摘要:

We report observations of a 7 &mgr;m diameter, 20 mm long carbon fibre Z‐pinch driven by a pulsed power generator delivering 85–100 kA with a 50 ns (10–90 &percent;) rise time. Time integrated soft x‐ray pinhole camera images show that the emission is from a series of bright spots distributed non‐uniformly along the pinch. The spots are about 100 &mgr;m in size and at a temperature of about 100 eV. The tenuous plasma between the spots is at higher temperatures of about 150 eV. x‐ray streak photography shows that bright spots do not emit simultaneously or in any particular spatial sequence. The first bright spot emits usually at about 30 ns. Each spot emits for a time less than 1 ns. Harder x‐rays are emitted from the anode. In all cases the bright spot emission is seen to occur only during the harder x‐ray pulse. Two pulses are seen. The first of 20 ns duration is observed at current initiation and the second 30–100 ns long occurs later at about 20–25 ns. Analysis of the x‐ray emission from the anode shows that the first pulses is consistent with a 150 keV, 3 kA electron beam and the second pulse with a beam of about 20 keV, 20 kA. The bright spots are also seen in optical streak photographs. The emission is also transient ‐ the duration of the brightest emission is of the order of 1 ns ‐ and the bright spots move axially. They sometimes bifurcate, occasionally combine. Observations with a 7 ns ruby laser show that the fibre pinch expands radially with a velocity>2.5 104 ms−1. Islands of high density form at about 8 ns. These islands are spatially coincident with the x‐ray bright spots and persist for a longer time (30 ns to 50 ns). The radial acceleration of the pinch becomes inward at 8 ns, suggesting that Rayleigh‐Taylor instability may be responsible for the instability.

ISSN:0094-243X    

DOI:10.1063/1.2949196

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have studied the development of instabilities, primarilym = 0modes, in CD2fiber z pinches. Two simultaneous optical diagnostics have been used in order to obtain an unambiguous picture of the dynamics. The first is two‐dimensional interferometer using a short‐pulse laser. The second is multi‐frame two‐dimensional schlieren/shadowgraphy camera. The interferometer serves as a check on the schlieren/shadowgraphy camera helping to overcome uncertainties in interpretation of the schlieren/shadowgraphy results. An x‐ray polychromator is used to measure electron temperature. Growth of the unstable modes is compared with predicted growth rates. There are indications that some forms of current prepulse can have a significant effect on the long‐term development of instabilities.

ISSN:0094-243X    

DOI:10.1063/1.2949197

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Z‐pinch plasmas created from fibres are less prone to macroscopic instabilities than predicted by ideal MHD theory. However, solid fibre experiments at the pulseline KALIF (2 MV, 900 kA) gave disappointing results with respect to driver‐load coupling and pinch plasma confinement. High power discharges led to current leaks and plasma expansion presumably due to lacking initial conductivity and compressibility. Therefore two alternative schemes have been investigated: Solid fibres were replaced by styrofoam fibres with about 1 &percent; solid density and plasmajets of a deuterium‐argon mixture. Analyses of the experimental results showed no major differences between styrofoam and solid fibres. However, the plasmajet experiments resulted in significant improvements with respect to the initial discharge behaviour. Unfortunately, severe pinch disruptions about 40 ns after discharge initiation prevented pinch formation and confinement. The high electric field of the pulseline KALIF and the low density of the jet plasma (E/n > 10−15 Vm2) resulted in runaway electrons and plasma erosion rather than in magnetic confinement to the pinch.

ISSN:0094-243X    

DOI:10.1063/1.2949198

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Universal formula for total power losses by a bounded medium due to emission of electromagnetic waves, both transverse and longitudinal, by free/bounded electrons in the regimes of nonlocal (non‐diffusion) heat transport in continuous/discrete spectra is obtained. The derivation is based on a method which generalizes the “escape probability method” in the theory of radiative transfer in resonance atomic lines. An analytic description for the deviations from Maxwellian distribution, caused by the transfer of intense radiation, is obtained within the framework of self‐consistent kinetic description of plasma electrons and wave intensity.

ISSN:0094-243X    

DOI:10.1063/1.2949199

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have developed a ray‐tracing code which enables us to calculate the spectrum from a 2‐D source simulation and compare directly with experimental data. This code also allows us to study the various spectral components which can potentially be used to determine the source from measured data.

