A simple gadget to measure the X-ray spectrum in NSTX K.L. Wong, K. Hill, A.L. Roquemore Presented at NSTX T&T group meeting February 19, 2007

Summary ________________________________________ _ Goal: obtain information on D e in NSTX from the X-ray spectrum Physics principle:kinetic eq:  f/  t = e/m E  f/  v + C(f) + LD e Lf L =  /  x - (e E A /m)  /  v 2 f = f (0) + f (1) + f (2) + … 0-th order: 0 = C(f (0) ) -> local Maxwellian 1st order: 0 = C(f (1) ) - e/m E  f (1) /  v -> Spitzer  2nd order: 0 = C(f (2) ) + LD e Lf (0) - (e E/m)  f (1) /  v f (2) gives information on D e Ref: K. Molvig et al., PRL (1978)

Alcator data _______________________________________ The nonthermal distribution was interpreted as due to particle diffusion by magnetic fluctuations, but …..

_______________________________________ _ Bremsstrahlung radiation/vol ~ n e n Z e 2 T e 1/2 (f->f) Radiative recombination (f->b) and line radiation due to collisional excitation (f->f) and dielectronic recombination (f->b) are also important The detector collects all photons along the sightline, it is important to have profiles of n e, n Z (or Z eff ),T e 1/2 and E oh [ i.e., s (  ) ] The geometry of the flux surface also important : hot electrons escaped from the center will be distributed over a larger volume of the outer flux surfaces [need weighting factor G] Other important factors

NSTX data ________________________________________ No tail electrons above 10 keV Higher h decays faster after HHFW off h (keV):  decay (ms): (+/-5) Need higher count rate

A simple gadget for NSTX _______________________________________ The old X-ray spectrometer is too far away from machine - count rate too low Need a new detector placed near a Be window for high count rate There are Si or Ge detectors operating at room temperature in atmosphere Try to use the old electronics - may need a new PHA [or C. Gentile] Can we use TRANSP to fit X-ray data ?