摘要:

In Plasma Focus devices operated with pure nitrogen, neon or argon (Z ≤ 18) with pinch current from 200 to 400 kA the emitting region is a column with several 100 &mgr;m in diameter and several mm in length (column mode). ForZ ≥ 18micropinches are observed. Usually micropinches and column emission is examined independently. Small Plasma Foci feature both modes simultaneously. In this paper the transition regime between column and micropinches is investigated with particular regard toZ=18(argon). Peculiarities in the emitted spectra are interpreted by the interaction of simultaneous existing column and micropinch plasma.

ISSN:0094-243X    

DOI:10.1063/1.2949171

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Soft X‐radiation mainly emitted by ‘micropinches’ is generated in the driver SPEED 2 by injection of heavy rare gases (e.g. argon) into a discharge of pure deuterium. It has been proved by a fast diagnostic in the VUV range based on a microchannelplate, that the short‐living micropinches with sub‐mm‐size are developing where neckings in the plasma column can lead to local radiative collapses as predicted by the collapse model.Spectra of the whole pinch column in the wavelength range close to the ArXVII‐resonance line (&lgr; = 0.3948 nm) were used to improve temperature and density determination. The results of computer simulated fits using a Monte‐ Carlo‐method for the photon transport including effects of optical density for evaluation of plasma parameters (electron density 1028m−3… 1029m−3, temperature 1 keV … 1.5 keV) agree well with estimates based on the corresponding model. Spatially resolved spectra reveal that about 90 &percent; of the line radiation stems from micropinches.The energy output in small channels of the water window is up to 45 Joules per discharge assuming an isotropic emission.

ISSN:0094-243X    

DOI:10.1063/1.2949172

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Gas puff target experiments as performed with the POSEIDON plasma focus (PF) device enable partial decoupling of the initial PF phases from the final compression phase. The influence of deuterium and argon gas puffing on pinch dynamics, neutron and X‐ray emission in 135 kJ discharges was investigated. Various diagnostic techniques including optical streak and framing as well as Schlieren and X‐ray pinhole photography, neutron, X‐ray and electron beam detection were applied. It was found that a large plasma focus can be operated in a controlled way with the injection of an additional gas target. Gas puffing causes a rise in the level of turbulence and results in an increased tendency of hot spot formation. With deuterium gas puffing the neutron yield could be increased by at least a factor of 1.3.

ISSN:0094-243X    

DOI:10.1063/1.2949173

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Heavy gas admixtures of up to several percent to the basic deuterium filling of the DPF78 plasma focus (28 kJ, 60 kV,&tgr;/4 = 1.5 &mgr;s) results in the formation of micropinches inside the 25 mm long pinch column. Dimensions of the micropinches, which range from 20 to 500 &mgr;m, were determined from X‐ray pinhole pictures and space resolved X‐ray spectra by means of the penumbra method. PIN‐diode array measurements have revealed that micropinches occur during a period of about 50 ns near the time of current maximum of 0.9 MA. Space resolved line emission of helium‐ and hydrogen‐like argon from single micropinches was measured side‐on and end‐on using two quartz crystal spectrometers. Observed Doppler shifts up to 8 mÅ between spectra of adjacent micropinches indicate velocities of up to 6·105m/s. Temperatures in the keV range and densities up to 3·1021cm−3were determined from the X‐ray spectra.

ISSN:0094-243X    

DOI:10.1063/1.2949174

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Micropinch formation is described as local collapses initiated in necked regions of a pinch plasma column by enhanced plasma radiation and particle outflow [1]. While the final stage of this formation is well known from soft X‐ray measurements (&lgr; < 2 nm) [2] the local and temporal conditions of the initial phase has not yet been clarified.Therefore a fast (ns) four frame pinhole camera system has been applied to the SPEED 2 plasma focus in order to investigate the micropinch formation process in a wavelength range from VUV to the soft X‐ray (0.4 nm).The experimental setup consists of a configuration of four pinholes each imaging the pinch plasma. These pictures are taken with a special microchannel plate which is divided into four independent sectors. Each sector can be independently gated by a short triggerpulse (FWHM 5 ns) leading to an exposure time of a few nanoseconds. Therefore four differently time delayed pictures are taken during a single discharge.Different filters allow to determine the spectral range of the detected radiation (4 nm – 8 nm) and to observe single micropinches (0.4 nm) in the plasma column. Comparing the images with time integrated soft X‐ray pinhole pictures it is realized that local neckings (m=0 type) are necessary but not sufficient conditions for micro‐pinch formation. It seems that only those neckings lead to micropinches where the plasma density and temperature are high enough to intensively emit line radiation.For details compare: P. Ro¨wekamp, F. Schmitz et al. “Spectral Investigations of Micropinches in the SPEED 2 Plasma Focus”.

