Measurements and modeling of Alfven eigenmode induced fast ion transport and loss in DIII-D and ASDEX Upgrade

Journal Article · Sun May 15 00:00:00 EDT 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3574663· OSTI ID:21537877

Van Zeeland, M A; Fisher, R K; Hyatt, A W ^[1]; Heidbrink, W W; Pace, D C; Muscatello, C M; Zhu, Y B ^[2]; Garcia Munoz, M; Geiger, B; Maraschek, M; Suttrop, W; Tardini, G ^[3]; Kramer, G J; White, R B; Gorelenkova, M; Gorelenkov, N N; Nazikian, R ^[4]; Aekaeslompolo, S ^[5]; Austin, M E ^[6]; Boom, J E ^[7]

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1. General Atomics, P.O. Box 85608 San Diego, California 92186-5608 (United States)
2. University of California-Irvine, University Dr., Irvine, California 92697-4575 (United States)
3. Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Boltzmannstr. 2, D-85748 Garching (Germany)
4. Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 (United States)
5. Aalto University, FI-02015 TKK (Finland)
6. University of Texas-Austin, 2100 San Jacinto Blvd, Austin, Texas 78712-1047 (United States)
7. FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Nieuwegein (Netherlands)

Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvenic activity including toroidicity-induced Alfven eigenmodes and reversed shear Alfven eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and increased drive due to multiple higher order resonances. Scans of injected 80 keV neutral beam power on DIII-D showed a transition from classical to AE dominated fast ion transport and, as previously found, discharges with strong AE activity exhibit a deficit in neutron emission relative to classical predictions. By keeping beam power constant and delaying injection during the current ramp, AE activity was reduced or eliminated and a significant improvement in fast ion confinement observed. Similarly, experiments in ASDEX Upgrade using early 60 keV neutral beam injection drove multiple unstable RSAEs. Periods of strong RSAE activity are accompanied by a large (peak {delta}S{sub n}/S{sub n{approx_equal}}60%) neutron deficit. Losses of beam ions modulated at AE frequencies were observed using large bandwidth energy and pitch resolving fast ion loss scintillator detectors and clearly identify their role in the process. Modeling of DIII-D loss measurements using guiding center following codes to track particles in the presence of ideal magnetohydrodynamic (MHD) calculated AE structures (validated by comparison to experiment) is able to reproduce the dominant energy, pitch, and temporal evolution of these losses. While loss of both co and counter current fast ions occurs, simulations show that the dominant loss mechanism observed is the mode induced transition of counter-passing fast ions to lost trapped orbits. Modeling also reproduces a coherent signature of AE induced losses and it was found that these coherent losses scale proportionally with the amplitude; an additional incoherent contribution scales quadratically with the mode amplitude.

• OSTI ID: 21537877
• Journal Information: Physics of Plasmas, Vol. 18, Issue 5; Other Information: DOI: 10.1063/1.3574663; (c) 2011 American Institute of Physics; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALFVEN WAVES
ASDEX TOKAMAK
BEAM INJECTION HEATING
CHARGED-PARTICLE TRANSPORT
DOUBLET-3 DEVICE
IONS
NEUTRAL ATOM BEAM INJECTION
PARTICLE LOSSES
PLASMA DIAGNOSTICS
REVERSED SHEAR
BEAM INJECTION
CHARGED PARTICLES
CLOSED PLASMA DEVICES
HEATING
HYDROMAGNETIC WAVES
LOSSES
PLASMA HEATING
RADIATION TRANSPORT
THERMONUCLEAR DEVICES
TOKAMAK DEVICES