### Abstract

The scaling of the magnetic and velocity fluctuations with Lundquist number (S) is examined experimentally over a range of values from 7 × 10^{4} to 10^{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 b̃∝S^{-0.18}, in agreement with recent numerical results. Fluctuations are almost independent of S at low (relative) density, b̃∝S^{-0.07}. The range of measured exponents is narrow and is in clear disagreement with theories predicting b̃∝S^{-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 (nτ_{E}∝β^{4/5}·T ^{-7/10}·A^{-3/5}·I_{φ}^{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's law prediction. The sawtooth period is determined by a resistive-Alfvénic hybrid time (T_{saw}∝√τ_{R}τ_{A}) rather than a purely resistive time.

Original language | English (US) |
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Pages (from-to) | 1004-1014 |

Number of pages | 11 |

Journal | Physics of Plasmas |

Volume | 5 |

Issue number | 4 |

DOIs | |

State | Published - Apr 1998 |

Externally published | Yes |

### All Science Journal Classification (ASJC) codes

- Condensed Matter Physics

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## Cite this

*Physics of Plasmas*,

*5*(4), 1004-1014. https://doi.org/10.1063/1.872670