Improved Collective Thomson Scattering measurements of fast ions at ASDEX upgrade

Understanding the behaviour of the confined fast ions is important in both current and future fusion experiments. These ions play a key role in heating the plasma and will be crucial for achieving conditions for burning plasma in next-step fusion devices. Microwave-based Collective Thomson Scatterin...

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Main Authors: Rasmussen, J, Nielsen, S K, Stejner, M, Salewski, M, Jacobsen, A S, Korsholm, S B, Leipold, F, Meo, F, Michelsen, P K, Moseev, D, Schubert, M, Stober, J, Tardini, G, Wagner, D, Upgrade, ASDEX
Format: Conference Proceeding
Language:English
Subjects:
ASDEX TOKAMAK
BEAM INJECTION HEATING
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Computer simulation
COMPUTERIZED SIMULATION
DISTRIBUTION FUNCTIONS
Feasibility studies
Heating
Ion distribution
Ion dynamics
MICROWAVE RADIATION
NEUTRAL ATOM BEAM INJECTION
PLASMA
SPACE-TIME
Subtraction
THOMSON SCATTERING
Upgrading
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Summary:Understanding the behaviour of the confined fast ions is important in both current and future fusion experiments. These ions play a key role in heating the plasma and will be crucial for achieving conditions for burning plasma in next-step fusion devices. Microwave-based Collective Thomson Scattering (CTS) is well suited for reactor conditions and offers such an opportunity by providing measurements of the confined fast-ion distribution function resolved in space, time and 1D velocity space. We currently operate a CTS system at ASDEX Upgrade using a gyrotron which generates probing radiation at 105 GHz. A new setup using two independent receiver systems has enabled improved subtraction of the background signal, and hence the first accurate characterization of fast-ion properties. Here we review this new dual-receiver CTS setup and present results on fast-ion measurements based on the improved background characterization. These results have been obtained both with and without NBI heating, and with the measurement volume located close to the centre of the plasma. The measurements agree quantitatively with predictions of numerical simulations. Hence, CTS studies of fast-ion dynamics at ASDEX Upgrade are now feasible. The new background subtraction technique could be important for the design of CTS systems in other fusion experiments.
ISSN:0094-243X
1551-7616
DOI:10.1063/1.4894036