Fast Gas Valve Research Articles

Influence of operating parameters on discharge mode of parallel-rail accelerator

Electromagnetic plasma accelerators which can generate hypervelocity and high density plasma jets have been widely used in the fields of nuclear physics and astrophysics. In this paper, an experimental platform of parallel-rail accelerator electromagnetically driven plasma is established, and the discharge modes under different discharge currents and gas injection conditions are studied through using magnetic probes, a spectrometer and an ICCD. A fast gas valve is used to inject argon into the rail electrode area. The time delay between the fast valve discharge and the parallel-rail accelerator discharge is fixed to be 450 μs. The waveform of power supply of the parallel-rail accelerator is a sinusoidal wave. The total capacitance is 120 μF, the total inductance is about 400 nH, and the maximum current is 170 kA. The fast valve current waveform is a double exponential waveform with a maximum current of 2.5 kA. When the discharge current is 40 kA, a current sheet with a certain thickness is generated, and the current sheet moves through different detection positions along the rail electrode at a certain velocity. Therefore, the working mode of the parallel-rail accelerator is the snowplow mode. As the discharge current increases, the trailing edge of the current channel is fixed during the current rising phase, and starts to move to the end of the rail during the current falling phase. A diffuse distributed current channel is formed, and the parallel-rail accelerator operates in a deflagration mode. As the gas injection mass increases, the current channel front velocity decreases to form a more concentrated distributed current channel, and the discharge mode turns into the snowplow mode. The stationary current channel in the deflagration mode is maintained mainly by ablating the electrode. The operating parameters mainly affect the rail voltage, which in turn affects the discharge mode of the parallel-rail accelerator. The rail voltage increases when the discharge current or the current rate of change increases. If the rail gap behind the current channel cannot withstand the high rail voltage under large discharge current or large current rate of change, the breakdown occurs, which results in the deflagration mode discharge.

On the Possibility of Initiating the Proton\u2013Boron Nuclear Fusion Reaction in the Plasma-Focus Device

In this paper, the possibilities to perform aneutronic fusion in Plasma Focus (PF) devices have been presented. For this purpose, an idea of doping plasma by means of laser ablation of a solid boron target during discharge in PF-24 was presented. Some estimates have been made, based on the processes occurring during the discharge in the PF system with gas injection using a fast gas valve, indicating that this method allows the generation of hydrogen–boron plasma. The yield of the 11B(p,α)αα reaction was calculated. The results presented in this paper show that this yield is high enough to register and measure the alpha particles emitted from the plasma column consisting boron and hydrogen. The estimates were made for the parameters characteristic for PF-24.

Radiative Characteristics of Reversed Polarity Gas-Puff Ar and Kr Plasmas

Experiments with regular and reversed polarities were carried out on the SHOTGUN-III Z-pinch device at Nihon University, Japan. SHOTGUN’s storage section consists of the 12- $\mu \text{F}$ fast capacitor bank, which was charged to 25 kV for these experiments and provided current up to 200 kA. The Ar and Kr gases were puffed between the electrodes through a hollow nozzle using a fast gas valve. Time-resolved X-ray detectors, time-integrated X-ray pinhole camera and two spectrometers, and an optical framing camera were applied for the study of radiative properties of Ar and Kr gas puffs. K-shell Ar spectra (3.9–4.2 A) and L-shell Kr spectra (6.3–7.6 A) show much intense He- and Li-like Ar and Ne- and Na-like Kr spectral features, respectively, and the evidence of the electron beams in reversed polarity experiments. The influence of reversed polarity on gas-puff plasma radiative characteristics and X-ray spectroscopic measurements is discussed. The advantages of using K-shell Ar and L-shell Kr for hot electron beam diagnostics are highlighted.

The JET-Enhanced Performance programme: More heating power and diagnostic capabilities in preparation for ITER

Since early 2000, the JET-Enhanced Performance (JET-EP) programme has been aiming at optimising JET for ITER-relevant plasma operations, from 2005 onwards. The overall heating capability of JET will be increased to 40 MW by upgrading the neutral beam system and building a new ITER-like ion cyclotron radio-frequency heating (ICRH) antenna with particularly stringent specifications. The new divertor will be able to absorb more than 300 MJ per shot and allow running high-triangularity ITER-like scenarios with a greater flexibility with respect to different plasma configurations. The control of extreme plasma shapes will be reinforced and a new disruption mitigation system using a very fast gas valve will be provided. The diagnostic capability will be enhanced by several new systems designed to address a number of crucial physical phenomena for ITER. To study tritium retention further, new technologically challenging erosion-redeposition diagnostics will be installed, particularly in the divertor region, both real time and integrating. New neutron detectors using the latest advances in scintillators and data recording techniques, detectors for fast α particles with high pitch angle and energy resolution, high-resolution Thomson scattering, with a 20 Hz repetition rate, which will provide temperature and density profiles with a spatial accuracy close to 2 cm are the leading items of this programme. New halo sensors will be installed to better understand disruption phenomena. New high-signal to noise bolometric tomography and an ambitious IR viewing system using a state of the art camera will also be added. This paper presents an overview, emphasising the main objectives and pointing out the various technological challenges and innovations.

