[en] Recent development of fast opening switch technology has led to this circuit study of the inductive energy pulsed power systems. In this paper, a comprehensive circuit analysis of basic inductive energy pulsed power systems has been carried out. It is noted that the circuit of system with inductive energy storage is the dual of that with capacitive energy storage. In the most of practical systems, the inductive energy is stored in a lumped inductor by a slow current charging and then rapidly released to a load by means of an opening switch. Such a system may be practical for generation of relatively slow output pulse. It is shown that as in the capacitive systems, a fast square pulse can be produced by using a transmission line as an energy storage in lieu of the lumped inductor, resulting in a high power multiplication. In addition, the authors propose other inductive energy circuits which may be useful for practical applications. These are the duals of well known capacitive energy circuits such as the LC generator and the Blumlein line. The output pulse waveforms, with relevant circuit parameters, are derived for a number of basic inductive energy storage circuits

[en] Phased array antennas with high directivity have a variety of applications. One of their applications is in RF heating for magnetically confined plasma fusion research. Among these RF heating schemes, waveguide arrays with careful phase control on each waveguide can act as a phased array antenna to deliver megawatts of power for heating fusion plasmas in the lower-hybrid range of frequencies (1 GHz-10 GHz). In order to achieve compactness, it is common to stack reduced height waveguide together to form the waveguide array. As long as the delivered power does not cause arcing in the waveguide, the waveguide height can be quite small. Due to this confined space in a stack of reduced height waveguides, power detection of the incident and reflected wave in the reduced height waveguide is extremely difficult. A new compact probe, which employs current loops, to monitor the incident and reflected wave from the narrow side of the reduced height waveguide has been developed. Its theory and performance will be reported in this paper

[en] The switch used in this experiment consists of a photoconducting slab (GaAs:Cr or InGaAs:Fe) on an insulating substrate on which metallic electrodes have been deposited in the configuration of a 50 Ω microstrip transmission line. The switch is connected in series with a 50 Ω coaxial transmission line and a power supply. A 2 W cw argon laser light is illuminated on the switch to allow conduction of current, which charges the transmission line. The opening of the switch was achieved by an abrupt interruption of the laser light by use of a Pockel's cell. The resultant output pulse, measured by a matched 50 Ω input impedance oscilloscope, shows a nearly perfect rectangular waveform. The rise time of the pulse, which is a measure of the switch opening time, is found to be ≅ 1 ns, which is limited by the rise time of the Pockel's cell used. The ultimate switch opening time would be constrained by the electron-hole pair recombination which is measured to be in the subnanosecond range for the material used in this experiment. A preliminary study indicates that in addition to the capability of fast repetition rate operation of the switch, the scaling to a higher voltage system appears to hold a good promise

[en] Laser activated semiconductor switches utilize instantaneous response of photoconductivity to turn on or turn off the current through the switch. It has been shown that the semiconductor switch is a good candidate for the fast opening switch applications. With a suitable choice of switch material, for which the carrier recombination time is very fast, the opening time can be as fast as subnanosecond with a very high repetition rate. The semiconductor switches can easily sustain a large voltage and conduct a high current. The authors report on the performance of high voltage operation of GaAs switches. The switches used were intrinsic GaAs and Cr: GaA of bulk devices of millimeter sizes. The range of bias voltage applied was 500 V to 2 kV. The light source was a Q-switched Nd:YAG laser with 10 ns pulse duration. The closing and opening speeds of the Cr:GaAs switches were limited by the rise time and fall time of the laser pulse. Typical off-resistances when the laser light illumination was turned off is higher than 20 MΩ, whereas the on-resistances with laser illumination can be as low as 1 Ω. Such a large ratio of off-resistance to on-resistance allowed switching efficiency of better than 99%

[en] Analytical techniques of improved sensitivity have revealed details of the concentrations and isotopic compositions of light elements for a comprehensive suite of samples from the Apollo 12 regolith. These samples show a wide spread in maturity, although maximum contents observed for solar wind elements are less than observed at other sites, possibly reflecting relative recency of craters at the Apollo 12 site. Isotopic composition of nitrogen is consistent with the idea that ¹⁵N/¹⁴N in the solar wind has increased with time, at least a major part of this increase having occurred in the past 3.1 Gyr. Sulfur isotope systematics support a model in which sulfur is both added to the regolith, by meteoritic influx, and lost, by an isotopically selective process. Most soils from this site are heavily contaminated with terrestrial carbon. (author)

[en] Experimental results have shown that the high harmonic fast wave (HHFW) at 30 MHz can provide substantial plasma heating and current drive for the NSTX spherical tokamak operation. However, the present antenna strap design rarely achieves the design goal of delivering the full transmitter capability of 6 MW to the plasma. In order to deliver more power to the plasma, a new antenna strap design and the associated coaxial line feeds are being constructed. This new antenna strap design features two feedthroughs to replace the old single feed-through design. In the design process, CST Microwave Studio has been used to simulate the entire new antenna strap structure including the enclosure and the Faraday shield. In this paper, the antenna strap model and the simulation results will be discussed in detail. The test results from the new antenna straps with their associated resonant loops will be presented as well

[en] A collaborative project between MIT and Princeton has been undertaken to fabricate a high power system for application of lower hybrid current drive (LHCD) on the Alcator C-MOD device. The ultimate goal of the project is to have the ability to apply up to 3 MW of 4.6 GHz rf power to drive current for the study of advanced tokamak operation on C-MOD. As part of the PPPL portion of the collaboration a high power wave-guide launching array has been designed and constructed to support 1.5 MW application to the plasma based on previous experimental power limits (and possibly supporting 2 MW application with advanced conditioning). In this paper we will describe the construction, calibration and testing techniques utilized and the results obtained during the construction phase

[en] MIT and PPPL have joined together to fabricate a high-power lower hybrid current drive (LHCD) system for supporting steady-state AT regime research on Alcator C-Mod. The goal of the first step of this project is to provide 1.5 MW of 4.6 GHz rf [radio frequency] power to the plasma with a compact launcher which has excellent spectral selectivity and fits into a single C-Mod port. Some of the important design, construction, calibration and testing considerations for the launcher leading up to its installation on C-Mod are presented here

[en] MIT and PPPL have joined together to fabricate a high-power lower hybrid current drive (LHCD) system for supporting steady-state AT regime research on Alcator C-Mod. The goal of the first step of this project is to provide 1.5 MW of 4.6 GHz rf power to the plasma with a compact launcher which has excellent spectral selectivity and fits into a single C-Mod port. Some of the important design, construction, calibration and testing considerations for the launcher leading up to its installation on C-Mod are presented here