Fast Ionization Gauge Research Articles

Study on the Sensitivity of Fast Ionization Gauge in Mixture Gas of Hydrogen and Helium

Study on the Sensitivity of Fast Ionization Gauge in Mixture Gas of Hydrogen and Helium

Measurement of transient neutral gas puff pressure in the NUDT_IPPTx by a fast ionization gauge

A gas injector was designed for the 400 J/pulse prototype of the planar inductive pulsed plasma thruster (IPPT) developed by the National University of Defense Technology (NUDT_IPPTx). As the gas puff distribution over the coil surface is critical to the NUDT_IPPTx functioning efficiently, a fast ionization gauge was developed to investigate the neutral gas pressure profiles to seek the critical time when the thruster is ignited. The gauge was calibrated for argon by using a capacitance manometer. Time-resolved pressure profiles have been acquired in the condition of the gas puff mass matching with the discharge energy and the drive coil parameters of the NUDT_IPPTx. It is demonstrated that the gas injector can supply a gas puff with a sufficiently steep (dp/dt ≈ 770 kPa s−1) leading and trailing edge, and the gas puff can be compressed against the drive coil as expected. The critical ignition moment is considered to appear at some instant between 525 μs and 650 μs after the valve trigger.

Real-time adjustable, 11 μs FWHM, 5 kHz, piezo electric pulsed atomic beam source.

This paper provides a detailed description of how to construct a pulsed atomic beam source [including a fast ionization gauge (FIG) for characterization] with a unique combination of characteristics. We include technical drawings for a real-time adjustable piezo electric actuated pulsed valve capable of generating a 11 μs duration pulse of gas at a repetition rate of >5 KHz, with a shot-to-shot stability of 0.6%, and maximum densities of 1015 particles/cm3. We also include details on how to construct a FIG, with a 4 μs rise time, to measure the pulse. We report a 3D density map of a supersonic expansion of helium gas with a speed ratio S = 46 and a calculated longitudinal temperature of 0.3 K. Finally, the results of a laser ionization test are provided in order to verify the performance of the pulsed valve in a typical experimental configuration.

The Mochi LabJet Experiment for Measurements of Canonical Helicity Injection in a Laboratory Astrophysical Jet

Abstract The Mochi device is a new pulsed power plasma experiment designed to produce long, collimated, stable, magnetized plasma jets when set up in the LabJet configuration. The LabJet configuration aims to simulate an astrophysical jet in the laboratory by mimicking an accretion disk threaded by a poloidal magnetic field with concentric planar electrodes in front of a solenoidal coil. The unique setup consists of three electrodes, each with azimuthally symmetric gas slits. Two of the electrodes are biased independently with respect to the third electrode to control the radial electric field profile across the poloidal bias magnetic field. This design approximates a shear azimuthal rotation profile in an accretion disk. The azimuthally symmetric gas slits provide a continuously symmetric mass source at the footpoint of the plasma jet, so any azimuthal rotation of the plasma jet is not hindered by a discrete number of gas holes. The initial set of diagnostics consists of current Rogowski coils, voltage probes, magnetic field probe arrays, an interferometer and ion Doppler spectroscopy, supplemented by a fast ion gauge and a retarding grid energy analyzer. The measured parameters of the first plasmas are ∼1022 m−3, ∼0.4 T, and 5–25 eV, with velocities of ∼20–80 km s−1. The combination of a controllable electric field profile, a flared poloidal magnetic field, and azimuthally symmetric mass sources in the experiment successfully produces short-lived (∼10 μs, ≳5 Alfvén times) collimated magnetic jets with a ∼10:1 aspect ratio and long-lived (∼100 μs, ≳40 Alfvén times) flow-stabilized, collimated, magnetic jets with a ∼30:1 aspect ratio.

