Production Of High-temperature Plasma Research Articles

A New Wide-Area Monitoring System of Electromagnetic Fields Around Megawatt-Class Amplifiers for Ion Cyclotron Range of Frequency Heating at a Fusion Test Facility

Nuclear fusion research requires the production of high-temperature plasma. One of the plasma heating methods is the use of radio frequency (RF) waves. The RF wave heating system uses a high-power amplifier, which poses a concern about the leakage electromagnetic fields. Therefore, a new wide-area multipoint electromagnetic monitoring system using personal RF monitors has been developed. The developed monitoring system was applied to the megawatt-class amplifiers for the “ion cyclotron range of frequency” (ICRF) heating system in the frequency range of ion cyclotron resonance from 30 to 40 MHz. As a result, the leakage magnetic field was less than the measurement sensitivity during the plasma experiment, in which the leakage electric field was detected with sufficient sensitivity. The leakage electric field becomes larger as the RF forward power increases, and thus the electric field would be radiated through the stub and/or high voltage supply line connected to the anode of tetrode in the ICRF amplifier. The electric field around the ICRF amplifiers did not exceed the reference level of International Commission on Non-Ionizing Radiation Protection (ICNIRP). The developed wide-area multipoint monitoring system will be useful for monitoring the leakage RF electromagnetic fields around the ICRF heating system at the future fusion devices.

Experimental Study for Comparison of H2and Ar–H2Gas Mixture Glow Discharge Wall Conditioning in ADITYA Tokamak

Low-temperature glow discharge wall conditioning (GDC) using H2 gas is effective in reduction of oxygen and carbon (low-Z) contained impurities on near surface region of the vacuum vessel wall. The high retention of hydrogen in vessel wall/components due to long operation of H2 GDC increases hydrogen outgassing during plasma operation and affects the production of high-temperature plasma in tokamak. The hydrogen retention can be reduced using inert gas GDC by sputter cleaning for short duration. But, in that case, the outgassing rate of the inert gas increases, which may impair the plasma performance. To overcome above problems, the GDC with hydrogen-inert gas mixture can be used for better removal of C and O surface contaminants and low hydrogen retention in the vacuum vessel surface. In ADITYA tokamak, H2 GDC is carried out regularly after plasma operations, while the GDC with argon–hydrogen (Ar–H2) mixture has been experimentally tested to observe the reduction of the oxygen and carbon impurities along with low hydrogen retention. In Ar–H2 GDC, the formation of the ArH+ hydride ions, which have quite long life and more energy compared with H2+ ions formed in H2 GDC for breaking the bond of wall molecules. A systematic comparative study of H2 GDC and Ar–H2 mixture GDC by changing the mixture ratio has been carried out in ADITYA tokamak. The relative levels of oxygen and carbon contain impurities have been measured using residual gas analyzer in both GDCs. We have observed a substantial reduction in oxygen and carbon impurities with a significant improvement in wall condition with Ar–H2 GDC compared with the H2 GDC. The effect of wall conditioning by Ar–H2 GDC on the performance of high-temperature plasma operation is presented in this paper.

Production of High-Temperature Plasmas During the Early Phases of a C9.7 Flare. II. Bi-directional Flows Suggestive of Reconnection in a Pre-flare Brightening Region

The 6 June 2007 16:55 UT flare was well observed with high time-cadence sparse raster scans by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. The observation covers an active region area of 240 arcsec × 240 arcsec with the 1 arcsec slit in about 160 seconds.

On the possibility of high-temperature plasma production by laser pulses irradiating a volume-structured medium formed upon the explosion of a thin conductor

The properties and parameters of volume-structured metal media produced by exploding thin conductors in a high-power electric discharge are analysed. Such media are proposed for the production of nonequilibrium high-temperature laser plasma as a high-power X-ray and neutron radiation source. The physics of the interaction of a high-power laser pulse with a volume-structured metal medium and the properties of produced nonequilibrium plasma are considered.

Yohkoh observations of plasma upflows during solar flares

Observations of two flares, an M 2.2 event on 16 December, 1991 and the precursor to an X1 flare on 15 November, 1991 are presented. Spectra obtained with the Bragg Crystal Spectrometer (BCS) are compared with data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide Band Spectrometer (WBS) on the satellite. For both events the creation of upflowing plasma is detected. While the first event seems to conform well to the chromospheric evaporation model for high temperature plasma production, the behaviour for the second event is more complex.

Research on pulsed and steady-state plasma guns and their applications in the Troitsk branch of Kurchatov Institute of Atomic Energy

The parameters of plasma guns developed and plasma streams generated are presented. The streams were used for the studies of plasma dynamics in a magnetic field, for high-temperature plasma production, for plasma injection into open magnetic traps, as well as for industrial applications. The main results in these areas of studies are presented.

Exploitation and development of particle beams at Culham Laboratory (invited)

Particle beams have been developed at the Culham Laboratory for many years, mainly for application to the production of high-temperature plasmas. These developments included demonstration of fundamental plasma physics such as particle trapping, heating, and current drive coupled to continuous advances in the physics and technology of ion beam production and transport. This work reached its zenith in production of multimegawatt high-proton fraction sources for the neutral beam injectors for JET. A new initiative is now coming for the development of negative ion based injectors. This wide ranging base of physics and technology provided a springboard for exploitation of beams in areas other than fusion. The last few years have seen increasing R and D at Culham in areas such as space, defense, surface treatment, and implantation. The applications have ranged from beams of H+ or H− to Xe+, from currents of less than 1 mA to currents of amperes and from energies of 50 eV to energies of hundreds of kilovolts. This paper describes some examples of these activities and relates them to the physics and technology base. Future areas of interest are also discussed.

