Reducing and measuring fluctuations in the MST RFP: Enhancement of energy confinement and measurement of the MHD dynamo

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A three- to five-fold enhancement of the energy confinement time in a reversed-field pinch (RFP) has been achieved in the Madison Symmetric Torus (MST) by reducing the amplitude of tearing mode fluctuations responsible for anomalous transport in the core of the RFP. By applying a transient poloidal inductive electric field to flatten the current density profile, the fluctuation amplitude {tilde b}/B decreases from 1.5% to 0.8%, the electron temperature T{sub e0} increases from 250 eV to 370 eV, the ohmic input power decreases from 4.5 MW to approximately 1.5 MW, the poloidal beta {beta}{sub 0} increases from 6% to 9%, ... continued below

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13 p.

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Den Hartog, D.J.; Almagri, A.F. & Cekic, M. September 1, 1996.

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A three- to five-fold enhancement of the energy confinement time in a reversed-field pinch (RFP) has been achieved in the Madison Symmetric Torus (MST) by reducing the amplitude of tearing mode fluctuations responsible for anomalous transport in the core of the RFP. By applying a transient poloidal inductive electric field to flatten the current density profile, the fluctuation amplitude {tilde b}/B decreases from 1.5% to 0.8%, the electron temperature T{sub e0} increases from 250 eV to 370 eV, the ohmic input power decreases from 4.5 MW to approximately 1.5 MW, the poloidal beta {beta}{sub 0} increases from 6% to 9%, and the energy confinement time {tau}{sub E} increases from 1 ms to {approximately}5 ms in I{sub {phi}} = 340 kA plasmas with density {tilde n} = 1 {times} 10{sup 19} m{sup -3}. Current profile control methods are being developed for the RFP in a program to eliminate transport associated with these current-gradient-driven fluctuations. In addition to controlling the amplitude of the tearing modes, we are vigorously pursuing an understanding of the physics of these fluctuations. In particular, plasma flow, both equilibrium and fluctuating, plays a critical role in a diversity of physical phenomena in MST. The key results: 1) Edge probe measurements show that the MHD dynamo is active in low collisionality plasmas, while at high collisionality a new mechanism, the `electron diamagnetic dynamo,` is observed. 2) Core spectroscopic measurements show that the toroidal velocity fluctuations of the plasma are coherent with the large-scale magnetic tearing modes; the scalar product of these two fluctuating quantities is similar to that expected for the MHD dynamo electromotive force. 3) Toroidal plasma flow in MST exhibits large radial shear and can be actively controlled, including unlocking locked discharges, by modifying E{sub r} with a robust biased probe. 24 refs.

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13 p.

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INIS; OSTI as DE97000183

Medium: P; Size: 13 p.

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  • 16. International Atomic Energy Agency (IAEA) international conference on plasma physics and controlled nuclear fusion research, Montreal (Canada), 7-11 Oct 1996

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  • Other: DE97000183
  • Report No.: DOE/ER/54345--281
  • Report No.: CONF-961005--6
  • Grant Number: FG02-96ER54345
  • Office of Scientific & Technical Information Report Number: 419960
  • Archival Resource Key: ark:/67531/metadc684524

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  • September 1, 1996

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  • July 25, 2015, 2:20 a.m.

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  • April 7, 2017, 12:48 p.m.

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Den Hartog, D.J.; Almagri, A.F. & Cekic, M. Reducing and measuring fluctuations in the MST RFP: Enhancement of energy confinement and measurement of the MHD dynamo, article, September 1, 1996; United States. (digital.library.unt.edu/ark:/67531/metadc684524/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.