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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: We describe here a new solid-state nuclear-magnetic-resonance (NMR) experiment for correlating anisotropic and isotropic chemical shifts of inequivalent nuclei in powdered samples. Spectra are obtained by processing signals arising from a spinning sample, acquired in independent experiments as a function of the angle between the axis of macroscopic rotation and the external magnetic field. This is in contrast to previously proposed techniques, which were based on sudden mechanical flippings or multiple-pulse sequences. We show that the time evolution of variable-angle-spinning signals is determined by a distribution relating the isotropic frequencies of the spins with their corresponding chemical shift anisotropies. Fourier transformation of these data therefore affords a two-dimensional NMR spectrum, in which line shapes of isotropic and anisotropic interactions are correlated. Theoretical and experimental considerations involved in the extraction of this spectral information are discussed, and the technique is illustrated by an analysis of 13C NMR anisotropy in glycine, cysteine, and p-anisic acid.

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: 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: 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.

Notes: Epitaxial YBa2Cu3O7−δ thin films on LaAlO3 deposited by plasma-enhanced metalorganic chemical vapor deposition were tested in a 100 GHz microwave cavity and as patterned 5.6 GHz resonators. Two films, both having high critical temperature ((approximately-greater-than)90 K) and high critical current density ((approximately-greater-than)106 A/cm2), exhibited low-power Q's of 5400 and 8000 as 5.6 GHz microstrip resonators when operated at 77 K. The equivalent surface resistances at 10 GHz are 1.7 and 1 mΩ, respectively. Despite the fact that these films are thinner than typical laser ablation films, the results are within a factor of 2 of the best laser ablation prepared YBa2Cu3O7−δ films.

Notes: We report the successful synthesis of superconducting YBa2Cu3O7−δ (YBCO) (100) thin films with alignment of the in-plane c axis. These films were grown on single crystal NdGaO3 (110) substrates. The twofold symmetry of the substrate surface is believed to lead to anisotropic alignment of the in-plane c axis of the epitaxial YBCO (100) film. X-ray diffraction studies indicate that over 80% of the film grew epitaxially with the YBCO [100] perpendicular to the substrate surface, and YBCO [001] aligned along one pseudo-cubic axis of the NdGaO3. The superconductivity onset of the film was measured to be 89 K by ac susceptibility.

Notes: We report the fabrication and characterization of thin-film grain boundary junctions in Tl-based superconductors on bicrystal substrates. Post-deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current-voltage curves had a strong dependence on θ. For θ≥10°, there was a two-to-three order of magnitude reduction in critical current density, and for θ≥20°, the current-voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well-behaved dc magnetic and rf field dependence, IcRn products as large as 300 μV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.