NUMERICAL COMPUTATIONS FOR ADIABATIC PARTICLE MOTION : Numeriska beräkningar för adiabatisk partikelrörelse

Sammanfattning: Axisymmetric mirrors have no collision free radial transport, but such magnetic fields may have problems with plasma stability (the tearing instability in particular). There are some means to improve plasma stability in axisymmetric mirrors by magnetic expander tanks or axisymmetric divertors, but plasma stability can still be a challenge in axisymmetric mirrors. An alternative is to use quadrupolar magnetic fields as a robust method to overcome the stability issues. A price may then be increased radial transport if the magnetic field design is done without strict consideration of asymmetries, which could result from manufacturing errors.The computations have been done with a hybrid reactor scenario in mind. Such a case have less demands for confinement, but the demands are still challenging. Confinement for about 200 longitudinal bounces is required in a hybrid reactor. The computations carried out here have confirmed that axial asymmetry may become dangerous for plasma confinement in quadrupolar mirror machines. Asymmetry in the range of a few percentage relative error will almost surely result in a too strong radial leakage (at least without a radial electric field). The computational results made in this paper may suggest that if the manufacturing error is kept below 0.15% relative error throughout the plasma confinement region, there is then a some margin for sufficient radial confinement quality. Such accuracies ought to be possible to achieve in the manufacturing process, possible combined with compensating magnetic fields to maintain a precise magnetic field design. The precision requirements in the design is still a bit challenging.