Showing papers in "Plasma Devices and Operations in 2009"
TL;DR: A short analysis of lithium properties presented in this paper was carried out in terms of lithium application in various systems of a fusion reactor and was intended for use by the engineers and researchers involved in activities on thermonuclear fusion.
Abstract: A short analysis of lithium properties presented in this article was carried out in terms of lithium application in various systems of a fusion reactor. The article is intended for use by the engineers and researchers involved in activities on thermonuclear fusion.
46 citations
TL;DR: A short review of the modern state of lithium use in experimental facilities and fusion devices is presented in this paper, which is intended to be used by the engineers and researchers involved in activiti...
Abstract: A short review of the modern state of lithium use in experimental facilities and fusion devices is presented. This paper is intended to be used by the engineers and researchers involved in activiti...
41 citations
TL;DR: In-vessel mirrors are necessary for optical diagnostics of plasmas in next-step fusion devices as mentioned in this paper, and these mirrors will be under the influence of the harsh fusion environment, and in these conditions th...
Abstract: In-vessel mirrors are necessary for optical diagnostics of plasmas in next-step fusion devices. These mirrors will be under the influence of the harsh fusion environment, and in these conditions th...
16 citations
TL;DR: In this paper, the axial and radial distributions of electron temperature and ion density have been measured using a double electric probe, and the location of the virtual cathode was found at around 0.7 cm from the mesh anode.
Abstract: The plasma properties from a DC pseudo-discharge have been studied in low-pressure nitrogen gas. The discharge took place between a virtual cathode and a mesh anode similar to a pulsed virtual cathode oscillator or vircators. The electric potential, electric field and space charge density of the glow discharge have been obtained in the axial and radial part of the glow discharge. The location of the virtual cathode was found at around 0.7 cm from the mesh anode. The axial and radial distributions of electron temperature and ion density have been measured using a double electric probe. The electron temperature varied between 0.5 and 1.4 eV, while the ion density varied from 7×1012 to 12×1012 cm−3, outside the electrodes.
13 citations
TL;DR: In this paper, a newly-constructed plasma focus (PF) device ODAK-3K is introduced to the literature and some results of first fusion research realized in this device are reported.
Abstract: In this study, a newly-constructed plasma focus (PF) device ODAK-3K is introduced to the literature and some results of first fusion research realized in this device are reported. The device has a ...
10 citations
ITER1
TL;DR: In this paper, the effect of ferromagnetic materials in building structures has been studied and it is shown that the magnetic field produced by the ITER tokamak complex can be significantly modified by the building in areas distant from the TOKAMAK.
Abstract: The stray magnetic field produced by the ITER tokamak complex, including the effect of ferromagnetic materials in building structures, has been studied. The results obtained show that the magnetic fields produced by the tokamak can be significantly modified by the ferromagnetic structures of the building in areas distant from the tokamak. It is shown that stray fields produced by the ITER tokamak complex can exceed 100 Gs in areas where service staff are possibly located. Such a level of stray fields should be in agreement with the medical and safety engineering limits as well as to ensure the normal operations of equipment sensitive to magnetic fields. The results are presented in the form of a set of field maps, which can be widely used for practical applications.
9 citations
TL;DR: In this paper, the authors used a multi-wall carbon nanotube (CNT) film as a cathode to produce argon gas in a scanning electron microscope at near-atmospheric pressure.
Abstract: Microplasma was produced in argon gas in a scanning electron microscope at near-atmospheric pressure using a multi-wall carbon nanotube (CNT) film as a cathode. It is demonstrated that with the CNT film used as a cathode, the breakdown voltage was much lower than the breakdown voltage when the conventional cathode made of flat metal film was used and the discharge was highly reproducible. These features of the gas discharge are defined by the field emission from the CNT cathode.
8 citations
TL;DR: In this article, distribution of energy density of a plasma flow in the KPU-30 pulse coaxial accelerator at continuous gas filling has been investigated and the influence of discharge parameters on energy density at various pressures of the working gas is demonstrated.
Abstract: Distribution of energy density of a plasma flow in the KPU-30 pulse coaxial accelerator at continuous gas filling has been investigated. The influence of discharge parameters on energy density at various pressures of the working gas is demonstrated. It is shown that the maximal plasma energy occurs in a pressure range of 0.02–0.05 torr. Distributions of energy density in the axial and radial directions are obtained. The focus point of the plasma flow is found and the plasma flow energy density at this point is measured.
