Experimental investigation of the ripple induced losses of perpendicularlyinjected beam ions in the low aspect ratio helical system CHS

Confinement of perpendicularly injected beam ions has been investigated exp erimentally both in the standard configuration and in the drift optimized c onfiguration of the CHS heliotron/torsatron by means of the neutron techniq ue. The experimental results indicate that the confinement, of trapped beam ions is poor in both configurations. The observed loss rate of trapped bea m ions was very high and this high rate is not explained by losses due to c harge exchange or collisional scattering from the timescale perspective. Fu ll gyro-motion following orbit calculations showed that in the peripheral r egion of CHS plasmas, trapped beam ions are promptly lost because they imme diately intersect the vacuum chamber wall due to their large Larmor radii. It also suggested that in the core domain the collisionless transition beha viour is the key to understanding the rapid loss of beam ions. It was shown that the magnetic moment of perpendicularly injected beam ions is not well conserved in CHS. The rapid losses of perpendicularly injected beam ions a re probably due to non-adiabatic effects resulting in the transition behavi our of energetic ions.