Excess Ion Heating and Diagnostic Requirements

1
Excess Ion Heating and Diagnostic Requirements

• Patrick Ross
• Energetic Particles Science Focus Group Meeting
• September 9, 2008

2
Outline

• Background
• Power Balance
• Excess Ion Heating in NSTX
• Excess Heating correlates with hgih frequency
  fast ion MHD
• NPA view of Fast Particles
• Additional Measurement Needs

3
Background-Power Balance

• Assuming no excess heating and only neoclassical
  heat transport

Pbi
QNC
Qie

• If there is excess heating, it can be calculated
  by

Using Transp we can calculate the power balance
terms for the discharge to check for excess
heating
4
Excess Ion Heating has been Observed
Transp calculated ion power balanced shows that
extra heating is required to satisfy the power
balance. The total power loss in the top graph
is the blue curve, while the total heating is the
red curve. The bottom plot, shows the total
extra heating required.
5
Heating Scales with Mode Amplitude, Similar to
Prediction
Reproduced from Gates, et al., Phys. Rev. Lett.,
87, 205003 (2001).
Stochastic heating has been theorized as a result
of high frequency, fast particle drive, MHD
modes. The calculated excess heating required
shows the same form as the stochastic heating of
the thermal ions.
6
Excess Heating Peaks Near where Alfvén Modes Peak
Radial Profiles of CAE modes
High frequency Alfvén modes (black radial
mode0 red radial mode1)
Excess heating as calculated by Transp. (Top is
heating density, bottom is total heating)
The required excess heating peaks around 134 cm,
which is near the peak amplitude of the high
frequency Alfvén modes. It is not yet clear if
the modes might be responsible for the excess
heating.
7
NPA Does Not Show Full Fast Ion Distribution
Saturation has occurred at full energy, but ONLY
that channel shows significant particle density.
The Neutral Particle Analyzer shows particles at
a given pitch angle. However, if energy from
fast particles lose energy preferentially (E- ),
then that would effectively be pitch angle
scattering, and might scatter particles out of
the NPA view.
Where did the fast ions go?
8
Additional Measurement Needs

• Measurements of n(v/v,r) to see spatial
  diffusion
• This should be solved by FIDA
• Measurements of n(E,pitch) to see pitch angle
  scattering
• This would require significant upgrades to the
  NPA
• Many channels of energy resolved data looking at
  the same location
• Also should improve the way TRANSP handles NPA
• Guiding center approximation not sufficient
• Full geometry, including position of NPA relative
  to beams my be necessary