Yong Ho Jung

Inclined slot-excited annular electron cyclotron resonance plasma source for hyperthermal neutral beam generation

An inclined slot-excited antenna (ISLAN) electron cyclotron resonance (ECR) plasma source is newly designed and constructed for higher flux hyperthermal neutral beam (HNB) generation. The developed ISLAN source is modified from vertical slot-excited antenna (VSLAN) source in two aspects: one is the use of inclined slots instead of vertical slots, and the other is a cusp magnetic field configuration rather than a toroidal configuration. Such modifications allow us to have more uniform arrangement of slots and magnets, then enabling plasma generation more uniform and thinner. Moreover, ECR plasma allows higher ionization rate, enabling plasma density higher even in submillitorr pressures, therefore decreasing the collision rate and∕or the reionization rate of the reflected atoms while passing through the plasma, and eventually getting higher flux of HNBs. In this paper, we report the design features and the plasma characteristics of the ISLAN source by doing plasma measurements and electromagnetic simulations. It was found that ISLAN source can be a high potential source for larger flux HNB generation; the source was found to give higher plasma densities and better uniformities than inductively coupled plasma source, particularly in low pressure ranges. Also, it is important that using ISLAN gives easier matching and better stability, i.e., ISLAN shows similar field patterns and good plasma symmetries irrespective of the variations of the mean diameter of the ring resonator and∕or the presence of a limiter or a reflector, and the operating pressures.

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.

Design and fabrication of a superconducting magnet for an 18 GHz electron cyclotron resonance ion/photon source NFRI-ECRIPS

A superconducting magnet was designed and fabricated for an 18 GHz ECR ion∕photon source, which will be installed at National Fusion Research Institute (NFRI) in South Korea. The magnetic system consists of a set of four superconducting coils for axial mirror field and 36 pieces of permanent magnets for hexapolar field. The superconducting coils with a cryocooler (1.5 W @ 4.2 K) allow one to reach peak mirror fields of 2.2 T in the injection and those of 1.5 T in the extraction regions on the source axis, and the resultant hexapolar field gives 1.35 T on the plasma chamber wall. The unbalanced magnetic force between the coils and surrounding yoke has been minimized to 16 ton by a coil arrangement and their electrical connection, and then was successfully suspended by 12 strong thermal insulating supports made of large numbers of carbon fibers. In order to block radiative thermal losses, multilayer thermal insulations are covered on the coil windings as well as 40-K aluminum thermal shield. Also new schemes of quench detection and safety system (coil divisions, quench detection coils, and heaters) were employed. For impregnation of the windings a special epoxy has been selected and treated to have a higher breaking strength and a higher thermal conductivity, which enables the superconductors to be uniformly and rapidly cooled down or heated during a quench.

Honeycomblike large area LaB6 plasma source for Multi-Purpose Plasma facility

A Multi-Purpose Plasma (MP(2)) facility has been renovated from Hanbit mirror device [Kwon et al., Nucl. Fusion 43, 686 (2003)] by adopting the same philosophy of diversified plasma simulator (DiPS) [Chung et al., Contrib. Plasma Phys. 46, 354 (2006)] by installing two plasma sources: LaB(6) (dc) and helicon (rf) plasma sources; and making three distinct simulators: divertor plasma simulator, space propulsion simulator, and astrophysics simulator. During the first renovation stage, a honeycomblike large area LaB(6) (HLA-LaB(6)) cathode was developed for the divertor plasma simulator to improve the resistance against the thermal shock fragility for large and high density plasma generation. A HLA-LaB(6) cathode is composed of the one inner cathode with 4 in. diameter and the six outer cathodes with 2 in. diameter along with separate graphite heaters. The first plasma is generated with Ar gas and its properties are measured by the electric probes with various discharge currents and magnetic field configurations. Plasma density at the middle of central cell reaches up to 2.6 x 10(12) cm(-3), while the electron temperature remains around 3-3.5 eV at the low discharge current of less than 45 A, and the magnetic field intensity of 870 G. Unique features of electric property of heaters, plasma density profiles, is explained comparing with those of single LaB(6) cathode with 4 in. diameter in DiPS.

