Nadja Vogel

Resonant atomic interfero- and shadowgraphy of vacuum arc with gallium cathode

The mechanism of the emission of neutral atoms of the cathode material into the discharge gap of a microsecond low-current vacuum arc with a liquid Ga cathode has been investigated by the method of subnanosecond resonance laser interfero- and shadowgraphy. It has been shown that the cathode material vaporization has a pronounced nonstationary character and occurs both isotropically and in the form of constricted weakly ionized jets with the atom concentration in a jet over 10/sup 17/cm/sup -3/.

Interferometric diagnostic of picosecond laser ablation in air

Investigations of a spatial density distribution at the focus of an intense picosecond Nd:YAG laser pulse ( A = 1064 nm) near a metallic target in air have been performed by interferometry and absorption photography with high temporal and spatial resolution (50 ps. < I μm). An effect of microchanneling and an intense shock-wave formation in laser-produced plasma were observed. Estimations show that the current density in the microchannel is of the order of 10 10 A/cm 2 . followed by the generation of a self-magnetic field in the narrow channel having a magnitude of 7 7 MG. When the power density of laser radiation was reduced to a value of the order of 9 x 10 9 w/cm 2 a significant change in electron density distribution has been estimated: a shock wave with a strong boundary front vanished. an electron density failed under the value of the order of 10 18 cm 3 .

Measurement of cathode spot parameters with pulsed laser diagnostics

The cathode spot formation within first 22 ns was investigated by laser absorption photography and ps-pulse interferometry. The discharge was initiated between W-, Ag-, AuNi-, Pd- electrodes with cathode-anode distance below 100 micrometers , the arc duration was some milliseconds and arc current 5 A. A ps-pulse holographic interferometer and momentary absorption photography enabled us to determinate spatial-temporal density distributions in the ignition phase of the cathode spot. An absolute electron density value of order of 3 - 1026 m-3 has been determined indicating high conductivity values of the metal vapor plasma. Present measurements show that cathode spot plasma is essentially non- ideal and verify theoretical calculations resulting in an ionization potential decrease in dense cathode plasmas.

The X-ray emission from vacuum discharge micro fragments at comparatively low applied voltages

The temporal evolution of X-ray emission of laser-induced discharges was investigated by means of a picosecond X-ray streak camera. Point-like structures with a divergence of order 10/sup -7/ and thin hot layers of intense X-ray radiation with life time from 30 ps to 1.5 ns in spectral range 100 eV-10 keV have been found in a comparatively low voltage vacuum discharge (U=150 V-2.7 kV) initiated by picosecond laser beam. Computer simulation shows that such X-ray generation is connected with a matter transition into extreme states when in local microvolumes of dense current carrying plasma the pressures can exceed values of 5 Mbar and the specific internal energies /spl epsi//spl ges/1 MJ/g.

Cathode spot energy transfer simulated by a focused laser beam

Minimum conditions for the formation of surface craters by laser irradiation were studied experimentally and theoretically for various metals. The critical power density for crater formation within 20 ns was about 10/sup 11/ W/m/sup 2/. It is therefore concluded that crater formation by ion bombardment requires an ion current density on the order of 10/sup 10/ A/m/sup 2/. >

Time resolved resonant laser diagnostics of the low current vacuum arc cathode spot

The resonant laser diagnostics combined with high speed IMACON 468 frame/streak camera was used as a technique for data acquisition. The experiments were performed with an arced vacuum gap formed by the capillary-type liquid-metal cathode and the plane anode in conditions of high oil-free vacuum. The evolution of observable cathode spot plasma is analysed in terms of cyclicity of the cathode spot operation.

Subnanosecond resonance laser diagnostics of the cathode spot region of low-current vacuum discharge

In this paper, the supplying of neutral atoms of the cathode material into the discharge gap at low-current microsecond vacuum arc with liquid Ga cathode was investigated employing the method of subnanosecond resonance laser diagnostics. It has been shown that vapours ejection has an essentially nonstationary character and it occurs both isotropically and in the form of contracted low-ionized plasma jets with atomic concentration of more than 10/sup 17/ cm/sup -3/.

The X-ray radiation from cathode spot fragments in laser-induced vacuum discharges

The temporal evolution of X-ray emission of laser-induced discharges was investigated by means of a picosecond X-ray streak camera. Point-like structures with small divergence and thin hot layers of intense X-ray radiation with life time from 30 ps to 1.5 ns in a spectral range 100 eV-10 keV have been found in a comparatively low voltage vacuum discharge (U/spl ap/150 V-2.7 kV) initiated by picosecond laser beam. The radiation of laser induced breakdown was investigated just after breakdown as well as with a delay time (up to 20 ns) relative to the ignition point by the laser beam in order to eliminate the X-ray radiation coming from the laser-produced plasma.

The dynamic of matter transition into extreme states initiated by high power micro beam of heavy ions

This paper deals with numerical investigation of interaction of short pulse (about of 100 ps) intense (with intensities up to 3/spl times/10/sup 16/ W/cm/sup 2/) micro beams of heavy ions with condensed matter. It had been established, that the extreme states of matter with compression in Gbar pressure range can be produced by the beam-generated strong shock waves. The original scheme of initiation of controlled thermonuclear fusion in micro volume of gold target with D-T mixture is considered where two colliding plasma fluxes (shock waves) are generated using only one ion micro beam.