Mode conversion heating and current drive in TFTR

Two new four-strap fast wave antennas, driven by 8 MW of rf source power at 30 MHz, were installed for the final run period of TFTR. These antennas were utilized with D-T target plasmas to perform experiments in mode conversion heating. Poor mode conversion efficiency seen in D-T during the 1996 run (typically ∼20% of the coupled rf power) is now believed to be due to ion cyclotron absorption by a small (∼0.5%) impurity of 7Li. This problem was remedied through the use of 6Li for wall conditioning. In contrast to the 1996 results, experiments performed with 6Li wall conditioning produced strong ion and electron heating in D-T plasmas.