Showing papers in "IEEE Transactions on Plasma Science in 2014"

Concept Design of CFETR Tokamak Machine

Abstract: China Fusion Engineering Test Reactor (CFETR) is a tokamak reactor; one design option under the consideration of the China National Integration Design Group employs superconducting magnets. The fusion power is at the range of 50-200 MW and the duty cycle (or burning time) was envisioned as 30%-50%. The plasma current will be 10 MA and the major and minor radii are 5.7 and 1.6 m, respectively. The concept engineering design including the magnet system, vacuum vessel (VV) system, and maintenance method has been carried out in the past years. The toroidal magnetic field strength at R0 is 5 T and the maximum flux swing provided by central solenoid winding will be 160 VS. The main design work, including the electromagnetic analysis of the magnet system, has already been carried out. This paper mainly probes into the VV design and optimization based on three types of maintenance ports. Furthermore, the maintenance method, counted as one of the most important design studies, is presented specifically in this paper. It includes the design of the maintenance ports and the remote handling system design, and so on. The next design stage will mainly include mechanical design, conductor stability, different types of divertor system design, and so on.

Physics Design of CFETR: Determination of the Device Engineering Parameters

Abstract: Chinese Fusion Engineering Test Reactor (CFETR) based on the tokamak approach with superconducting magnet technology is envisioned to provide 200-MW fusion power and operate with a goal of an annual duty factor of 0.3-0.5. This report based on a zero-dimensional system study using extrapolations of current physics by considering engineering constraints, is focused on qualitative determination of the engineering parameters of the device. Conservative assumptions of plasma performance based on present day existing experiments were made to assure achievable goals, since CFETR could be a near-term project to bridge the gaps between ITER and DEMO. The baseline of 200-MW fusion power in standard H-mode for a duration longer than 1000 s and in a modest improved H-mode (or hybrid mode) with H98 ≤ 1.3 for steady-state operation derive a device of R=5.7 m, a=1.6 m in size with Bt=5 T, and total heating and current drive source power of 80 MW. More ambitious operating modes with higher fusion power reaching the alpha-particle dominated self-heating regime for burning plasma study is possible with the same device hardware, if the more advanced physics is incorporated. Since large vacuum chamber design, possible upgrades both on physics and technologies enable operation of the device with larger plasma configuration and provide potentials to demonstrate key physics issues relevant to DEMO.

Review on the History, Research, and Applications of Electrohydrodynamics

Abstract: Corona discharge refers to the phenomenon when the electric field near a conductor is strong enough to ionize the dielectric surrounding it but not strong enough to cause an electrical breakdown or arcing between conductors or other components. This phenomenon is unwanted and dangerous in high-voltage systems; however, a controlled corona discharge may be used to ionize a fluid and induce motion by directly converting the electrical energy into kinetic energy. Phenomena that involve the direct conversion of electrical energy into kinetic energy are known as electrohydrodynamic (EHD) and have a variety of possible applications today. This paper contains a literature review of the research regarding the EHD effects associated with corona discharges, from the first observation of the phenomenon to the most recent advancements on its mathematical modeling, as well as the advancements on specific applications, such as thrust, heat transfer improvement, boundary layer enhancement, drying, fluid pumping, and cooling.

