摘要:

This paper describes the vacuum Czerny–Turner spectrometer with a 1.33 m focal length installed on the RFX fusion experiment. The optics are coated with MgF2and the image intensifier, protected by a vacuum sealed MgF2window, features a dual photocathode system, CsTe on one half and S20 on the other; thus the instrument covers efficiently the wide spectral range from the MgF2limit to the near infrared. Sensitivity at short wavelengths is limited by the reflectance of mirrors and the transmittance of the MgF2window. The detector is completed by a fast optical multichannel analyzer whose 1024 photodiodes can be read out in a time of 250 &mgr;s. The instrument can also be operated in a duochromator mode by deflecting the diffracted beam onto a second detector system, where two photomultipliers are applied to two exit slits, one fixed and the other remotely movable in such a way that the intensity ratios of two lines can be monitored for diagnostic purposes. Some examples of obtained spectra illustrating the instrument performance and comprising first results from the RFX plasma are presented.

ISSN:0034-6748    

DOI:10.1063/1.1143425

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Video images with 2 &mgr;s exposures of the Li+emission in Li pellet ablation clouds have been obtained in a variety of Tokamak Fusion Test Reactor tokamak discharges. The pellet clouds are viewed from behind the pellet, which is injected from the outside midplane. In this view, the emission forms an elongatedcigarshape with the long dimension of the cigar aligned with the local magnetic field. In some cases, two distinct parallel cigars can be seen simultaneously, displaced vertically from one another by ∼5 cm. Measurements using a ten channel array of position sensitive photodiodes show that the mean position of the ablation cloud emission can oscillate vertically by ∼4 cm with periods in the 60–100 &mgr;s range, and that these oscillations are highly correlated with ‘‘bursts’’ in the cloud emission. The tilt of the cloud is also measured as a function of time as the pellet traverses the plasma, and in this way the poloidal field profile is obtained. (The total transit time of the pellet is ∼1 ms.) Magnetohydrodynamic equilibrium reconstructions ofqprofiles have been determined using these measurements.

ISSN:0034-6748    

DOI:10.1063/1.1143849

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Following charge exchange between fast neutral atoms and impurities, emission from the charge exchange product can take two forms. The first is prompt radiation due to rapid cascading of the excited electron following the charge exchange event. In addition, as a result of electron impact excitation from the ground state before ionization, the impurity can subsequently radiate at the chosen wavelength. Depending on the beam‐sightline geometry, plasma density, and species observed, the emission of this ‘‘ion plume’’ can rival the prompt emission, making it a potentially important consideration for ion temperature and density measurements. Direct measurements of this ion plume radiation after the charge exchange event have been made for He+ions (n=4–3, 4686 A˚) and C5+ions (n=8–7, 5292 A˚). The ratios of plume radiation to prompt charge exchange radiation for these transitions is compared to predictions from modeling, and good agreement is found. This work was supported by U.S. Department of Energy Contract No. DE‐AC02‐76‐CHO‐3073.

ISSN:0034-6748    

DOI:10.1063/1.1143426

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A code for calculating the actual spectral line shapes in magnetically confined plasmas of the tokamak type is described. The code determines the resulting line shape averaged along the line‐of‐sight of the spectrometer, starting from prescribed thermal temperature, ion emissivity, and flow profiles, for a plasma immersed in a magnetic field. In addition, the influence on the impurity linewidths of nonthermal fluctuating velocities due to fluctuating electric fields and to possible magnetic fluctuations is also included. Typical applications of the code to spectral data analysis in the TJ‐I tokamak are given.

ISSN:0034-6748    

DOI:10.1063/1.1143427

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A He–Ne interferometer is used to measure the line‐integrated electron density in the plasma of an operating plasma opening switch (POS). A heterodyne technique is used, where an acousto‐optic modulator generates a 40‐MHz frequency shift between the reference and scene beams. The phase shift is calculated numerically from the zero‐crossing times of the beat signal. The precision of the phase measurement is ±0.5°, however, several nonplasma sources of phase shift are present just after the current through the POS is interrupted. In particular, charged particle flow into the vacuum window results in a negative phase shift. This anomalous phase shift is effectively eliminated by using magnets to deflect the particles away from the window. Measurements during POS shots show a localized decrease in line density prior to current interruption.

ISSN:0034-6748    

DOI:10.1063/1.1143428

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A novel ‘‘point‐diffraction’’ interferometer has been implemented on the Los Alamos solid fiberZ‐pinch experiment. The laser beam is split into two legsafterpassing through the plasma. The reference leg is filtered with a pin‐hole aperture and recombined with the other leg to form an interferogram. This allows compact mounting of the optics and relative ease of alignment. TheZ‐pinch experiment employs a pulsed‐power generator that delivers up to 700 kA with a 100 ns rise time through a fiber of deuterium or deuterated polyethylene (CD2) that is 5‐cm long and initially solid with radiusr≊15 &mgr;m. The interferometer, using a &Dgr;t≊200 ps pulse from a Nd:YAG laser frequency doubled to &lgr;=532 nm, measures the electron line density and, assuming azimuthal symmetry, the density as a function of radial and axial position. Calculations predict Faraday rotations of order &pgr;/2 for plasma and current densities that this experiment was designed to produce. The resulting periodic loss of fringes would provide the current density distribution.

ISSN:0034-6748    

DOI:10.1063/1.1143429

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new instrument at the NOVA laser facility has been developed to measure absolute levels of scattered light at up to seven angles simultaneously from laser‐produced plasmas. The multiple‐angle time‐resolving spectrometer (MATRS) both temporally (t=120 ps) and spectrally (&lgr;=1 A˚) resolves light scattered from the plasma at or near the laser wavelength. MATRS has been used to study parametric instabilities in plasmas pertinent to laser fusion. Measurement of the angular dependence of the scattered light from these processes will provide a clear test of convective theory. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.

ISSN:0034-6748    

DOI:10.1063/1.1143430

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Holographic polaro‐interferometry represents a flexible tool for studying density and magnetic fields in an ICF plasma. The polarization and the changes in beam phase are recorded in a single hologram. Using the polarization information, the magnetic field (i.e., the Faraday rotation) of the plasma can be determined, while the density profile can be inferred from the change in beam phase. The experimental setup uses a Mach–Zender arrangement to form the hologram/interferogram. A single beam is passed through the plasma. This beam is split when entering the Mach–Zender arrangement. The reference beam is passed through a spatial filter to erase phase information generated from the passage through the plasma. This diagnostic is being developed for application to ICF plasmas. It will be tested initially on a long‐scale length plasma generated by an exploding wire. An interferogram is presented.

ISSN:0034-6748    

DOI:10.1063/1.1143431

出版商:AIP    

年代:1992

数据来源: AIP