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Ion Heating by Alfven Waves and Reconnection in NSTX

Ion Heating by Alfven Waves and Reconnection in NSTX. Laboratory Astrophysics Invited session of April APS meeting, Dallas, Texas. Two laboratory examples of ion heating relevant to space plasma physics. First example has no evidence of thermal ion heating, but mechanism is understood.

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Ion Heating by Alfven Waves and Reconnection in NSTX

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  1. Ion Heating by Alfven Waves and Reconnection in NSTX Laboratory Astrophysics Invited session of April APS meeting, Dallas, Texas

  2. Two laboratory examples of ion heating relevant to space plasma physics • First example has no evidence of thermal ion heating, but mechanism is understood. • Second example we have clear evidence of heating and at least two potential mechanisms.

  3. Energy flow "restricted" at two points in channel. First point restricts total flow into channel, Second point restricts flow to ions Wave saturates at point where drive and damping energy flows are equal. Fast Ion Energy Wave Energy Thermal ions Channeling of fast ion energy through waves to thermal ions

  4. Broad constraints on power to wave, based on wave drive physics • Only full-energy ions (<70%) • Only flatten to half-energy (<25%) • Only perpendicular energy (<50%)? • Bump-on-tail only near axis (50%). • Net, <5% of beam power?

  5. Power flow from waves to thermal ions: • The CAE can be Landau damped or stochastic interactions with the ions can also provide damping[Drake, McChesney, Bailey, Sanders, Chen, Gates,…]. • An estimate of the heating power can be made from the total energy in the wave and the damping (growth) rate, • Pheat ≈ Ewavegdamp • ≈ (4x10-4 MW) N <B2(G)>vol [V/Vplasma] g (104/s) • For 1 MW of heating, Brms(all modes) ≈ 50 G; • <dB2>1/2modes/B ≈ <dn2>1/2modes/n ≈ 1-1.5 %

  6. Difficult to push ion heating power to significant level. • For 1MW, need 20 modes with average amplitude of 5 G and damping rate 5 times observed, or; • or 20 modes with amplitude of 1.5 G and g/w ≈ 15%.

  7. Ion heating during magnetic reconnection events • Long history in tokamaks, rfp's, etc. • Often, some kind of wave heating has been invoked, but • Helander proposed "run-away" ion heating just from electric field.

  8. Helander’s Ion Acceleration Model

  9. IRE-Induced Ion Acceleration in Ohmic Plasmas: Waveforms

  10. IRE-Induced Ion Acceleration in Ohmic Plasmas: Spectra •Deuterium and hydrogen thermal ions are accelerated by an IRE event in an Ohmic plasma.

  11. High frequency waves sometimes seen at IRE's • Often not seen. • Not correlated with ion heating. • Toroidaly mode number n=0? • Frequency seems too low to be responsible for ion heating.

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