NSTX Supported by XP-917: FIDA Red-Blue spectra W. Heidbrink, M. Podestá, E. Ruskov UC Irvine and the NSTX Research Team College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec NSTX Results Review Meeting Sept. 15, 2009
Variety of plasma conditions tested • Goal: Make MHD-quiescent discharges to investigate the red-blue FIDA spectra variation • 65 keV to avoid MHD • No TAE, but some GAE/CAE • Ne variations change NB deposition profile • Ip and BT variations change the pitch in fNB(E,R,q ) 90 keV A-beam 65 keV B-beam Times of interest
Theory predicts different red & blue spectra E > 14keV E > 14keV Da at rest Ch.8 • Peak of red profile shifted inwards by 5-10cm. Blue spectra stronger outwards • PITCH of magnetic field lines alters detected Doppler shift – stronger effect • Large gyro radii (~ 5-10cm) are a weaker effect
Background subtraction often works well • The desired FIDA signal is excited by a heating beam • The “Net” signal is : (Beam On) - (Beam Off) • Prominent impurity lines nicely “disappear” • “Net Active” has the expected shape • Expect “Net Passive” to be zero - it is small & flat in this case
Red and blue spectra compared by plotting vs. E :Blue-shifted data looks better than the red-shifted data • No signal is expected above ~ 60keV but all signals are > 0 baseline shift caused by light scattering? • Blue spectra usually have the same baseline shift for active & passive views • Red spectra often have different shifts for active & passive views unidentified contamination? • Both red & blue spectral shapes resemble theory Absolute magnitude of experiment exceeds theory for both red & blue
The red:blue ratio for experiment is much larger than for theory • Integrate spectra from E ~ 15-50 keV with baseline subtracted • Error bars estimated from baseline shifts or passive spectra that aren’t flat • Blue profile shape close to theory • Ignoring suspicious large points (R > 140cm), red profile shape is OK too • In theory, red:blue <~ 0.5 • In experiment red ~ blue Note on theory: the large predicted difference is due to the large pitch of the field line in a ST co-going ions are heading up towards lens at R>R0
Peak intensity scales like theory for both red & blue spectra • Fit peak of spatial profile for all shots in the XP • Correlation coefficient r for experiment w/ theory ~0.9 for both red & blue sides • Magnitude is off: experiment 2.3 x larger for blue 3.6 x larger for red • Variation in ne most important factor (more than BT or Ip) • No correlation between experimental red:blue ratio and theoretical ratio Evidently, something is right about measurement and theory but something is also wrong.
Discussion • FIDA code predictions agree well with D3D data • Standard procedure used for both NSTX & D3D • TRANSP beam distribution function at the guiding center, averaged over an appropriate time interval (~100ms) • Measured Ne, Te, Ti, Nimp , W and EFIT02 equilibria • Possible issues: • S/N worse than D3D, in spite of having more efficient collection optics: signal is low due to single 65keV beam • Unresolved impurity lines on the red side (less likely) • Problem with TRANSP calculated fNB(E,R,q ) ?
Conclusions • FIDA spectral shape and parametric dependencies are consistent with expectations • Absolute magnitude is discrepant (preliminary result--currently searching for mistakes) • Trying to understand baseline shifts — leading hypothesis is scattered cold D light • Why does red:blue ratio differ from theory? —leading hypothesis is impurity contamination on red side • Alternative hypothesis: CAE distort distribution
Theory spectra calculated for all XP-917 shots NOTE the scale change ! ph / s cm2 BT sign flipped • Detailed analysis and comparison to experiment to be done