Measurement of the energy and power radiated by a pulsed blackbody x-ray source
H.C. IvesW. A. StygarD. L. FehlLynnette RamirezS. C. DropinskiD. WallJ. S. AnctilJ. McGurnJ. PyleD. L. HansonB. N. AllisonMichael BerningerElliot BryceG. A. ChandlerM. E. CuneoA. J. FoxT. L. GillilandC.L. HaslettR. J. LeeperDavid F. LewisM. A. LuceroM.G. MazarakisD. H. McDanielJ. L. McKenneyJ. A. MillsL. P. MixJ. L. PorterM. B. RitcheyL. E. RugglesJ. F. SeamenW. W. SimpsonR. B. SpielmanJ. TorresM. VargasT. C. WagonerLarry K. WarneMathew William York
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We have developed a diagnostic system that measures the spectrally integrated (i.e. the total) energy and power radiated by a pulsed blackbody x-ray source. The total-energy-and-power (TEP) diagnostic system is optimized for blackbody temperatures between 50 and 350 eV. The system can view apertured sources that radiate energies and powers as high as 2 MJ and 200 TW, respectively, and has been successfully tested at 0.84 MJ and 73 TW on the $Z$ pulsed-power accelerator. The TEP system consists of two pinhole arrays, two silicon-diode detectors, and two thin-film nickel bolometers. Each of the two pinhole arrays is paired with a single silicon diode. Each array consists of a $38\ifmmode\times\else\texttimes\fi{}38$ square array of 10-$\ensuremath{\mu}\mathrm{m}$-diameter pinholes in a 50-$\ensuremath{\mu}\mathrm{m}$-thick tantalum plate. The arrays achromatically attenuate the x-ray flux by a factor of $\ensuremath{\sim}1800$. The use of such arrays for the attenuation of soft x rays was first proposed by Turner and co-workers [Rev. Sci. Instrum. 70, 656 (1999)]. The attenuated flux from each array illuminates its associated diode; the diode's output current is recorded by a data-acquisition system with 0.6-ns time resolution. The arrays and diodes are located 19 and 24 m from the source, respectively. Because the diodes are designed to have an approximately flat spectral sensitivity, the output current from each diode is proportional to the x-ray power. The nickel bolometers are fielded at a slightly different angle from the array-diode combinations, and view (without pinhole attenuation) the same x-ray source. The bolometers measure the total x-ray energy radiated by the source and---on every shot---provide an in situ calibration of the array-diode combinations. Two array-diode pairs and two bolometers are fielded to reduce random uncertainties. An analytic model (which accounts for pinhole-diffraction effects) of the sensitivity of an array-diode combination is presented.Keywords:
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A field of view (FoV) of the resistive bolometer systems specialized for the total radiated power analysis has been designed with bolometer systems having multiple-apertures in JT-60SA. The multi-aperture bolometer system can reduce the required number of bolometer channels for the determination of the total radiated power. The FoV design has been carried out to minimize unobserved and overlapping regions with the following requirements: (i) independent determination of the divertor and the main plasma radiation, (ii) limitation of the use of only three diagnostic ports, and (iii) a redundant FoV design. With the designed FoV, the whole plasma of JT-60SA is viewed by only five bolometers and five replicated bolometers having the same FoV for redundancy. A signal evaluation with the designed FoV with a predetermined radiation profile indicates that even the lowest performing bolometer exhibits a signal to noise (S/N) ratio of 300 or more. The evaluated S/N ratio is high enough for the total radiated power analysis. Using the designed FoV, the total radiated power over the plasma profile can be determined within 5.3% using only five bolometers.
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This paper describes the work done to develop a bolometer post processor that converts volumetric radiated power values taken from a UEDGE solution, to a line integrated radiated power along chords of the bolometers in the DIII-D tokamak. The UEDGE code calculates plasma physics quantities, such as plasma density, radiated power, or electron temperature, and compares them to actual diagnostic measurements taken from the scrape off layer (SOL) and divertor regions of the DIII-D tokamak. Bolometers are devices measuring radiated power within the tokamak. The bolometer interceptors are made up of two complete arrays, an upper array with a vertical view and a lower array with a horizontal view, so that a two dimensional profile of the radiated power may be obtained. The bolometer post processor stores line integrated values taken from UEDGE solutions into a file in tabular format. Experimental data is then put into tabular form and placed in another file. Comparisons can be made between the UEDGE solutions and actual bolometer data. Analysis has been done to determine the accuracy of the plasma physics involved in producing UEDGE simulations.
