Excess Ion Heating and Diagnostic Requirements

Patrick RossEnergetic Particles Science Focus

Group MeetingSeptember 9, 2008

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

Background-Power Balance

NCiei QQWP

NCieiexcess QQWPQ

• Assuming no excess heating and only neoclassical heat transport:

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

Pbi

Qie

W

QNC

Using Transp we can calculate the power balance terms for the discharge to check for excess heating

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.

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.

Excess Heating Peaks Near where Alfvén Modes Peak

Excess heating as calculated by Transp. (Top is heating density, bottom is total heating)

High frequency Alfvén modes (black: radial mode=0; red: radial mode=1)

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.

Radial Profiles of CAE modes

NPA Does Not Show Full Fast Ion Distribution

Saturation has occurred at full energy, but ONLY that channel shows significant particle density.

Where did the fast ions go?

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.

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