8 citations
TL;DR: An attempt is made to analyze the obtained results of investigations into behavior of in-vessel mirrors in ITER (International Thermonuclear Experimental Reactor) for proper operation of optical and laser methods of burning plasma diagnostics.
Abstract: A wide experimental program on investigation of behavior of in-vessel mirrors in the present-day fusion devices is being implemented. The program is coordinated by the International Tokamak Physics Activity (ITPA) and now more than 10 fusion devices are involved in mirror studies. The aim of these investigations is to find solutions for several important tasks that arise with the necessity of using in-vessel mirrors in ITER (International Thermonuclear Experimental Reactor) for proper operation of optical and laser methods of burning plasma diagnostics. To date quite a large amount of information has been accumulated in the frame of this program. An attempt is made in this paper to analyze the obtained results.
7 citations
ITER1
TL;DR: In this article, the influence of global elements of the ITER tokamak complex building on the gas breakdown (BD) was studied and the scenario of plasma initiation was designed and simulated using virtual coils with currents producing a magnetic field in the BD region similar to that from the building.
Abstract: The stray magnetic fields produced at plasma initiation (in particular at the gas breakdown (BD)) by the ITER tokamak complex building have been studied. The influence of global elements of the tokamak complex building is estimated. The scenario of plasma initiation was designed and simulated using virtual coils with currents producing a magnetic field in the BD region similar to that from the building.
6 citations
TL;DR: In this article, in situ measurements of the laser reflectivity have been performed under the irradiation with low-energy helium ions in stainless steel, Mo and W. Although fine roughness on the specimen surface was observed in irradiated materials, the size is too tiny to explain the present degradation of the reflectivity by using a Bennett's equation.
Abstract: To evaluate the optical reflectivity deterioration of first mirrors for plasma diagnostics, in situ measurements of the laser reflectivity have been performed under the irradiation with low-energy helium ions in stainless steel, Mo and W. Surface morphology and radiation damage in sub-surface region have also been examined using scanning electron microscope, atomic force microscope and transmission electron microscope. It is found that the deterioration of the reflectivity under the irradiation with helium ions is very severe and depends on the ion energy, fluence and wavelength. Although fine roughness on the specimen surface was observed in irradiated materials, the size is too tiny to explain the present degradation of the reflectivity by using a Bennett's equation. On the other hand, from the present observation a strong correlation between the deterioration of the reflectivity and the formation of radiation damages in the surface and sub-surface regions of the laser penetration depth is suggested.
TL;DR: In this paper, the spectral resolution of X-ray bent crystal spectrometers has been investigated and a toroidal Johann-Johansson type spectrometer is suggested and its resolution is estimated.
Abstract: This paper presents the analysis of the geometrical components in the evaluation of the spectral resolution of X-ray bent crystal spectrometers. A toroidal Johann–Johansson type spectrometer is suggested and its resolution is estimated. Emphasis is made on the study of asymmetrically cut schemes. Generally used expansion techniques up to second order are added by calculations of the third term where second order becomes zero.
TL;DR: In this paper, the properties of the field emission from multi-walled carbon nanotubes (CNTs) in air used to generate the microplasma at near-atmospheric pressure were investigated in a removable gas cell built into a scanning electron microscope.
Abstract: The properties of the field emission (FE) from multi-walled carbon nanotubes (CNTs) in air used to generate the microplasma at near-atmospheric pressure were investigated in a removable gas cell built into a scanning electron microscope. The gaps between the electrodes were adjusted from 5 to 100 μm and the pressure was changed from 0 to 100 kPa. The obtained results have shown that the FE properties of the CNTs at 10 kPa and lower pressures were the same as those in vacuum. At a pressure more than 10 kPa, the FE threshold voltage in air was higher than those in vacuum, and increased with increasing atmospheric pressure. When the FE threshold voltage became higher than that of the gas breakdown, the microplasma was ignited before the FE initiation. Thus, the FE properties of the CNTs in air were stable when the FE potential was lower than the voltage of conventional gas discharge with CNT cathode.
TL;DR: In this article, electron field emission (FE) from carbon nanotubes (CNTs) in atmospheric pressure Ar gas was measured using a needle for anode and a CNT specimen for cathode.
Abstract: Electron field emission (FE) from carbon nanotubes (CNTs) in atmospheric pressure Ar gas was measured. The FE measurements were carried out using a needle for anode and a CNT specimen for cathode. The FE current usually appeared at several hundred volts at applied voltage to the anode at the gap length from 15 to 100 μm. When the applied voltage was lower than a conventional gas breakdown voltage around 300 V, the FE in Ar gas was stable and reproducible even at atmospheric pressure. There was no damage on the surface of CNT cathode in SEM observation after the FE operation in Ar gas. When the applied voltage was increased to more than the gas breakdown voltage, a conventional gas discharge took place resulting in destroying the CNT cathode surface.
