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Mar 2007

Volume 78, Issue 3, Articles (03xxxx)

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Rev. Sci. Instrum. 78, 031101 (2007); http://dx.doi.org/10.1063/1.2709758 (20 pages)

Thomas F. Kelly and Michael K. Miller
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Mega-ampere submicrosecond generator GIT-32

B. M. Kovalchuk, A. V. Kharlov, V. N. Kiselev, E. V. Kumpyak, V. B. Zorin, V. V. Chupin, and A. V. Morozov

Rev. Sci. Instrum. 78, 033501 (2007); http://dx.doi.org/10.1063/1.2712800 (5 pages) | Cited 1 time

Online Publication Date: 13 March 2007

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The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 μF, 40 nH, 100 kV) capacitors, connected in parallel. It stores ∼ 18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Ω damping resistors in discharge circuit of each capacitor and 1.34 MA/530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator ( ∼ 0.05 Ω). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40–80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200×3200×400 mm3 and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus.
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52.50.Dg Plasma sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.75.Kq Plasma switches (e.g., spark gaps)
52.25.Fi Transport properties
52.58.Lq Z-pinches, plasma focus, and other pinch devices
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Langmuir probe system for dusty plasmas under microgravity

M. Klindworth, O. Arp, and A. Piel

Rev. Sci. Instrum. 78, 033502 (2007); http://dx.doi.org/10.1063/1.2714036 (7 pages) | Cited 15 times

Online Publication Date: 14 March 2007

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This article describes a fully automated 2D-scanning Langmuir probe system for dusty plasmas under microgravity. The design combines necessary features such as random sampling, radio frequency compensation, and a compact mechanical design. The various aspects of the probe implementation and the contamination problem in the dusty plasma environment are discussed and the functionality of the system is demonstrated by measurements performed on parabolic flights.
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52.70.Ds Electric and magnetic measurements
52.27.Lw Dusty or complex plasmas; plasma crystals

Main characteristics of the fast disruption mitigation valve

S. A. Bozhenkov, K.-H. Finken, M. Lehnen, and R. C. Wolf

Rev. Sci. Instrum. 78, 033503 (2007); http://dx.doi.org/10.1063/1.2712798 (7 pages) | Cited 12 times

Online Publication Date: 15 March 2007

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The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s−1 for Ar and 1500 bar l s−1 for He.
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89.20.Bb Industrial and technological research and development
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Modeling magnetic fields measured by surface probes embedded in a cylindrical flux conserver

R. P. Golingo

Rev. Sci. Instrum. 78, 033504 (2007); http://dx.doi.org/10.1063/1.2713435 (5 pages)

Online Publication Date: 19 March 2007

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Calculating magnetic fields at the surface of a flux conserver, perfect conductor, for displaced plasma currents is useful for understanding modes of a Z-pinch. The magnetic fields measured at the flux conserver are a sum of the magnetic fields from the plasma current and the eddy currents which form in the walls to keep the flux constant. While the magnetic field at the wall from the plasma current alone is easily calculated using the Biot–Savart law, finding the eddy currents in the flux conserver which satisfy the boundary conditions can be a tedious process. A simple method of calculating the surface magnetic field for a given Z-pinch displacement off-axis is derived for a cylindrical flux conserver. This relationship does not require the explicit calculation of the eddy currents, saving time when analyzing surface magnetic probe measurements. Analytic expressions can be used to describe the surface magnetic field which increase the understanding of the magnetic probe measurements.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.40.Hf Plasma-material interactions; boundary layer effects

Measurement of the Dα spectrum produced by fast ions in DIII-D

Y. Luo, W. W. Heidbrink, K. H. Burrell, D. H. Kaplan, and P. Gohil

Rev. Sci. Instrum. 78, 033505 (2007); http://dx.doi.org/10.1063/1.2712806 (11 pages) | Cited 26 times

Online Publication Date: 21 March 2007

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Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit Dα light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of ∼ 1 ms, spatial resolution of ∼ 5 cm, and energy resolution of ∼ 10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the Dα measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.
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52.70.Nc Particle measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.55.Fa Tokamaks, spherical tokamaks
52.50.Gj Plasma heating by particle beams
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.20.Dq Particle orbits

Particle positioning techniques for dusty plasma experiments

Yuriy Ivanov and André Melzer

Rev. Sci. Instrum. 78, 033506 (2007); http://dx.doi.org/10.1063/1.2714050 (7 pages) | Cited 12 times

Online Publication Date: 21 March 2007

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Video microscopy is a widely applied diagnostic to investigate the structure and the dynamics of particles in dusty plasmas. Reliable algorithms are required to accurately recover particle positions from the camera images. Here, four different particle positioning techniques have been tested on artificial and experimental data of dusty plasma situations. Two methods that rely on pixel-intensity thresholds were found to be strongly affected by pixel-locking errors and by noise. Two other methods—one applying spatial bandpass filters and the other fitting polynomials to the intensity pattern—yield subpixel resolution under various conditions. These two methods have been shown to be ideally suited to recover particle positions even from small-scale fluctuations that are used to derive the normal mode spectra of finite dust clusters.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
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