Recent Advances in the Worldwide Fusion Gyrotron Development

Abstract: Progress in the worldwide development of high-power gyrotrons for magnetic confinement fusion plasma applications is presented. Gyrotron oscillators are used for electron cyclotron heating, electron cyclotron current drive, stability control, and plasma diagnostics. After technology breakthroughs in the research on gyrotron components in the 1990s, significant progress has been achieved in the 2000s, in the field of long-pulse and continuous wave (CW) operation for a wide range of frequencies. Currently, the development of 1-MW-class CW gyrotrons for the tokamak ITER (170 GHz), the stellarator Wendelstein 7-X (140 GHz), and the tokamaks DIII-D and JT-60SA (110 GHz) has been very successful in EU, Japan, Russia, and USA. The Japan 170-GHz ITER gyrotron holds the energy world record of 2.88 GJ (0.8 MW at 1-h pulse duration). For this progress in the field of high-power long-pulse gyrotrons, innovations such as the realization of high-efficiency stable oscillation in very high-order cavity modes with low ohmic losses, the use of single-stage depressed collectors for energy recovery (efficiency enhancement and simpler power supplies), highly efficient internal quasi-optical (q.o.) mode converters (low level of internal stray radiation), and synthetic diamond windows have essentially contributed. The total tube efficiencies are around 50% and the purity of the linearly polarized fundamental Gaussian output mode is 97% and higher. Power modulation technologies for stabilization of neoclassical tearing modes have proceeded. Future prospects of advanced high-power fusion gyrotrons are in the areas of two- and three-frequency gyrotrons, fast step-wise frequency tuneability, higher unit power (coaxial cavities), and higher frequencies for more efficient plasma stabilization and noninductive current drive as well as reliability, availability, maintainability and inspectability for next step fusion power stations. The GYCOM step-tuneable 1-MW gyrotron for ASDEX Upgrade employing a broadband travelling-wave-resonator window (with two diamond disks) operates at 105, 117, 127 and 140 GHz. The EU 170 GHz coaxial-cavity gyrotron prototype achieved in millisecond pulses the power of 2.1 MW at 46% efficiency and 96% Gaussian mode purity. A new power record of second harmonic oscillation has been achieved in the subterahertz band (83 kW/389 GHz/3 ms) in Japan for application to collective Thomson scattering diagnostics. A fundamental frequency 670-GHz gyrotron with pulsed magnet generated 210 kW in 20-30- μs pulses at 20% efficiency (collaboration of institutions in Russia and USA).

Effects of Reentry Plasma Sheath on the Polarization Properties of Obliquely Incident EM Waves

Abstract: A novel and simple analytical technique referred to as transmission line analogy is developed and modified to study the transmission properties of the perpendicular polarized wave and the parallel polarized wave obliquely incident on the reentry plasma sheath. Based on the transmission coefficients, the effects of the plasma sheath on the polarization property of obliquely incident electromagnetic (EM) waves are studied. Taking the GPS navigation right hand circularly polarized wave as an example, the influences of incident angle and plasma parameters, including the electron density and the collision frequency on the EM wave’s polarization property are studied. Numerical results indicate that the larger the incident angle and the lower the collision frequency is, the worse the deterioration of the polarization property. In addition, the polarization property deteriorates most seriously when the cutoff frequency of the peak electron density is closest to the frequency of the EM waves.

Plasma Medical Science for Cancer Therapy: Toward Cancer Therapy Using Nonthermal Atmospheric Pressure Plasma

Abstract: We have been developing novel ultrahigh density atmospheric pressure plasma sources and succeeded in the selective killing ovarian cancer cells against normal ones. Furthermore, we have found out the plasma-activated medium (PAM) also killed glioblastoma brain tumor cells selectively against normal ones and the chemical products in the PAM have long lifetime healing effects. To clarify the mechanism, interactions of plasma with the organism and the medium where the organism belongs were investigated on the viewpoint of intracellular molecular mechanism.

Development of Electrodeless Plasma Thrusters With High-Density Helicon Plasma Sources

Abstract: Helicon plasma sources are very useful in many aspects and are applicable to many fields across science and technology, as they can supply high-density $({\sim}10^{13}~{\rm cm}^{-3})$ plasmas with a broad range of external operating parameters. In this paper, developed, featured sources with various sizes are characterized along with discussions on their particle production efficiency. This paper aims to develop systems that can realize schemes with completely electrodeless plasma production and acceleration. This is expected to mitigate the existing problems of the finite lifetimes inherent in electric plasma propulsion tools. Experimental and theoretical approaches that implement such schemes are presented.

Computational Methods in the Warp Code Framework for Kinetic Simulations of Particle Beams and Plasmas

