High harmonic fast wave current drive experiments on NSTX

Phased-array experiments were performed with the 30-MHz, 12-element HHFW antenna array on NSTX for rf powers in the 2-4.5 MW range. Relative phase shift of the array was scanned from pi/6 to pi/2 to create k(z) spectral peaks between 3 and 7.6 m(-1); it was also possible to switch from pi/2 to pi/4 phasing during a shot. Typical plasma parameters were I-p similar to 0.5 MA, B-T similar to 0.45 T, and n(e)(0) similar to 1-3x10(19) m(-3), and T-e(0) similar to 1-3 keV. Electron heating was observed even at the highest wave phase velocities, reaching 1.3 keV with 2.2 MW at -pi/6 phasing and 2.7 keV with 2.9 MW at -pi/3. Lower plasma loading and higher central heating efficiency are observed for counter-CD phasing. MSE measurement of the current profile is not yet available; therefore, the rf-driven portion of the plasma current is calculated from the difference in loop voltage between co- and counter-CD phasing. The normalized current drive efficiency for k(z) = 7.6 m(-1) is gammasimilar to 0.035x10(19) A(.)W(-1.)m(-2) for both D and He plasmas.