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Atomic physics studies of highly charged ions on tokamaks using x-ray spectroscopy

Description: An overview is given of atomic physics issues which have been studied on tokamaks with the help resolution x-ray spectroscopy. The issues include the testing of model calculations predicting the excitation of line radiation, the determination of rate coefficients, and accurate atomic structure measurements. Recent research has focussed primarily on highly charged heliumlike (22 less than or equal to Z less than or equal to 28) and neonlike (34 less than or equal to Z less than or equal to 63) ions, and results are presented from measurements on the PLT and TFTR tokamaks. Many of the measurements have been aided by improved instrumental design and new measuring techniques. Remarkable agreement has been found between measurements and theory in most cases. However, in this review those areas are stressed where agreement is worst and where further investigations are needed. 19 refs., 13 figs., 2 tabs.
Date: July 1, 1989
Creator: Beiersdorfer, P.; von Goeler, S.; Bitter, M. & Hill, K.W.
Partner: UNT Libraries Government Documents Department

Determination of Fe charge-state distributions in PLT by Bragg crystal x-ray spectroscopy

Description: A curved-crystal Bragg x-ray spectrometer has been used to measure K..cap alpha.. or 1s-2p radiation from highly stripped Fe XVIII to Fe XXV impurity ions in the PLT tokamak. The spectrometer has sufficient energy resolution (approximately < 4 eV at 6400 eV) to distinguish between the different ionization states of iron by measuring the energy shift of the K..cap alpha.. x rays. The measured wavelengths agree well with theory and with spectra from solar flares and from laser-produced plasmas. The distribution of Fe charge states in the center of the discharge has been inferred from a comparison of the measured x-ray spectrum with theory. The shape of the spectrum depends strongly on electron temperature (T/sub e/) in the range T/sub e/ = 800 to 1500 eV. Within the factor of two uncertainty in L-shell ionization cross sections, measured intensities agree with theory, which is based on coronal equilibrium, indicating that the ion life-time in the center of the plasma is approximately equal to or greater than the equilibration time.
Date: August 1, 1978
Creator: Hill, K.W.; von Goeler, S. & Bitter, M.
Partner: UNT Libraries Government Documents Department

Experimental study of the x-ray transitions in the heliumlike isoelectronic sequence

Description: The wavelengths of the transition 1s2p /sup 1/P/sub 1/ ..-->.. 1s/sup 2/ /sup 1/S/sub 0/ in heliumlike potassium, scandium, titanium, vanadium, chromium, and iron have been measured with an experimental precision of ..delta..lambda/lambda approx. 1/20,000. The data typically agree within error bars with recent theoretical predictions which include quantum electrodynamical corrections. However, the comparison shows that there are systematic differences between data and predictions, which indicate a need to include additional corrections in the calculations. In particular, it is found that the experimental wavelengths are consistently shorter than the calculated values by amounts which depend on the particular theoretical prediction used in the comparison. Measurements of the wavelengths of ..delta..n greater than or equal to 2 x-ray transitions in heliumlike argon, scandium, titanium, vanadium, chromium, and iron are also presented. 42 refs., 8 figs., 2 tabs.
Date: May 1, 1989
Creator: Beiersdorfer, P.; Bitter, M.; von Goeler, S. & Hill, K.W.
Partner: UNT Libraries Government Documents Department

X-ray diagnostics for TFTR

Description: A short description of the x-ray diagnostic preparation for the TFTR tokamak is given. The x-ray equipment consists of the limiter x-ray monitoring system, the soft x-ray pulse-height-analysis-system, the soft x-ray imaging system and the x-ray crystal spectrometer. Particular attention is given to the radiation protection of the x-ray systems from the neutron environment.
Date: December 1, 1982
Creator: von Goeler, S.; Hill, K.W. & Bitter, M.
Partner: UNT Libraries Government Documents Department

Measurement of wall radiation in the soft x-ray region of PDX

Description: A detector setup with three LN-cooled Si(Li) diodes is used to measure soft x-ray spectra (0.8 to 20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. This setup is part of a pulse-height-analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is increased very much during the neutral beam heating with an enhancement factor of at least 10 over OH wall radiation. Since we measure the plasma and the wall radiation at the same time, these measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g., Ti-K/sub ..cap alpha../) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x-ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation (like charge particle bombardment of the wall).
Date: January 1, 1985
Creator: Sesnic, S.; Tenney, F.H.; Bitter, M.; Hill, K.W. & von Goeler, S.
Partner: UNT Libraries Government Documents Department

