Comparison of ion temperature diagnostics on the Madison symmetric torus reversed-field pinch

Abstract

There have been three ion temperature diagnostics operating on the Madison symmetric torus ͑MST͒ for the past two years: ͑i͒ Charge-exchange recombination spectroscopy ͑CHERS͒, which measures the temperature of fully stripped impurity (C 6ϩ) ions, and has a spatial resolution of Ϯ1 cm and a time resolution of 3 ms; ͑ii͒ Rutherford scattering ͑RS͒, which measures the temperature of the bulk majority (D ϩ) ions, and has a spatial resolution of roughly Ϯ7 cm and a time resolution of 30 s; and ͑iii͒ the ion dynamics spectrometer ͑IDS͒, which measures a chordal average of the temperature of partially stripped impurity (C 4ϩ) ions, with a time resolution of 10 s. The first two diagnostics use neutral beams, while the third is passive. The classical ion energy equilibration time ii Ͻ1 ms between all ion species, so we naively expect that all ion temperature measurements should agree in steady state. Here we present simultaneous measurements of: CHERS and RS profiles in high-current burst-free pulsed poloidal current drive ͑PPCD͒ discharges; CHERS and RS profiles in standard high-current discharges; and IDS and RS profiles in standard low-current discharges. Measurements in standard discharges are made a long time before and after magnetic reconnection events, during which there is believed to be a large, nonclassical input of energy to the ions. RS and CHERS measurements consistently agree; IDS measurements are consistently less than RS measurements, due to the effect of the C 4ϩ emission profile on the IDS measurements.

Emission intensities and line ratios from a fast neutral helium beam

“…The total beam density on entry to the plasma is the sum of the ground state and metastable state populations and is estimated to be N b ϳ 1.6ϫ 10 10 cm −3 . 13 Also indicated in the plot is the calculated fraction of each population at the experimental observation point, i.e., at d = 58 cm. It is clearly seen that all three populations are attenuated as the beam propagates through the plasma.…”

“…Plasmas 14, 083301 ͑2007͒ observation point is ϳ2.5 cm͒. 13 The background light is then subtracted from the beam emission view to yield the net beam emission. The first wavelength ͑e.g., 667.8 nm He I͒ is monitored by two grating monochromators with a PMT detector at the exit slit.…”