Soft X-ray emission from He plasma in a 3.3 kJ plasma focus system is investigated without and with preionization by a 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 4 pi geometry is measured as a function of He gas filling pressures. The highest soft X-ray yield, of 0.25 +/- 0.01 J, is obtained at a filling pressure of 125 Pa without preionization, which increases to 0.50 +/- 0.02 J with preionization at a filling pressure of 150 Pa. The total X-ray yield without preionization, 1.50 +/- 0.07 J, is observed at a filling pressure of 125 Pa and this is enhanced to 2.44 +/- 0.11 J with preionization at a filling pressure of 150 Pa. The preionization makes the focus filament symmetric and enhances its volume.
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.
In this paper, we study the effect of current sheath symmetry on pinched plasma intensity in Amirkabir Plasma Focus (APF) facility (16kV, 36 f and 115nH) 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.
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.
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 source wave propagating along an external static magnetic field) when the ion motion is neglected, a linearly polarized electromagnetic source plane wave splits into four longitudinal oscillating modes, one stationary longitudinal mode and eight travelling electron wave modes ( four of them are transmitted and four are reflected). For the particular values of the source wave frequency and magnitude of the external magnetic field some of the created modes in plasma might be resonantly excited.
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.
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.
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 the mirror material should perform its functions. This article describes experiments that have been carried out to evaluate the prospect of amorphous mirrors retaining their optical characteristics under the impact of deuterium or argon plasma ions of different energy. The experiments were undertaken with the use of mirror samples prepared from amorphous alloys Vitreloy-1 and Vitreloy-4. The data reported demonstrate the principal ability of mirrors made of amorphous materials to preserve the initial optical quality in the process of long-term sputtering, and should be considered as proof of the possibility of using amorphous metal mirrors in the erosion-dominated zone of a fusion reactor.
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 activities on thermonuclear fusion.
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.
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.
Electromagnetic forces and possible magnetoelastic buckling caused by interaction with the toroidal magnetic field are analysed for the in-vessel poloidal field coils of the tokamak T-15 upgrade. Analytical expressions for the forces and critical currents have been derived. The analysis shows that the stiffness of the in-vessel coils provides the stability of the coils with sufficient safety margins.
Measurement of an internal magnetic field distribution in magnetically confined fusion devices is indispensable for both understanding the plasma physics and controlling plasmas. A polari-interferometer based on the Faraday effect has been used for such a purpose. This paper describes performance evaluations of a part of the polarimeter with photoelastic modulators (PEMs) of the short-wavelength far-infrared (FIR) laser polari-interferometer. The wavelengths of the light source are 57.2 and 47.7 m, which are suitable for a high-density operation and large fusion devices. The PEM for the FIR region is newly developed with high-resistive silicon in which absorption of the FIR laser is small. The polarization angle is successfully measured and an angle resolution of 0.01 with a time resolution of 1ms is achieved. A drift of the baseline of about 0.1 for 1000s is observed and is found to be caused by changes in the room temperature.
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.
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.
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-20dB. The frequency multiplier and mixer deformed the signal and the band-pass filter is used effectively to attain high signal-to-noise ratio.
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 may affect the particle reflection on solid surfaces were made.
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.
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.
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 maximal energy input of 3 kJ and is used for both plasma and D–D reaction explorations. Experiments with deuterium have shown that peak current of I peak=39 kA flows between the electrodes at P=11.5 mbar for the operation voltage of V=14 kV. An average total neutron yield is measured around 3.3×105 neutrons per shot using CR-39 plastic detectors located in different places opposite to the anode inside the PF chamber. Neutron anisotropy and pressure-dependent neutron yields are also determined for a series of shots.
