ALBERT

Notes: The midplane microwave heating system in the ELMO Bumpy Torus (EBT) [in Proceedings of the Sixth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, 1976 (IAEA, Vienna, 1977), Vol. II, p. 145] was supplemented with power launched from the high-field side of the fundamental resonance by an antenna in the magnet coil throat. Up to 43 kW of polarized (extraordinary mode), 28 GHz power was successfully launched with one antenna. Measurements were made of changes in the core and hot-electron ring plasma parameters when throat-launch power was added. In sharp contrast to initial expectations, the bulk core-plasma parameters were degraded while the ring parameters, in the launch cavity, were improved. These results are consistent with a modified picture of electron-cyclotron heating (ECH) in EBT. A picture of localized microwave absorption and particle losses is supported by additional measurements.

Notes: Several diagnostics measure the particle sources and losses in the Tandem Mirror Experiment-Upgrade (TMX-U) plasma. An absolutely calibrated high-speed (0.5 ms per frame) filtered (6561 A(ring)) video camera measures the total ionization source as a function of radius. An axial view of the plasma automatically integrates the axial variations within the depth of field of the system. Another camera, viewing the plasma radially, measures the axial source variations near the deuterium fueling source. Axial ion losses are measured by an array of Faraday cups that are equipped with grids for repelling electrons and are mounted at each end of the experiment. Unequal ion and electron (nonambipolar) radial losses are inferred from net current measurements on an array of grounded plates at each end. Any differences between the measured particle losses and sources may be attributed to ambipolar radial losses and/or azimuthal asymmetries in the particle-loss profiles. Methods of system calibration, along with details of computer data acquisition and processing of this relatively large set of data, are also presented.

Notes: Beam from the accelerator for research was available for a total period of 3900 h last year and unscheduled maintenance time was reduced by a factor of almost 2. An arc discharge tube conditioning test was conducted on the top five units of the accelerator and a test with macropulsed beam was accomplished. The main problems during the year were vacuum leaks and voltage "tics.''

Notes: Photoconductors are very promising x/γ-ray detectors and x-ray bolometers for pulsed x/γ-ray measurements. They are fast, sensitive, and theoretically flat in spectral response for low energy x rays. We report our tests of InP:Fe, GaAs, and GaAs:Cr, both neutron damaged and undamaged, at Nova laser, Febetrons, and electron linear accelerators. The temporal and spectral responses are discussed.

Notes: Historically GaAlAs alloys grown by molecular-beam epitaxy have high deep level concentrations (〉1016 cm−3), low luminescent efficiency with broad peaks, and are difficult to dope controllably below mid 1016 cm−3. We report the effect that the low incident antimony molecule fluxes during growth appear to help reduce the density of deep levels below 1014 cm−3, which then allows reproducible doping control in the low 1015 cm−3 range. Exciton-dominated photoluminescence with half widths ∼4.0 meV are now routinely achieved using this technique. Further evidence for the quality improvement of AlGaAs by heavy atom (Sb) doping comes from high 4 K two-dimensional electron gas mobilities for low sheet electron densities, e.g., 1.3×106 cm2/V s for n=2×1011 cm−2. SIMS profiles of antimony content are presented and estimates of incorporated concentrations are given.

Notes: A new, large-area, high-uniformity, flash x-ray source that efficiently couples electrical energy to photon energy has been successfully constructed and tested on the 1-MV, 2-MA electron accelerator SPEED (short pulse experimental electron device). The source employs 18 individual blade diodes arranged in the configuration of a frustum. Each blade was magnetically isolated on the real-cathode side of an anode foil, but not on the virtual-cathode side. The operation of the diode was heavily diagnosed using 24 Rogowski coils, a vacuum voltage monitor, p-i-n diode detectors, an 80-element TLD array, and a fast-framing x-ray pinhole camera. The individual blade diodes were found to exhibit line pinching, end-to-end pinching, and minimal electron reflexing through the Ta anode foil, with a radiation yield that agreed with Monte Carlo simulations. The end-to-end pinch location could be controlled by tapering the anode–cathode gap. The impedance depended on only the smallest spacing, and was independent of pinch location.

