M. Ripa

Comparison of computed and measured parameters of a driver for fast capillary discharge

The authors were attracted by numerous applications of coherent soft X-rays and decided to build a fast capillary discharge, despite it is generally understood as a relatively sophisticated apparatus. From the beginning they paid great attention to its design: they performed a lot of modelling and optimisation. The present paper aims at comparison of the designed (computed) parameters with the measured value.

Amplification of spontaneous emission of neon-like argon in a fast gas-filled capillary discharge

The evolution of the CAPEX facility and its basic diagnostics are described. The experiments carried out in the last modification of this facility accomplished with the demonstration of amplified spontaneous emission of neon-like argon (Ar8+) at the wavelength 46.88 nm. The first version of the facility, CAPEX1, operated with a plastic capillary and had a short high-power passive prepulse and an imperfect gas-filling system. In the second version, CAPEX2, a ceramic capillary was used, the prepulse amplitude was lowered, and the gas-filling system was improved. In the third, most successful version, CAPEX3, the capillary bending was reduced, a longer external prepulse was used, and the gas-filling system was further optimized. For each version, results of X-ray measurements are presented and interpreted.

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.

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.

Spectroscopic study of 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 a ceramics capillary for former plastic one, in remarkable reduction of the pre-ionization current, and in change of Ar filling and pumping geometry. The soft X-ray spectroscopic measurements prior to and after this reconstruction are described. It is shown that the reconstruction resulted in appearance (under certain conditions) of the strong spectral line at the wavelength of laser transition (46.9 nm) that dominates the spectrum even at exposition 50 ns.

Axial particle and soft X-ray emission from the fast capillary discharge

Measurements with a pair of deflecting electrodes and solid-state track detector indicated highly collimated intense particle stream from the fast capillary discharge. Also positively biased collector behind the deflecting electrodes registered some peaks belonging to ions. On the other hand, measurements with Faraday cup were not successful due to giant photoemission. Amplified soft X-ray spontaneous emission has not yet been found.

Influence of initial and boundary discharge conditions on soft X-ray amplification in the fast gas-filled-capillary discharge

Summary form only given. It is just ten years since it was experimentally shown by J.J. Rocca (Colorado State University) that gas-filled-capillary discharges are capable to lase in soft X-ray region, first on Ne-like argon (/spl lambda/=46.9 nm), later on Ne-like sulfur (/spl lambda/=60.8 nm), and Ne-like chlorine (/spl lambda/=52.9 nm). However, transition to shorter wavelengths turned to be very difficult even with new powerful apparatus designed for this purpose. Since that time many laboratories have tried to repeat amplification on argon, if nothing else. Only when the role of pre-pulse had been at least partly understood the first amplifications on argon outside Colorado State University were achieved. Recently we summarized this effort and presented our method of internally generated pre-pulse (by capacitive/resistive coupling of the capillary high-voltage electrode with the pulse forming line). Simultaneously we offered our explanation of lower and upper pre-pulse limit (based on different conductivity profile (along the capillary radius) for the fully and partly ionized pre-plasma). In our present paper, we describe our experiments with externally generated prepulse and with different methods of capillary filling by the gas. An influence on soft X-ray radiation is studied with the help of a soft X-ray PIN diode (time-development of the emitted soft X-ray radiation) as well as of a soft X-ray spectrograph (time resolved soft X-ray spectra). It is expected that more precise conditions for reaching population inversion and amplification in the soft X-ray region will be given.

Spectroscopic determination of turbulent Langmuir fields in a REB-heated plasma

Spectroscopic measurements of the Stark component of plasma emission lines have proved to be an efficient tool at determining the strength of turbulent Langmuir fields excited in a plasma by an intense relativistic electron beam (REB). Recently, at the REBEX experimental facility, H/sub /spl alpha// and H/sub /spl beta// line profiles with excellent spectral, temporal and spatial resolution have been obtained by means of an advanced imaging spectrograph combined with a gated image intensifier. In this paper we report model calculations of the H/sub /spl alpha// line profiles, which make it possible to distinguish the Stark component of the investigated lines from the strong Doppler background observed in the experiment, and, thus, to estimate the level of the Langmuir turbulence in the REBEX plasma.

Observations of REB-induced plasma turbulence by using high-resolution imaging spectroscopy

We report the first use of the high-resolution imaging spectroscopic apparatus for diagnostics of a relativistic electron beam (REB)-heated plasma, the excellent spectral, spatial and temporal resolution of which enabled us to obtain precise profiles of plasma emission lines, which are suitable for interpretation within the framework of existing theoretical models of the beam-induced plasma turbulence.