Abstract: The Warp code (and its framework of associated tools) was initially developed for particle-in-cell simulations of space-charge-dominated ion beams in accelerators, for heavy-ion-driven inertial fusion energy, and related experiments. It has found a broad range of applications, including nonneutral plasmas in traps, stray electron clouds in accelerators, laser-based acceleration, and the focusing of ion beams produced when short-pulse lasers irradiate foil targets. We summarize novel methods used in Warp, including: time-stepping conducive to diagnosis and particle injection; an interactive Python-Fortran-C structure that enables scripted and interactive user steering of runs; a variety of geometries (3-D $x$ , $y$ , $z$ ; 2-D $r$ , $z$ ; 2-D $x$ , $y$ ); electrostatic and electromagnetic field solvers; a cut-cell representation for internal boundaries; the use of warped coordinates for bent beam lines; adaptive mesh refinement, including a capability for time-dependent space-charge-limited flow from curved surfaces; models for accelerator lattice elements (magnetic or electrostatic quadrupole lenses, accelerating gaps, etc.) at user-selectable levels of detail; models for particle interactions with gas and walls; moment/envelope models that support sophisticated particle loading; a drift-Lorentz mover for rapid tracking through regions of strong and weak magnetic field; a Lorentz-boosted frame formulation with a Lorentz-invariant modification of the Boris mover; an electromagnetic solver with tunable dispersion and stride-based digital filtering; and a pseudospectral electromagnetic solver. Warp has proven useful for a wide range of applications, described very briefly herein. It is available as an open-source code under a BSD license. This paper describes material presented during the Prof. Charles K. (Ned) Birdsall Memorial Session of the 2013 IEEE Pulsed Power and Plasma Science Conference. In addition to our overview of the computational methods used in Warp, we summarize a few aspects of Ned's contributions to plasma simulation and to the careers of those he mentored.

Design of a Metamaterial-Based Backward-Wave Oscillator

Abstract: In this paper, we present the design of a microwave generator using metamaterials (MTMs) in a negative index waveguide interacting with a high-power electron beam. The microwave structure is formed by inserting two MTM plates loaded with complementary split-ring-resonators (CSRRs) into a rectangular waveguide. Electromagnetic simulations using the high-frequency structure simulator code confirm the presence of a negative index TM-like mode suitable for use in a backward-wave oscillator (BWO). Particle-in-cell (PIC) simulations using the computer simulation technology (CST) Particle Studio code are performed to evaluate the efficiency of an S-Band MTM-based BWO (MTMBWO) excited by a 500 keV, 80-A electron beam. After about 250 ns, the MTMBWO reaches a saturated output power of 5.75 MW with an efficiency of 14% at a frequency near 2.6 GHz. The MTMBWO is also modeled by representing the MTM plates, which consist of CSRRs, as dielectric slabs whose effective permittivity is given by a Lorentzian model. The dielectric slab model is also simulated with the CST PIC code and shows good qualitative agreement with the simulations including the CSRR loaded plates. A cold test structure was fabricated from brass to test the theoretical predictions of the microwave transmission versus frequency of the negative index waveguide. Test results using a vector network analyzer showed very good agreement with the simulations for the excitation of the negative index TM-like mode near 2.6 GHz. The proposed structure appears to be promising for use in a MTMBWO high-power microwave generator.

Pulsed Power Generation by Solid-State LTD

Abstract: A solid-state linear transformer driver stack has been developed to demonstrate pulsed power generation and output pulse shaping. It consists of 30 modules each using 24 power metal–oxide–semiconductor field-effect transistors as switches. The output voltage of the stack is the superposition of the voltage pulse of each module no matter if the modules are switched synchronously or not. In synchronous operation, the output voltages of all modules are added up to reach an output voltage up to \(\sim 29\) kV with a maximum output current of \(\sim 240\) A. The pulsewidth is variable in the range of 50–170 ns. On the other hand, by carrying out separate switching of different modules, the output waveform can be varied by performing pulse shaping. The control signals for pulse shaping experiment are generated using an field-programmable gate array board that allows potentially automatic waveform optimization.

Large-Scale Pulsed Power Opportunities and Challenges

Abstract: Pulsed power applications are widespread, ranging from microscopic devices up to systems that are major installations and cost many millions of dollars. This paper describes some of the approaches used for the larger systems that have been built and discusses their engineering challenges. Basic energy storage approaches include electrostatic (capacitors), magnetic (inductors), inertial (flywheels), electrochemical (batteries), and fuel or explosives. Systems based on these approaches each have their own requirements and challenges but also have many common components. An example of one potential future large-scale opportunity—launch to space—is given and the need to develop more competitive economic approaches is discussed.

Study on Wideband Sheet Beam Traveling Wave Tube Based on Staggered Double Vane Slow Wave Structure

Abstract: In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in X-direction and the other is used to compress the electron beam in Y-direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz.

