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 similar to 20% of the coupled rf power) is now believed to be due to ion cyclotron absorption by a small (similar to 0.5%) impurity of Li-7. This problem was remedied through the use of Li-6 for wall conditioning. In contrast to the 1996 results, experiments performed with Li-6 wall conditioning produced strong ion and electron heating in D-T plasmas.