V. I. Tumanov

ABLATION OF POLY(METHYL METHACRYLATE) BY A SINGLE PULSE OF SOFT X-RAYS EMITTED FROM Z-PINCH AND LASER-PRODUCED PLASMAS

The efficiency of ablation induced in poly(methyl methacrylate) (PMMA) by single soft X-ray pulses emitted from Z-pinch and laser-produced plasmas was determined. X-ray ablation of PMMA was found to be less efficient than that of teflon (PTFE). Nonthermal effects of the radiation on the polymer structure play a key role in the mechanisms of the ablation, i.e. the ablation can be explained by the formation of radiation-chemical scissions of the polymer chain followed by blowoff of low-molecular fragment fluid into the vacuum. The most promising application of this phenomenon seems to be micropatterning/micromachining.

Study of the plasma in a preformed Z-pinch constriction

The development of a preformed constriction in cylindrical agar-agar loads at currents of up to 3 MA is studied experimentally. The loads 3–5 mm in diameter have a mass density of 0.1 g/cm3 and are filled with different materials. Due to the implosion of the constriction to a minimum size of 40–70 µm, a hot dense plasma (with the electron density ne=1022 cm−3, electron temperature Te=0.8–1.5 keV, and ion temperature Ti=3–12 keV) is produced. It is found that the ion temperature substantially exceeds the electron temperature. The lifetime of the high-temperature plasma determined from the FWHM of a soft X radiation (SXR) pulse is shorter than 5 ns, the radiation power of photons with energies of ≥1 keV is higher than 0.5×1010 W, and their total energy attains 50 J. High-speed photography in the VUV, SXR, and optical spectral regions indicates the protracted generation of the high-temperature plasma. Calculations by the two-dimensional ideal MHD model of the Z-pinch show that the most important consequence of the protracted plasma generation in the constriction region is that the current is intercepted by a freshly produced plasma. In the course of plasma generation, the current near the axis inside the region of radius 50 µm is at most one-half of the total current. After the plasma generation comes to an end, almost the entire current is concentrated in this region for several nanoseconds; this process is accompanied by a sharp increase in the plasma temperature.

Diagnostic arrangement on S-300 facility

A set of experiments on neutron and x-ray generation was performed on the S-300 facility for the last few months. The S-300 facility is a pulse generator with electric current achieving 3.5 MA, voltage 400–500 kV, and rise time ∼100 ns. (Chernenko et al., Proc. of the 11th International Conference of Power Particle Beams, Prague, 1966, p. 154). It is designed as van eight-module machine transmitting electromagnetic power to the low-inductive load through the vacuum line with self-magnetic isolation. Diagnostic techniques and methods on S-300 used are described in this article. Ten-channel polychromator is used for the soft x-ray and vacuum ultraviolet bands (50–500 eV) measurements with spectral resolution of 5%–20% and time resolution less than 2.5 ns. Radiated power measurements in the region of 0.1–10 keV are performed by vacuum x-ray diodes and semiconductor detectors equipped with different filters. Curved crystal x-ray spectrography is intended for plasma density, electron, and ion temperature evalu...

Ablation of PMMA, PTFE, and Si by soft x-rays emitted from hot dense plasma

The efficiency and threshold of ablation of polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), and monocrystalline silicon by single pulses of soft x-rays emitted from Z-pinch, plasma-focus, and laser-produced plasmas were investigated. The Z-pinch was driven by the S-300 pulsed-power machine (Kurchatov Institute, Moscow) and the plasma focus was realized in the PF-1000 machine (Institute of Plasma Physics and Laser Microfusion, Warsaw). Higher temperature plasma than with the discharge plasmas was obtained by focusing the near-infrared beam from the PALS high-power iodine laser system (Czech Academy of Sciences, Prague) on the surface of a metallic slab target. The role of nonthermal processes in x-ray ablation was evaluated. Possible ways to use x-ray ablation for micromachining are discussed.

Dynamics of the wire array implosion

The tungsten wire liner is accelerated to the Al wire of 120 mm in diameter located in the axis of the array liner at 3 MA maximum current. The pinch phase was studied by the streak and pinhole cameras, spectrograph, x-ray and visual frame and schlieren diagnostics. The spectral, temporal and spatial resolving records confirmed only a small stabilizing role of the wire in the pinched phase of the implosion.

Dense Z-pinch neck development dynamics investigation on S-300 generator

The experimental investigations of neck development dynamics in the Z-pinch with 0.1 g/cm/sup 3/ density were carried out on an 8-module pulsed power generator, the S-300 (4 MA, 100 ns). The objective of these experiments was a study for the possibility of obtaining plasmas with extra-high parameters in the Z-pinch neck region, corresponding to the fusion ignition conditions.

Concept of the high-energy photon emission from the wire array Z-pinch

Z-pinches are the laboratory sources of x-rays offering a large variety of diverse applications. As a discharge load, the liners and the fibers are often used.