Investigation of Plasma Facing Components in Plasma Focus Operation

Both aspects of the plasma–wall interactions, counter effect of plasma and materials, have been considered in our experiments. The AEOI plasma focus, Dena, has Filippov-type electrodes. The experimental results verify that neutron production increases using tungsten as an anode insert material, compared to the copper one. The experiments show decrement of the hardness of Aluminum targets outward the sides, from 135 to 78 in Vickers scale. The sputtering yield is about 0.0065 for deuteron energy of 50 keV.     

Plasma Limiter Based on Surface Wave Plasma Excited by Microwave

A novel plasma limiter, in which the plasma is excited by surface wave, is presented. The breakdown time of some gases filled in the limiter were calculated as a function of gas pres- sure, ionization degree and density of seed electrons under low pressure （0.01 -1 Torr） and high pressure （10 -1000 Torr） cases. The results show that the limiter filled with Xe with a pressure of 0.9 Torr, seed electron density of 10^16 m^-3, and ionization degree of 10^-4, has a breakdown time of approximate 19.6 ns.     

Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device

Plasma source is the most important part of the laboratory plasma platform for fundamental plasma experimental research. Barium oxide coated cathode plasma source is well recognized as an effective technique due to its high electron emission current. An indirectly heated oxide coated cathode plasma source has been constructed on a linear magnetized plasma device. The electron emission current density can reach 2 A/cm 2 to 6 A/cm ² in pulsed mode within pulse length 5–20 ms. A 10 cm diameter, 2 m long plasma column with density 10 ¹⁸ m ⁻³ to 10 ¹⁹ m ³ and electron temperature T_e ≈ 3–7 eV is produced. The spatial uniformity of the emission ability is less than 4% and the discharge reproducibility is better than 97%. With a wide range of the plasma parameters, this kind of plasma source provides great flexibility for many basic plasma investigations. The detail of construction and initial characterization of oxide coated cathode are described in this paper.     

Miniature Coaxial Plasma Injector for Diagnostics by Beam Plasma Interaction

A miniature coaxial gun has been used to study the interaction between plasma beam and low density plasma formed in glow discharge. The peak discharge current flow between the coaxial electrodes was 5.25 kA as a single pulse with pulse width     

Plasma Confinement Characteristics in Heliotron J--Spontaneous Change of Plasma Confinement State

Spontaneous transition of the plasma confinement mode was observed in the helicalaxis heliotron device “Heliotron J“ for three different plasma heating schemes, i.e. ECHonly, NBI-only and the combination of ECH and NBI. The transition seems to occur above a certain critical density. In addition to the confinement transition, a spontaneous shift of the hitting position of the divertor plasma flux on the wall was observed. This shift could be related with the change of the edge field topology caused by non-inductive toroidal currents.     

Experimental Study of Plasma Materials' Interaction in Plasma Focus “Dena”

It is widely recognized that plasma material interaction in fusion devices is a critical issue that affects the overall machine performance. The process of material selection with a low degradation effect on the confined plasma and on the nuclear fusion production in tokamaks is of great importance. However, plasma materials' interaction studies in tokamaks have some limitations, so it is suggested that a new method for investigating this phenomenon be developed. The high capabilities of plasma focus devices allow one to simulate the interaction studies of tokamak plasma and first-wall materials. Our experiments were performed on a 90-kJ Filippov-type plasma focus, Dena. Experimental results clearly show the influence of materials on the neutron yield and neutron production mechanisms.     

Production of a High-Mach-Number Plasma Flow for an Advanced Plasma Space Thruster

A higher specific impulse and a larger thrust are required for a manned interplanetary space thruster. Prior to a realization of a fusion-plasma thruster, a magneto-plasma-dynamic arcjet (MPDA) powered by a fission reactor is one of the promising candidates for a manned Mars space thruster. The MPDA plasma is accelerated axially by a self-induced j × B force. Thrust performance of the MPDA is expected to increase by applying a magnetic nozzle instead of a solid nozzle. In order to get a much higher thruster performance, two methods have been investigated in the HITOP device, Tohoku University. One is to use a magnetic Laval nozzle in the vicinity of the MPDA muzzle for converting the high ion thermal energy to the axial flow energy. The other is to heat ions by use of an ICRF antenna in the divergent magnetic nozzle. It is found that by use of a small-sized Laval-type magnetic nozzle, the subsonic flow near the muzzle is converted to be supersonic through the magnetic Laval nozzle. A fast-flowing plasma     

Spectroscopic Measurements of the Plasma from a Plasma Gun,(I)

Line broadening of He I 4471 Å and He ‖ 4686 Å radiated from plasma generated in a Marshall type coaxial plasma gun are measured by a 340 cm Ebert type spectrometer. Doppler shift measurements indicates that a plasma blob is accelerated during about 5 μsec from the initiation of gun discharge and leaves the plasma gun, while an unacceleratee 1 plasma remains in the gun throughout the discharge period. Most of the line broadening on the He ‖ 4686 Å is due to Doppler broadening, and Stark broadening is negligible. The accelerated plasma from the gun gradually loses the velocity component perpendicular to the axis of the plasma gun as it travels through the vacuum vessel.     

Plasma Diagnosis for Microwave ECR Plasma Enhanced Sputtering Deposition of DLC Films

Application of the Langmuir probe in plasma circumstance for deposition of diamond-like carbon(DLC) thin films usually faces the problem of rapid failure of the probe due to surface insulative coating.In this paper,we circumvent the problem by using the floating harmonic probe technique.In the real circumstance of DLC film deposition,the floating harmonic probe worked reliably over 3 hours,correctly indicating the ion density and electron temperature.The technique was practically used to measure the ion density and electron temperature in DLC film deposition processes using the microwave ECR plasma enhanced sputtering.Combined with the Raman spectroscopic characterization of the films,the conditions for deposition of DLC films were investigated.     

Esterification by the Plasma Acidic Water:Novel Application of Plasma Acid

This work explores the possibility of plasma acid as acid catalyst in organic reactions. Plasma acidic water was prepared by dielectric barrier discharge and used to catalyze esterification of n-heptanioc acid with ethanol. It is found that the plasma acidic water has a stable and better performance than sulfuric acid, meaning that it is an excellent acid catalyst. The plasma acidic water would be a promising alternative for classic mineral acid as a more environment friendly acid.     

Construction of Larger Area Density-Uniform Plasma with Collisional Inductively Coupled Plasma Cells

The plasma density and electron temperature of a multi-source plasma system composed of several collisional inductively coupled plasma （ICP） cells were measured by a doubleprobe. The discharges of the ICP cells were shown to be independent of each other. Furthermore, the total plasma density at simultaneous multi-cell discharge was observed to be approximately equal to the summation of the plasma density when the cells discharge separately. Based on the linear summation phenomenon, it was shown that a larger area plasma with a uniform density and temperature profile could be constructed with multi-collisional ICP cells.