. Garate, F. Giammanco, W. W. Heidbrink, W. Harris, R. McWilliams, E. Paganini, E. Trask Slides available at http://hal900.ps.uci.edu/aps2008/.
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T. Roche, F. Brandi, E. P. Garate, F. Giammanco, W. W. Heidbrink, W. Harris, R. McWilliams, E. Paganini, E. Trask
Slides available at http://hal900.ps.uci.edu/aps2008/
FRC with a Flux Coil configuration. The plasma forms around the inner coil instead of r=0.
Pietrzyk, Vlases, Brooks, Hahn, Raman, Nuc. Fus. 1987
Each Probe consists of 4 tips protruding from a 50cm shaft. Two of the tips are completely exposed to the plasma. The other two are separated from each other and only exposed to 180 degrees of theplasma.
The probe on the bottom is the final version. The tips are much shorter, made out of tantalum instead of platinum and have a radius of 0.4mm. It is the only version that didn’t suffer from arcing.
These shots exhibit functionality of the Mach Probe. Probe is located at z=-8cm with tips facing opposite arrays of plasma guns. Flux will be greater and arrive earlier on the tip closer to guns. In all cases larger signal is from expected tip.
Here the plasma is not magnetized. This probe works as expected in these conditions.The Mach Probe Works
Bz at z = 0 cm quickly reverses and maintains reversal until it begins to decay around 70 micro-seconds.
Br at r = 25 cm takes on the appropriate shape and decays as the driving flux coil
The field null, or B = 0, forms around -10 cm < z < 10 cm and r ~ 25 cm.
The chord used to determine the line density from the ion saturation current was the same for the interferometer except that the laser also traveled through the outer region of the containment area. The density in that region is assumed to be small. The features of these methods are similar.
A and B refer to the two signal tips. When a tip is faced ‘Up’ it faced the direction of plasma current. A ratio greater than 1 denoted a flow velocity ‘Up’. This graph shows that the tips gave conflicting results. After many iterations it was determined that the environment during a full shot was too noisy to make a precise enough measurement to determine the flow velocity. It became obvious that the probe tips do not agree with each other.
Using the argument of pressure balance, density may be derived from the magnitude of the magnetic field. There is an offset of a constant of integration. Here pressure was set to zero at the maximum of the magnetic field. At 40 ms the peak of the density is at r = 24 cm and ni =1.25 x 1014. Ti assumed to be 10eV.
Density profiles at ~40us exhibit same features and magnitudes.
These data show a similar density evolution. A different series of shots were used which may account for the discrepancies as the lifetime of the plasma was longer for the magnetic shots.
The spike to -1300V makes measuring anything referenced to the plasma difficult.
These signals must be decoupled from our scope ground. In this simple experimentcurrent on the line was measured using a set of passive Pearson probes.
The rigid rotor predicts the following plasma model
A. Qerushi, Doctoral Thesis,
To perform this simulation a choice of distribution function must be made. A shifted maxwellian in canonical momentum space was selected.
Betatron orbit and associated effective potential
Drift orbit and associated effective potential
The number of betatron orbits leads us to believe that we will not able to distinguish drift orbits where betatron orbits are present. However, if drift orbits exist in the region where betatron orbits do not, they may be seen there.
Differential signal amplifier. Placed as close as possible to the collector and dummy.
Optical Isolation Amplifier
Circuit. Its purpose is to take the signal with a largeoffset from scope groundand decouple it.
Axis of Symmetry
Mach probe measurements have been successful
IEA simulation suggests viability of probe
Finish construction of Ion Energy Analyzer and