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Notes: The two most sensitive TFTR fission-chamber detectors were absolutely calibrated in situ by a D-T neutron generator (∼5×107 n/s) rotated once around the torus in each direction, with data taken at about 45 positions. The combined uncertainty for determining fusion neutron rates, including the uncertainty in the total neutron generator output (±9%), counting statistics, the effect of coil coolant, detector stability, cross calibration to the current mode or log Campbell mode and to other fission chambers, and plasma position variation, is about ±13%. The NE-451 (ZnS) scintillators and 4He proportional counters that view the plasma in up to 10 collimated sightlines were calibrated by scanning the neutron generator radially and toroidally in the horizontal midplane across the flight tubes of 7 cm diam. Spatial integration of the detector responses using the calibrated signal per unit chord-integrated neutron emission gives the global neutron source strength with an overall uncertainty of ±14% for the scintillators and ±15% for the 4He counters. © 1995 American Institute of Physics.

Notes: The liquid coating (LC) has been employed to apply epoxy and lubricant over the surface of rapidly solidified Nd–Fe–B powder particles. The LC led to an improvement of physical and magnetic properties for the powders and magnets compared to the dry blending and the encapsulation methods. The LC powders have excellent flowability and can be used for bonded magnets requiring very close tolerances; further bonded magnets made using this powder posses higher strength.© 1999 American Institute of Physics.

Notes: Epitaxial YBa2Cu3O7−δ thin films grown by laser ablation on MgO (100) substrates were investigated for microwave applications. By systematically varying the growth conditions, we obtained films with various microstructures, low-frequency superconducting properties, and microwave performance. The surface resistances were determined from a measured unloaded quality factor in a 8.6-GHz microstrip resonator. Surface resistance was found to correlate most directly with the degree of grain alignment as revealed by electron channeling and x-ray diffraction studies. Films grown at optimal conditions gave a scaled surface resistance of 0.6 mΩ at 77 K and 10 GHz.

Notes: In D-T plasmas, the understanding of the physics of confined α particles is extremely valuable for the future fusion plasma device. Among the various proposed α diagnostics, an X-mode collective Thomson scattering system employing a high-power gyrotron source (P(approximately-equal-to)200 kW, f=60 GHz, pulse length (approximately-equal-to)0.5 s, and modulation frequency=10–25 kHz) is being designed for TFTR. The detailed description of the gyrotron source, transmission lines, optical designs, beam and viewing dump design, and receiver system will be presented in this paper. In particular, the test results of the beam and viewing dump indicate that the stray light can be reduced by 60 dB. The background emission level (∼20 eV) near 60-GHz range during high Q discharge may also be reduced with beam and viewing dump further. The optical system is designed to measure the radial profile of α particles and to orient the incident wavevector (k0) to test the electromagnetic effects of the scattered spectrum. Prior to the study of α physics in D-T plasmas, this scattering system will be used to measure not only a bulk ion temperature but also the scattered spectrum due to fast ions produced by NB and ICRF heating in TFTR. This work was supported by the U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.

Notes: The protocol agreement allowing the design of the International Thermonuclear Engineering Reactor (ITER) to proceed will be signed early this year. There is already a small U.S. Program evaluating diagnostic capability for this device and there will shortly be an international effort on diagnostics to ensure satisfactory integration of the diagnostic systems with all the complex systems that will be developed for this large ignited tokamak. The diagnostic studies, at least initially, will depend heavily on the output information provided by the conceptual design activity (CDA). ITER provides a very large plasma (R=6.0 m, a=2.15 m) with high average density (〈ne(approximately-greater-than)∼1.0×1020 m−3), and temperatures (〈Te(approximately-greater-than)∼〈Ti(approximately-greater-than)≥10 keV). It is highly elongated and could have primarily noninductive current drive so that its pulse length can be very long (t≤2 weeks) to allow significant blanket testing in its technology phase. These parameters lead to considering new diagnostic methods for some measurements. A set of specifications for the diagnostic measurements were developed, and a corresponding set of diagnostic instruments was proposed during the CDA. The specifications for spatial and temporal measurement of the plasma parameters are very similar to those achieved on present day large tokamaks, where, on the whole, the access to the plasma is much more open and there is a negligible radiation background in which the diagnostics have to perform.The specifications require that many diagnostic signals participate in the control of complex fuelling, heating, and current drive schemes, so it is clear that the diagnostic design issues for these burning plasmas must be addressed early in ITER's design life. This is particularly true because penetrations through the first wall are at a premium and only small holes can be tolerated because of radiation streaming. The needs for Research and Development, necessary to demonstrate the feasibility of diagnostic techniques for the ITER plasma parameters and the radiation environment were also addressed. In the area of radiation impact on diagnostic components, some priorities have been set and testing programs have been started. This report will address the present activities on diagnostics in the U.S. Program to address some of the problems left over from the CDA.

