Puff Valve Research Articles

A fast rise-rate, adjustable-mass-bit gas puff valve for energetic pulsed plasma experiments.

A fast rise-rate, variable mass-bit gas puff valve based on the diamagnetic repulsion principle was designed, built, and experimentally characterized. The ability to hold the pressure rise-rate nearly constant while varying the total overall mass bit was achieved via a movable mechanical restrictor that is accessible while the valve is assembled and pressurized. The rise-rates and mass-bits were measured via piezoelectric pressure transducers for plenum pressures between 10 and 40 psig and restrictor positions of 0.02-1.33 cm from the bottom of the linear restrictor travel. The mass-bits were found to vary linearly with the restrictor position at a given plenum pressure, while rise-rates varied linearly with plenum pressure but exhibited low variation over the range of possible restrictor positions. The ability to change the operating regime of a pulsed coaxial plasma deflagration accelerator by means of altering the valve parameters is demonstrated.

Extreme ultraviolet-induced photoionized plasmas

In this work photoionized plasmas were created by irradiation of He or Ne gases with a focused extreme ultraviolet (EUV) beam from one of two laser–plasma sources employing Nd:YAG laser systems. The first of them was a 10 Hz laser–plasma EUV source, based on a double-stream gas-puff target, irradiated with a 3 ns per 0.8 J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector. The second source was based on a 10 ns per 10 J per 10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector. Gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Spectral measurements in the EUV range were performed. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions.

Tomographic imaging system for measuring impurity line emission in a field-reversed configuration

A 16 chord optical tomography system has been developed and implemented in the flux coil generated-field reversed configuration (FRC). The chords are arranged in two fans of eight, which cover ~35% of the vessel area at the midplane. Each illuminate separate photomultiplier tubes (PMTs) which are fitted with narrow band-pass filters. In this case, filters are centered at 434.8 nm to measure emission from singly ionized argon. PMT crosstalk is negligible. Background noise due to electron radiation and H(γ) line radiation is <10% of argon emission. The spatial resolution of the reconstruction is 1.5 cm. Argon is introduced using a puff valve and tube designed to impart the gas into the system as the FRC is forming. Reconstruction of experimental data results in time-dependent, 2D emissivity profiles of the impurity ions. Analysis of these data show radial, cross-field diffusion to be in the range of 10-10(3) m(2)∕s during FRC equilibrium.

Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling

An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5×1019 m−3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 μs. With gas puffing, the density is sustained at ne≈1.5×1019 m−3. However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 μs. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S−0.05±0.07 and S0.5±0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.

Thermal instability of electrolytic capacitor bank used for gas puff valve

It is shown that self-heating of electrolytic capacitors causes the output current of a capacitor bank to increase with successive shots even though the charge voltage is held constant. Self heating of only 10 °C can cause a near tripling in the gas output of the gas puffing valves commonly used in spheromak research. By using metallized polypropylene film capacitors instead of electrolytic capacitors the reproducibility is substantially improved (the shot-to-shot variation in gas output is reduced to be &amp;lt;0.5%).

High-current electron beam generation by a pulsed hollow cathode

In this paper the parameters of a hollow-cathode electron source and the generated electron beam are presented. A gas puff valve is used to provide a sharp pressure gradient between the cathode cavity and the accelerating gap. To produce the plasma inside the hollow cathode we used a pulse forming network (10 kV, 5–10 μs, 5 Ω). Generation of a high-current electron beam was achieved under an accelerating voltage of 20-kV amplitude and 500-ns pulse duration. The parameters of the He gas and the plasma inside the cathode and the accelerating gap were studied by electrical and optical diagnostics for different gas pressures and discharge current amplitudes. It was found that the operation of the hollow cathode is characterized by a negative anode potential fall and that the plasma density and temperature inside the hollow cathode do not exceed 5×1012 cm−3 and 14 eV, respectively. The parameters of the electron beam were studied for different discharge current amplitudes and anode grid cell sizes. It was shown that efficient electron beam generation with a beam current amplitude of up to 300 A is achieved without significant increase of the plasma potential. Space-charge neutralization processes in the accelerating gap explain the excess of the electron current density above its space-charge-limited value, in agreement with the measured potential distribution in the accelerating gap. The results of computer simulations of the hollow-cathode operation are in satisfactory agreement with the obtained experimental data.

Anisotropic Etching of n+-Polysilicon Using Beam Plasmas Generated by Gas Puff Plasma Sources

Generation of pulsed chlorine beam plasmas using a nozzle beam system generated from an electron cyclotron resonance (ECR) discharge plasma source with a high-speed gas puff valve (gas puff plasma source) has been studied. Simulations of gas flow, and measurements of plasma parameters and their etching properties have also been discussed, comparing the experimental results with those of conventional ECR plasmas using an almost identical reactor. The time-averaged electron temperatures around a wafer were lower than those in the ECR plasmas for time-averaged pressure of 0.1-2 mTorr. The instantaneous ion energy distributions of the beam plasmas incident on the wafer had wider high-energy tails than those in the ECR plasmas. Thus, anisotropic etching profiles of n+-polysilicon were obtained at the position of the wafer (Bz∼200 G) where notching phenomena were observed in the ECR plasmas.