Development status of the 18 GHz superconducting electron cyclotron resonance ion source at National Fusion Research Institutea)

A new superconducting 18 GHz electron cyclotron resonance ion source is being developed at the National Fusion Research Institute in South Korea. This source will be dedicated for future application of highly charged ions in the area of matter interaction, diagnostic imaging, and probing. In this paper, we describe the status of the source development consisting of a double electrode biased disk, sputtering systems for metal ion production, diagnostic ports for the extraction region, a variable gap extraction-Einzel lens system, and a low energy beam transport system.

Hydrogen Generation from the Dissociation of Water Using Microwave Plasmas

Hydrogen is produced by direct dissociation of water vapor, i.e., splitting water molecules by the electrons in water plasma at low pressure (<10–50 Torr) using microwave plasma discharge. This condition generates a high electron temperature, which facilitates the direct dissociation of water molecules. A microwave plasma source is developed, utilizing the magnetron of a microwave oven and a TE10 rectangular waveguide. The quantity of the generated hydrogen is measured using a residual gas analyzer. The electron density and temperature are measured by a Langmuir probe, and the neutral temperature is calculated from the OH line intensity.

Comparison of Reactor Type for Pollution Control by Using the Pulsed Corona Discharge

Abstract We investigated efficiency of removal of NO and NOx for applied voltage, repetition frequency and energy according to reactor type (wire-plate and wire-cylinder type reactor). Characteristics of Reactor type by pulsed corona discharge could be analyzed through these Results. Because it is very difficult to measure the conduction current for calculation of energy transferred into the reactor in the corona discharge, conduction current was obtained indirectly and the necessary energy for removal of NO and NOx was calculated from conduction current. Removal efficiency of NO and NOx for control variable (applied voltage, pulse repetition frequency, energy transferred into the reactor and removed quantity etc.) in the wire-cylinder type reactor was higher than that in the wire-plate type reactor.

Development of Two Propulsion Systems with Helicon Plasma

Two space propulsion systems, which are called K2H (KBSI-KAIST-Hanyang University) and DiPS (Diversified Plasma Simulator) devices, are being developed in parallel to explore the space propulsion parameters and optimal helicon operation conditions with the concept of VASIMR (Variable Specific Impulse Magnetoplasma Rocket). Both devices utilize the open-ended magnetic configuration. K2H has three regions such as helicon source, ion cyclotron resonance heating (ICRH), magnetic nozzle and expansion regions. DiPS is the space plasma simulator and composed of three major sections: helicon plasma source, extraction region and space simulation region. Helicon plasmas are generated for both devices by 13.56 MHz rf power using M=+1 right-helical antenna at pressure of several mTorr. Initial plasma parameters such as density, temperature, and drift velocity were measured by a laser induced fluorescence (LIF) system and a fast scanning electric probe system with an rf-compensated Langmuir probe and a Mach probe at ICRH and magnetic nozzle region. The results are given as follows: plasma density n = 1011 - 1013 cm-3 (K2H) and 1012 - 1013 cm-3 (DiPS), electron temperature Te = 3 - 9eV (K2H) and 2 - 4 eV (DiPS), ion temperature Ti = 0.144 - 0.164 eV (K2H), and drift velocity vd = 0.8 - 1.55 km/s (K2H). A simple analysis of the results is provided.

New technique deducing plasma potential by a capacitive coupling method in spraying dielectric barrier discharge plasmas

A new method to measure the plasma potential in an atmospheric dielectric barrier discharge (DBD) plasmas is developed for a new spraying DBD plasma source, which is sustained by electric fields generated by flowing plasmas at the outer region of the electrodes, since conventional electric probe can not be applied due to arcing. The new technique is to measure the spatially averaged plasma potential by using a capacitive coupling method with calculation of collisional sheath thickness.

Optimization of Hanyang University Plasma Focus Device as a Neutron Source

The optimum focusing conditions of the Hanyang University Plasma Focus (HUPF) device have been obtained by determining maximum power input to the focusing plasma while changing pressure at one fixed electrode, which leads to the maximum neutron generation. Six electrodes of different lengths have been used according to the snow-plow model to determine the conditions for the maximum neutron production of the HUPF device, namely 1.6×108 (n/shot) with 17 cm electrode length and a 3.4 Torr pressure.