Hyun-Jong You

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.

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.

Design and testing of a multi-triggered spark gap switch for 2-15 kJ plasma focus device

Summary form only given, as follows. A multi-channel spark gap switch has been widely used in high current and low inductance pulse forming network to obtain switching of fast rise time and high current pulses. Inductance and resistance of a spark gap switch rapidly decrease with increase of channels and electrode erosion is reduced by lower current density. In this work, an electrically multi-triggered spark gap switch was developed to be used as a multi-channel spark gap switch in a 2-15 kJ plasma focus device with a capacitor of Maxwell No 32169 (capacitance, 32 uF, inductance 65 nH). The geometry of the multi-triggered spark gap switch is similar to an annular-type rail gap switch. The large bodies of dielectric that surround the electrodes were designed to prevent arcing along the exterior of the gap. The dielectric material is translucent polycarbonate which has high Izod impact strength. By using translucent polycarbonate, the breakdown in the gap switch could be visually observed. The main electrodes and trigger are made of stainless steel. The minimum gap spacing in this switch is 7 mm and the trigger is located between two main electrodes. The trigger is similar to the main electrode of the trigatron switch. In parenthesis, five different trigger-pins are located in the main trigger-plate and these are isolated with dielectric material. Therefore, six different trigger signals can be generated with a time difference of a few micro-seconds.

Beam Profile Measurements with a Slit-Faraday Cup and a Wire Scanner for a Newly Developed 18 GHz Superconducting ECR Ion Source and its LEBT

In this presentation we show results of beam profile measurements by a slit-Faraday cup and a wire scanner. Argon 8+ beams were generated in a new liquid heliumfree superconducting electron cyclotron resonance ion source (ECRIS). The ECRIS, named SMASHI, was successfully developed at the National Fusion Research Institute in 2014, and in the future it will be dedicated for highly charged ions matter interaction research facility (HIMIRF). Before designing HIMIRF terminals after low energy beam transport (LEBT), it is necessary to characterize the beam properties of the source and its LEBT line. The beam profile measurements have been done after an analyzing dipole magnet (DM). The slitFaraday cup and the wire scanner were installed at 25 cm and 120 cm from the exit flange of the DM, respectively. Between the two diagnostics an Einzel lens was positioned to control the focusing of diverged beams. Here, with the measurements we checked the present beam alignments in the LEBT, and studied the dependence of beam profile variation on the operations of beam optics such as steering magnets and Einzel lens. INTRODUCTION A new superconducting 18 GHz electron cyclotron resonance ion source and its low energy beam transport were developed at the National Fusion Research Institute in South Korea [1]. The source, named SMASHI (Superconducting Multi-Application Source of Highlycharged Ions), will be dedicated for future application of highly charged ions in the area of matter interaction, diagnostic imaging, and probing. In this proceeding, we briefly describe SMASHI and its LEBT. Then, we show preliminary results of beam charge spectra of He, O, Ar, Xe ion beams. In order to characterize the beam properties in the LEBT, we also measured beam profiles by a slit-FC system and a wire scanner, by which the beam alignments of the source and the LEBT are checked. Variations of beam profiles are studied with respect to different settings of ion optics in the LEBT. SOURCE DESCRIPTION Figure 1 shows the overall section view of SMASHI. As an ECRIS for generating multiply/highly-charged ions, SMASHI has following main features: twofrequency heating(18, 18+Δ GHz), high power-capable plasma chamber, remotely-positional variable gap extraction system, capability to generate a wide range of ion elements from gas to metal, and two diagnostic ports for the extraction region. All these features are highly oriented to the generation of diverse highly charged ions (HCI). Most of all, due to the helium-free SC magnet, SMASHI can be more economically operated with low power consumption, which therefore enabling the full system of ECRIS operated on a high-voltage platform. Microwave Injection In Fig. 1, the microwave injection side can be viewed. Normally, the injection electrode is located at the maximum position of the axial magnetic field, and depending on the source condition it can be moved to other optimum positions by adjusting the bellows. In the injection electrode two WR62 waveguide ports, an onaxis sputtering hole, a centered-perforated biased disk, two diagnostic/oven holes, and one gas hole were arranged [1]. The WR62 ports, placed well out of the plasma pattern, are separated by 120◦ from each other. The biased disk is shaped as a triangle with a thru-hole in its center, into which the on-axis sputtering target is inserted. The sputtering target system is remotely positional and designed to easily exchange different materials. Extraction System The extraction system, shown in Fig. 1, is a pullerEinzel lens system consisting of 3 electrodes. Each electrode is supported and guided by 4 rods fixed to the extraction chamber. The distance between electrodes can be adjusted when necessary. The whole extraction system is remotely positional by a motor-driven-control, where the gap between the plasma electrode and the puller electrode is adjustable by 20–50 mm. Table 1 summarizes the extraction conditions and beam characteristics. The resulted rms emittance for Ar was calculated by using IGUN with the inclusion of the magnetic field and charge state distribution (CSD). The resulting beam radius and the momentum of Ar beam are 33 mm and 41 mrad, respectively. Table 1: Extraction Conditions and Beam Characteristics Extraction voltage 30 (10-30) kV Gap distance 33 (20-50) mm Einzel lens (negative) 30 (10-30) kV Rms emittance for Ar at 500 mm from plasma electrode 48 mm mrad (Rmax=33 mm, Amax=41 mrad) ___________________________________________ *This work was supported by R&D Program of ‘Plasma Convergence & Fundamental Research’ through the National Fusion Research Institute of Korea (NFRI) funded by the Government funds #hjyou@nfri.re.kr Proceedings of IBIC2015, Melbourne, Australia MOPB035 Overview and Commissioning ISBN 978-3-95450-176-2 113 C op yr ig ht

