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PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-3779
DTSTART:20151109T180000Z
DTEND:20151109T190000Z
DTSTAMP:20260312T013154Z
LAST-MODIFIED:20151105T180448Z
LOCATION:2241 Physics Bldg 
SUMMARY:Dynamics of a reconnection-driven runaway ion tail in a revers
 ed field pinch plasma/ Effect of Resonant Magnetic Perturbations on 3D
  equilibria in the MST RFP \, Plasma Physics (Physics/ECE/NE 922) Semi
 nar\, Jay Anderson/Stefano Munaretto\, UW Madison\, Plasma Physics
DESCRIPTION:Jay Anderson:<br>
\nNon-collisional heating and energizati
 on of ions is a powerful process in<br>
\nreversed-field pinch (RFP) p
 lasmas and in many astrophysical settings.  <br>
\nTearing activity in
  the RFP (including linearly and nonlinearly driven modes<br>
\nwhich 
 span the plasma column) saturates through dynamo-like feedback on<br>

 \nthe current density profile\, rapidly releasing magnetic energy and 
 inducing <br>
\na strong impulsive\, parallel-to-B electric field as p
 oloidal magnetic flux is <br>
\nconverted to toroidal flux. The global
  reconnection leads to strong ion heating <br>
\nwith a known anisotro
 py in temperature (T_perp > T_{||})\, suggestive of a <br>
\nperpendic
 ular bulk heating mechanism. <br>
\nIn the subset of strongest reconne
 ction events\, multiple mechanisms combine to<br>
\ncreate a most inte
 resting ion distribution.  Runaway of the reduced-friction naturally h
 eated ions generates an asymmetric ion tail with E_{||} >> E_perp.  Th
 e tail is reinforced by a confinement asymmetry\, where runaway ions a
 pproach the limit of classical cross-field transport despite magnetic 
 stochasticity from the broad spectrum of tearing modes.  Confinement i
 s lower in other regions of the<br>
\nv_perp/v_{||} plane and reduces 
 to Rechester-Rosenbluth-like transport experienced by thermal particle
 s. <br>
\n<br>
\n<br>
\nStefano Munaretto:<br>
\n The orientation of 3
 D\, stellarator-like equilibria in the MST RFP can now be controlled w
 ith application of an m = 1 RMP. This has led to greatly improved diag
 nosis\, revealing enhancements in both the central electron temperatur
 e and density. Coupled to a recent advance in the V3FIT code\, reconst
 ructions of the 3D equilibria have also been dramatically improved. Th
 e RMP also inhibits the generation of high-energy > 20 keV electrons t
 hat is otherwise common with the 3D state. This state occurs when the 
 normally broad spectrum of core-resonant m = 1 tearing modes condenses
 \, with the innermost resonant mode growing to large amplitude\, reach
 ing ~ 8% of the axisymmetric field strength. This occurs in plasmas of
  sufficiently large Lundquist number ~ IpTe^3/2\, and the duration of 
 the state is maximized with zero applied Bt (infinite toroidal beta). 
 As the dominant mode grows\, eddy current in MST's conducting shell sl
 ows the mode's rotation. This leads to locking of the 3D structure\, b
 ut with an orientation that varies randomly shot to shot\, making diag
 nosis difficult. An m = 1 RMP can now be applied with an array of sadd
 le coils at the vertical insulated cut in the shell. With an amplitude
  br/B ~ 10% and a tailored temporal waveform\, the RMP can force the 3
 D structure into any desired orientation relative to MST's diagnostics
 . A recent advance in V3FIT allows calculation of the substantial heli
 cal image current flowing in MST's shell\, which has in turn allowed s
 elf-consistent utilization of both external and internal (Faraday rota
 tion) measurements of the magnetic field. The ORBIT code predicts redu
 ced stochasticity and improved confinement of high-energy electrons wi
 thin the 3D structure. The suppression of these electrons by the m = 1
  RMP may reflect a change to the central magnetic topology. The genera
 tion of these electrons is unaffected by non-resonant perturbations\, 
 such as m = 3. 
URL:https://www.physics.wisc.edu/events/?id=3779
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