Ion Heating by Alfven Waves and Reconnection in NSTX

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
Channeling of fast ion energy through waves to
thermal ions

• 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.

4
Broad constraints on power to wave, based on wave
drive physics

• Only full-energy ions (lt70)
• Only flatten to half-energy (lt25)
• Only perpendicular energy (lt50)?
• Bump-on-tail only near axis (50).
• Net, lt5 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
  dampingDrake, 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 Ewave gdamp
• (4x10-4 MW) N ltB2(G)gtvol V/Vplasma g
  (104/s)
• For 1 MW of heating, Brms(all modes) 50 G
• ltdB2gt1/2modes/B ltdn2gt1/2modes/n 1-1.5

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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
Helanders 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.
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High frequency waves sometimes seen at IRE's

• Often not seen.
• Not correlated with ion heating.
• Toroidaly mode number n0?
• Frequency seems too low to be responsible for ion
  heating.