Particle acceleration in active galactic nuclei

Multifrequency observations of Active Galactic Nuclei (AGN) from radio to the X-ray band have now provided evidence that they are site of production of high temperature plasmas (kT > 100 MeV) with strong tails of suprathermal particles. This hot phase is necessarily mixed with a distribution of dense, cold clouds, which scatter, absorb and reprocess the radiation from the hot plasma and relativistic particles, and contribute to form the observed spectra. The generation of high temperature, relativistic plasmas and suprathermal particles is a very challenging problem, not only in the framework of the study of AGN as such, but also in the more general context of the origin of high-energy cosmic rays. In this review we discuss the physical processes which have been suggested to operate in AGN, with special attention for the aspects connected with the generation of specific and/or bulk relativistic energies. Extended radio sources are discussed in these Proceedings by dr. Scheuer as a typical environment where ultra-high-energy cosmic rays (UHECR) may be produced, either by mechanisms based on ordered fields or by stochastic acceleration processes. AGN, which are often associated with them, might appear to be an even better source of high energy particles because of their compactness and global energetics. However they are characterized by high photon densities; correspondingly photomeson losses reduce the final specific energies of the particles allowed to escape. In this sense we may conclude that AGN deliver large amounts of energy into the surrounding components (for instance the extended radio lobes), but are not likely to be the prime generators of the nuclear component of cosmic rays above 10 18 eV. Conversely the neutrino component might be an important product of compact galactic cores and, as such, would represent in perspective a method for investigating AGN. We conclude with some remarks about the possibility of further accelerating energetic particles emerging from AGN in the large scale structures of the local Supercluster, as a viable alternative to explain the generation of extragalactic UHECR.

A Spectroscopic Temperature Measurement of Converging Detonations by the Emission Spectral Matching Method

Experimental studies on converging detonations have been performed aiming at application to high-power pulse lasers and production of hightemperature plasmas. Viewing that the duration time of the detonation is relatively short (< 10 μs) at the converging point, spectroscopic measurements have often been used as diagnostic techniques. In the present study, the emission of CN violet bands from a converging point was analyzed using a microdensitometer. In order to determine the temperature at the converging point of a detonation, a method of matching the entire emission spectra was utilized. The anticipated emission spectra of the observed band can be theoretically calculated with a combination of the gasdynamic quantities, assuming Boltzmann distributions for rotational, vibrational and electronic energy levels. After several trial-and-error processes, the best fit was obtained for T = 11 000 K, N = 7.5 x 1016/cc and the Lorentian broadening half-width Wl = 0.003 nm : The detonation was produced using equi-molar oxyacetylene mixtures at P1 = 60 Torr (8.0 x 103 Pa) and T1 = room temperature in an 80-cm-dia. double-disc-type detonation chamber. It was found, as a result, that unavoidable doppler broadening inherent to high temperature experiments and a wide slit function could be handled with no essential difficulty and a correct rotational/vibrational temperature could be obtained.

Production of High Temperature Plasma by Means of Pulsed Discharge in High Pressure Gas

The possibilities of pulsed gas isolation are investigated as one of fusion approaches. It is essentially based on the production and use of transient, high pressure gas tube. Several types of discharge in a high pressure gas tube are displayed and studied.

Concept of Vortex Gas Tunnel and Application to High Temperature Plasma Production

To obtain a high temperature plasma insulated by gas of atmospheric pressure, a newly developed gas flow system is proposed which induces an extremely larger pressure difference in the radial direction (over several hundreds Torrs) compared with the conventional one (several Torrs). This concept of “gas tunnel” in strong vortex gas flow has been verified by the experiment. Several points of excellence on the production of a high temperature plasma in the “gas tunnel” are emphasized.

Laser application for investigations of the high-temperature and plasma phenomena

The wide power dispersion and high effective temperature of radiation call forth the useful application of lasers for the investigation of high-temperature and gas dynamical processes as well as in plasma physics. By means of lasers, it is possible to investigate the phase transition in any substance, determine the thermophysical parameters, and study the phase transition kinetics in the wide interval of temperature and pressure. It is also possible to study the state equation and optical properties of various substances at high temperatures. The powerful lasers permit production of high-temperature plasmas of any chemical composition and the strong shock wave in the gases and dense media. The maximum obtained velocities reach up to 300 km/s and temperatures more than 100 eV. The described plasma is an interesting object for study of various elementary processes taking place in the equilibrium as well as in the nonequilibrium state of the substance.

The production of high temperature plasmas by intense laser pulses

The possibility of producing dense high temperature plasmas by heating magnetically contained plasma with a pulsed laser beam is considered. The process requires high ion densities (> 1017 cm-3) to be maintained during the heating period, and the magnetic field strength required to contain such a plasma has been calculated in terms of both the kinetic pressure and Bohm diffusion of the plasma. Radiation and conduction losses from the plasma are also considered, and it is concluded that temperatures of the order of 106 °K should be obtainable within present-day limits of field strength and photon flux.

Collective interactions and the problem of high-temperature plasma production

Collective interactions and the problem of high-temperature plasma production

Collective interactions and the problem of high-temperature plasma production

Collective interactions and the problem of high-temperature plasma production