Confinement in the RFP: Lundquist number scaling, plasma flow, and reduced transport

Conference · Thu Oct 01 04:00:00 EDT 1998

OSTI ID:291144

Fiksel, G; Almagri, A F; Anderson, J K ^[1]

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1. and others

Global heat and particle transport in the reversed field pinch (RFP) result primarily from large-scale, resistive MHD fluctuations which cause the magnetic field in the core of the plasma to become stochastic. Achieving a better understanding of t his turbulent transport and identifying ways to reduce it are critical RFP development issues. The authors report measurements of the Lundquist number (S-scaling) of magnetic and ion flow velocity fluctuations in the Madison Symmetric Torus (MST) RFP. The S-scaling of magnetic fluctuations in MST is weaker than previous measurements {tilde b}/B {approximately} S{sup {minus}1/2} in smaller (lower S) RFP plasmas. Impurity ion flow velocity fluctuations (measured with fast Doppler spectroscopy) have a scaling similar to the magnetic fluctuations, falling in the range {tilde V}/V{sub A} {approximately} S{sup {minus}[0.08-0.10]}. The MHD dynamo ({tilde V} x {tilde b}) up to 15 V/cm was measured in the plasma core. Interestingly, the scaling of the MHD dynamo ({tilde V} x {tilde b}) {approximately} S{sup {minus}[0.64-0.88]} is stronger than for its constituents, a result of decreased coherency between {tilde V} and {tilde b} with increasing S. A weak S-scaling of magnetic fluctuations implies fluctuation suppression measures (e.g., current profile control) may be required in higher-S RFP plasmas. Two types of current profile modifications have been examined--inductive and electrostatic. The inductive control halves the amplitude of global magnetic fluctuations and improves the confinement by a factor of 5. The electrostatic current injection, localized in the edge plasma, reduces edge resonant fluctuations and improves the energy confinement. In addition, regimes with confinement improvement associated with the plasma flow profile are attained.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Energy Research, Washington, DC (United States)
• DOE Contract Number: FG02-96ER54345
• OSTI ID: 291144
• Report Number(s): DOE/ER/54345--309; CONF-981064--; ON: DE99001039; IN: IAEA-F1-CN-69/EX4/5
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
HEAT TRANSFER
MST DEVICE
PLASMA CONFINEMENT
PLASMA DRIFT
RADIATION TRANSPORT
SAWTOOTH OSCILLATIONS
SCALING LAWS