Ion Cyclotron Resonance Heating in a Toroidal Octupole

A 1 MW� 2 msec pulse of rf power at the ion cyclotron frequency (2.6 MHz) has been used to heat the ions from < 1 eV to 350 eV in a toroidal octupole device. The ion temperature is limited by charge exchange loss and agrees quantitatively with theoretical predictions. No parametric decay waves, enhanced diffusion, or other deleterious effects except for a high neutral re­ flux are observed to accompany the heating. Ion cyclotron resonance heating is a promising technique for raising the ion temperature in a Tokamak reactor above the level that can be achieved with ohmic heating alone. Many of the Tokamak-related problems can be studied on toroidal multipole devices which can operate over a wide range of parameters. The small toroidal octupole 1 at the University of Wisconsin has been used to study ICRH for a number of years, and we previously reported 2 ion temperatures of about 100 eV with 500 kW of 1 MHz for 1 msec. We have recently upgraded the oscillator to 1 MW of 2.6 MHz for 2 msec and redesigned the coupling structure in an attempt'to increase the ion temperature above 100 eV. We report here experiments in which ion temperatures of about 350 eV are observed with no deleterious effects except for a high neutral reflux which limits the ion temperature by charge exchange. A cross section of the toroidal octupole de­ vice is shown in Fig. 1. The magnetic field in the experiments to be de­ scribed is purely poloidal and is produced by the currents in four solid copper hoops which-link an iron transformer core 2 FERROMAGNETIC �ELECTROSTATIC ION=E=X T�RAC=T OR ::::;: =JdJ ENERGY ANALYZER I