Notes: Present-day tokamak x-ray imaging (XIS) and pulse height analysis (PHA) diagnostics will require special shielding and x-ray optics to permit use on fusion reactors without prohibitive noise and detector damage from neutrons and gamma rays; x-ray curved-crystal spectrometers (XCS) may work with extensive shielding and collimation, but radiation damage of crystals and attainment of adequate impurity concentrations for ion-temperature measurement are concerns. We consider the use of one or more reflections at grazing incidence from x-ray mirrors or from Bragg layered synthetic microstructures (LSM) to decouple the x-ray diagnostic from the direct fusion neutron beam. We present calculations of expected x-ray line brightnesses from ITER and total instrument throughput. We also consider the use of hollow glass capillaries embedded in radiation shields to precede the XIS detector and reduce the ratio of neutron plus gamma radiation to x rays by a factor of ∼0.01 or better. Compatibility of capillary schemes with the PHA and XCS are discussed.

Notes: We have fabricated and measured 5 GHz microstrip resonators from a series of YBa2Cu3O7−δ thin films grown on LaAlO3(001) substrates by in situ laser ablation. We have studied the correlations between unloaded quality factor and various film properties, such as transition temperature, width of transition, critical current density, narrowness of x-ray rocking curve, sharpness of electron channeling pattern, and most important substrate temperature during growth. We found that in general, higher transition temperature, higher critical current density, sharper transition, sharper channeling pattern, and narrower x-ray rocking curve correlate positively with good microwave performance. The best quality factor exists for a narrow growth temperature window (around 800 °C). We also report the dependence of quality factor on device power for each film.

Notes: Scalings for the stored energy and neutron yield, determined from experimental data, are applied to both deuterium-only and deuterium–tritium plasmas in different neutral-beam-heated operational domains in the Tokamak Fusion Test Reactor [Nucl. Fusion 25, 1167 (1985)]. The domain of the data considered includes the Supershot, high poloidal beta, low-mode, and limiter high-mode operational regimes, as well as discharges with a reversed magnetic shear configuration. The new important parameter in the present scaling is the peakedness of the heating beam fueling profile shape. Ion energy confinement and neutron production are relatively insensitive to other plasma parameters compared to the beam fueling peakedness parameter and the heating beam power when considering plasmas that are stable to magnetohydrodynamic modes. However, the stored energy of the electrons is independent of the beam fueling peakedness. The implication of the scalings based on this parameter is related to theoretical transport models such as radial electric field shear and ion temperature gradient marginality models. Similar physics interpretation is provided for beam heated discharges on other major tokamaks.

Notes: We report results of the TFTR fission detector calibration performed in December 1988. A NBS-traceable, remotely controlled 252Cf neutron source was moved toroidally through the TFTR vacuum vessel. Detection efficiencies for two 235U detectors were measured for 930 locations of the neutron point source in toroidal scans at 16 different major radii and vertical heights. These scans effectively simulated the volume-distributed plasma neutron source and the volume-integrated detection efficiency was found to be insensitive to plasma position. The Campbell mode is useful due to its large overlap with the count rate mode and large dynamic range. The resulting absolute plasma neutron source calibration has an uncertainty of ±13%.

Notes: The pending approach of significant alpha particle populations in D-T plasmas in TFTR and JET and in the burning plasma devices, CIT and ITER, has led to detailed study of the measurement of the alpha particles both directly and through their potential effects on the plasma. The possible diagnostics of alpha particles, previously reviewed, for example, by Zweben [S. J. Zweben, Rev. Sci. Instrum. 57, 1723 (1986)], for use on such devices have been narrowed down to a relatively small number of possibilities. Small scintillator detectors at the wall have proven very effective in detecting the escaping T and p fusion products from the D-D reaction and hence mocking-up the relevant studies of loss required by ITER. Development of high-power pulsed microwave scattering systems for investigating the fast confined alphas is in progress for TFTR and JET. Selection of the right frequency and mode will be needed for CIT and ITER but this technique has the major advantage of being able to conform to readily available access. The use of a carbon impurity pellet to provide a suitably dense ablation target cloud so that the spectra of the emitted helium light will provide data on the energy distribution of these fast alphas is also being developed. For the slowing-down group (Eα≤500 keV), charge exchange recombination spectroscopy using a source beam of neutrals is the most probable diagnostic but it becomes limited by the penetration of the beams. But, in addition to the direct measurement of the alphas, or of the neutrons, to give information on their source profile and time behavior, they significantly heat the plasma and also, potentially, lead to new instability modes which could lead to enhanced loss of themselves or of the plasma. These instabilities have been extensively analyzed recently so that methods for identifying their presence can now be evaluated. These diagnostics, and some aspects of their implementation on TFTR, CIT, and ITER will be described. This work was supported by U.S. DOE contract No. DE-AC02-76-CHO-3073.