Home / Store / Journals / Electronic Articles / Fusion Science and Technology / Volume 52 / Number 2
V. Shevchenko, G. Cunningham, A. Gurchenko, E. Gusakov, B. Lloyd, M. O'Brien, A. Saveliev, A. Surkov, F. Volpe, M. Walsh
Fusion Science and Technology
Volume 52 / Number 2 / August 2007 / Pages 202-215
Format:electronic copy (download)
Burning plasma spherical tokamaks (STs) rely on off-axis current drive (CD) and nonsolenoid start-up techniques. Electron Bernstein waves (EBWs) may provide efficient off-axis heating and CD in high-density ST plasmas. EBWs may also be used in the plasma start-up phase because EBW absorption and CD efficiency remain high even in relatively cold plasmas. EBW studies on the Mega Ampere Spherical Tokamak (MAST) can be subdivided into four separate subjects: thermal electron cyclotron emission observations from overdense plasmas, EBW modeling, proof-of-principle EBW heating experiments with the existing 60-GHz gyrotrons, and EBW assisted plasma start-up at 28 GHz. These studies are also aimed at determining the potential for a high-power EBW system for heating and CD in MAST. The optimum choice of frequency and launch configuration is a key issue for future applications in MAST. This paper describes diagnostics, modeling tools, and high-power radio frequency systems developed specifically for EBW research in MAST. The experimental methodology employed in proof-of-principle EBW heating experiments along with experimental results is discussed in detail. EBW heating via the ordinary-extraordinary-Bernstein (O-X-B) mode conversion has clearly been observed for the first time in an ST.
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