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Plasma Sci. Technol.  
  Plasma Sci. Technol.--2015, 17 (5)   Published: 22 April 2015
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Basic Plasma Phenomena

Study of Current Sheath Velocity and Its Distribution Using Tridimensional Magnetic Probe in Sahand Plasma Focus

M. A. MOHAMMADI 1,2 and S. HEDYEH 1
Plasma Sci. Technol. 2015, 17 (5): 353-357 ;  doi: 10.1088/1009-0630/17/5/01
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Show Abstract ( 214 )

The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33±0.28 (cm/µs) and 3.92±0.75 (cm/µs) with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 (cm/µs) at the radial phase and 1.14 ± 0.09 (cm/µs) at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum (FWHM) of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.

Magnetically Confined Plasma

The Coupling Structure Features Between (2,1) NTM and (1,1) Internal Mode in EAST Tokamak Hot!

SHI Tonghui (石同辉), WAN Baonian (万宝年), SUN Youwen (孙有文), et al.
Plasma Sci. Technol. 2015, 17 (5): 358-365 ;  doi: 10.1088/1009-0630/17/5/02
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Show Abstract ( 245 )

In the discharge of EAST tokamak, it is observed that (2,1) neoclassical tearing mode (NTM) is triggered by mode coupling with a (1,1) internal mode. Using singular value decomposition (SVD) method for soft X-ray emission and for electron cyclotron emission (ECE), the coupling spatial structures and coupling process between these two modes are analyzed in detail. The results of SVD for ECE reveal that the phase difference between these two modes equals to zero. This is consistent with the perfect coupling condition. Finally, performing statistical analysis of r 1/1 , ξ 1/1 and w 2/1 , we find that r 1/1 more accurately represents the coupling strength than ξ 1/1 , and r 1/1 is also strongly related to the (2,1) NTM triggering, where r 1/1 is the width of (1,1) internal mode, ξ 1/1 is the perturbed amplitude of (1,1) internal mode, and w 2/1 denotes the magnetic island width of (2,1) NTM.

Inertially Confined Plasma

Nuclear Fusion Within Extremely Dense Plasma Enhanced by Quantum Particle Waves

MIAO Feng (苗峰) 1,ZHENG Xianjun (曾宪俊) 2,DENG Baiquan (邓柏权) 3
Plasma Sci. Technol. 2015, 17 (5): 366-371 ;  doi: 10.1088/1009-0630/17/5/03
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Show Abstract ( 222 )

Quantum effects play an enhancement role in p-p chain reactions occurring within stars. Such an enhancement is quantified by a wave penetration factor that is proportional to the density of the participating fuel particles. This leads to an innovative theory for dense plasma, and its result shows good agreement with independent data derived from the solar energy output. An analysis of the first Z-pinch machine in mankind’s history exhibiting neutron emission leads to a derived deuterium plasma beam density greater than that of water, with plasma velocities exceeding 10000 km/s. Fusion power could be achieved by the intersection of four such pinched plasma beams with powerful head-on collisions in their common focal region due to the beam and target enhanced reaction.

Low Temperature Plasma

On the Characteristics of Coaxial-Type Microwave Excited Linear Plasma: a Simple Numerical Analysis

CHEN Longwei (陈龙威) 1,MENG Yuedong (孟月东) 1,ZUO Xiao (左潇) 1,et al.
Plasma Sci. Technol. 2015, 17 (5): 372-383 ;  doi: 10.1088/1009-0630/17/5/04
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Show Abstract ( 232 )

To unveil the characteristics and available propagation mechanism of coaxial-type microwave excited line-shape plasma, the effects of parameters including microwave power, work- ing pressure, dielectric constant, and external magnetic field on the plasma distribution were numerically investigated by solving a coupled system of Maxwell’s equations and continuity equa- tions. Numerical results indicate that high microwave power, relatively high working pressure, low dielectric constant, and shaped magnetic field profiles will help produce a high-density and uniform plasma source. Exciting both ends by microwave contributed to the high-density and uni- form plasma source as well. Possible mechanisms were analyzed by using the polarization model of low temperature plasma. The generation and propagation processes of the line-shape plasma mainly depend on the interaction of three aspects, i.e. the transmitted part, penetration part and absorptive part of the electromagnetic field. The numerical results were qualitatively consistent with available experimental results from literature. More elaborate descriptions of the three as- pects and corresponding interactions among them need to be investigated further to improve the properties of the line-shape plasma.

