First results on currentless plasma production and heating by ECR waves in the L-2 stellarator

To produce and heat currentless plasma in the L-2 stellarator, extraordinary polarized (E-vector perpendicular to B-vector) microwave radiation is utilized. The microwave power beam is directed into the vacuum vessel through a vertical port, which, because of the specific distribution of the magnetic field module in L-2, is equivalent to feeding from the strong-field side. At a beam power of 80 to 100 kW, a plasma with Tsub(e) approx.= 450-500 eV, Tsub(i) approx.= 60 eV, and n-barsub(e) approx.= 6x1012cm-3, and a total energy content of about 80 J is obtained; 30 to 50% of the microwave power is absorbed in the plasma. The absorption is shown to depend on nsub(e) and to decrease for nsub(e)(O) approx.= nsub(cr). Collisionless heating of ions is recorded. Apparently, the observed broadening of the microwave spectrum scattered by the plasma hints at the appearance of some plasma instabilities resulting in the excitation of plasma oscillations. (author)