X-ray diagnostics of tokamak plasmas

Description: This paper discusses the influence that salinity has on the bioavailability of the two largest classes of contaminants, trace metals and organic compounds will be discussed. Although data on contaminant toxicity will be used to draw inferences about chemical availability, this discussion will focus on the properties that contaminants are likely to exhibit in waters of varying salinities. In addition, information on physiological changes that are affected by salinity will be used to illustrate how biological effects can alter the apparent availability of contaminants.
Date: April 1, 1993
Creator: Bitter, M.; Hsuan, H.; Hill, K.W. & Zarnstorff, M.
Partner: UNT Libraries Government Documents Department

Reduced optical transmission of SiO[sub 2] fibers used in controlled fusion diagnostics

Description: We have subjected a silica core fiber optic cable to 4 years of low-level neutron and gamma radiation from Princeton's TFTR controlled fusion experiment The accumulated dose was 200 Gy. As a result of the radiation, we have measured increased attenuations of 100--300 db/km in the visible part of the spectrum, and a decrease of the numerical aperture. An attempt to decrease this damage by photobleaching failed. We argue that this failure is not unexpected, since the rate of damage is so slow and the time scale so long that the self-annealing process keeps the residual damage at the irreducible level seen in other experiments. The implications of these findings for controlled fusion diagnostics during upcoming experiments with highly reactive deuterium-tritium plasmas are discussed.
Date: February 1, 1993
Creator: Ramsey, A.T.; Adler, H.G. & Hill, K.W.
Partner: UNT Libraries Government Documents Department

Gridded ionization chamber for detecion of x-ray wave activity in tokamak plasmas

Description: In order to carry out X-ray observations of magnetohydrodynamic wave activity of the plasma during DD and DT (deuterium-beam-heated deuterium and tritium plasmas, respectively) operation of the Tokamak Fusion Test Reactor (TFTR), we will need detectors not susceptible to nuclear radiation damage. We have investigated the use of gridded ionization chambers as fast nondamageable X-ray detectors. A prototype chamber is described, which was tested on the PDX tokamak. These tests and laboratory tests with a pulsed X-ray source suggest that the detector has sufficient sensitivity and speed for the required measurements.
Date: November 1, 1982
Creator: Goldman, M.A.; Hill, K.W.; Moshey, E.A.; Sauthoff, N.R. & von Goeler, S.
Partner: UNT Libraries Government Documents Department

High-resolution bent-crystal spectrometer for the ultra-soft x-ray region

Description: A multichannel vacuum Brag-crystal spectrometer has been developed for high-resolution measurements of the line emission from tokamak plasmas in the wavelength region between 4 and 25 /angstrom/. The spectrometer employs a bent crystal in Johann geometry and a microchannel-plate intensified photodiode array. The instrument is capable of measuring high-resolution spectra (lambda/..delta..lambda approx. 3000) with fast time resolution (4 msec per spectrum) and good spatial resolution (3 cm). The spectral bandwidth is ..delta..lambda/lambda/sub 0/ = 8/angstrom/. A simple tilt mechanism allows access to different wavelength intervals. In order to illustrate the utility of the new spectrometer, time- and space-resolved measurements of the n = 3 to n = 2 spectrum of selenium from the Princeton Large Torus tokamak plasmas are presented. The data are used to determine the plasma transport parameters and to infer the radial distribution of fluorinelike, neonlike, and sodiumlike ions of selenium in the plasma. The new ultra-soft x-ray spectrometer has thus enabled us to demonstrate the utility of high-resolution L-shell spectroscopy of neonlike ions as a fusion diagnostic. 43 refs., 23 figs.
Date: October 1, 1988
Creator: Beiersdorfer, P.; von Goeler, S.; Bitter, M.; Hill, K.W.; Hulse, R.A. & Walling, R.S.
Partner: UNT Libraries Government Documents Department

