Experimental scaling of fluctuations and confinement with Lundquist number in the reversed-field pinch
- Department of Physics, University of Wisconsin---Madison, Madison, Wisconsin53706 (United States)
The scaling of the magnetic and velocity fluctuations with Lundquist number (S) is examined experimentally over a range of values from 7{times}10{sup 4} to 10{sup 6} in a reversed-field pinch (RFP) plasma. Magnetic fluctuations do not scale uniquely with the Lundquist number. At high (relative) density, fluctuations scale as {tilde b}{proportional_to}S{sup {minus}0.18}, in agreement with recent numerical results. Fluctuations are almost independent of S at low (relative) density, {tilde b}{proportional_to}S{sup {minus}0.07}. The range of measured exponents is narrow and is in clear disagreement with theories predicting {tilde b}{proportional_to}S{sup {minus}1/2}. At high relative density, the scaling of the energy confinement time follows expectations for transport in a stochastic magnetic field. A confinement scaling law (n{tau}{sub E}{proportional_to}{beta}{sup 4/5}{center_dot}T{sup {minus}7/10}{center_dot}a{sup {minus}3/5}{center_dot}I{sub {phi}}{sup 2}) is derived, assuming the persistent dominance of stochastic magnetic diffusion in the RFP and employing the measured scaling of magnetic fluctuations. The peak velocity fluctuations during a sawtooth cycle scale marginally stronger than magnetic fluctuations but weaker than a simple Ohm{close_quote}s law prediction. The sawtooth period is determined by a resistive-Alfv{acute e}nic hybrid time (T{sub saw}{proportional_to}{radical} ({tau}{sub R}{tau}{sub A}) ) rather than a purely resistive time. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 625842
- Journal Information:
- Physics of Plasmas, Vol. 5, Issue 4; Other Information: PBD: Apr 1998
- Country of Publication:
- United States
- Language:
- English
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