ISSN:0094-243X    

DOI:10.1063/1.2949176

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Angular and energetic characteristics of the reacting deuterons were evaluated using a fitting procedure applied to the neutron fluence anisotropy data measured on different axial emissive zones of a plasma focus device. A relative large angular distribution and medium energy values (50÷100 keV) characterize the forward escaping deuterons from pinch zone, which produce ≈60&percent; from total neutron yield. In the pinch region the dominance of the reacting deuterons with large radial velocity components and a backward moving deuteron component were put into evidence.

ISSN:0094-243X    

DOI:10.1063/1.2949177

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Experiments on the implosion of multilayer cascade light liners were carried out on the IMRI‐3 (0.3 MA,T/4 = 700 ns) and IMRI‐4 (0.24 MA, 900 ns) installations. It has been demonstrated that when using three sequantial cascades, owing to the suppression of the Rayleigh‐Taylor instability, the ratior10/rf ∼ 70(wherer10is the initial radius of the outer cascade) can be achieved. The input energy density and the X‐ray output therein h are observed to increase (respectively, up to 1 kJ and 200 J for Kr). Measurements performed with the use of a grating spectrograph for different gases have shown that the temperature in the plasma column formed in liner implosion increases with atomic number.

ISSN:0094-243X    

DOI:10.1063/1.2949179

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Thin bubbles (&dgr; < 1 &mgr;m) are imploded by a coaxial snowplough. The current sheet remains separated from the dense part of the bubble‐liner, the latter compressing a deuterium plasma to ion densities> 1020 ions/cm3. Cylindrical and quasi‐spherical implosions are obtained. Results of Schlieren and soft X‐ray photography are reported. The application of the spherical implosions to the generation of an intense hohlraum radiation and to fibre super‐pinches are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2949180

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

PegasusIIis the upgraded version of Pegasus, a pulsed power machine used in the Los Alamos Above Ground Experiments (AGEX) program. The goal of the program is to produce an intense (>100 TW) source of soft x‐rays from the thermalization of the KE of a 1 to 10 MJ collapsing plasma source. The radiation pulse should have a maximum duration of several tens of nanoseconds and will be used in the study of fusion conditions and material properties. This paper addresses z‐pinch experiments done on a capacitor bank where the radiating plasma source is formed by an imploding annular aluminum foil driven by the JxB forces generated by the current flowing through the foil.

ISSN:0094-243X    

DOI:10.1063/1.2949181

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A number of z‐pinch experiments have been conducted at Los Alamos on the Pegasus capacitor bank in which 2‐cm high, 5‐cm radius, thin foil loads were imploded with currents in excess of 3 MA. Two‐dimensional (2‐D) radiation mag‐netohydrodynamic (RMHD) simulations of these implosions have been performed to model the implosion dynamics and subsequent generation of an x‐ray pulse. Comparisons of the simulation instability development with visible light framing camera photographs show good agreement in wavelength and amplitude and illustrate the instability evolution from short to long wavelengths and a final disruption of the imploding plasma shell. The calculations also show good agreement with experimental timing and measured current and voltage waveforms, and also reproduce features characteristic of the x‐ray output. These include a broad pulsewidth, and the presence of multiple peaks and small time scale structures, features which cannot be reproduced by one‐dimensional (1‐D) models. X‐ray spectra obtained from the calculated pinch also reproduce qualitative features in the measured spectra.

ISSN:0094-243X    

DOI:10.1063/1.2949182

出版商:AIP    

年代:1994

数据来源: AIP