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Particle acceleration during merging-compression plasma start-up in the Mega Amp Spherical Tokamak
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McClements, K. G., Allen, J. O., Chapman, Sandra C., Dendy, R. O., Irvine, S. W. A., Marshall, O., Robb, D., Turnyankiy, M. and Vann, R. G. L. (2017) Particle acceleration during merging-compression plasma start-up in the Mega Amp Spherical Tokamak. Plasma Physics and Controlled Fusion, 60 (2). 025013. doi:10.1088/1361-6587/aa98fa ISSN 0741-3335.
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Official URL: https://doi.org/10.1088/1361-6587/aa98fa
Abstract
Magnetic reconnection occurred during merging-compression plasma start-up in the Mega Amp Spherical Tokamak (MAST), resulting in the prompt acceleration of substantial numbers of ions and electrons to highly suprathermal energies. Accelerated field-aligned ions (deuterons and protons) were detected using a neutral particle analyser at energies up to about 20 keV during merging in early MAST pulses, while nonthermal electrons have been detected indirectly in more recent pulses through microwave bursts. However no increase in soft X-ray emission was observed until later in the merging phase, by which time strong electron heating had been detected through Thomson scattering measurements. A test-particle code CUEBIT is used to model ion acceleration in the presence of an inductive toroidal electric field with a prescribed spatial profile and temporal evolution based on Hall-MHD simulations of the merging process. The simulations yield particle distributions with properties similar to those observed experimentally, including strong field alignment of the fast ions and the acceleration of protons to higher energies than deuterons. Particle-in-cell modelling of a plasma containing a dilute field-aligned suprathermal electron component suggests that at least some of the microwave bursts can be attributed to the anomalous Doppler instability driven by anisotropic fast electrons, which do not produce measurable enhancements in soft X-ray emission either because they are insufficiently energetic or because the nonthermal bremsstrahlung emissivity during this phase of the pulse is below the detection threshold. There is no evidence of runaway electron acceleration during merging, possibly due to the presence of three-dimensional field perturbations.
| Item Type: | Journal Article | |||||||||||||||||||||
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| Subjects: | Q Science > QC Physics | |||||||||||||||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | |||||||||||||||||||||
| Library of Congress Subject Headings (LCSH): | Magnetic reconnection, Particle acceleration, Deuterons, Culham Centre for Fusion Energy -- Experiments | |||||||||||||||||||||
| Journal or Publication Title: | Plasma Physics and Controlled Fusion | |||||||||||||||||||||
| Publisher: | Institute of Physics Publishing Ltd. | |||||||||||||||||||||
| ISSN: | 0741-3335 | |||||||||||||||||||||
| Official Date: | 20 December 2017 | |||||||||||||||||||||
| Dates: |
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| Volume: | 60 | |||||||||||||||||||||
| Number: | 2 | |||||||||||||||||||||
| Article Number: | 025013 | |||||||||||||||||||||
| DOI: | 10.1088/1361-6587/aa98fa | |||||||||||||||||||||
| Status: | Peer Reviewed | |||||||||||||||||||||
| Publication Status: | Published | |||||||||||||||||||||
| Access rights to Published version: | Open Access (Creative Commons) | |||||||||||||||||||||
| Copyright Holders: | UK Atomic Energy Authority | |||||||||||||||||||||
| Date of first compliant deposit: | 7 November 2017 | |||||||||||||||||||||
| Date of first compliant Open Access: | 2 May 2018 | |||||||||||||||||||||
| RIOXX Funder/Project Grant: |
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