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Beam-ion confinement for different injection geometries

W W Heidbrink1, M Murakami2, J M Park2, C C Petty3, M A Van Zeeland3, J H Yu4 and G R McKee5

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The DIII-D tokamak is equipped with neutral beam sources that inject in four different directions; in addition, the plasma can be moved up or down to compare off-axis with on-axis injection. Fast-ion data for eight different conditions have been obtained: co/counter, near-tangential/near-perpendicular and on-axis/off-axis. Neutron measurements during short beam pulses assess prompt and delayed losses under low-power conditions. As expected, co-injection has fewer losses than counter, tangential fewer than perpendicular and on-axis fewer than off-axis; the differences are greater at low current than at higher current. The helicity of the magnetic field has a weak effect on the overall confinement. Fast-ion Dα (FIDA) and neutron measurements diagnose the confinement at higher power. The basic trends are the same as in low-power plasmas but, even in plasmas without long wavelength Alfvén modes or other MHD, discrepancies with theory are observed, especially in higher temperature plasmas. At modest temperature, two-dimensional images of the FIDA light are in good agreement with the simulations for both on-axis and off-axis injection. Discrepancies with theory are more pronounced at low fast-ion energy and at high plasma temperature, suggesting that fast-ion transport by microturbulence is responsible for the anomalies.


PACS

52.55.Fa Tokamaks, spherical tokamaks

28.52.Cx Fueling, heating and ignition

52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

52.35.Ra Plasma turbulence

52.50.Gj Plasma heating by particle beams

52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Subjects

Nuclear physics

Plasma physics

Dates

Issue 12 (December 2009)

Received 6 May 2009, in final form 3 September 2009

Published 29 October 2009



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