TY - JOUR
T1 - Modeling and experiments on differential pumping in linear plasma generators operating at high gas flows
JF - Journal of Applied Physics
Y1 - 2009
A1 - van Eck, H. J. N.
A1 - Koppers, W. R.
A1 - van Rooij, G. J.
A1 - W. J. Goedheer
A1 - Engeln, R.
A1 - D.C. Schram
A1 - Cardozo, N. J. L.
A1 - Kleyn, A. W.
KW - BEHAVIOR
KW - EXPANSION
KW - FACILITY
KW - INTERACTIONS
KW - ITER
KW - JET
KW - Monte Carlo methods
KW - NEUTRAL GAS
KW - PISCES
KW - plasma flow
KW - plasma simulation
KW - plasma-wall
KW - PSI
KW - SIMULATION MONTE-CARLO
KW - SURFACE INTERACTION
KW - Tokamak devices
AB - The direct simulation Monte Carlo (DSMC) method was used to investigate the efficiency of differential pumping in linear plasma generators operating at high gas flows. Skimmers are used to separate the neutrals from the plasma beam, which is guided from the source to the target by a strong axial magnetic field. In this way, the neutrals are prevented to reach the target region. The neutral flux to the target must be lower than the plasma flux to enable ITER relevant plasma-surface interaction (PSI) studies. It is therefore essential to control the neutral gas dynamics. The DSMC method was used to model the expansion of a hot gas in a low pressure vessel where a small discrepancy in shock position was found between the simulations and a well-established empirical formula. Two stage differential pumping was modeled and applied in the linear plasma devices Pilot-PSI and PLEXIS. In Pilot-PSI a factor of 4.5 pressure reduction for H-2 has been demonstrated. Both simulations and experiments showed that the optimum skimmer position depends on the position of the shock and therefore shifts for different gas parameters. The shape of the skimmer has to be designed such that it has a minimum impact on the shock structure. A too large angle between the skimmer and the forward direction of the gas flow leads to an influence on the expansion structure. A pressure increase in front of the skimmer is formed and the flow of the plasma beam becomes obstructed. It has been shown that a skimmer with an angle around 53 degrees gives the best performance. The use of skimmers is implemented in the design of the large linear plasma generator Magnum-PSI. Here, a three stage differentially pumped vacuum system is used to reach low enough neutral pressures near the target, opening a door to PSI research in the ITER relevant regime.
VL - 105
SN - 0021-8979
UR - ://000264774000061
N1 - ISI Document Delivery No.: 427IWTimes Cited: 0Cited Reference Count: 36
U1 - Fusion Physics
U5 - f708d5ab049f127fc32d123e7e46c0e9
ER -