Single Shot and Vectorial Characterization of Intense Electric Field in Various Environments With Pigtailed Electrooptic Probe

Abstract: In this paper we illustrate the ability of electrooptic sensors to perform electric (E)-field vectorial measurements. Thanks to their frequency response spreading over nine decades and to their measurement dynamics reaching 120 dB, these sensors are of high interest for some applications (near field mapping, energy line monitoring, electromagnetic compatibility, and so on). Furthermore, due to their fully dielectric structure and millimetric size, almost no perturbation is induced on the E-field to be measured, even in the near field region. This paper is focused on high-intensity pulsed E-field characterization in different environments such as air, water (bioelectromagnetism applications), or plasmas ( in situ assessment of the E-field associated to an electric discharge and to the induced plasma). The use of such a technology for electrical equipment and energy line monitoring is also investigated.

On OH Density of an Atmospheric Pressure Plasma Jet by Laser-Induced Fluorescence

Abstract: For room-temperature atmospheric pressure plasma jets (RT-APPJs), because of the gas flow, the OH density at a given position is different from the case without the gas flow. In this paper, an OH density decay model, which includes the main loss processes of OH and gas flow effect, is present. Based on the model, the simulation results have a very good agreement with the OH decay behavior measured by laser-induced fluorescence. The absolute OH density of the RT-APPJ is obtained when the best fit is achieved, which is about $2.4\times 10^{13}~{\rm cm}^{-3}$ at 5 mm away from the plasma jet nozzle and 1 $\mu{\rm s}$ after the discharge. In addition, to control the OH density, the effect of voltage polarity, applied voltage magnitude, pulse frequency, pulsewidth on the OH density is also investigated and discussed.

Particle-in-Cell Simulation and Optimization of Multigap Extended Output Cavity for a W-Band Sheet-Beam EIK

Abstract: In this paper, a multigap extended output cavity was designed by 3-D simulations, which served as the output cavity for a W-band sheet-beam extended interaction klystron (SBEIK). In our numerical design, the circuit dimensions were systematically optimized by parametric finite-difference time-domain simulations, and the equivalent circuit for the output cavity was also analyzed. The proper external loading was selected by using a region of loss in 3-D, and the output power was optimized. The results were verified by using the coupler and the waveguide. The 2π mode of the optimized five-gap extended output cavities had an ohmic Q (Q0) of 1343.5, an external Q (Qe) of 501.6, and a loaded Q (QL) of 365.2 at 94.5 GHz. The 3-D particle-in-cell simulations predict that the output cavity of the SBEIK (75 kV and 4 A) can stably produce more than 50 kW of output power using a prebunched beam.

Low-Ripple and High-Precision High-Voltage DC Power Supply for Pulsed Power Applications

Abstract: This paper describes the design and implementation of a three-phase resonant converter with low ripple and high control accuracy. Based on a three-phase LCC-type resonant converter-which has advantages of low ripple, highefficiency, and high-power density compared with a single-phase converter-a high-voltage power supply with low ripple (<;0.1%) was designed. In addition to the general merits of an LCC-type resonant converter operating at continuous conduction mode- including soft switching, low conduction loss, and current source characteristics-the proposed scheme uses only one phase under a light-load condition by having different leg designs of the gate drive circuit and snubber parameters. This allows the design to overcome the operational constraints of the general LCC-type resonant converter. The distinctive design of the three-phase converter structure provides high efficiency and low ripple not only during rated operation, but also under light-load conditions. In order to analyze the high performance of the proposed scheme from no load to rated load, a PSPICE simulation was carried out. Comparison results with a conventional LCC-type resonant converter based on a single-phase structure are analyzed from the viewpoints of output ripple, losses, and operable load range. Using the proposed converter, a 20-kV, 20-kW high-voltage dc power supply design and implementation was presented with a superior gate drive circuit. Finally, the superiority of the proposed converter was verified through a simulation and experimental results. It was experimentally confirmed that the developed power supply achieves high performance in terms of efficiency (98%), operable load range (0.5-20 kV), and low ripple (0.05%), with a high power density.

