Radiative power losses from impurities in high-density plasmas confined by high magnetic fields

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" Radiative power losses from impurities in high-density plasmas confined by high magnetic fields "
M. J. May M. Finkenthal

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113245
Doc. No	:	TLpq304419186
Main Entry	:	M. Finkenthal
	:	M. J. May
Title & Author	:	Radiative power losses from impurities in high-density plasmas confined by high magnetic fields\ M. J. MayM. Finkenthal
College	:	The Johns Hopkins University
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	172
Abstract	:	Quantifying and controlling the radiative power losses from impurities in the tokamak fusion plasma is crucial for obtaining ignition conditions. In the present work, therefore, losses from impurities have been measured in different operating regimes of the Alcator C-Mod Tokamak and the Frascati Tokamak Upgrade (FTU) plasmas. The major radiating intrinsic impurity in both tokamaks was molybdenum sputtered from the armor tiles covering all the plasma facing surfaces. The radiative power losses from the molybdenum ions accounted for usd{>}80\%usd of the total radiative power losses in ICRF heated plasmas and usd{\sim}60\%usd in ohmically heated plasmas. Molybdenum could radiate as much as several thousand kW with concentrations as high as usd\rm{\sim}1\times 10\sp\ particles/cm\sp3usd or usd{\sim}0.001usd of the plasma (electron) density. The radiative losses were found to increase linearly with increasing ICRF power and to vary weakly with the central electron density of the plasma. The other major intrinsic impurities in Alcator C-Mod Tokamak, carbon and boron, radiated at most usd{\sim}100usd kW from the plasma and had concentrations in ohmically heated plasmas of usd\rm{\sim}1.7\times 10\ particles/cm\sp3usd and usd\rm{\sim}6.3\times 10\sp\ particles/cm\sp3,usd respectively. At Alcator C-Mod Tokamak, the total radiative power losses were measured with bolometric systems. The contribution to the total radiative losses from each major impurity and the impurity concentrations were determined spectroscopically from the line brightnesses of XUV (soft X-ray and extreme ultraviolet) transitions. The line brightnesses were interpreted via a detailed atomic physics model which included the Multiple Ionization State Transport (MIST) code, the ab initio atomic rates from the Hebrew University-Jerusalem Lawrence Livermore Atomic Code (HULLAC) and a collisional radiative model. At the FTU Tokamak, brightnesses from impurity emission measured with an X-ray crystal spectrometer were interpreted with a similar atomic physics model which included the molybdenum rates from HULLAC. The prototype XUV Polychromator which used low resolution MLMs as dispersive elements was designed, constructed and photometrically calibrated at The Johns Hopkins University and was extensively used for the work presented here. The resolution of the MLM varied from usd\rm\Delta\lambda\sim 0.5\Ausd at usd\rm\lambda = 30\Ausd to usd\rm\Delta\lambda\sim 7\Ausd at usd\rm\lambda = 120\A .usd The XUV Polychromator had each of its three channels configured for a different region of the XUV spectral range. The molybdenum spectral lines of interest were the resonant 3s-3p transition of usd\rm Mo\sp{31+}usd at 127.9 A, the usd\rm 3s\sp2usd-3s3p transition of usd\rm Mo\sp{30+}usd at 116.0 A, and the 3p-3d transitions of usd\rm Mo\sp{23+}usd to usd\rm Mo\sp{25+}usd between 65 and 85 A. The resonant transitions of usd\rm C\sp{4+}usd at 40 A, usd\rm C\sp{5+}usd at 33.4 A and usd\rm B\sp{4+}usd at 48.6 A were also monitored as well as the low charge states of usd\rm Mo\sp{14+}usd and usd\rm Mo\sp{15+}usd between 45 to 55 A. The XUV Polychromator measured both the spectra and the time histories of the emission lines. The temporal response of the instrument was usd{\sim}1usd ms. The photometric and wavelength calibrations of the XUV Polychromator are presented. (Abstract shortened by UMI.)
Subject	:	Fluid dynamics
	:	Fluid dynamics
	:	Gases
	:	Gases
	:	Pure sciences
	:	Radiation