Design studies for ITER x-ray diagnostics

Description: Concepts for adapting conventional tokamak x-ray diagnostics to the harsh radiation environment of ITER include use of grazing-incidence (GI) x-ray mirrors or man-made Bragg multilayer (ML) elements to remove the x-ray beam from the neutron beam, or use of bundles of glass-capillary x-ray ``light pipes`` embedded in radiation shields to reduce the neutron/gamma-ray fluxes onto the detectors while maintaining usable x-ray throughput. The x-ray optical element with the broadest bandwidth and highest throughput, the GI mirror, can provide adequate lateral deflection (10 cm for a deflected-path length of 8 m) at x-ray energies up to 12, 22, or 30 keV for one, two, or three deflections, respectively. This element can be used with the broad band, high intensity x-ray imaging system (XIS), the pulseheight analysis (PHA) survey spectrometer, or the high resolution Johann x-ray crystal spectrometer (XCS), which is used for ion-temperature measurement. The ML mirrors can isolate the detector from the neutron beam with a single deflection for energies up to 50 keV, but have much narrower bandwidth and lower x-ray power throughput than do the GI mirrors; they are unsuitable for use with the XIS or PHA, but they could be used with the XCS; in particular, these deflectors could be used between ITER and the biological shield to avoid direct plasma neutron streaming through the biological shield. Graded-d ML mirrors have good reflectivity from 20 to 70 keV, but still at grazing angles (<3 mrad). The efficiency at 70 keV for double reflection (10 percent), as required for adequate separation of the x-ray and neutron beams, is high enough for PHA requirements, but not for the XIS. Further optimization may be possible.
Date: January 1, 1995
Creator: Hill, K. W.; Bitter, M.; von Goeler, S. & Hsuan, H.
Partner: UNT Libraries Government Documents Department

Reduced optical transmission of SiO{sub 2} fibers used in controlled fusion diagnostics

Description: We have subjected a silica core fiber optic cable to 4 years of low-level neutron and gamma radiation from Princeton`s TFTR controlled fusion experiment The accumulated dose was 200 Gy. As a result of the radiation, we have measured increased attenuations of 100--300 db/km in the visible part of the spectrum, and a decrease of the numerical aperture. An attempt to decrease this damage by photobleaching failed. We argue that this failure is not unexpected, since the rate of damage is so slow and the time scale so long that the self-annealing process keeps the residual damage at the irreducible level seen in other experiments. The implications of these findings for controlled fusion diagnostics during upcoming experiments with highly reactive deuterium-tritium plasmas are discussed.
Date: February 1, 1993
Creator: Ramsey, A. T.; Adler, H. G. & Hill, K. W.
Partner: UNT Libraries Government Documents Department

X-ray diagnostics of tokamak plasmas

Description: This paper discusses the influence that salinity has on the bioavailability of the two largest classes of contaminants, trace metals and organic compounds will be discussed. Although data on contaminant toxicity will be used to draw inferences about chemical availability, this discussion will focus on the properties that contaminants are likely to exhibit in waters of varying salinities. In addition, information on physiological changes that are affected by salinity will be used to illustrate how biological effects can alter the apparent availability of contaminants.
Date: April 1, 1993
Creator: Bitter, M.; Hsuan, H.; Hill, K. W. & Zarnstorff, M.
Partner: UNT Libraries Government Documents Department

Optimization of the Configuration of Pixilated Detectors Based on the Shannon-Nyquist Theory for the X-Ray Spectroscopy of Hot Tokamak Plasmas

Description: This paper describes an optimization of the detector configuration, based on the Shannon-Nyquist theory, for two major x-ray diagnostic systems on tokamaks and stellarators: x-ray imaging crystal spectrometers and x-ray pinhole cameras. Typically, the spectral data recorded with pixilated detectors are oversampled, meaning that the same spectral information could be obtained using fewer pixels. Using experimental data from Alcator C-Mod, we quantify the degree of oversampling and propose alternate uses for the redundant pixels for additional diagnostic applications.
Date: June 13, 2012
Creator: Wang, E.; Beiersdorfer, P.; Bitter, M.; Delgado-Aprico; Hill, K. W. & Pablant, N.
Partner: UNT Libraries Government Documents Department

Conditioning of the graphite bumper limiter for enhanced confinement discharges in TFTR

