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Development of Electron Bernstein Wave Research in MAST

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


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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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