Multilevel High-Voltage Pulse Generation Based on a New Modular Solid-State Switch

Abstract: This paper describes a modular solid-state switching cell derived from the Marx generator concept to be used in topologies for generating multilevel unipolar and bipolar high-voltage (HV) pulses into resistive loads. The switching modular cell comprises two ON/OFF semiconductors, a diode, and a capacitor. This cell can be stacked, being the capacitors charged in series and their voltages balanced in parallel. To balance each capacitor voltage without needing any parameter measurement, a vector decision diode algorithm is used in each cell to drive the two switches. Simulation and experimental results, for generating multilevel unipolar and bipolar HV pulses into resistive loads are presented.

Dual Discharge Modes Operation of an Argon Plasma Generated by Commercial Electronic Ballast for Remote Plasma Removal Process

Abstract: An argon plasma generated between the cone-shaped electrode powered by commercial electronic ballast and grounded plane electrode has been investigated Since the electronic ballast has positive and negative cycle in a period, two different discharge modes of remote plasma—the normal glow discharge mode and the hollow cathode discharge mode—have been observed It is noted that the hollow cathode discharge mode has wider operation window in gas pressure than the glow discharge one The glow discharge started to be extinguished at pressure higher than 41 torr and turned to the hollow cathode discharge mode in the holes on ground plate, while the hollow cathode discharge mode kept growing until 10 torr These results show that the stable operation window of the system could be defined by the glow discharge mode rather than the hollow cathode discharge mode and could be improved by optimizing the applied voltage waveform and electrode configuration

Production of Ammonia by Heterogeneous Catalysis in a Packed-Bed Dielectric-Barrier Discharge: Influence of Argon Addition and Voltage

Abstract: Ammonia was synthesized from nitrogen and hydrogen in a dielectric-barrier discharge reactor packed with glass spheres and MgO pellets at atmospheric pressure. The addition of argon to nitrogen and hydrogen, and increasing the peak voltage, led to increases in discharge power and uniformity, gas temperature, and the fraction of hydrogen converted to ammonia.

Extension of the Pierce Model to Multiple Transmission Lines Interacting With an Electron Beam

Abstract: A possible route toward achieving high-power microwave (HPM) devices is through the use of novel slow-wave structures, represented by multiple coupled transmission lines (MTLs), and whose behavior when coupled to electron beams has not been sufficiently explored. We present the extension of the 1-D linearized Pierce theory to MTLs coupled to a single electron beam. We develop multiple formalisms to calculate the k-ω dispersion relation of the system and find that the existence of a growing wave solution is always guaranteed if the electron propagation constant is larger than or equal to the largest propagation constant of the MTL system. We verify our findings with illustrative examples that bring to light unique properties of the system in which growing waves were found to exist within finite bands of the electron propagation constant and also present possible means to improve the gain. By treating the beam-MTL interaction as distributed dependent current generators in the MTL, we derive relations characterizing the power flux and energy exchange between the beam and the MTLs. For the growing wave, we show that the beam always behaves as an energy source causing power flux along the transmission lines. The theory developed in this paper is the basis for the possible use of degenerate band edges in periodic MTL systems for HPM amplifiers.

Variational Formulation of Macroparticle Models for Electromagnetic Plasma Simulations

Abstract: A variational method is used to derive a self-consistent macroparticle model for relativistic electromagnetic kinetic plasma simulations. Extending earlier work, discretization of the electromagnetic Low Lagrangian is performed via a reduction of the phase-space distribution function onto a collection of finite-sized macroparticles of arbitrary shape and discretization of field quantities onto a spatial grid. This approach may be used with lab frame coordinates or moving window coordinates; the latter can greatly improve computational efficiency for studying some types of laser-plasma interactions. The primary advantage of the variational approach is the preservation of Lagrangian symmetries, which in our case leads to energy conservation and thus avoids difficulties with grid heating. In addition, this approach decouples particle size from grid spacing and relaxes restrictions on particle shape, leading to low numerical noise. The variational approach also guarantees consistent approximations in the equations of motion and is amenable to higher order methods in both space and time. We restrict our attention to the 1.5-D case (one coordinate and two momenta). Simulations are performed with the new models and demonstrate energy conservation and low noise.

Transition From Construction to Operation Phase of the Wendelstein 7-X Stellarator

Abstract: Assembly of the superconducting stellarator Wendelstein 7-X is well advanced, and commissioning of the device is being prepared. A first draft of the commissioning tasks has been developed and will be discussed in this paper.