Intense ion beam from a magnetically insulated diode with magnetically controlled gas-breakdown ion source

A magnetically insulated diode with an active anode source has been developed which produces a high-quality intense ion beam. The anode plasma of annular shape is produced independently of the main diode power pulse by the inductive breakdown of a radially expanding gas cloud supplied by a fast puff valve and nozzle configuration. The diode was developed on a 1010-W pulsed power generator that typically produces 150-kV, l-μs pulses. Prompt ion beam turn-on was attained in this diode when an adequate delay between pulsing the plasma source and delivering the diode power pulse was chosen. The neutral atom density in the diode accelerating gap was sufficiently low that the presence of the neutrals did not limit the beam pulse duration. When the puff valve was filled with H2 gas, a pure proton beam was produced, within the 20% uncertainty of the measurement technique. Proton beam pulses longer than 1 μs and current densities higher than 100 A/cm2 at 70–150 keV were generated.

Simple, fast, puff valve

A simple, fast, reliable diamagnetically driven gas puff valve is described. It offers an extremely quick rise time (∼100 μs) and a large pressure rise rate (∼270 Pa/μs at a distance of 13.5 cm) with an input energy of only 90 J (600 V on a 500 μF capacitor). Because the valve can be operated with such a small input energy, solid-state switching devices are adequate and the operation of the valve will not produce the amount of electrical noise that other valves needing higher energy often do. Our valve achieves high-density puffs at relatively low plenum pressure (380 kPa, 3.8 atm), permitting it to be extremely simple in design and easy to operate. The entire package (valve plus driving circuit) is small in size; it can fit in a volume 4 in. in diameter by 8 in. long. The valve holds about 60 cm3 of gas and has an outlet opening of 1/4 in. in diameter.

Unsteady adiabatic isentropic expansion of gas into vacuum from a toroidal puff valve

Observations were made on the expansion of polyatomic (CF4) and diatomic (O2) gases into vacuum from a toroidal puff valve. Fast ionization gauge measurements have been compared with an unsteady adiabatic isentropic model. Observed temporal and spatial gas density profiles closely followed model predictions until the arrival of gas reflected from the upstream wall of the vacuum vessel.

Space-charge-neutralized proton beam transport in an axial magnetic field

The generation and transport of a 1-MV, 5-kA, 50-ns annular proton beam has been studied. The diode is magnetically insulated with a full-cusp field geometry. Beam transport in a 6-kG axial magnetic field is measured for injection into vacuum and neutral gas. The neutral gas background is supplied by a fast puff valve system. The gas background is found to enhance the space-charge neutralization of the beam. Under these conditions the beam divergence is &amp;lt;1° and the annular profile is maintained throughout the 30-cm transport region. We discuss a simplified model of the beam injection process to explain the experimental results.

Deposition of plasma-polymerized acetylene by an intense pulsed RF plasma source

An inductively coupled, intense, pulsed RF plasma source deposited plasma-polymerized acetylene at a rate of 127 AA per discharge. The potassium bromide substrate was located 18-cm downstream from the RF coil. A puff valve admitted parent acetylene gas just before the transient RF current was applied. Fourier transform infrared (FTIR) spectra showed that carbon-to-carbon double bonds were formed. Scanning-electron-microscope images showed that the film thickness after 79 discharges was 1 mu m. A photodiode showed substantial light emission for about 30 mu s during each discharge. >

Solenoid gas puff imploding liner x-ray source

There is a worldwide effort to produce a soft x-ray source for submicron microlithography to manufacture future generation large scale integrated microchips. The gas puff plasma discharge has been suggested as a viable alternative for low volume facilities which require relatively low throughputs with a single aligner station. The repetition rate for such systems is limited by the large gas flow into the vacuum system with the standard electromechanical puff valve. A unique puff arrangement is being developed which will limit the dead gas flow and, in principle, will allow for the development of high repetition rate systems. In this arrangement, the gas flows continuously from a low-pressure plenum through an annular aperture into the Z-pinch electrode gap. A discharge through a single turn solenoid coil mounted on the outside of the plenum inductively heats the gas, temporarily increasing the mass flow to produce a low mass (&amp;lt;1 μg), preionized liner which is imploded by a Z-pinch current discharge. (Multiturn coils have also been used. However, all the experiments reported in this paper used a single turn configuration.) Experiments were carried out with a variety of low-energy (&amp;lt;2.5 kJ) drivers including capacitor banks, peaking capacitors, and dc charged paper/castor oil Blumleins. Radiation measurements in the ultrasoft and soft x-ray regions were made using x-ray diodes, p-i-n diodes, and a time integrated pinhole camera. A slug model coupled to a capacitor bank or Blumlein circuit solver is used to estimate the liner dynamics as well as the load current and voltage.

