O. Frolov

Design of a laser-triggered driver for fast capillary discharge

We are developing a new upgraded capillary discharge device. The assembled set-up consists of a Marx generator, a pulse forming line, a gas-filled laser-triggered spark gap and a ceramic capillary. The special attention has been paid to the design of the spark gap. The laser triggering of this spark gap ensures a very low jitter in comparison with the present capillary discharge device CAPEX, where the main spark gap works in a self-breakdown regime. The description of the assembled apparatus, the main predicted parameters of the designed device (such as capillary current, capillary current rise-rte, and/or voltage at the end of pulse forming line) are presented.

Soft X-ray radiation of fast-capillary-discharge CAPEX 2

The paper reports on technological modifications of the capillary discharge experiment CAPEX, especially in capillary region. A temporal evolution of axial soft X-ray radiation and a spectroscopic measurement in the soft X-ray region on the modified capillary are presented as well. The strong spectral line at the wavelength of laser transition (Ne-like Ar, γ=46.9 nm) was observed.

Wire Exploding in a Focus of Converging Cylindrical Shock Wave in Water - Introductory Remarks

It is expected that, just as the proximity of a wall stabilizes a Z-pinch in a capillary, the proximity of a wall (solid or liquid) can also stabilize an exploding wire placed in a capillary or in liquid (water), the density of which can be further increased by a suitably focused shock wave. A wire explosion will be used in our new apparatus CAPEX-U (current amplitude 100 kA, quarter period 70 ns) with free optical axial access to both (high voltage and ground) electrodes and with a four-channel laser- triggered main spark gap. As a driver for converging cylindrical shock waves in water a separate test apparatus was designed and assembled: a strong acoustical wave will be generated at the cylindrical chamber-surface (covered by porous ceramics) by a multi-streamer corona-like discharge that burns to a co-axial cylindrical mesh/foil electrode. Expected pressure amplitude at the axis approaches 1 GPa. Applications of wire explosion in the focus of a cylindrical shock wave in water to inertial confinement fusion as well as to soft X-ray lasers will be briefly mentioned.

Application of EUV optics to surface modification of materials

We report results of experiments connected with surface modification of materials with an intense extreme ultraviolet (EUV) laser beam. Irradiated by the laser beam from a discharge-plasma EUV source (with wavelength of 46.9 nm) based on a high-current capillary discharge driver, the samples have been investigated by atomic-force microscope (AFM). The laser beam is focused with a spherical Si/Sc multilayer-coated mirror on polymethylmethacrylate (PMMA), gold-covered- PMMA and gallium arsenide (GaAs) samples. It turned out that desorption and ablation regimes, which are observed in all these cases strongly depends on substrate materials.

A laser-triggered driver for fast capillary discharge device

We are developing a new upgraded capillary discharge device. The assembled set-up consists of a Marx generator, a pulse forming line, a gas-filled laser-triggered spark gap and a ceramic capillary. Special attention has been paid to the design of the spark gap. The laser triggering of this spark gap ensures a very low jitter in comparison with the present capillary discharge device CAPEX, where the main spark gap works in a self-breakdown regime. The description of the assembled apparatus, the main predicted parameters of the designed device (such as capillary current, capillary current rise-rate, and voltage at the end of pulse forming line) are presented

Interactive system for the interpretation of atomic spectra

A method described in this paper enables the simplification and specification of the process of interpreting some spectroscopic measurements. Tabulated spectroscopic data are transformed into the form that provides a clear idea of mutual proportions of spectral line intensities of the given element depending on the selected temperature.

Excitation and Radiation of Highly Ionised Ions in the Fast Gas‐Filled‐Capillary Discharge

The capillary experiment CAPEX was reconstructed to approach conditions suitable for creation of population inversion in Ne‐like Ar. The reconstruction consisted in substitution of ceramics capillary for former plastic one, in remarkable reduction of pre‐ionisation current, and in change of Ar filling and pumping geometry. The soft X‐ray spectroscopic measurements were performed with survey flat field spectrograph. It is shown that under certain conditions the strong spectral line at the wavelength of laser transition (46.9 nm) appears and dominates the spectrum even at exposition 50 ns.

Pre-discharge - one of the key conditions for soft X-ray amplification in the fast gas-filled-capillary discharge

Summary form only given, as follows. The most exciting feature, why capillary discharges are a subject of interest at present, is their potential to lase. This was proved by J. J. Rocca (Colorado State University), who not only demonstrated lasing on Ne-like argon (/spl lambda/=46.9 nm), Ne-like sulfur (/spl lambda/=60.8 nm), and Ne-like chlorine (/spl lambda/=52.9 nm), but also achieved a saturation limit on argon.

Ablation-erosion analyses of various fusion material surfaces and developments of surface erosion monitors for notification of fusion chamber maintenance times, as an example: Visible light transparent SiC and up-conversion phosphors applied to plasma facing surface structures, useful for versatile purposes to protect and diagnose fusion chambers and so on

Two kinds of pulsed lasers in Japan and Czech Republic were used to irradiate various sample materials to investigate the surface erosion thresholds under very hazardous environments including nuclear fusion chambers. The first was ArF laser in ILT and the second was XUV laser in IPP. These data were in-cooperated with our former data to build up our material strength data for our succeeding applications of various materials to a variety of fields. As an example, we proposed surface erosion monitors to notice the fusion chamber maintenance times with which the facilities can be protected from the collapses under very severe operation conditions. These kinds of monitors are expected to be useful for future different kinds of mechanical structures not only for the fusion chambers but also various chambers for many purposes. Special upconversion phosphors are also newly proposed to be used as the candidate materials to measure the thermal inputs onto the front surfaces of the armor structures. Optical transparent SiC was also newly tested to enrich our data base for our future diagnostic and protection possibilities.

Spontaneous and artificial direct nanostructuring of solid surface by extreme ultraviolet laser with nanosecond pulses

Nanostructuring can be either spontaneously appearing (such as laser-induced periodic surface structures, and diffraction patterns – for example, in windows of grid proximity-standing at the ablated target-surface) or artificially created (like – as we hoped – interference patterns) that can be in some extend controlled. Due to that a new interferometer (belonging to wave-front division category) with two aspheric mirrors has been developed. Each of these mirrors reflects approximately one half of incoming laser beam and focuses it into a point image. Both focused beams have to intersect each other, and in the intersection region an interference pattern was expected. However, the first tests showed that some other spontaneously appearing interference pattern with substantially larger fringe-pitch is generated. The origin of this idle interference pattern is discussed.