Development of a fast valve for mitigating disruptions in tokamaks

In support of our disruption mitigation profram, a fast gas valve has been constructed and tested on TEXTOR at FZJ Juelich. Its main features have been shown to be: (1) rapid response time: 0.5 ms; (2) amount of injected gas: variable, 2–1000 mbar×l; (3) linear dependence of the number of injected particles on the gas pressure; (4) capability of working in a strong magnetic field; (5) sort of gas: any. The valve has the standard CF 35 flange, commonly used in vacuum engineering. All the components that have contact with vacuum were made of stainless steel, except for the closing aluminum piston. To prevent gas leaking directly from the bottles to the experimental vessel there are also two safety valves, closing the bottles before the shot. The required control equipment includes a high power supply and the combined controller for the safety valves and baratrons, both being able to work with TTL control signals. During tests and experiments on TEXTOR and ASDEX-Upgrade, the valve showed successful operation with three gas types: He, Ne, Ar.

Techniques for the measurement of ionization times in ECR ion sources using a fast sputter sample and fast gas valve

Two techniques for the discrete injection of material into an Electron Cyclotron Resonance ion source (ECRIS) have been developed for the purpose of measuring the ionization and confinement times of ion species. Previously only solid materials in conjunction with a pulsed laser were used in these studies due to the discrete material introduction produced by this configuration. The first method replaces the pulsed laser with a fast high voltage pulse applied to a sputter sample. The high voltage pulse has a rise time of 100 ns, fall time of 80.0 μs, and variable pulse duration. The second method utilizes a fast-pulsed gas valve capable of producing a gas pulse 160 μs in width. These pulse widths are well below the ionization times of the lower charge states and thus allows for time measurements to be made of all charge states. Both of these techniques can be employed to study the effects of rf power, coil configuration, biased disk, and gas mixing on ionization and confinement times. Rise times for neon, argon, and gold will be presented.

Simulation-Based Methods for Developing Fuel Cell Propulsion Control Systems

General Motors / Opel is working on fuel cell technology and its integration in vehicles. The requirement for shorter development times in combination with still rapidly changing technological approaches calls for new adapted methods for the controls development of fuel cell propulsion systems. The present contribution introduces a consistent development and simulation environment which efficiently supports all phases of the controls development process from defining the control functions to offline and real-time powertrain simulation to the application of the control algorithm to the real vehicle. As an example, the use of this environment is shown for the development of a fast gas valve positioning control.

Novel gas-doping technique for local spectroscopic measurements in pulsed-power systems

A novel method for doping plasmas in pulsed-power experiments with gaseous elements has been developed. A fast gas valve, a nozzle, and a skimmer are used to generate an ultrasonic gas beam that is injected into a planar-geometry microsecond plasma-opening switch (POS). An array of ionization probes with relatively high spatial and temporal resolutions was developed for diagnosing the absolute injected-gas density and its spatial profile. The properties of the gas column were also studied using spectroscopy of line emission that results from the interaction of the doped gas with the POS prefilled plasma. The doped column is found to have a width of ≈1 cm and a density of (0.8–1.7)×1014 cm−3. Observations of characteristic emission lines from the doped atoms and their ions allow for various spectroscopic measurements, such as the magnetic field from Zeeman splitting and the ion velocity distributions from Doppler shifts, that are local in three dimensions. It is shown that this gas doping technique can also be used to study proton-dominated plasmas that cannot be studied with simple emission spectroscopy due to the lack of light emitting ions. The variety of gases used with this method, together with the small valve dimensions and its fast opening, make it potentially useful for broad diagnostics of various short-duration plasma experiments.

A fast gas valve

A gas valve capable of injecting 1 Pa m3 of gas into a vacuum system in less than 2 ms is described. An approximate theory is developed for the performance of this type of valve. The theory shows how the injection range of the valve may be greatly extended, particularly for lower injection quantities at shorter times.

A fast gas valve for plasma sampling

A fast gas valve for plasma sampling

A fast gas valve for plasma sampling (in isotope separation study)

The construction and operation of a fast acting gas valve is described. The valve, which has a measured sampling time of 150 mu s, has been used to extract samples from a transient rotating neon plasma for the purpose of studying isotope separation effects in the plasma. The motion of the valve was investigated optically. The valve sampling time was determined by a novel method, which utilized the discharge itself.

Fast gas valve for plasma research: R. S. Lowder and F. C. Hoh, Rev. Sci. Instrum., 33 (11), Nov. 1962, 1236–1238

Fast gas valve for plasma research: R. S. Lowder and F. C. Hoh, Rev. Sci. Instrum., 33 (11), Nov. 1962, 1236–1238

Fast Gas Valve for Plasma Research

A new type of fast gas valve has been developed for plasma experiments requiring a rapid injection of gas into a vacuum. The valve can be opened and closed within 70 μsec and the gas injection is highly reproducible. A fast opening and closing of the valve, which consists of a low weight aluminum disk sealing against a soft O-ring, is achieved by energizing a coil placed on the O-ring side of the disk and allowing the disk to hit a nearby piece of aluminum and bounce back onto the O-ring. The density distribution of the expanding gas in the vacuum region near the valve was mapped out at particular times shortly after the opening of the valve by using a fast gas gauge. Comparative measurements with a spring loaded valve showed the present valve to have a shorter opening time and much better reproducibility.