A high resolution Mirnov array for the Mega Ampere Spherical Tokamak

• Published in: Review of scientific instruments 2009-12, Vol.80 (12), p.123507-123507-10
• Main Authors: Hole, M. J., Appel, L. C., Martin, R.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALPHA PARTICLES; BEAM INJECTION HEATING; COMPUTERIZED SIMULATION; DESIGN; ELECTRIC CURRENTS; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; MAGNET COILS; NEUTRAL ATOM BEAM INJECTION; OSCILLATIONS; PLASMA; PLASMA DIAGNOSTICS; PLASMA SIMULATION; PLASMA WAVES; RESOLUTION; SPHEROMAK DEVICES
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.3272713

Over the past two decades, the increase in neutral-beam heating and α particle production in magnetically confined fusion plasmas has led to an increase in energetic particle driven mode activity, much of which has an electromagnetic signature which can be detected by the use of external Mirnov coils. Typically, the frequency and spatial wave number band of such oscillations increase with increasing injection energy, offering new challenges for diagnostic design. In particular, as the frequency approaches the megahertz range, care must be taken to model the stray capacitance of the coil, which limits the resonant frequency of the probe; model transmission line effects in the system, which if unchecked can produce system resonances; and minimize coil conductive shielding, so as to minimize skin currents which limit the frequency response of the coil. As well as optimizing the frequency response, the coils should also be positioned to confidently identify oscillations over a wide wave number band. This work, which draws on new techniques in stray capacitance modeling and coil positioning, is a case study of the outboard Mirnov array for high-frequency acquisition in the Mega Ampere Spherical Tokamak, and is intended as a roadmap for the design of high frequency, weak field strength magnetic diagnostics.