ISSN:0094-243X    

DOI:10.1063/1.2949202

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Using Saturn as a driver, we are pursuing both photoresonantly pumped and photoionization/recombination lasers. Our lasing targets are gas cells with thin windows that are pumped by a z pinch 2 cm away radiating 10 TW. In both schemes the lasant and gas fill is neon. To increase our chances of measuring the resonantly photopumped lasing transition we have introduced potassium into a sodium z pinch and have eliminated oxygen from the gas cell windows. We have measured the spatial dependence of ionization balance across the gas cell, and this measurement is consistent with propagation of a shock front across the gas cell target. We have measured blue‐shifted satellites to several Li‐like neon transitions that may indicate return‐current driven jetting a high 1.5e8 cm/sec velocity. Using a gold z‐pinch we have shown that keV radiation is necessary to excite the He‐like lines of neon. An attempt at a single shot gain measurement also indicates that radiation is not the only source of gas cell heating.

ISSN:0094-243X    

DOI:10.1063/1.2949203

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

X‐ray spectroscopy with high spectral (up to&Dgr;&lgr;/&lgr; = 10−4) and spatial resolution (up to microns) is discussed. Devices based on crystals, difraction and Bragg‐Fresnel elements and there application in Z‐ and X‐pinches experiments are observed.

ISSN:0094-243X    

DOI:10.1063/1.2949204

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Experiments at the high current (up to 2.5 MA) Z‐pinch facility “ANGARA‐V‐1” were performed with Al, Cu, W and CD2wires and outer Ar, Xe and D2gas shells (p=0–1.8 atm). Single shot soft X‐ray spectra were recorded by means of a curved X‐ray cristal spectrograph in a wide spectral wavelength interval. The characteristic X‐ray emission lines of H‐, He‐ and Li‐like ions were analysed with the elaborated spectra simulation codes “SAT” and “META”. The electron temperature Te, density neand ionisation temperature Tzwere determined with respect to the non‐equilibrium plasma state, optical thickness and electron beam excitation. Additional information about the plasma developement was obtained from the emission lines of Na, Cl and Si, which were added to the wire material for diagnostic purposes. For Ar we obtained electron temperatures up toTe ∼ 1.2 keVand electron densities of aboutne ∼ 1021 cm−3, for AlTe ∼ 600 eV,ne ∼ 3·1020 cm−3. A low ionisation temperature in practically all discharges indicates non‐equilibrium states of overheated plasmas. Information about the plasma geometrie was obtained from pinhole framings in different spectral ranges. Discharges with copper wires showed a strong decrease of the hot spot creation with outer gas shells. Pinhole framings were analysed with a high resolution by means of a topographical method.

ISSN:0094-243X    

DOI:10.1063/1.2949205

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The influence of highly energetic electrons and nonstationarity on the H‐like resonance line and its adjacent He‐like satellites 1s21‐2121′ are investigated. Both of this effects result in an additional population (besides the dielectronic capture channel) of the autoionising 2121′‐levels through the excitation from the metastable levels of single excited He‐like ions. This channel can be rather strong especially for double excited levels with low rates of dielectronic capture, which are widely used for density diagnostics. It is shown, that the neglection of the non‐equilibrium plasma state and the excitation by highly energetic electrons can result in serious overestimations of the electron density and temperature. Fully time dependent simulations are carried out for an experimental aluminium spectrum from a low inductance vacuum spark. We show that effects of highly energetic electrons and nonstationarity provide electron temperatures two times lower and electron densities an order of magnitude lower than simulations based upon thermal‐equilibrium interpretations.

ISSN:0094-243X    

DOI:10.1063/1.2949206

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

There are presented hollow cylindrical gas‐puff plasmas of electrical discharges at GPX device (200 kA, 40 kV, 1&mgr;s, Ne/Ar‐mixture) experimental results. Investigation of plasma with time and spatial resolution in wide spectral range was enabled by the set of diagnostics. Plasma processes were investigated in visible and IR light by frame and streak cameras, in XUV by transmission grating spectrograph and XRD, in sort X‐rays by convex and spherically bent crystal spectrograph, X‐ray crystal microscope, pin‐holes, pin‐diodes. Plasma parameters (ne = 1019–1022 cm−3,Te = 0.2–1.3 keV) were controlled by spectroscopic methods using H‐ and He‐like Ne and Ar spectra. Kink instability and hot spots were observed simultaneously in maximum X‐ray emission regimes. Also argon K&agr;line emission from plasma was observed. Plasma stabilization methods are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2949207

出版商:AIP    

年代:1994

数据来源: AIP