Description: A strong pumping effect has been observed with plasma operation on the toroidal graphite bumper limiter on TFTR. The pumping effect was induced by conditioning the limiter with a short series (10 to 20) of low density deuterium- or helium-initiated discharges. The density decay constant (tau/sub p/*) for gas-fueled ohmic discharges was reduced from tau/sub p/* > 10 s before conditioning to a minimum value of tau/sub p/* = 0.15 s after conditioning, corresponding to a reduction in the global recycling coefficient from approx.100% to less than 50%. Coincident with the low recycling conditions, low current neutral-beam-fueled discharges show global energy confinement times which are enhanced by a factor of two over results with an unconditioned limiter. Two models are proposed for the observed pumping effects: (1) a depletion model based on pumping of hydrogenic species in the near-surface region of the limiter after depletion of the normally saturated surface layer by (carbon and helium) ion-induced desorption; and (2) a codeposition model based on pumping of hydrogenic species in carbon films sputtered from the limiter by the conditioning process.
Date: May 1, 1987
Creator: Dylla, H.F.; LaMarche, P.H.; Ulrickson, M.; Goldston, R.J.; Heifetz, D.B.; Hill, K.W. et al.
Partner: UNT Libraries Government Documents Department

Low-energy x-ray emission from magnetic-fusion plasmas

Description: Complex, transient, spatially inhomogeneous tokamak plasmas require careful diagnosis. As the reactor regime is approached, soft x rays become more important as a versatile diagnostic tool and an energy-loss mechanism. Continuum emission provides a measure of electron temperature and light impurity content. Impurity lines serve as a probe for ion and electron temperature, impurity behavior, and radiative cooling. The entire spectrum yields vital information on instabilities and disruptions. The importance of impurities is illustrated by the extensive efforts toward understanding impurity production, effects, and control. Minute heavy impurity concentrations can prevent reactor ignition. Si(Li) - detector arrays give a broad overview of continuum and line x-ray emission (.3 to 50 keV) with moderate energy (200 eV) and time (50 ms) resolution. Bragg crystal and grating spectrometers provide detailed information on impurity lines with moderate to excellent (E/..delta..E = 100 to 23,000) resolving power and 1 to 50 ms time resolution. Imaging detector arrays measure rapid (approx. 10 ..mu..s) fluctuations due to MHD instabilities and probe impurity behavior and radiative cooling. Future tokamaks require more diagnostic channels to avoid spatial scanning, higher throughput for fast, single-shot diagnosis, increased spectral information per sample period via fast scanning or use of multi-element detectors with dispersive elements, and radiation shielding and hardening of detectors.
Date: April 1, 1982
Creator: Hill, K.W.; Bitter, M.; Eames, D.; von Goeler, S.; Goldman, M.; Sauthoff, N.R. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the central ion and electron temperature of tokamak plasmas from the x-ray line radiation of high-Z impurity ions

Description: This paper describes measurements of the central ion and electron temperature of tokamak plasmas from the observation of the 1s - 2p resonance lines, and the associated dielectronic (1s/sup 2/nl - 1s2pnl, with n greater than or equal to 2) satellites, of helium-like iron (Fe XXV) and titanium (Ti XXI). The satellite to resonance line ratios are very sensitive to the electron temperature and are used as an electron temperature diagnostic. The ion temperature is deduced from the Doppler width of the 1s - 2p resonance lines. The measurements have been performed with high resolution Bragg crystal spectrometers on the PLT (Princeton Large Torus) and PDX (Poloidal Divertor Experiment) tokamaks. The details of the experimental arrangement and line evaluation are described, and the ion and electron temperature results are compared with those obtained from independent diagnostic techniques, such as the analysis of charge-exchange neutrals and measurements of the electron cyclotron radiation. The obtained experimental results permit a detailed comparison with theoretical predictions.
Date: April 1, 1982
Creator: Bitter, M.; von Goeler, S.; Goldman, M.; Hill, K.W.; Horton, R.; Roney, W. et al.
Partner: UNT Libraries Government Documents Department

Measurements of the charge state distribution and transport of iron impurity ions in TFTR plasmas by a multi-chord x-ray crystal spectrometer

Description: The radial charge-state distribution and transport of iron impurity ions in ohmically heated TFTR plasmas has been determined by a detailed comparison of the x-ray spectra obtained from a high resolution multi-chord crystal spectrometer with the predictions from plasma modeling calculations. 9 refs., 3 figs., 1 tab.
Date: April 1, 1989
Creator: Bitter, M.; Hsuan, H.; Hill, K.W.; Hulse, R.A.; von Goeler, S.; Johnson, D. et al.
Partner: UNT Libraries Government Documents Department

