A. Okino

Miniature hybrid plasma focus extreme ultraviolet source driven by 10 kA fast current pulse

A miniature hybrid plasma focus device, operated in xenon gas medium and driven by a 10kA fast current pulse, has been used to generate extreme ultraviolet radiation in the range of 6–15nm. At present the radiation characteristics from xenon plasma were mainly assessed qualitatively using standard tools such as visible light framing camera, extreme ultraviolet (EUV) pinhole camera, and EUV photodiode. Strong pinching of xenon plasma is indicative from both visible and EUV imagings. The maximum size of the EUV emitting zone is estimated to be of the order of 0.21×1.55mm and the estimated value is within the accepted value as benchmarked by industries. The EUV intensity measurement by photodiode showed fairly isotropic radiation at least in a half solid angle. This device can be developed further as a competent source for EUV metrology or lithography applications.

Study of low current capillary discharge for compact Soft X‐ray laser

Capillary discharge experiments were carried out to get a lasing of Ne‐like Ar. The relation between the appearance of the laser output and the instabilities of longitudinal modes has been studied by side‐view observation. And observation of lasing at a low discharge current of 9 kA provides us a possibility of designing a compact and high‐repetition‐rate soft X‐ray laser by use of a semiconductor switch instead of a gap switch.

Development of a new multi-plasma gas inductively coupled plasma torch

Summary form only given. A new multi-plasma gas inductively coupled plasma (ICP) torch is designed and developed. With the new ICP torch, Ar, He, O/sub 2/, N/sub 2/, CO/sub 2/ and air plasma can be successfully generated in the atmospheric pressure. The torch has smaller area gas inlet and smaller distance between the gas inlet and the plasma generating region to generate an adequate vortex flow at the plasma generating region even with helium gas which has higher kinematic viscosity than other gases. Furthermore, helium has higher thermal conductivity than other gas and so the RF input power for helium ICP was limited by melting of the torch. In our helium ICP, the RF input power was limited only 800 W. To overcome this problem, the new torch has gas cooling system. The torch consists of coaxial three quartz glass tube and the carrier gas, the plasma gas and the cooling gas flow between the tubes. Helium ICP could be generated up to 1900 W at the plasma gas flow rate of 15 L/min. Torch melting was not observed with any plasma gases with air cooling. Results of spectroscopic measurements of the emission properties and the plasma temperature of ICPs are presented.

Excitation/ionization process of aqueous solutions in high-power pulsed microplasma

Atmospheric ICP (Inductively Coupled Plasma) has been widely used for elemental analysis because of its excellent excitation/ionization ability. In recent years, target of elemental analysis has shifted to smaller amount samples such as nano-particles and bio-cells. However, conventional ICP source consumes too large amount of plasma gas and sample (∼1 mL/min). To realize efficient analysis of samples and high performance mobile elemental analysis system, we have studied and developed high-power microplasma source. With this device, stable plasma can be generated at a few watts of dc electric input power and with small amount of plasma gas (ca. 200 mL/min). However, input power was limited to a few watts because electrode will melt and damage. As a result, the plasma temperature and electron number density are not so high as that of ICP. Thus, the electrode must be protected from over heating to obtain sufficiently high analytical performance.

Spectroscopic characteristics of high power pulse operated multi-gas microplasma sourece for elemental analysis

In this study, we have developed a microplasma source for elemental analysis. A high power pulse driven microplasma device was developed and tested. Short (<1 mus) but high voltage (-2.5 kV) pulse is applied for plasma ignition and then long (-10 mus) and relatively low voltage (-0.5 kV) pulse is applied for excitation and ionization of analytes. As a result, the peak electric power of 40 kW was achieved and 1500 times higher emission intensity compare with DC discharge was observed. In addition, stable plasma can be generated using not only helium or argon, but neon, nitrogen, oxygen, air and CO2 gases. It was difficult to detect halogen elements by Ar-ICP because halogens has higher excitation potential. But, in this study, halogens could be detected with high sensitivity by helium plasma. Measurement results of small amount samples and spectroscopic characteristics of the microplasma will be reported.

Development of Xe and Sn discharge EUV light source

A high rep-rate, compact and low-debris xenon Z-pinch discharge system has been designed and fabricated as an EUV light source, in which a newly developed gas jet-type Z-pinch source is used. The discharge head has a coaxial double nozzle and diffuser. Xenon Z-pinch plasma that emits EUV light is produced in between the inner nozzle and the corresponding diffuser. An annular shell of a helium gas curtain produced by the outer nozzle is specially designed for shielding the debris and suppressing the inner gas expansion. In this work, in order to get higher EUV output power, a new pulse power supply system has been developed. This power supply delivers a current with amplitude of 22 kA, rise time of 110 ns and pulse duration of 260 ns to a low inductance load. In addition, a laser triggered discharge produced tin plasma light source has been developed. Experimental parameters such as electrode separation and laser irradiation power are varied to optimize EUV emission power. It is found that EUV emissions cannot be obtained when the laser irradiation power is too high.

