1. Investigation of Energetic ICRF Minority Protons on Alcator C-Mod 48th APS-DPP 10/31/2006 V. Tang*, P.T. Bonoli, J. Liptac, R.R. Parker, J.C. Wright, MIT PSFC E.F. Jaeger, ORNL R.W. Harvey, CompX
*Now at LLNL

2. Introduction
Hollow minority proton temperature profiles are found for a series of low density (ne0~1e20, 0.5MW, 5.4T) D(H) C-Mod discharges with on-axis heating resonance using a new multichannel Compact Neutral Particle Analyzer (CNPA)1.
These proton temperatures scale with the Stix2 parameter and show phase-space anisotropy as expected for ICRF heating.
Comparisons with full-wave/Fokker-Planck solvers using a new synthetic diagnostic are good and provide physical understanding of off-axis phenomenon.
1Tang et al, Rev. Sci Instrum., 2006.
2Stix, Nuc. Fusion, 1975.

3. CNPA Sightline and Setup
F-Port vertical detectors(Ch1-3), Ro~65 to 70 cm
The F-port top three
channel Si array
C-Port horizontal(Ch4) detector at mid-plane
V-perpendicular
V-parallel
In mid-plane velocity coordinates
F-Port DNB
Alcator C-Mod Cross Section
Machine Ro=66.8cm
Magnetic Ro~69cm

4. Z~7cm, or r/a~0.3 T~75keV R~65cm T~90keV Active/Passive Count Rate
Detailed modeling of CX partners, including halo and impurity CX are required.
Get flux surface averaged temperature by using 2D model distribution.
Passive Only
T~52keV
Horizontal
Energy(keV)

5. Teff: CNPA vs. r/a=0 Varied nH/ne and RF power for 13 discharges.
CNPA count rate data indicate peak of the fast ion temperature profiles at r/a~
All CNPA temperatures are hotter than r/a=0 temperatures.
Profiles are hollow.
Reheat data Teff
(r/a=0)
CNPA peak Teff
13 discharges
Stix Parameter Scaling

6. Wave and Fokker-Planck Solvers
AORSA1/CQL3D2 matches CNPA and reheat temperature data.
TORIC53/FPPRF4 can not reproduce experimental results.
Data suggest that accurate tracking of the 2-D minority distribution is required—trapped particles are preferentially heated.
1Jaeger et al, PRL, Harvey & McCoy, IAEA TCM, 1992.
3Brambilla, PPCF, Hammett, PhD Thesis, 1986.

7. AORSA/CQL3D Synth. Spectra Signal~+/-6cm Active A.U. Log Scale Passive
Simulated spectra are reasonably matched by data.
A move of the bulk signal outward by 1-2cm would result in an active/passive count ratio match; this ratio is sensitive to details of the model CX profiles.
Need to include neoclassical spatial diffusion.
Synth. Diagnostic,
Ch 3

8. Summary and Future Work
Uncovered off-axis peaking and scaling of minority proton temperatures in low density C-Mod plasmas.
Full-wave/Fokker-Planck modeling indicates that the primary physics responsible is preferential heating of trapped minority protons.
Detail comparison with TORIC/ORBIT-RF* in progress.
Hollow minority proton profiles potentially explain features of C-Mod’s TAE data-see next talk.
*Choi et al, Nuc. Fusion, 2006.