@inproceedings{13bf2e8e41e8498ca346cb7fef8299cf,
title = "HHFW heating and current drive studies of NSTX H-mode plasmas",
abstract = "30 MHz high-harmonic fast wave (HHFW) heating and current drive are being developed to assist fully non-inductive plasma current (I p) ramp-up in NSTX. The initial approach to achieving this goal has been to heat I p=300kA inductive plasmas with current drive antenna phasing in order to generate an HHFW H-mode with significant bootstrap and RF-driven current. Recent experiments, using only 1.4 MW of RF power (P RF), achieved a non-inductive current fraction, f NI∼0.65. Improved antenna conditioning resulted in the generation of I p=650kA HHFW H-mode plasmas, with f NI∼0.35, when P RF≥2.5MW. These plasmas have little or no edge localized mode (ELM) activity during HHFW heating, a substantial increase in stored energy and a sustained central electron temperature of 5-6 keV. Another focus of NSTX HHFW research is to heat an H-mode generated by 90 keV neutral beam injection (NBI). Improved HHFW coupling to NBI-generated H-modes has resulted in a broad increase in electron temperature profile when HHFW heating is applied. Analysis of a closely matched pair of NBI and HHFW+NBI H-mode plasmas revealed that about half of the antenna power is deposited inside the last closed flux surface (LCFS). Of the power damped inside the LCFS about two-thirds is absorbed directly by electrons and one-third accelerates fast-ions that are mostly promptly lost from the plasma. At longer toroidal launch wavelengths, HHFW+NBI H-mode plasmas can have an RF power flow to the divertor outside the LCFS that significantly reduces RF power deposition to the core. ELMs can also reduce RF power deposition to the core and increase power deposition to the edge. Recent full wave modeling of NSTX HHFW+NBI H-mode plasmas, with the model extended to the vessel wall, predicts a coaxial standing mode between the LCFS and the wall that can have large amplitudes at longer launch wavelengths. These simulation results qualitatively agree with HHFW+NBI H-mode data that show decreasing core RF heating efficiency and increasing RF power flow to the lower divertor at longer launch wavelengths.",
keywords = "RF Heating and Current Drive, Spherical Torus",
author = "G. Taylor and Bonoli, \{P. T.\} and Green, \{D. L.\} and Harvey, \{R. W.\} and Hosea, \{J. C.\} and Jaeger, \{E. F.\} and Leblanc, \{B. P.\} and R. Maingi and Phillips, \{C. K.\} and Ryan, \{P. M.\} and Valeo, \{E. J.\} and Wilson, \{J. R.\} and Wright, \{J. C.\}",
year = "2011",
doi = "10.1063/1.3664985",
language = "English (US)",
isbn = "9780735409781",
series = "AIP Conference Proceedings",
pages = "325--332",
booktitle = "Radio Frequency Power in Plasmas - Proceedings of the 19th Topical Conference",
note = "19th Topical Conference on Radio Frequency Power in Plasmas ; Conference date: 01-06-2011 Through 03-07-2011",
}