Fully Ionized and Total Silicon Abundances in the Alcator-C Tokamak

Petrasso, R. D.; Séguin, F.H.; Loter, N.; Marmar, E.; Rice, J. E.

doi:10.1103/physrevlett.49.1826

Cited by 24 publications

(14 citation statements)

References 13 publications

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“…power functions for fully stripped hydrogen and carbon ions. 6,7 For array B and relevant Alcator conditions, only ~~ 2% of detected x rays are from molybdenum ions. This is primarily because the filter greatly reduces the intense A« = 1 transitions that occur around 2.5 keV [see Fig.…”

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confidence: 99%

“…3(b) depicts the asymptotic source-free equilibrium profile for molybdenum, predicted by the appropriate mixed-regime theory 6,9 (molybdenum in the Pfirsch-Schluter regime, carbon and hydrogen in the plateau regime). Peaking of molybdenum is significantly driven by the carbon profile, 6 yielding a Taylor-type solution 10 w Mo l«Mo(0) -"C 1 * c (0)| < Z M</ Z C>* (r<4cm), (7) mass ratios. 6 Temperature and hydrogen gradients are subdominant in shaping molybdenum profiles for r < 4 cm.…”

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Observations of Centrally Peaked Impurity Profiles Following Pellet Injection in the Alcator-CTokamak

et al. 1986

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Observations of Centrally Peaked Impurity Profiles Following Pellet Injection in the Alcator-CTokamak

et al. 1986

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“…This method can be refined through the use of multiple arrays of detectors with different absorption filters to yield some spectroscopic resolution. and thus discrimination between different ionization states of a single impurity 9 , 1 1 or different impurities. 0 "" In certain circumstances, this information can be used to estimate the average ionic charge (Zeff) of the plasma.…”

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“…The electron density is obtained with a six channel far infrared interferometer, 9 and the temperature is measured with a ten-channel Electron Cyclotron Emission (ECE) grating polychromator. 2 " The ECE system is calibrated against a single channel ruby laser Thomson scattering diagnostic."…”

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“…This filter is therefore responsive mainly to the continuum from radiative recombination into the ground state of the fully stripped aluminum for the plasma conditions in TEXT. 9 An important feature of this filter combination is that the difference between the Filter G and Filter D responses is due only to the small window around 1.5 keV. Thus this difference signal is strongly dominated by the He-like aluminum contribution.…”

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X-ray imaging arrays for impurity transport studies on the Texas Experimental Tokamak

Wenzel

Petrasso

1990

Review of Scientific Instruments

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Three multichannel soft x-ray imaging arrays are used for impurity transport studies on the Texas Experimental Tokamak. The entire system has a total of 92 broadband x-ray detectors that view the plasma at the same toroidal location from three different poloidal angles: Array A is a 40-channel vertically-viewing set of silicon surface barrier diodes (SBDs); Array B is* a 40-channel horizontally-viewing set of SBDs; and Array C is a 12-channel set of p-intrinsic-n (pin) detectors viewing the plasma from 450 above the horizontal plane. Array B is absolutely calibrated, Array A is relatively calibrated in situ. and Array C is cross-calibrated relative to Array B. In this article we describe the primary components of the system: 1) the specific x-ray diodes used for the arrays and their spectral sensitivities; 2) the corresponding electronics necessary for data acquisition; and 3) the vacuum system for the arrays. Furthermore we describe a novel krypton edge absorption filter which discriminates between the resonance line radiation of He-like and H-like aluminum injected into TEXT plasmas. I IntroductionSoft x-ray emissivity measurements constitute a valuable diagnostic technique for studying impurity transport in laboratory plasmas. For plasmas with electron temperatures exceeding a few hundred electron-volts, X radiation is produced during electron collisions with ions through the mechanisms of bremsstrahlung, radiative recombination, and line radiation.'-" The intensity of this radiation emitted from a plasma depends on the electron density (nr), electron temperature (Te), and the density and ionization states of impurity ions in the plasma. 2 Measurements of the broadband x emissions can therefore be used to directly determine local plasma parameters.With the objective of measuring impurity density profiles we can, with independent and simultaneous measurements of ne(r) and Te(r) as well as some qualitative knowledge of the impurities, begin to infer the level of impurities in the plasma from measurements of broadband x-ray brightness profiles." This method can be refined through the use of multiple arrays of detectors with different absorption filters to yield some spectroscopic resolution. and thus discrimination between different ionization states of a single impurity 9 , 1 1 or different impurities. 0 "" In certain circumstances, this information can be used to estimate the average ionic charge (Zeff) of the plasma. This is an especially important quantity because it is often directly related to four important properties of the plasma: 1) the radiative component of the power balance; 2) the current density profile in a tokamak; 3) the extent to which the fuel ions (hydrogen) are diluted; and 4) the efficacy of auxiliary heating methods. In addition to the behavior of impurities intrinsic to the tokamak, we may study general impurity transport by injecting, via laser ablation, 1 5 small amounts of known elements into the plasma. 16 9 "'' 1 7 In this sort of experiment confusion over the source of particles is...

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