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

Abstract: Europe is devoting significant joint efforts to develop and to manufacture MW-level gyrotrons for electron cyclotron heating and current drive of future plasma experiments. The two most important ones are the stellarator Wendelstein W7-X at Greifswald and the Tokamak ITER at Cadarache. While the series production of the 140 GHz, 1 MW, CW gyrotrons for the 10-MW electron cyclotron resonance heating system of stellarator W7-X is proceeding, the European GYrotron Consortium is presently developing the EU-1 MW, 170 GHz, CW gyrotron for ITER. The initial design had already been initiated in 2007, as a risk mitigation measure during the development of the advanced ITER EU-2-MW coaxial-cavity gyrotron. The target of the ITER EU-1-MW conventional-cavity design is to benefit as much as possible from the experiences made during the development and series production of the W7-X gyrotron and of the experiences gained from the earlier EU-2-MW coaxial-cavity gyrotron design. Hence, the similarity of the construction will be made visible in this paper. During 2012, the scientific design of the ITER EU-1-MW gyrotron components has been finalized. In collaboration with the industrial partner Thales electron devices, Velizy, France, the industrial design of the technological parts of the gyrotron is being completed. A short-pulse prototype is under development to support the design of the CW prototype tube. The technological path toward the EU ITER-1 MW gyrotron and the final design will be presented.

The Selective Characterization of Nonthermal Atmospheric Pressure Plasma Jet on Treatment of Human Breast Cancer and Normal Cells

Abstract: The aim of this paper is to investigate the effect of nonthermal atmospheric pressure plasma jet on human breast cancer and normal cells. High voltage, dc-pulsed power supply was used to generate low temperature helium plasma in atmospheric pressure. In this paper, cancer and normal cells were exposed to plasma during four time steps. For further exploration, Doxorubicin as common chemotherapy drug was employed to compare the efficacy of plasma treatment with convectional cancer therapy. Also, the Caspase-Glo 3/7 assay was obtained to reveal the death process of cancer and normal cells. The results of MTT and apoptosis assay showed that the plasma treatment has drastically reduced the viability of breast cancer cells, while it has no significant damage to the normal cells. In addition, after plasma treatment three different zones were formed in the plate, which will represent the detachment of cells from plate surface. Moreover, adding 5% oxygen to the helium plasma will lead to enhancement of cancer cells viability reduction. In addition, the outcome of this paper has verified that the plasma treatment successfully overcomes drug treatment in inhibition of the cancer cells viability, while decreases the adverse effect of drug treatment.

Electric Field and Temperature Dependence of Electrical Conductivity in Biaxially Oriented Polypropylene Films

Abstract: In pulsed power systems, metallized film capacitors facilitate the operation of the film with a relatively small margin to its dc breakdown strength. Electrical conduction in metallized biaxially oriented polypropylene (BOPP) film may result in the leakage in high energy density capacitors and thus the reduction of the energy efficiency. This paper investigates the mechanism of the electric field and temperature dependence of electrical conduction in the BOPP film capacitor. A proposed model for the electrical conductivity takes into consideration both the Poole-Frenkel effect and field-enhanced carrier mobility. Experiments are performed to measure the electrical conductivity of the BOPP film at different electric fields and temperatures.

Estimation of Critical Axial Magnetic Field to Prevent Anode Spots in Vacuum Interrupters

Abstract: Previous works have shown a linear anode spot formation threshold current (I th ) dependence on the critical axial magnetic field (AMF), B crit AMF , in a vacuum under applied AMFs of up to ~110 mT. However, the effects of the contact design parameters (e.g., contact diameter, contact gap, and contact material) on this dependence have not yet been revealed. Here, we define this dependence as k, which signifies the critical AMF strength per unit arc current needed to prevent an anode spot in a vacuum arc. The objective of this paper is to determine k as a function of the contact design parameters in AMF vacuum interrupters (VIs), including the contact diameter, the arc extinguishing contact gap, and the contact materials, to prevent anode spot formation. Experiments were conducted in a demountable vacuum chamber, in which an external Helmholtz AMF coil was installed coaxially around a pair of butt-type contacts. The contact diameter D was in the 12-100 mm range and the arc extinguishing contact gap l was in the 12-24 mm range. Three contact materials were investigated: 1) oxygen-free high-conductivity Cu; 2) CuCr25 (25% weight of Cr); and 3) CuCr50 (50% weight of Cr). The BAMF applied by the external coil was uniform and varied from 0 to 110 mT. The experimental results showed that k = qD -α , where D is the contact diameter, and q and α are constants. The k increased linearly but slowly with l, from 6.6 to 7.1 mT/kA when l increased from 12 to 24 mm. In addition, the k values obtained for the different contact materials were similar to each other. With D = 60 mm and l = 24 mm, k only varied from 6.3 to 7.1 mT/kA among the three contact materials. Therefore, the influence of l and the contact materials on k was insignificant when compared with that of D. This data could be useful for compact AMF VI designs in which anode spots do not form.