TL;DR: In this paper, the authors used the experimental setup equipped with a magnetic deflection momentum analyzer and the time-of-flight energy analyzer of neutrals to characterize the carbon-adsorbed layers by measuring energy distribution of particles reflected from the surface.
Abstract: In fusion experiments, plasma erodes walls of devices containing various elements including carbon. The eroded carbon penetrates into edge plasma and is transported backwards forming the carbon-adsorbed layers on the surfaces of components like mirrors for optical plasma diagnostics. To characterize the carbon-adsorbed layers by measuring energy distribution of particles reflected from the surface, we have used the experimental setup equipped with a magnetic deflection momentum analyzer and the time-of-flight energy analyzer of neutrals. Ion beams in the energy range 1–2 keV irradiated the samples of Mo and W with carbon deposition on them that were prepared in separate plasma chambers. The beams produced ions and neutrals with characteristic emission angle and energy distribution depending upon conditions of the sample surfaces. Experimental results are compared with the numerical calculation model ACAT (Atomic Collisions in Amorphous Targets) and the evaluations on how the structure of deposition layers...
TL;DR: In this article, the effect of current sheath symmetry on pinched plasma intensity in Amirkabir Plasma Focus (APF) facility (16,kV, 36μ f and 115 nH) by the magnetic probes was studied.
Abstract: In this paper, we study the effect of current sheath symmetry on pinched plasma intensity in Amirkabir Plasma Focus (APF) facility (16 kV, 36 μ f and 115 nH) by the magnetic probes. The arrival times of current sheath reaching to the probes, the signals of hard X-ray (HXR) and also discharge current signal are recorded simultaneously. The simulated trajectory, velocity and intensity of current sheath are compared with the experimental results. There seems to be a good accordance among current sheath symmetry, pinched plasma intensity and HXR yield.
TL;DR: In this article, a long line-shaped microwave plasma has been generated, in helium and argon gas pressure, over a pressure range of 1-50torr over the pressure range.
Abstract: Long line-shaped microwave plasma has been generated, in helium and argon gas pressure, over a pressure range of 1–50 torr To this end, waves of 245 GHz are fed into a narrow flat rectangular waveguide, through a tapered waveguide The power of microwave is coupled to the discharge gas through a linear-slot antenna The discharge is realized in a rectangular Pyrex tube, placed-in along the slot groove position In this configuration the microwave is cut off, but the evanescent wave with a long wavelength is propagated and employed to produce the plasma Measurements of the field distribution in the waveguide revealed that the wavelength of the excited field increases as waveguide width decreased to a width close to the cut-off width of 613 mm The relative intensities of He I lines show very high uniformity along the whole line plasma length, and helium excitation temperatures were in the range of 3000–5000 K
TL;DR: In this paper, a printed circuit board based on Rogowski coils has been used to measure the plasma current on the Joint Texas Experimental Tokamak (J-TEXT) and the measurements have shown that this novel PCB Rogowski coil works perfectly and is very suitable for studies of disruption, equilibrium reconstruction, etc.
Abstract: Compared with the conventional Rogowski coils made by winding wire loops, a printed circuit board (PCB) based on Rogowski coils has some favourable advantages for current measurements, such as large effective area, good linearity, high frequency response, precise geometry and thin profile. This type of Rogowski coil has been widely applied in electrical systems as the current sensor. Nevertheless, the PCB Rogowski coils are introduced for the first time to measure the plasma current on the Joint Texas Experimental Tokamak (J-TEXT). The measurements have shown that this novel PCB Rogowski coil works perfectly and is very suitable for studies of disruption, equilibrium reconstruction, etc.
TL;DR: In this paper, the synthesis of carbon nanomaterials by pulse microplasma in the chamber of a scanning electron microscope equipped with a special discharge cell was reported, and the peak current density of the methane microplasmine was higher than 5 kA cm−2 and the pulse width was almost 10 nns.
Abstract: Synthesis of carbon nanomaterials by pulse microplasma in the chamber of a scanning electron microscope equipped with a special discharge cell is reported. The peak current density of the methane microplasma was higher than 5 kA cm−2, and the pulse width was almost 10 ns. After 5 s operation, there could be observed some carbon nanomaterials deposited on the cathode of the platinum film besides melted spots.