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This paper describes the work done to develop a bolometer post processor that converts volumetric radiated power values taken from a UEDGE solution, to a line integrated radiated power along chords of the bolometers in the DIII-D tokamak. The UEDGE code calculates plasma physics quantities, such as plasma density, radiated power, or electron temperature, and compares them to actual diagnostic measurements taken from the scrape off layer (SOL) and divertor regions of the DIII-D tokamak. Bolometers are devices measuring radiated power within the tokamak. The bolometer interceptors are made up of two complete arrays, an upper array with a vertical view and a lower array with a horizontal view, so that a two dimensional profile of the radiated power may be obtained. The bolometer post processor stores line integrated values taken from UEDGE solutions into a file in tabular format. Experimental data is then put into tabular form and placed in another file. Comparisons can be made between the UEDGE solutions and actual bolometer data. Analysis has been done to determine the accuracy of the plasma physics involved in producing UEDGE simulations.
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Two design techniques for the field of view (FoV) of a resistive bolometer system for the analysis of the total radiated power have been developed. The first technique is a new concept of the resistive bolometer system having multiple apertures to achieve a large viewing angle with one bolometer channel. The second technique is an optimization technique of the bolometer location in the major radial direction to minimize error of the analysis. Both techniques have been examined with a virtual tokamak device. By a FoV designed with both techniques, the total radiation power of several radiation profiles can be determined within 3% error of the analysis with one bolometer channel.
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Abstract : A blackbody radiation source was used to evaluate a self-calibrating, phosphorous-doped silicon bolometer, with the objective of establishing an NBS- traceable calibration of the bolometer. The experimental results are inconclusive, since the response of the bolometer to its integral thin-film heater power was found to be linear and the response to the NBS-calibrated blackbody power was not linear. This discrepancy suggests the possible existence of a blackbody design problem. The problem should be resolved by repeating the calibration using another NBS-calibrated infrared source.
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The resistive bolometer system has been successfully employed on experimental advanced superconducting tokamak for the first time to measure the radiated power of plasma. The bolometer detectors are based on 4 μm thick Pt absorbers deposited on 1.5 μm thick SiN membranes. The system consists of 3 cameras with a total of 48 channels. The detector and the system setup are described in detail. The detector calibration and typical measurement results are presented as well.
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On present-day magnetic-confinement fusion experiments, the performance of multi-channel bolometer diagnostics has typically evolved over time through experience with earlier versions of the diagnostic and experimental results obtained. For future large-scale fusion experiments and reactors, it is necessary to be able to predict the performance as a function of design decisions and constraints. A methodology has been developed to predict the accuracy with which the volume-integrated total radiated power can be estimated from the measurements by a resistive bolometer diagnostic, considering, in particular, its line-of-sight geometry, étendues of individual lines of sight, bolometer-sensor characteristics, and the expected noise level that can be obtained with its electronics and signal chain. The methodology depends on a number of assumptions in order to arrive at analytical expressions but does not restrict the final implementation of data-processing of the diagnostic measurements. The methodology allows us to predict the performance in terms of accuracy, total-radiated power level, and frequency or time resolution and to optimize bolometer-sensor characteristics for a set of performance requirements. This is illustrated for the bolometer diagnostic that is being designed for the ITER experiment. The reasonableness, consequences, and limitations of the assumptions are discussed in detail.
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A carbon bolometer, used as a high speed thermometer for observing heat pulses in solids at low temperatures, is described. In conjunction with a KCl substrate, the carbon bolometer was compared with a thin film superconducting bolometer. The carbon bolometer was found to have a frequency response flat to at least 2.5 kHz.
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