Low Pressure Operation of Radially Convergent Beam Fusion Using Differentially-Pumped Ion Sources

Radially convergent beam fusion (RCBF) has been studied for practical use as a portable neutron/proton source for various applications such as landmine detection and positron emission tomography. In a conventional RCBF device using a glow discharge, the neutron/proton production rate is proportional to the cathode current because beam-background reactions are dominant in contrast with the original RCBF concept. However, since the neutron/proton production rate of beam-beam reactions is proportional to the cathode current squared, beam-beam reactions have a potential to increase the neutron/proton production rate in a high cathode current region. In this study, a new RCBF system using differentially-pumped ion sources was designed for the low pressure operation without the glow discharge. In the RCBF chamber, a cylindrical grid cathode is concentrically placed on the axis of a cylindrical mesh anode, and two ion sources are oppositely mounted around the mesh anode. The ion sources allow the RCBF device to be operated at a pressure of 10-4 Torr in the RCBF chamber, which is much lower than that of 10-1 Torr in the ion sources. Generated ions in the ion sources are extracted through each orifice by the pressure gradient and the extraction electric field, and then accelerated to the RCBF cathode. At first, a performance as differential pumping system and discharge characteristics of ion sources were investigated. Then, the neutron production rate at a lower pressure compared with that of a conventional RCBF device was measured. Neutron production rate at a pressure of 0.30 mTorr was proportional to the ion current to the power of 1.19-1.23. This implies that the fraction of beam-beam reactions was increased by the reduction of background pressure in the RCBF chamber.

D-D and D-/sup 3/He proton measurements of cylindrical radially convergent beam fusion

Summary form only given. Radially convergent beam fusion (RCBF) device is a compact fusion neutron/proton source with extremely simple configuration, high controllability, and hence high safety. It has been mainly studied for practical use as a portable neutron source for various applications such as landmine detection, and the results of previous studies indicate that the RCBF device has a high potential as a neutron source. On the other hand, however, the RCBF device as a proton source has not been investigated sufficiently. In this study, not only neutrons but also protons generated by D-D and D-3He reactions in a cylindrical RCBF device were measured for practical proton source. In order to detect protons, a solid-state detector (SSD) was used. However, there is a difficulty in applying the SSD to the RCBF device. The SSD can not discriminate protons from X-rays, which are produced simultaneously in the RCBF device. In addition, it is difficult to stop the X-rays with a metallic foil filter because of its high transmittance. Therefore, a new proton counting system based on magnetic deflection was designed and used to eliminate the X-rays. The system has three magnetic deflectors, which consist of a pair of neodymium magnets. The SSD position in this system was determined by a calculation of the deflected proton trajectory. At first, the cylindrical RCBF device was operated using only deuterium gas. Generated D-D protons of 3.03 MeV were measured with and without this proton counting system, and the count rate was compared with that of D-D neutrons. Then D-3He protons of 14.7 MeV were counted feeding not only deuterium gas but also helium-3 gas. By comparing D-3He proton and D-D neutron count rates, the optimal ratio of helium-3 gas to deuterium gas was obtained

Research of capillary Z pinch extreme-ultraviolet light source

A preliminary study of a tabletop multi-mode z-pinch x-ray souce is presented. The goal of development of this device was to obtain high densities and temperatures in plasmas of high atomic number elements with two different types of loads: vacuum spark and small (micronscale) wires. In the first mode, the device can be used for x-ray spectroscopic research and calibration of x-ray and vacuum ultraviolet (VUV) diagnostics instrumentation. In the second mode, single wire and x-pinch loads were applied. The device was developed on the basis of a W calibration source developed under a previous Sandia contract, and subsequently transferred to UNR. The existing system was substantially modified to lower the inductance and increase reliability. The system uses a railgap switch, a low-inductance vacuum interface, and a low-voltage (<25 kV), low-impedance, vacuum coaxial transmission line. Circuit modeling of the modified system predicted more than 100 kA into a plasma load from its DC-charged 3 microfarad, 25 kV capacitor bank, with a time to peak current of about 700 ns. This system is compact, and uses no transformer oil or deionized water. The total energy stored in the capacitors bank is up to 800 I with a charge voltage of up to 25 kV. The measured time to peak current is near 700 ns, and typical maximum current of 10&110 kA. The x-ray output energy, pulse duration, and x-ray images fram this plasma source were studied with PCD and XRD diodes and a time-gated pinhole camera.

Fundamental characteristics of pulse-operated helium inductively coupled plasma

Summary form only given. Since an inductively coupled plasma (ICP) has been introduced as an excitation and ionization source for trace elemental analysis, argon ICP has been widely used. However, argon ICP does not exhibit efficient performance for high ionization energy elements such as nonmetals, rare gases and halogens. According to Penning ionization mechanism, the ionization capability of plasma source is limited by the ionization and the metastable energy of the plasma gas species. Therefore, if helium ICP is developed, it is possible to ionize all elements effectively because helium has the larger metastable excitation energy (19.81 eV) than that of argon and the largest ionization energy (24.58 eV). We have generated and studied a stable helium ICP at the atmospheric pressure using a vortex flow enhanced torch. Though it is necessary for the high power drive (more than I kW) to derive high ionization efficiency, it can not apply because of a melting of the quartz torch. In this study, to overcome this problem, pulse-operated helium ICP, which is sustained low power (200-300 W) and applied high power pulse (more than 500 W) using amplitude modulation, is proposed and constructed (pulse frequency: 10-1000 Hz, pulse width: 25-2000 5s). The fundamental characteristics of the line emission intensity and the excitation temperature are measured for several degree of modulation.