Gas Pressure Measurements in Pure and Mixed Gases at Around 1.0 Pa by Using ASDEX Type Fast Ionization Gauge

Gas Pressure Measurements in Pure and Mixed Gases at Around 1.0 Pa by Using ASDEX Type Fast Ionization Gauge

Measurement of neutral gas pressure in the D-module of GAMMA 10/PDX by using ASDEX type fast ionization gauge.

In the divertor simulation experiments in the GAMMA 10/PDX tandem mirror, pressure of the neutral gas was investigated by using a fast ionization gauge. The gauge was absolutely calibrated for hydrogen gas by using a capacitance manometer. Change of the gauge sensitivity due to the magnetic field of GAMMA 10/PDX was also evaluated. The typical gas pressure measured in detached plasma experiments was 0.1-10 Pa. The degree of plasma detachment determined from the reduction of heat flux was enhanced as the gas pressure increases. Rapid increase of the gas pressure under the plasma flow was also observed.

Compact permanent magnet H⁺ ECR ion source with pulse gas valve.

Compact H(+) ECR ion source using permanent magnets is under development. Switching the hydrogen gas flow in pulse operations can reduce the gas loads to vacuum evacuation systems. A specially designed piezo gas valve chops the gas flow quickly. A 6 GHz ECR ion source equipped with the piezo gas valve is tested. The gas flow was measured by a fast ion gauge and a few ms response time is obtained.

Production of neutral gas by micrometeoroid impacts

We present the first direct laboratory measurement of vapor produced by simulated micrometeoroid bombardment. New in situ observations from the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft, and the anticipation of results from the Lunar Atmosphere and Dust Environment Explorer (LADEE), have highlighted the uncertainty surrounding the role of micrometeoroid impacts in sustaining planetary exospheres. In a recent series of experiments, the quantity of neutral molecules generated by impacts of simulated micrometeorids of 0.1–1μm radius was measured using a fast ion gauge, over a speed range of 1–10km/s. The quantity of neutrals released per unit projectile mass, N/m, is consistent with a power law N/m=vβ in the projectile speed v, with β∼2.4. At the highest speeds tested, the number of neutrals liberated is equivalent to 5% of the atoms in the projectile; complete vaporization is projected at speeds exceeding 20km/s.

Beamline duct monitoring of the TJ-II neutral beam injectors

In the stringent geometry of TJ-II NBI ducts, beam reionization can reduce beam transmission by a significant fraction. The re-emitted gas from direct beam impact areas acts as “seed” gas for reionization losses. In order to monitor and control reionization losses two diagnostics have been commissioned: infrared thermography of the beam path and Fast Ion gauge measurements of the pressure buildup at the duct exit during beam pulses in the absence of magnetic field. An upper limit of 20% for reionization losses in a well-conditioned duct has been obtained from infrared thermography. The gas dynamics has been studied, obtaining the re-emitted gas flow (6–12mbarls−1) and a limit for the characteristic time constant of the emission process (<100ms).

A new high intensity and short-pulse molecular beam valve

In this paper, we report on the design and performance of a new home-built pulsed gas valve, which we refer to as the Nijmegen Pulsed Valve (NPV). The main output characteristics include a short pulse width (as short as 20 μs) combined with operating rates up to 30 Hz. The operation principle of the NPV is based on the Lorentz force created by a pulsed current passing through an aluminum strip located within a magnetic field, which opens the nozzle periodically. The amplitude of displacement of the opening mechanism is sufficient to allow the use of nozzles with up to 1.0 mm diameter. To investigate the performance of the valve, several characterizations were performed with different experimental methods. First, a fast ionization gauge was used to measure the beam intensity of the free jet emanating from the NPV. We compare free jets from the NPV with those from several other pulsed valves in current use in our laboratory. Results showed that a high intensity and short pulse-length beam could be generated by the new valve. Second, the NPV was tested in combination with a skimmer, where resonance enhanced multiphoton ionization combined with velocity map imaging was used to show that the NPV was able to produce a pulsed molecular beam with short pulse duration (~20 μs using 0.1% NO/He at 6 bars) and low rotational temperature (~1 K using 0.5% NO/Ar at 6 bars). Third, a novel two-point pump-probe method was employed which we label double delay scan. This method allows a full kinematic characterization of the molecular beam, including accurate speed ratios at different temporal positions. It was found that the speed ratio was maximum (S = 50 using 0.1% NO/He at 3 bars) at the peak position of the molecular beam and decreased when it was on the leading or falling edge.