A Cascaded Microsecond-Pulse Generator for Discharge Applications

Abstract: Gas discharges using pulsed power are a promising and efficient approach for producing low-temperature plasmas at atmospheric pressure. Pulsed power generators vary widely in performance and should be chosen according to the load and application requirements. In this paper, a microsecond-pulselength high voltage (HV) generator is developed for atmospheric-pressure plasma jets that use a cascade-type voltage circuit. The electrical parameters including voltage amplitude, pulse repetition frequency, and pulsewidth, are determined by the trigger system. The voltage amplitude can be up to 10 kV and the pulse repetition frequency varies from 1 Hz to 5 kHz. The unipolar output pulse can be either positive or negative, with either square or triangular wave profile that can also be controlled by the optical trigger system. When the output pulse is a square wave, the rising edge is about 100 ns, the falling edge is approximately \(2~\mu \) s, and the pulsewidth at the top varies from 0.5 to 30 \(\mu \) s. When the output pulse is a triangular wave, the base of the pulse is from 7 to 62 \(\mu \) s, and the stepped rising edge is from 5 to 30 \(\mu \) s. The HV pulse generator is used for producing helium plasma jets into open air. Preliminary experimental data show the effects of the pulse voltage amplitude, pulse repetition frequency, and pulsewidth on plasma jets, and confirm that the generator can provide a good performance for driving cold plasma jets.

Design and Analysis of Divertor Scraper Elements for the W7-X Stellarator

Abstract: A set of new water-cooled divertor components is being designed for the Wendelstein 7-X stellarator to protect the edges of the primary plasma facing components during the bootstrap current evolution (~ 40 s). These new components, referred to as scraper elements (SEs), will intercept field lines and associated heat flux that would otherwise overload the main target edges in certain operational scenarios. The SEs are calculated to experience peak heat fluxes ~15-16 MW/m2 and will be constructed from carbon fiber reinforced composite monoblocks of a type that has been qualified for ITER. The heat flux distribution and magnitude is calculated from field line following in a 3-D magnetic field that includes the contribution from plasma currents. The heat flux calculations are coupled with an engineering design in an iterative process to generate SEs that meet the design criteria while reducing the geometric complexity of the elements.

Induced liquid phase flow by RF Ar cold atmospheric pressure plasma jet

Abstract: The plasma of an atmospheric pressure plasma jet strongly interferes with a liquid when it just touches the liquid surface. The gas flow of the jet exerts a force on the liquid surface pushing it downwards, while the plasma exerts a force which is partly counteracting the gas flow induced force. The downward force in the centre of the liquid recipient causes the liquid to circulate with a circulation time of ~2 sec. Due to this circulation the color change of a dye proceeds homogeneously.

Properties of Soil Treated With Ozone Generated by Surface Discharge

Abstract: Chemical contamination in plants, soil, and ground water has become serious by overuse of pesticides and nitrogen fertilizers in agriculture. We propose the use of ozone generated by atmospheric pressure plasma for soil disinfection as one of the plasma applications into agriculture. Because ozone has strong oxidation potential to decompose organic substances in soil, it is considered to be one of the candidates as potential alternative to both pesticide and nitrogen fertilizer. In this paper, fundamental studies on changes in acidity and amounts of nitrogen nutrients, bacteria, mold, and soil DNA remained in soil after ozone treatment were carried out with a system using a quartz chamber. Surface barrier discharge that operates in atmospheric oxygen was used in the system as the ozone generator. In addition, growth of radishes that seeded on soils in pots that were treated by ozone diffusion method was also evaluated.