Boundary Effect of Planar Glow Dielectric Barrier Discharge and Its Influence on the Discharge Structure

XU Shaowei (徐绍伟), LI Lulu (李璐璐), and OUYANG Jiting (欧阳吉庭)
Plasma Sci. Technol. 2015, 17 (5): 384-391 ;  doi: 10.1088/1009-0630/17/5/05
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The dielectric barrier discharge (DBD) in the glow regime in neon has been investi- gated by experiment and two-dimensional (2D) fluid modeling. The discharge was carried out in a planar DBD system with segmented-electrodes driven by square-wave voltage. The results show that the glow DBD originates in the center of the electrode and expands outward to the electrode edge during each half cycle of the voltage, forming a radial structure. The discharge decays firstly in the inner area but sustains longer in the edge area, showing a reversed discharge area. The discharge cannot completely cover the entire electrode surface, but remains a border of non- or weak discharge. The fluid modeling shows a similar result in agreement with the experiments. The simulations indicate that the electric field in the edge area is distorted due to the boundary effect so that the electric field and charge distribution are different from that in the inner part. The distorted field reduces the longitudinal component near the edge and causes the local field to be lower than that in the center, and hence makes the discharge behindhand. It also induces a transverse field that makes the discharge extend radially outward to the edge. The boundary effect plays an important role in the glow DBD structure.

Plasma Technology

A Steam-Plasma Igniter for Aluminum Powder Combustion

Sanghyup LEE, Kwanyoung NOH, Jihwan LIM, Woongsup YOON
Plasma Sci. Technol. 2015, 17 (5): 392-401 ;  doi: 10.1088/1009-0630/17/5/06
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Show Abstract ( 225 )

High-temperature ignition is essential for the ignition and combustion of energetic metal fuels, including aluminum and magnesium particles which are protected by their high- melting-temperature oxides. A plasma torch characterized by an ultrahigh-temperature plasma plume fulfills such high-temperature ignition conditions. A new steam plasma igniter is designed and successfully validated by aluminum power ignition and combustion tests. The steam plasma rapidly stabilizes in both plasma and steam jet modes. Parametric investigation of the steam plasma jet is conducted in terms of arc strength. A high-speed camera and an oscilloscope method visualize the discharge characteristics, and optical emission spectroscopy measures the thermochemical properties of the plasma jet. The diatomic molecule OH fitting method, the Boltzmann plot method, and short exposure capturing with an intensified charge coupled device record the axial distributions of the rotational gas temperature, excitation temperature, and OH radical distribution, respectively. The excitation temperature at the nozzle tip is near 5500 K, and the gas temperature is 5400 K.

The Effects of Gas Composition on the Atmospheric Pressure Plasma Jet Modification of Polyethylene Films

SUN Jie (孙洁) 1,QIU Yiping (邱夷平) 2
Plasma Sci. Technol. 2015, 17 (5): 402-408 ;  doi: 10.1088/1009-0630/17/5/07
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Polyethylene (PE) films are treated using an atmospheric pressure plasma jet (APPJ) with He or He/O 2 gas for different periods of time. The influence of gas type on the plasma–polymer interactions is studied. The surface contact angle of the PE film can be effec- tively lowered to 58 o after 20 s of He/O 2 plasma treatment and then remains almost unchanged for longer treatment durations, while, for He plasma treatment, the film surface contact angle drops gradually to 47 o when the time reaches 120 s. Atomic force microscopy (AFM) results show that the root mean square (RMS) roughness was significantly higher for the He/O 2 plasma treated samples than for the He plasma treated counterparts, and the surface topography of the He/O 2 plasma treated PE films displays evenly distributed dome-shaped small protuberances. Chemical composition analysis reveals that the He plasma treated samples have a higher oxygen content but a clearly lower percentage of –COO than the comparable He/O 2 treated samples, suggesting that differences exist in the mode of incorporating oxygen between the two gas condition plasma treatments. Electron spin resonance (ESR) results show that the free radical concentrations of the He plasma treated samples were clearly higher than those of the He/O 2 plasma treated ones with other conditions unchanged.

Spectral Analysis of the Light Flash Produced by a Natural Dolomite Plate Under Strong Shock

TANG Enling (唐恩凌) 1,XU Mingyang (徐名扬) 1,ZHANG Qingming (张庆明) 2,et al.
Plasma Sci. Technol. 2015, 17 (5): 409-414 ;  doi: 10.1088/1009-0630/17/5/08
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In order to obtain the elemental compositions of the projectile and target materials during 2A12 aluminum projectile shot on a natural dolomite plate, three kinds of experiments have been conducted using a spectral acquirement system established on a two-stage light gas gun for impact velocities ranging from 2.20 km/s to 4.20 km/s, at the same projectile incidence angle of 30 o . Experimental results show that the elemental compositions of the projectile and target materials in the strong shock experiments have a good agreement with the original elemental compositions of the projectile and target. In addition, the relations between spectral radiant intensity and elemental compositions of the projectile and target materials have been obtained for different impact velocities, in which the spectral radiant intensity of the main elements in the material increases with increasing impact velocity, and more elements appear with increasing impact velocity since more energy would result from a higher velocity impact.