Neutral pressure measured by fast ionization gauge in HL-2A

A fast ionization gauge capable of working in a strong magnetic field and noisy environment is developed for the pressure measurement in the main chamber and the divertor chamber of the HL-2A tokamak. The neutral pressure in the main chamber evidently decreases after in-situ siliconization. Improvement of boundary plasma confinement is observed with SMBI or PI fueling after siliconization. The neutral pressure in the main chamber for divertor configuration is 50% lower than that for limiter one. The pressure in the divertor chamber rises when the strike point moves toward the bottom of the vertical target plates. The maximum pressure compression of is 24. The relative high pressure in the main chamber is contributed primarily by plasma limiter interaction due to the short distance from separatrix to limiter and secondly by neutral flux from the divertor chamber to the main chamber by leaks in HL-2A.

Analyses of edge plasma characteristics in HL-2A

The edge plasma characteristics are studied by both a movable array of Mach/Reynolds stress/Langmuir 10-probes in the boundary region and the fixed flush probe arrays on the 4 divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The dependence of the Reynolds stress on poloidal flow in the edge plasma is analysed. The result indicates that the sheared poloidal flow in tokamak plasma can be induced by the radial gradient of Reynolds stress. In the divertor experiments of HL-2A, the profiles of the electron temperature, density and floating potential on divertor plates are measured by the flush probe arrays. The edge electron temperature in divertor configuration is higher than that in limiter configuration. The temperature asymmetry between outer and inner target plates is observed. The result of magnetic surface reconstructed from 18 Mirnov coils signals is presented. Both the particle recycling and the impurity flux in the bulk plasma during divertor discharges are discussed. Neutral gas pressure in divertor chamber, measured by fast ionization gauge during divertor discharge, is given.

Electron impact ionization of large krypton clusters

We show that the detection of ionization of very large van der Waals clusters in a pulsed jet or a beam can be realized by using a fast ion gauge. Rapid positive feedback electron impact ionization and fragmentation processes, which are initially ignited by electron impact ionization of the krypton clusters with the electron current of the ion gauge, result in the appearance of a progressional oscillation-like ion spectrum, or just of a single fast event under critical conditions. Each line in the spectrum represents a correlated explosion or avalanche ionization of the clusters. The phenomena have been analysed qualitatively along with a Rayleigh scattering experiment of the corresponding cluster jet.

High harmonic generation at 1 kHz repetition rate with a pulsed valve

High harmonic generation at 1 kHz repetition rate is reported. A piezoelectric pulsed valve together with a femtosecond Ti:Sapphire laser both operating at 1 kHz are employed to generate high harmonic radiation in xenon and argon. The characteristics of the valve have been analyzed by using a fast ion gauge and a time-of-flight mass-spectrometer.

Characteristics of carbon sheet pump in application experiments to a high-temperature plasma device

Carbon sheet pump (CSP), which has been developed for reduction of hydrogen recycling in the large helical device (LHD) of National Institute for Fusion Science, is applied to an actual plasma device for the first time to evaluate the pumping characteristics. A small scale of pump module is manufactured and installed in the GAMMA-10 tandem mirror device and the module is exposed to charge-exchange neutrals emitted from ICRF-heated hot-ion plasmas. Temporal evolution of the pressure is measured with a fast ionization gauge installed in the test chamber during the plasma discharge and a significant difference between CSP-on and CSP-off is observed under good reproducibility. The dependence on the ICRF power is investigated and the pressure difference between on and off is found to increase with the ICRF power. These phenomena indicating the pumping ability of CSP are observed to continue during more than 300 plasma shots, which shows the effectiveness of CSP in controlling hydrogen recycling. The result of thermal desorption experiments of CSP after being exposed to charge-exchange neutrals is also described.

