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

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.

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

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)

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~0.3-0.4. 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

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, 2003. 2Harvey & McCoy, IAEA TCM, 1992. 3Brambilla, PPCF, 1999. 4Hammett, PhD Thesis, 1986.

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

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.