Experimental Study of the Unsteady Actuation Effect on Induced Flow Characteristics in DBD Plasma Actuators

Sohrab Gholamhosein POURYOUSSEFI, Masoud MIRZAEI
Plasma Sci. Technol. 2015, 17 (5): 415-424 ;  doi: 10.1088/1009-0630/17/5/09
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The main aim of this paper is to investigate unsteady actuation effects on the oper- ation of dielectric barrier discharge (DBD) plasma actuators and to study induced flow character- istics of steady and unsteady actuators in quiescent air. The parameters affecting the operation of unsteady plasma actuators were experimentally measured and compared with the ones for steady actuators. The effects of excitation frequency and duty cycle on the induced flow pattern prop- erties were studied by means of hot-wire anemometers, and the smoke visualization method was also used. It was observed that the current and the mean induced velocity linearly increase with increasing duty cycle while they are not sensitive to excitation frequency. Furthermore, with increasing excitation frequency, the magnitude of vortices shedding from the actuator decreases while their frequency increases. Nevertheless, when the excitation frequency grows beyond a cer- tain level, the induced flow downstream of the actuator behaves as a steady flow. However, the results for steady actuators show that by increasing the applied voltage and carrier frequency, the velocity of the induced flow first increases and then decreases with actuator saturation and the onset of the emission of streaky glow discharge.

Fusion Engineering

The Timing System of the Neutral Beam Injector on EAST

SHENG Peng (盛鹏), HU Chundong (胡纯栋), ZHAO Yuanzhe (赵远哲), et al.
Plasma Sci. Technol. 2015, 17 (5): 425-429 ;  doi: 10.1088/1009-0630/17/5/10
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Show Abstract ( 216 )

In order to synchronize the elements of the EAST Neutral Beam Injector (NBI) spatially located in several places, a distributed Timing System (TS) is developed in this paper. The timing system provides a clock reference for synchronization and an interlock protection of the EAST NBI system. It sends timing signals to field devices, controls the pulse widths of the timing sequences, and provides a sampling clock for the Data Acquisition System (DAS). The timing system also generates analog waveforms to control power supplies and gas supplies according to the operator’s configuration. The timing system is developed on a PXI (PCI eXtensions for Instrumentation) platform consisting of a LabVIEW workstation and a timing control terminal. The timing control terminal consists of a timing node and several control interface crates. Two timing nodes are configured in one beam line. Each node is responsible for the timing sequence, analog generation and feedback control for one ion source. The architecture and implementation of the timing system are presented in this paper.

Recent Progress of the HL-2A Multi-Channel HCOOH Laser Interferometer/Polarimeter

LI Yonggao (李永高), ZHOU Yan (周艳), DENG Zhongchao (邓中朝), et al.
Plasma Sci. Technol. 2015, 17 (5): 430-434 ;  doi: 10.1088/1009-0630/17/5/11
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Show Abstract ( 254 )

A multichannel methanoic acid (HCOOH, λ=432.5 µm) laser interferome- ter/polarimeter is being developed from the previous eight-channel hydrogen cyanide (HCN, λ=337 µm) laser interferometer in the HL-2A tokamak. A conventional Michelson-type interom- eter is used for the electron density measurement, and a Dodel-Kunz-type polarimeter is used for the Faraday rotation effect measurement, respectively. Each HCOOH laser can produce a linearly polarized radiation at a power lever of ∼30 mW, and a power stability <10% in 50 min. A beam waist (diameter d0 ≈12.0 mm, about 200 mm away from the outlet) is finally determined through a chopping modulation technique. The latest optical layout of the interferometer/polarimeter has been finished, and the hardware data processing system based on the fast Fourier transform phase- comparator technique is being explored. In order to demonstrate the feasibility of the diagnostic scheme, two associated bench simulation experiments were carried out in the laboratory, in which the plasma was simulated by a piece of polytetrafluoroethene plate, and the Faraday rotation effect was simulated by a rotating half-wave plate. Simulation results agreed well with the initial ex- perimental conditions. At present, the HCOOH laser interferometer/polarimeter system is being assembled on HL-2A, and is planned to be applied in the 2014–2015 experimental campaign.

Optimization of the Water-Cooled Structure for the Divertor Plates in EAST Based on an Orthogonal Theory

LI Lei (李磊), YAO Damao (姚达毛), LIU Changle (刘常乐), ZHOU Zibo (周自波), et al.
Plasma Sci. Technol. 2015, 17 (5): 435-440 ;  doi: 10.1088/1009-0630/17/5/12
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An orthogonal experimental scheme was designed for optimizing a water-cooled structure of the divertor plate. There were three influencing factors: the radius R of the water- cooled pipe, and the pipe spacing L 1 and L 3 . The influence rule of different factors on the cooling effect and thermal stress of the plate were studied, for which the influence rank was respectively R > L 1 > L 3 and L 3 > R > L 1 . The highest temperature value decreased when R and L 1 increased, and the maximum thermal stress value dropped when R, L 1 and L 3 increased. The final optimized results can be summarized as: R equals 6 mm or 7 mm, L 1 equals 19 mm, and L 3 equals 20 mm. Compared with the initial design, the highest temperature value had a small decline, and the maximum thermal stress value dropped by 19% to 24%. So it was not ideal to improve the cooling effect by optimizing the geometry sizes of the water-cooled structure, even worse than increasing the flow speed, but it was very effective for dropping the maximum thermal stress value. The orthogonal experimental method reduces the number of experiments by 80%, and thus it is feasible and effective to optimize the water-cooled structure of the divertor plate with the orthogonal theory.

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