Notes: A series of experiments was performed with an Applied-B ion diode on the Particle Beam Fusion Accelerator-I, with peak voltage, current, and power of approximately 1.8 MV, 6 MA, and 6 TW, respectively. The purpose of these experiments was to explore issues of scaling of Applied-B diode operation from the sub-TW level on single module accelerators to the multi-TW level on a low impedance, self-magnetically insulated, multimodule accelerator. This is an essential step in the development of the 100-TW level light ion beam driver required for inertial confinement fusion. The accelerator and the diode are viewed as a whole because the power pulse delivered by the 36 imperfectly synchronized magnetically insulated transmission lines to the single diode affects module addition, diode operation, and ion beam focusability. We studied electrical coupling between the accelerator and the diode, power flow symmetry, the ionic composition of the beam, and the focusability of the proton component of the beam. Scaling of the diode impedance behavior and beam quality with electrical drive power is obtained from comparison with lower-power experiments.The diode impedance lifetime was about 10 ns, several times shorter than for lower-power experiments. Azimuthal and top-to-bottom variations of the diode and ion currents were found to be approximately ±10%, compared with an estimated requirement of 5%–7% uniformity to avoid focal blurring by self-magnetic field effects. The ion production efficiency was 80%–90%. However, only 50%±10% of the ion current was carried by protons; the balance was carried by multiply charged carbon and oxygen ions. Activation measurements showed a proton beam energy of approximately 50 kJ. A gas cell filled with 5 Torr of argon was used for beam transport. The macroscopic divergence was 15±10 mrad and the microscopic divergence was 20±15 mrad, values that are similar to those from lower-power experiments. A model of beam focusing is formulated that predicts the proton charge focused onto 0.47-cm radius lithium targets, taking into account beam purity, magnetic bending, small-angle multiple scattering, and intrinsic divergence. The model results and activation measurements of the number of protons focused onto targets agree, and indicate that the spatially averaged (over about 3 cm2) peak focal power was about 0.5 TW/cm.2 The most important limitations on power concentration were found to be the low proton content of the beam, the short impedance lifetime of the diode, and the asymmetric current feed of the accelerator. The short impedance lifetime limited the power coupled to the diode, and caused the voltage at peak ion power to be low, which exacerbates the small-angle scattering problem. The asymmetric feed caused focal blurring through nonuniform self-magnetic bending. At least partly because of the experience gained with low impedance beams during these experiments, the next generation accelerator, the 100-TW Particle Beam Fusion Accelerator-II, has been configured to produce a 25–30-MV Li+ beam rather than a 5-MV proton beam. off

Notes: The liquid-helium distribution system for the FSU superconducting linear accelerator has been installed and a preliminary evaluation of the system performance has been made. A heat leak of about 30 W was anticipated for the entire system. With two of the five cryostats in place, we estimate an overhead heat leak for the piping system of about 37 W.

Notes: Diverse plasmas have been observed in the magnetospheres of Earth and other planets, and in interplanetary space. Recently, measurements were made by a space probe at Comet Giacobini–Zinner. In these various plasma regimes investigated during the space era, plasma characteristics vary widely: particle densities range from 〈0.01 to 1000 per cc, energies from 〈1 eV to many MeV, temperatures from 〈1 eV to 〉1000 eV, and bulk flow speeds from near stationary to 〉1000 km/s. A variety of plasma-wave activity and instabilities characterize these plasmas. The measurements are made with several different generic types of instruments including electrostatic analyzers and systems which combine electrostatic analysis with time-of-flight or magnetic analysis in order to identify ions and their charge states. This paper outlines the plasma regimes found in space, discusses instrument design principles and constraints imposed by limited spacecraft resources, describes a few instruments, and highlights a small selection of scientific results derived from diagnostics of space plasmas.

Notes: Thomson scattering systems capable of providing snapshot profiles of electron temperature and density with high spatial resolution (〉50 points) have become routine diagnostics on the Princeton large torus (PLT), Princeton divertor experiment (PDX), and tokamak fusion test reactor (TFTR) tokamaks. The design parameters of these systems are compared. Particular attention is given to describing those new components and techniques which have contributed most to improved data quality and reliability in the ten-year evolution of these systems. Examples of recent TFTR Te(R) and ne(R) profiles are presented.