9.3 Dynamic Control of Cusp Loss

Experimental results and computer simulation studies on the dynamic control of cusp loss are presented. The steady‐state plasma is fed into a cusped magnetic field along the spindle axis. The plasma density at the center is 10¹¹ cm⁻³, and ${\mathrm{T}}_{\mathrm{e}}\mathrm{\hspace{0.17em}\simeq \hspace{0.17em}}{\mathrm{T}}_{\mathrm{i}}\text{\hspace{0.17em}≃\hspace{0.17em}10\hspace{0.17em}}\mathrm{eV}$ . The rf electric field whose frequency is near the ion cyclotron frequency is applied perpendicularly to the line cusp and to both point cusps. When the rf field is applied the ion density at the center increases by a factor of two and its mean energy reaches up to 50 eV. From the increase of ion density, the increase of decay time by about a factor of ten is estimated. The number density of high‐energy ions above 100 eV confined in the cusp increases by a factor of over fifty. The computer simulation of the rf effect on the line loss suppression indicates a good agreement with the experimental results.