Observations related to TAE on NSTX

1
Observations related to TAE on NSTX

• E D Fredrickson
• PPPL
• May 30, 2006

2
Many "TAE" seem to have frequencies on the low
side

• Uncertainty in q, how to factor rotational shear
  and width of TAE gap - this shot should have good
  q-profile data.

• Careful analysis of q available for this shot.
• Nova analysis suggests that these modes are in
  the gap below the TAE gap.

3
Radial profile can be measured with reflectometer
(in L-mode)

• Higher frequency bursts tend to not have phase
  inversion, peak amplitude around 125cm.
• The lower frequency mode looks like it does have
  a phase inversion.
• This data can be compared to Nova predictions -
  but hasn't been done yet.

4
Some "real" TAEs are probably seen

• The second n4 mode (blue) is in the right
  frequency range for TAE.

• Not all of this behavior is easy to understand
  the two n3 (green) modes after 0.325s are
  probably both not TAE.

5
Behavior of mode was studied in xp607

• Mode tends to be bursting with source 'A', but
  with 'C', variety of behavior was seen.
• At very low density, cascade-type behavior was
  seen, but probably not typical cascade modes.
• As density was raised (affecting fast ion
  distribution?), mode behavior evolved.

6
Modes are "cascade-like" at lower density (lt 2.5
x 1013 /cm3)

• Multiple upchirps are seen for for same toroidal
  mode number.
• "Saturated" frequency too low for TAE?

• Unfortunately, these were only seen with source
  'C', and we would like to document q-profile
  evolution.

7
Multiple chirps are seen at higher density

• TAE show one or two slowish upward frequency
  chirps.
• Upward frequency chirps for different ns occur
  at different times - not like cascades

8
At higher density, chirping parts are gone, but
remnants persist

• Seen for densities in the range above 3.5 x
  1013/cm3

• Perhaps consistent with idea that frequency chirp
  represents transition between different radial
  structure / poloidal harmonics.

9
Summary

• Modes originally classified as TAE-like, may not
  be TAE.
• Identification depends critically on accurate
  measurement of q profile (as well as density and
  rotation profiles).
• Variety of chirping behavior could provide clue
  to evolution of mode structure.