Computer Controlled Pulsed Pecvd Reactor for Laboratory Scale Deposition of Plasma Polymerized Thin Films

AbstractA pulsed PECVD reactor has been successfully constructed for laboratory scale studies of plasma polymerized thin films. A computer control system based on National Instrument's LABVIEW software controls power supply sequence, feed injection, and introduction of RF energy. An optical fiber and a photo diode allow the user to monitor the emitted light for each pulse. A fast ionization gauge is used to characterize the pressure evolution over time, subsequent to acetylene gas injection. Substrates with diameter as large as 10 cm can be accommodated within the reactor. Both aniline liquid and acetylene gas have been used as reactor feed. The deposited plasma-polymerized films were characterized using AFM and SEM. Electrical conductivity of plasma polymerized acetylene film was also measured

Time-of-flight analysis of neutral cluster beams through detection of charged particles produced by cluster impact on a channeltron

A method for time-of-flight analysis of neutral cluster beams is presented. It is based on the use of a channeltron as a fast flux-sensitive detector of high-speed neutral particles in a beam. The impact of neutral clusters on the channeltron surface causes the emission of charged particles, which can be detected by the channeltron itself. We show that a channeltron can be used for the characterization of velocity distributions in analogy with fast ion gauges but without requiring any ionization device. This method has also the advantage of being selectively sensitive to the cluster component of seeded supersonic beams.

Characterization of Pulsed Supersonic Cvd System For Diamond Growth

ABSTRACTAn ultra-high vacuum chemical vapor deposition system using pulsed, supersonic jets of halogenated hydrocarbon precursors has been constructed with the intention of growing diamond thin films. Experimental results from this system should determine whether the hyperthermal activation of precursors improves the carbon incorporation efficiency of film growth. The jets, produced by commercially available pulsed valves, were characterized with a fast ionization gauge. Parameters such as valve backing pressure and the pulse width were varied to optimize material flux and avoid the formation of boundary layers above the substrate that could reduce the kinetic energy of the precursors.

A simple fast pulse gas valve using a dynamic pressure differential as the primary closing mechanism

In this article we describe a simple fast pulse gas valve developed for use in a plasma discharge experiment. The valve delivers 1017–1019 molecules per pulse varied by changing the voltage on the electromagnetic driver power supply. Valve pulse widths are observed to be less than 300 μs full width at half maximum with a rise time of less than 100 μs resulting in a maximum gas flow rate of ∼1022 molecules per second. An optical transmission technique was used to determine the mechanical opening and closing characteristics of the valve piston. A fast ionization gauge (FIG) was used for diagnosis of the temporal character of the gas pulse while the total gas throughput was determined by measuring the change in pressure per pulse in a small test chamber with a convectron tube gauge. Calibration of the FIG was accomplished by comparing the net change in pressure in a large chamber as measured by the FIG to the net change in pressure in a small test chamber as measured by the convectron tube gauge.

Neutral pressure studies with a fast ionization gauge in the divertor region of the DIII-D tokamak

An ionization gauge, specially designed to operate in the high magnetic fields of present-day tokamaks (1–6 T) and with electronics designed for fast time response and high noise rejection, was installed and operated in the new pumping plenum in the divertor region of DIII–D. This plenum, formed by a toroidally symmetric baffle, is used to compress neutrals to high pressures (≳1 mTorr) to allow for high particle removal rates when a pump is added inside the plenum. Pressures of 2–20 mTorr were measured with the fast gauge under the baffle, compared to less than 1 mTorr measured by a similar gauge also installed in the divertor but outside the baffle. A detailed description of the fast gauge, its operation, and its calibration is provided.