Development of large-area ECR plasma source for the deposition of copper metallization

Summary form only given. Deposition of continuous and conformal copper seed layer for metallization of very large-scale integration (VLSI) fabrication using an electron cyclotron resonance (ECR) plasma source with DC sputter has been studied. As an ECR plasma source, permanent magnets (PM)-embedded Lisitano antenna (O378 mm) which can be made independently of the wavelength1 could be used. It was operated in the pressure range of 0.2 to 1.5 mTorr and power range of 500 to 2000 W. The argon plasma has been observed to have an electron density of ∼5×1010 cm−3 and electron temperature of 5 eV for a microwave power of 750 W and gas pressure of 0.5 mTorr. The process parameters were microwave power (500∼2000 W), sputter voltage (100∼800 V), operating pressure (0.1∼0.5 mTorr), chuck bias (0∼100W). After that we were analyzed films thickness, uniformity, step coverage, resistivity by SEM, probe station and TEM. Our results show that can be free from problem like overhang effect and poor step coverage compared with conventional method (PVD).

SLot-excited long racetrack ECR plasma source for roll-to-roll (scanning) processing

Summary form only given. A SLot-excited ANtenna (SLAN) long racetrack ECR plasma source was newly designed and fabricated. The source can be utilized for roll-to-roll plasma processing such as thin film encapsulation of large-area OLED (organic light emitting diode) panel and functioning or modification of fabric surface. The source was designed to be long, sub-millitorr pressure operated, and to have high density uniform plasma. The above features were accomplished by a slot-excited long racetrack ring resonator, toroidal geometry of magnetic field ECR configuration, and reinforced microwave electric distributions around the central region of plasma chamber. Also the source was made to be high-power microwave capable by using a waveguide aperture excitation instead of an insertion rod coupling which has been always problematic in high power operation. It is also designed that plasma profile (uniformity) can be adjustable by a newly employed tail plunger, which was attached to the opposite side of the waveguide aperture in the racetrack ring resonator. Experiments showed successful plasma generation and stable operation in the Ar pressure range of 0.2–10 mTorr with the microwave power of 0.5–3 kW. As expected, the plasma is measured to be uniform (<10 %) in the direction of straight track and to have Gaussian profiles in the direction of scanning direction.

Optimization of the LaB6 Cathode for Divertor Plasma Simulator (DiPS)

A steady-state high density LaB₆ dc plasma source is developed for the divertor plasma simulator (DiPS), which is a linear device for the studies on various electric probes, plasma-wall interactions, atomic processes, and for the development of plasma diagnostics. Since the LaB₆ is very weak against the thermal shock, which is possibly caused by the overflow of the discharge current in a flash, and leads to cracking the LaB₆ plate, the source is to be designed lower the thermal stress for stable and longer operation. Thermal shock can be mitigated by optimizing the configurations of the magnetic and electric fields with floating electrode. Magnetic cusp is formed between the LaB₆ cathode and anode in order for ion bombardment to the LaB₆ plate to be uniform over the surface and in order for electrons to follow the field lines and to wet the surface of the anode uniformly. Electric field is generated such that the maximum outflow of electrons toward the anode can be maximized by adjusting the direction of the field and by locating a floating electrode between LaB₆ cathode and anode. The LaB₆ source is composed of a cylindrical LaB₆ plate with 4 inches in diameter, graphite heater and Ta heat shield. From the different electric and magnetic field configurations, the LaB ₆ dc plasma source is optimized as n_e=10¹⁴ cm^-3 (Ar), 10¹³ cm^-3 (He), T_e=2 - 3 eV (Ar), 5 - 10 eV (He) and T_i les 0.2 eV (Ar)

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.