High-power radio-frequency plasma source

A high-power radio-frequency plasma source was built and tested for an antenna frequency of 2.45 MHz. A puff valve fed hydrogen gas into a plasma chamber made from 4-in.-diam Pyrex tubing. A helical antenna was wound directly around this chamber. The plasma source was surrounded by a magnetic bucket which used a longitudinal line-cusp geometry. For 20 kW of rf input power, the peak electron density was 2.0×1019 m−3, the electron temperature was 2.0 eV, the ion temperature was 0.9 eV, and the atomic hydrogen density was 4.4×1019 m−3. For 90 kW of rf input power, the peak electron density was 8.9×1019 m−3, the electron temperature was 2.5 eV, the ion temperature was 3.0 eV, and the atomic hydrogen density was 2.3×1019 m−3. The plasma source had a typical current efficiency of 6 A/kW. A theoretical model for the plasma loading resistance was developed.

Balanced puff valve for imploding gas-puff experiments

The design of a fast-acting high-pressure puff valve for use in imploding gas-puff experiments is presented. By using a pressure-balanced valve design, the valve can operate at pressures up to 500 psia. Fast opening (≊200 μs) is achieved by using a fast-moving sliding hammer to open the valve. Balanced valves as well as fast-opening valves using sliding hammers are both well-known technologies; however, this design is the first one to incorporate both features in a single design resulting in a fast-acting high-pressure puff valve.

Laser Extraction of an Electron Beam from a Modified Elongated Betatron Accelerator

The Modified Elongated Betatron Accelerator (MEBA) that was developed at UCI has demonstrated injection, trapping and confinement of about 1012 electrons. The electrons have been accelerated to about 1 MeV. They occupy an annular region 80 cm long with a 6 cm radius and a thickness of about 0.5 cm. We propose to contract this annular beam from 80 cm to a few centimeters by moving the magnetic mirrors. Then the beam will be extracted by means of a laser-initiated channel to guide the beam across the magnetic field. This will be accomplished with a gas puff valve to inject benzene gas and a KrF laser. In this paper, we describe the necessary modifications of the accelerator to accomplish laser extraction of the beam.

Collective Acceleration of Light and Heavy Ions

The collective acceleration of ions (H, D, He, C, N, Ne, Al, Ar, Fe, Cu, Xe) from a well localized plasma immediately downstream of a relativistic electron beam diode is experimentally investigated. The ions are produced either by electron impact on a well confined gas cloud from a fast rise puff valve or by a high power (1OJ, 15ns), Q-switched ruby laser pulse incident on solid material. Peak ion energies up to 5 MeV/nucleon were observed using a 1.5 MeV, 35 kA, 30 ns electron beam pulse. Ion energy diagnostics include nuclear activation, range-energy/ track etching, and time of flight measurements. The effect of a strong applied axial magnetic field (1-10 kilogauss) on the acceleration process has also been studied.

Experimental Studies of Heavy Ion Collective Acceleration at the University of Maryland

The collective acceleration of ions (H, C, N) from a well-localized ion source immediately downstream of a relativistic electron beam diode is experimentally investigated. The ions are produced either in a well-confined gas cloud from a fast rise puff valve or from a solid material that is placed behind the anode and bombarded by a short, 1 joule ruby laser pulse. With a 1.2 MeV, 30 kA, 30 ns electron beam pulse, 11 MeV protons and 20 MeV nitrogen ions were observed (by foil activation diagnostics) when the electron beam was fired through the well-localized gas cloud, and 20 MeV carbon ions were observed when the beam was fired through a laser-produced carbon plasma.

Operation of a High-Current Xenon Source

A multi-aperture Ehlers-type source has been constructed and operated to produce a 60 mA Xe/sup +1/ beam. The multi-aperture source utilizes a 13 hole aperture in a circular pattern producing a beam 25 mm in diameter. An accel--decel extraction system was used, producing a 22.5 keV beam whose normalized emittance at 29 mA was 0.027 ..pi.. cm--mrad. The neutralized beam was transported one meter through two magnetic quadrupole triplets to the entrance of a 20 cm accelerating gap consisting of five intermediate electrodes with a total voltage drop of 500 kV. The vacuum in the extraction region was held to 10/sup -5/ Torr by usng a puff valve and two 1500 1/sec turbo pumps. Multi-wire profile monitors just ahead of the column entrance measured the beam size, which was in good agreement with single-particle transport calculations.

Improved Fast Opening Gas Puff Valve

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