TL;DR: In this paper, a five-channel far-infrared (FIR) laser interferometer was designed to measure the line averaged electron density on the Experimental Advanced Superconducting Tokamak (EAST).
Abstract: A five-channel far-infrared (FIR) laser interferometer was designed to measure the line averaged electron density on the Experimental Advanced Superconducting Tokamak (EAST). An improved deuterium cyanide laser was used as the light source. The waveguides were used because of a long distance between the laser and the detectors. Each part of the interferometer is described in detail.
TL;DR: In this article, a broadband frequency-tunable system, which has a fast and stable hopping operation, has been developed in the large helical device, for constructing an accurate heterodyne phase detection system, a single-sideband modulation technique is applied.
Abstract: In order to measure the internal structure of fluctuation, a broadband frequency-tunable system, which has a fast and stable hopping operation, has been developed in the large helical device. For constructing an accurate heterodyne phase detection system, a single-sideband (SSB) modulation technique is applied. Recently, high performance (SSB) modulators have been available in the wide band frequency range and its sideband rejection is around−20 dB. The frequency multiplier and mixer deformed the signal and the band-pass filter is used effectively to attain high signal-to-noise ratio.
TL;DR: In this article, a new vacuum system is designed and developed on the Joint Texas Experimental tokamak (J-TEXT), which consists of two pumping stations, a Taylor discharge cleaning (TDC) system and gas puffing.
Abstract: A new vacuum system is designed and developed on the Joint Texas Experimental tokamak (J-TEXT), which consists of two pumping stations, a Taylor discharge cleaning (TDC) system and gas puffing. With this system, the vacuum vessel of the J-TEXT tokamak can easily reach the vacuum conditions which allow the operation of the machine. The sub-control system of the vacuum pumping systems with the self-protection function is reliable and easy to use. Inside the chamber, the base pressure can be lowered to 6.4×10−6 Pa, and the total leakage and outgassing rates in 12 h is below 1.5×10−8 Pa m3/s. Moreover, the TDC sub-system is used to clean the first facing walls of vacuum chamber to guarantee good wall conditions of the device before each run of the experimental campaign on the J-TEXT tokamak. The basic functions of the vacuum system meet the essential requirements for the present experiments on the J-TEXT tokamak.
TL;DR: In this article, the authors investigated the effects of laser irradiation to the helium-irradiated surface on the optical reflectivity of fiber-form nanostructured tungsten and showed that when the structure is finer, the recovery rate becomes low, typically less than half; moreover it decreases with the number of pulses.
Abstract: Fiberform nanostructured tungsten is formed on tungsten surface by helium plasma irradiation under a specific condition. It is revealed that the optical reflectivity of tungsten is significantly decreased by the formation of the nanostructure. We present the experimentally obtained necessary condition to form the structure in the linear plasma device NAGDIS-II. We investigate the effects of laser irradiation to the helium-irradiated surface on the optical reflectivity. It is revealed that the sub-ms laser pulse irradiation alleviates the surface roughness and recovers the optical reflectivity. However, when the structure is finer, the recovery rate becomes low, typically less than half; moreover, it decreases with the number of pulses.
TL;DR: In this paper, the lifetime of pure electron plasma has been studied in an electromagnetic multi-ring trap, which was housed inside a bore tube and surrounded by a superconducting solenoid, and a magnetic field was used to ensure radial confinement of electron plasma, while an electrostatic harmonic potential well was used for its axial confinement.
Abstract: Confinement of pure electron plasma has been studied in an electromagnetic multi-ring trap. The trap was housed inside a bore tube and surrounded by a superconducting solenoid. A magnetic field of 5 T was used to ensure radial confinement of electron plasma, while an electrostatic harmonic potential well was used for its axial confinement. The lifetime of the electron plasma was found to be strongly dependent on the temperature of the bore tube. In the case of electron plasma of 7×109 electrons and when the temperature of the bore tube changed from room temperature to 40 K, the lifetime also changed from 40 to 3700 s. A significant improvement in the electron plasma lifetime was observed when a rotating electric field with optimum parameters was applied. When the bore tube was operated at room temperature with the rotating electric field, the electron plasma lifetime increased up to 2200 s.
TL;DR: In this article, soft X-ray emission from He plasma in a 33kJ plasma focus system is investigated without and with preionization by α particles Silicon PIN diodes and a multi-pinhole camera with absorption filters.
