Two frequency ICRF operation on TFTR

Modifications have been made to allow two of the ICRF antennas (bays L and M) on TFTR to operate at either of two frequencies, 43 MHz or 64 MHz. The two frequency operation will allow a combination of 3He-minority and H-minority heating at near full field on TFTR. Distributing the RF power between different ion species is expected to result in lower energy minority ions which have better confinement and better energy coupling to the bulk plasma. The higher frequency, 64 MHz, may also be useful in direct electron heating and current drive experiments at lower toroical fields. The two frequency capability was accomplished by lengthening the resonant loops (2λ at 43 MHz, 3λ at 64 MHz) and replacing the conventional quarter wave impedance transformers with a tapered impedance design. The other two antennas (bays K and N) will operate at a fixed frequency, 43 MHz. Models of the antenna, resonant loops, and impedance matching system are presented