Evaluation of soft x-ray average recombination coefficient and average charge for metallic impurities in beam-heated plasmas

Description: The soft x-ray continuum radiation in TFTR low density neutral beam discharges can be much lower than its theoretical value obtained by assuming a corona equilibrium. This reduced continuum radiation is caused by an ionization equilibrium shift toward lower states, which strongly changes the value of the average recombination coefficient of metallic impurities anti ..gamma.., even for only slight changes in the average charge, anti Z. The primary agent for this shift is the charge exchange between the highly ionized impurity ions and the neutral hydrogen, rather than impurity transport, because the central density of the neutral hydrogen is strongly enhanced at lower plasma densities with intense beam injection. In the extreme case of low density, high neutral beam power TFTR operation (energetic ion mode) the reduction in anti ..gamma.. can be as much as one-half to two-thirds. We calculate the parametric dependence of anti ..gamma.. and anti Z for Ti, Cr, Fe, and Ni impurities on neutral density (equivalent to beam power), electron temperature, and electron density. These values are obtained by using either a one-dimensional impurity transport code (MIST) or a zero-dimensional code with a finite particle confinement time. As an example, we show the variation of anti ..gamma.. and anti Z in different TFTR discharges.
Date: May 1, 1986
Creator: Sesnic, S.S.; Bitter, M.; Hill, K.W.; Hiroe, S.; Hulse, R.; Shimada, M. et al.
Partner: UNT Libraries Government Documents Department

Unresolved dielectronic satellites of the resonance line of heliumlike iron (Fe XXV)

Description: (1s/sup 2/nl - 1s2pnl, n greater than or equal to 3) dielectronic satellites of the resonance line of Fe XXV at 1.85 A have been observed from PLT (Princeton Large Torus) tokamak discharges and are used for a detailed comparison with theory. The necessary corrections for Doppler broadening measurements are discussed, and accurate satellite to resonance line ratios allowing for a determination of the total dielectronic recombination rate of Fe XXV are derived.
Date: February 1, 1981
Creator: Bitter, M.; von Goeler, S.; Hill, K.W.; Horton, R.; Johnson, D.; Roney, W. et al.
Partner: UNT Libraries Government Documents Department

Measurements of the intercombination and forbidden lines from helium-like ions in Tokamaks and Electron Beam Ion Traps

Description: The paper reviews the results from tokamak experiments for the line ratios x/w, y/w, and z/w from helium-like ions with Z in the range from 14 to 28. With exception of the DITE experiments, where these line ratios were found to be in agreement with theoretical predictions, all other tokamak experiments yielded values that were significantly larger than predicted. The reasons for these discrepancies are not yet understood. It is possible that radial profile effects were not properly taken into account in the majority of the tokamak experiments. The paper also gives a short historical review of the X-ray diagnostic developments and also presents very recent data from a new type of X-ray imaging crystal spectrometer, which records spatially resolved spectra with a spatial resolution of about 1 cm in the plasma. These new data can be Abel inverted, so that it will be possible to determine line ratios at each radial position in the plasma. Effects of radial profiles, which may have affected the chord-integrated measurements of the past, will thus be eliminated in the future.
Date: August 22, 2007
Creator: Bitter, M; Hill, K W; von Goeler, S; Stodiek, W; Beiersdorfer, P; Rice, J E et al.
Partner: UNT Libraries Government Documents Department

Atomic data for the ITER Core Imaging X-ray Spectrometer

Description: The parameters of the ITER core plasmas will be measured using the Core Imaging X-ray Spectrometer (CIXS), a high-resolution crystal spectrometer focusing on the L-shell spectra of highly ionized tungsten atoms. In order to correctly infer the plasma properties accurate atomic data are required. Here, some aspects of the underlying physics are discussed using experimental data and theoretical predictions from modeling.
Date: June 15, 2012
Creator: Clementson, J.; Beiersdorfer, P.; Biedermann, C.; Bitter, M.; Delgado-Aparicio, L. F.; Graf, A. et al.
Partner: UNT Libraries Government Documents Department

Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas

Description: A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and vφ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and nuclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.
Date: February 27, 2008
Creator: Hill, K W; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E et al.
Partner: UNT Libraries Government Documents Department

Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas

Description: A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and vφ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and uclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.
Date: January 29, 2008
Creator: Hill, K. W.; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E et al.
Partner: UNT Libraries Government Documents Department