Return To: Session EX4 - Innovative Concepts, Reversed Field &
Prev Page: (EX4/4) Reversed Field Pinch Experiment on a New
Next Page: (EX4/6) Plasma Confinement in the GAMMA 10 Tandem

(EX4/5) Confinement in the RFP: Lundquist Number Scaling, Plasma Flow, and Reduced Transport

G. Fiksel¹,A. F. Almagri¹, J. K. Anderson¹, T. M. Biewer¹, D. L. Brower², C-S. Chiang¹, B. E. Chapman¹, J. T. Chapman¹, D. J. Craig¹, N. A. Crocker¹, D. J. Den Hartog¹, P. W. Fontana¹, C. B. Forest¹, Y. Jiang², A. K. Hansen¹, D. Holly¹, N. E. Lanier¹, K. A. Mirus¹, S. C. Prager¹, J. S. Sarff¹, U. Shah³, J. C. Sprott¹, M. R. Stoneking⁴, and E. Uchimoto⁵

¹ Department of Physics, University of Wisconsin-Madison, WI, USA
² Department of Electrical Engineering, University of California - Los Angeles, CA, USA
³ Department of Electrical Engineering, Rennselear Polytechnic Institute, Troy, NY, USA
⁴ Department of Physics, Lawrence University, Appleton, WI, USA
⁵ Department of Physics and Astronomy, University of Montana, Missoula, MT, USA

Abstract.  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 this turbulent transport and identifying ways to reduce it are critical RFP development issues. We report measurements of the Lundquist number scaling (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 $\sim$ S^-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_A $\sim$ S^{- [0.08 - 0.19]}. The MHD dynamo $\langle$$\tilde{V}$×$\tilde{b}$$\rangle$ up to 15 V/m was measured in the plasma core. Interestingly, the scaling of the MHD dynamo $\langle$$\tilde{V}$×$\tilde{b}$$\rangle$ $\sim$ S^{- [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.

Read the full paper in PDF format.