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Enhancing The Mode Conversion Efficiency In JET Plasmas With Multiple Mode Conversion Layers
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Abstract [en]

The constructive interference effect described by Fuchs et al. [ 1] shows that the mode conversion and thereby the overall heating efficiency can be enhanced significantly when an integer number of fast wave wavelengths can be folded in between the high field side fast wave cutoff and the ion-ion hybrid layer(s) at which the ion Bernstein or ion cyclotron waves are excited. This effect was already experimentally identified in (He-3)-D plasmas [ 2] and was recently tested in (He-3)-H JET plasmas. The latter is an 'inverted' scenario, which differs significantly from the (He-3)-D scenarios since the mode-conversion layer is positioned between the low field side edge of the plasma and the ion-cyclotron layer of the minority He-3 ions (whereas the order in which a wave entering the plasma from the low field side encounters these layers is inverted in a 'regular' scenario), and because much lower He-3 concentrations are needed to achieve the mode-conversion heating regime. The presence of small amounts of He-4 and D in the discharges gave rise to an additional mode conversion layer on top of the expected one associated with He-3-H, which made the interpretation of the results more complex but also more interesting: Three different regimes could be distinguished as a function of X[He-3], and the differing dynamics at the various concentrations could be traced back to the presence of these two mode conversion layers and their associated fast wave cutoffs. Whereas (1-D and 2-D) numerical modeling yields quantitative information on the RF absorptivity, recent analytical work by Kazakov [3] permits to grasp the dominant underlying wave interaction physics.

Place, publisher, year, edition, pages
, AIP Conference Proceedings, 1406
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Applied Nuclear Physics
URN: urn:nbn:se:uu:diva-287125DOI: 10.1063/1.3664981ISI: 000301041300065OAI: oai:DiVA.org:uu-287125DiVA: diva2:922223
19th Topical Conference on Radio Frequency Power in Plasmas/US-Japan Workshop on RF Physics, JUN 01-03, 2011, Newport, RI
Available from: 2016-04-22 Created: 2016-04-22 Last updated: 2016-04-22

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Cecconello, MarcoHellesen, Carl
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Applied Nuclear Physics
Fusion, Plasma and Space Physics

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