The Bootstrap Current and Neutral Beam Current Drive in DIII-D

Journal Article · Sat Oct 15 00:00:00 EDT 2005 · Fusion Science and Technology

OSTI ID:20854291

Politzer, P A ^[1]

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1. General Atomics (United States)

Noninductive current drive is an essential part of the implementation of the DIII-D Advanced Tokamak program. For an efficient steady-state tokamak reactor, the plasma must provide close to 100% bootstrap fraction (f{sub bs}). For noninductive operation of DIII-D, current drive by injection of energetic neutral beams [neutral beam current drive (NBCD)] is also important. DIII-D experiments have reached {approx}80% bootstrap current in stationary discharges without inductive current drive. The remaining current is {approx}20% NBCD. This is achieved at {beta}{sub N} [approximately equal to] {beta}{sub p} > 3, but at relatively high q{sub 95} ({approx}10). In lower q{sub 95} Advanced Tokamak plasmas, f{sub bs} {approx} 0.6 has been reached in essentially noninductive plasmas. The phenomenology of high {beta}{sub p} and {beta}{sub N} plasmas without current control is being studied. These plasmas display a relaxation oscillation involving repetitive formation and collapse of an internal transport barrier. The frequency and severity of these events increase with increasing {beta}, limiting the achievable average {beta} and causing modulation of the total current as well as the pressure. Modeling of both bootstrap and NBCD currents is based on neoclassical theory. Measurements of the total bootstrap and NBCD current agree with calculations. A recent experiment based on the evolution of the transient voltage profile after an L-H transition shows that the more recent bootstrap current models accurately describe the plasma behavior. The profiles and the parametric dependences of the local neutral beam-driven current density have not yet been compared with theory.

• OSTI ID: 20854291
• Journal Information: Fusion Science and Technology, Vol. 48, Issue 2; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA); ISSN 1536-1055
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAM CURRENTS
BEAM INJECTION HEATING
BOOTSTRAP CURRENT
COMPUTERIZED SIMULATION
CONTROL
CURRENT DENSITY
CURRENT-DRIVE HEATING
DOUBLET-3 DEVICE
ELECTRIC POTENTIAL
MODULATION
NEOCLASSICAL TRANSPORT THEORY
NEUTRAL ATOM BEAM INJECTION
OPERATION
OSCILLATIONS
PLASMA
PLASMA SIMULATION
RADIATION TRANSPORT
RELAXATION
STEADY-STATE CONDITIONS
TRANSIENTS