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Feb 2011

Volume 82, Issue 2, Articles (02xxxx)

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back to top Nuclear Physics, Fusion and Plasmas

Practical selection of emission lines of He I to determine the photon absorption rate

Shin Kajita and Noriyasu Ohno

Rev. Sci. Instrum. 82, 023501 (2011); http://dx.doi.org/10.1063/1.3548923 (5 pages) | Cited 1 time

Online Publication Date: 10 February 2011

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A combination of helium line intensities and a collisional radiative model has been used to measure electron density and temperature. However, radiation trapping of resonance lines may disturb the measurements due to disturbances in the population distribution of helium atoms. In this study, we show that the principal contribution of radiation trapping in helium plasma can be evaluated by additionally measuring one or two specific line intensities from the singlet state. The inclusion of the effects of radiation trapping sufficiently compensates for anomalous increases in the electron density and temperature, and consequently yields proper values. An experiment was performed in the divertor simulator NAGDIS-II, and the method's validity was confirmed by comparing the spectroscopically obtained results and the values from the electrostatic probe method.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.65.-y Plasma simulation
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments

M. Inomoto, K. Abe, T. Yamada, A. Kuwahata, S. Kamio, Q. H. Cao, M. Sakumura, N. Suzuki, T. Watanabe, and Y. Ono

Rev. Sci. Instrum. 82, 023502 (2011); http://dx.doi.org/10.1063/1.3553283 (5 pages)

Online Publication Date: 16 February 2011

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A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.
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84.60.Ve Energy storage systems, including capacitor banks

Improved hydrogen ionization rate in enhanced glow discharge plasma immersion ion implantation by enlarging the interaction path using an insulating tube

Zhuo Wang, Ying Zhu, Liu He Li, Qiu Yuan Lu, Fu Shun He, Dan Dan Dun, Fen Li, Ricky K. Y. Fu, and Paul K. Chu

Rev. Sci. Instrum. 82, 023503 (2011); http://dx.doi.org/10.1063/1.3544022 (6 pages)

Online Publication Date: 16 February 2011

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A small pointed hollow anode and large tabular cathode are used in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). Electrons are repelled from the substrate by the electric field formed by the negative voltage pulses and concentrate in the vicinity of the anode to enhance the self-glow discharge process. To extend the application of EGD-PIII to plasma gases with low ionization rates, an insulating tube is used to increase the interaction path for electrons and neutrals in order to enhance the discharge near the anode. Results obtained from numerical simulation based on the particle-in-cell code, finite element method, and experiments show that this configuration enhances the ionization rate and subsequent ion implant fluence. The process is especially suitable for gases that have low ionization rates such as hydrogen and helium.
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52.77.Dq Plasma-based ion implantation and deposition
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.80.Hc Glow; corona
52.65.Rr Particle-in-cell method
02.70.Dh Finite-element and Galerkin methods

Registration of Alfvén resonances in TCABR tokamak by the scanning reflectometer at sideband frequencies

L. F. Ruchko, A. G. Elfimov, C. M. Teixeira, J. I. Elizondo, E. Sanada, R. M. O. Galvão, M. E. Manso, and A. Silva

Rev. Sci. Instrum. 82, 023504 (2011); http://dx.doi.org/10.1063/1.3541756 (4 pages)

Online Publication Date: 22 February 2011

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A frequency scanning O-mode reflectometer was used for studies of plasma density oscillations during local Alfvén wave (LAW) excitation in the Tokamak Chauffage Alfvén Brésilien (TCABR) at the frequency fA = 5 MHz. It was found that the spectrum of the reflectometer output signal, which consists mainly of the “beat” frequency fB, is modified by the LAW excitation, and two additional frequency peaks appear, which are symmetrical in relation to the LAW excitation frequency f = fA ± fB. This result opens the possibility to improve the efficiency of studying the LAW induced density oscillations. The symmetry of these frequency peaks yields the possibility of finding the microwave frequency at which the reflectometer cutoff layer coincides with radial position of the LAW resonance zone in the TCABR tokamak.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Fa Tokamaks, spherical tokamaks
52.25.-b Plasma properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.70.Gw Radio-frequency and microwave measurements

Design and performance of a punch mechanism based pellet injector for alternative injection in the large helical device

J. S. Mishra, R. Sakamoto, G. Motojima, A. Matsuyama, and H. Yamada

Rev. Sci. Instrum. 82, 023505 (2011); http://dx.doi.org/10.1063/1.3541807 (7 pages) | Cited 1 time

Online Publication Date: 22 February 2011

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A low speed single barrel pellet injector, using a mechanical punch device has been developed for alternative injection in the large helical device. A pellet is injected by the combined operation of a mechanical punch and a pneumatic propellant system. The pellet shape is cylindrical, 3 mm in diameter and 3 mm in length. Using this technique the speed of the pellet can be controlled flexibly in the range of 100–450 m/s, and a higher speed can be feasible for a higher gas pressure. The injector is equipped with a guide tube selector to direct the pellet to different injection locations. Pellets are exposed to several curved parts with the curvature radii Rc = 0.8 and 0.3 m when they are transferred in guided tubes to the respective injection locations. Pellet speed variation with pressure at different pellet formation temperatures has been observed. Pellet intactness tests through these guide tubes show a variation in the intact speed limit over a range of pellet formation temperatures from 6.5 to 9.8 K. Pellet speed reduction of less than 6% has been observed after the pellet moves through the curved guide tubes.
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28.52.Cx Fueling, heating and ignition
28.52.Av Theory, design, and computerized simulation
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.-b Plasma properties

Work function measurements during plasma exposition at conditions relevant in negative ion sources for the ITER neutral beam injection

R. Gutser, C. Wimmer, and U. Fantz

Rev. Sci. Instrum. 82, 023506 (2011); http://dx.doi.org/10.1063/1.3541790 (7 pages) | Cited 7 times

Online Publication Date: 23 February 2011

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Cesium seeded sources for surface generated negative hydrogen ions are major components of neutral beam injection systems in future large-scale fusion experiments such as ITER. The stability and delivered current density depend highly on the work function during vacuum and plasma phases of the ion source. One of the most important quantities that affect the source performance is the work function. A modified photocurrent method was developed to measure the temporal behavior of the work function during and after cesium evaporation. The investigation of cesium exposed Mo and MoLa samples under ITER negative hydrogen ion based neutral beam injection relevant surface and plasma conditions showed the influence of impurities which result in a fast degradation when the plasma exposure or the cesium flux onto the sample is stopped. A minimum work function close to that of bulk cesium was obtained under the influence of the plasma exposition, while a significantly higher work function was observed under ITER-like vacuum conditions.
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52.55.Fa Tokamaks, spherical tokamaks
52.50.Gj Plasma heating by particle beams
52.50.Dg Plasma sources
52.25.Vy Impurities in plasmas
28.52.Fa Materials
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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