Abstract: Soft X-ray emission from He plasma in a 33 kJ plasma focus system is investigated without and with preionization by α particles Silicon PIN diodes and a multi-pinhole camera with absorption filters are employed for time-resolved and time-integrated X-ray analyzes, respectively X-ray emission in 4π geometry is measured as a function of He gas filling pressures The highest soft X-ray yield, of 025±001 J, is obtained at a filling pressure of 125 Pa without preionization, which increases to 050±002 J with preionization at a filling pressure of 150 Pa The total X-ray yield without preionization, 150±007 J, is observed at a filling pressure of 125 Pa and this is enhanced to 244±011 J with preionization at a filling pressure of 150 Pa The preionization makes the focus filament symmetric and enhances its volume
TL;DR: In this paper, it was shown that the efficiency of energy conversion of the LCP whistler wave mode into the magnetic field of the wiggler is nearly of the same order of magnitude as the previously considered energy conversion efficiency of the RCP whistlers wave mode.
Abstract: A linearly polarized electromagnetic source wave splits into six traveling wave modes (three of them are right-hand circularly-polarized (RCP) modes and three are left-hand circularly-polarized (LCP) modes) due to the interaction with a suddenly created magnetoplasma medium When the angular frequency of the source wave is in the low-frequency region, the magnetoplasma supports two whistler wave modes (one is the transmitted RCP and the other is the reflected LCP) It is shown that the efficiency of energy conversion of the LCP whistler wave mode into the magnetic field of the wiggler is nearly of the same order of magnitude as the efficiency of the previously considered energy conversion of the RCP whistler wave mode
TL;DR: In this paper, the transformation of a linearly polarized electromagnetic source wave in a suddenly created cold magnetized and weakly nonlinear plasma is considered in the case of longitudinal propagation.
Abstract: The transformation of a linearly polarized electromagnetic source wave in a suddenly created cold magnetized and weakly nonlinear plasma is considered. In the case of longitudinal propagation (a so...
TL;DR: In this article, a cumulative phenomenon of nitrogen gas at a pressure of 3.3 torr in a 1.2 kJ coaxial plasma focus discharge device was investigated experimentally.
Abstract: A cumulative phenomenon of nitrogen gas at a pressure of 3.3 torr in a 1.2 kJ coaxial plasma focus discharge device was investigated experimentally. Variations of nitrogen gas density in the axial phase along the inter-electrode region were estimated experimentally from the plasma current sheath (PCS) dynamics in terms of its velocity, acceleration as well as axial magnetic force data. An inclination angle of PCS with the axial distance was estimated. Investigations of the ratios of radial and axial magnetic force as well as the magnetic pressures coupled to PCS were studied. The variation of the trapping fraction η with the axial distance was computed theoretically based on a snow-plow model and was compared with experimental results.
TL;DR: In this article, the authors report on the representative microwave diagnostics and their contribution to plasma confinement physics and their measurements have clarified the physics issues such as stability, wave phenomena and fluctuation-induced transport.
Abstract: Microwave to millimeter-wave diagnostic techniques such as interferometry, reflectometry, scattering and radiometry have been powerful tools for diagnosing magnetically confined plasmas. Recent advances in electronic devices and components together with computer technology have enabled the development of advanced diagnostics in microwave to millimeter-wave region. The two-dimensional and three-dimensional profiles of plasma density/temperature and dynamic behaviors of their fluctuations are measured by using the advanced diagnostic systems. The measurements have clarified the physics issues such as stability, wave phenomena and fluctuation-induced transport. We report here on the representative microwave diagnostics and their contribution to plasma confinement physics.
TL;DR: In this paper, currentvoltage characteristics (CVCs) of a transferred arc in a limited volume are reported, which is explained by a long-lived ring-shaped vortex flow in the chamber, powered by the forces that at high currents act as an electromagnetic pump accelerating plasma in the direction of current expansion.
Abstract: Current–voltage characteristics (CVCs) of a transferred arc in a limited volume are reported. Experiments were carried out with a setup developed to reproduce the conditions which occur in a tundish equipped with a plasma system to keep the steel temperature at a predefined level. The experimental setup consists of a test chamber in which a plasma torch with a transferred arc is inserted on the top of the chamber cover and the anode is attached at the bottom. A ‘hysteresis’ of the CVC curves was observed during an increase and a decrease in the arc current. This phenomenon is explained by a long-lived ring-shaped vortex flow in the chamber, which is powered by the forces that at high currents act as an electromagnetic pump accelerating plasma in the direction of current expansion.