摘要:

A soft x‐ray pulse height analysis (PHA) system is begin used at the Rijhuizen Tokamak Project to study the electron velocity distribution. A liquid nitrogen cooled Si(Li) detector is used to view the plasma along a tangential line of sight. A gas cell in combination with Al foils is used for filtering. The data‐acquisition system is set up in such a way that 16 subsequent spectra, of 1ms–1 s duration and in the energy range 4–30 keV, can be measured during a single tokamak discharge. The PHA system has been used extensively for measuring the electron temperature, the effective charge numberZeff, and the species and concentrations of high‐Zimpurities in the plasma. Special attention was devoted to study the effect on the electron velocity distribution of electron cyclotron resonance heating (ECRH) power (60 GHz, up to 180 kW) launched in the ordinary mode from the low‐field side. During application of ECRH the temperature deduced from PHA always exceeds the value from Thomson scattering. This deviation can be explained by the presence of nonthermal components in the electron velocity distribution. Finally, the effect of boronization of the vacuum vessel on the impurity concentration was studied.  

ISSN:0034-6748    

DOI:10.1063/1.1143481

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Measurements are presented on the contributions from dielectronic satellite transitions from upper configurations 1s2lnl’,n≥3 to the characteristic x‐ray emission of heliumlike Fe24+. The measurements were carried out on the electron beam ion trap at Livermore using high‐resolution Bragg‐crystal spectroscopy. By eliminating uncertainties in the location and magnitude of the satellite contributions inherent in theoretical predictions the measurements improve the use of the resonance line emission of heliumlike Fe24+as a diagnostic of ion temperature and rotation velocity of high‐temperature plasmas.

ISSN:0034-6748    

DOI:10.1063/1.1143482

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Present‐day tokamak x‐ray imaging (XIS) and pulse height analysis (PHA) diagnostics will require special shielding and x‐ray optics to permit use on fusion reactors without prohibitive noise and detector damage from neutrons and gamma rays; x‐ray curved‐crystal spectrometers (XCS) may work with extensive shielding and collimation, but radiation damage of crystals and attainment of adequate impurity concentrations for ion‐temperature measurement are concerns. We consider the use of one or more reflections at grazing incidence from x‐ray mirrors or from Bragg layered synthetic microstructures (LSM) to decouple the x‐ray diagnostic from the direct fusion neutron beam. We present calculations of expected x‐ray line brightnesses from ITER and total instrument throughput. We also consider the use of hollow glass capillaries embedded in radiation shields to precede the XIS detector and reduce the ratio of neutron plus gamma radiation to x rays by a factor of ∼0.01 or better. Compatibility of capillary schemes with the PHA and XCS are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143483

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A high throughput scanning soft x‐ray monochromator that uses a flat multilayer mirror in a near normal incidence configuration was built and tested in the Plasma Spectroscopy laboratory at Johns Hopkins University and operated on the DIII‐D tokamak. Depending upon the mirror used, the monochromator covers the range 10–170 A˚, with a resolution of 0.25 to 10.8 A˚. The instrument was photometrically calibrated between 10 and 45 A˚. Spectra from DIII‐D were obtained under a variety of discharge conditions over the entire range of the instrument. This paper describes the monochromator, the photometric calibration, and presents initial results.

ISSN:0034-6748    

DOI:10.1063/1.1143484

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A simple multifoil Ross filter spectrometer for monitoring principal (i.e.,n=2−1) soft x‐ray lines of H‐ and He‐like carbon and oxygen has been installed on the Madison symmetric torus reversed‐field pinch. It consists of four silicon surface barrier diodes, each covered by a different multilayer foil filter but viewing a common plasma volume. Each filter is composed of a combination of thin film absorbers with strategically located absorption edges, giving a peak transmission of around 10% at a wavelength of interest (C v40.30 A˚, C vi33.74 A˚, O vii21.70 A˚, O viii18.90 A˚) with good rejection of the others. A linear combination of these four lines is isolated by a given filter and a matrix inversion of the four simultaneous measurements produces the intensities of the individual lines. The time evolution of these lines shows evidence of radial shell structure and gives useful information of the dynamics of the electron temperature during sawtooth activity. This multifoil spectrometer provides a simple and inexpensive alternative to grazing incidence spectrometers as a monitor of C and O influx and radiated power in high temperature tokamaks, and may be especially applicable in a high neutron flux environment.

ISSN:0034-6748    

DOI:10.1063/1.1143485

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An insertable target x‐ray probe has been designed which may be used for two different purposes: measurement of superthermal electron temperature and drift speed, and measurement of the local magnetic field line pitch, both with fast time resolution (1 &mgr;s). The diagnostic is intended for use on the Madison Symmetric Torus (MST) reversed‐field pinch. For the first application, the probe is fitted with six detectors, three viewing the part of the target facing toward the incident electrons, and three viewing the part facing away; each set of three has 0.3, 0.6, and 1.2 mil Be filters for energy discrimination. By subtracting signals from detectors with the same filter but opposing views and dividing signals from detectors with different filters but the same view, one can derive the electron drift speed and parallel temperature. For the second application, the six detectors are replaced by a single position‐sensitive detector, which produces a signal indicating the position of the ‘‘hot spot’’ on the target, and therefore the field line pitch. The diagnostic can withstand high temperatures and can therefore be inserted further into the plasma than electrostatic probes.

ISSN:0034-6748    

DOI:10.1063/1.1143486

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Soft x‐ray pinhole imaging has proven to be an exceptionally useful diagnostic for qualitative observation of impurity radiation from field reversed configuration plasmas. We used a four frame device, similar in design to those discussed in an earlier paper [E. A. Crawford, D. P. Taggart, and A. D. Bailey III, Rev. Sci. Instrum.61, 2795 (1990)] as a routine diagnostic during the last six months of the Large s Experiment (LSX) program. Our camera is an improvement over earlier implementations in several significant aspects. It was designed and used from the onset of the LSX experiments with a video frame capture system so that an instant visual record of the shot was available to the machine operator as well as facilitating quantitative interpretation of intensity information recorded in the images. The camera was installed in the end region of the LSX on axis approximately 5.5 m from the plasma midplane. Experience with bolometers on LSX showed serious problems with ‘‘particle dumps’’ at the axial location at various times during the plasma discharge. Therefore, the initial implementation of the camera included an effective magnetic sweeper assembly. Overall performance of the camera, video capture system, and sweeper is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143487

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have developed a diagnostic for measuring the blackbody temperature of a dense plasma produced in a high power capillary discharge. This diagnostic can be described as a filtered x‐ray pinhole framing camera. The camera consists of a stripline microchannel plate and a filtered pinhole array. The camera is capable of producing two‐dimensional images with time and spectral resolution. We utilize this camera to measure the temperature of a dense optically thick plasma. The imaging also enables us to determine temperature profiles and spatial effects which cannot be determined with other methods such as filtered x‐ray diodes. We will present a complete description of the camera, our procedure for using it, and results from the experiment we carried out.

ISSN:0034-6748    

DOI:10.1063/1.1143488

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The x‐ray emission was measured from a Dense Plasma Focus (DPF) device. The high density plasma is generated by an electrical discharge in rarefied‐neon gas between electrodes in a Mather‐type plasma focus configuration. A curved‐crystal x‐ray spectrograph, a pinhole camera, and an active‐filtered photodiode were the diagnostics viewing the axial output of the pinched‐plasma region. The x‐ray pinhole images indicate a pinched volume roughly 8 mm in length with a nearly circular cross section of about 300 &mgr;m in diameter. The digitized spectral traces were computer processed to obtain absolute x‐ray line intensities. The neon plasma yielded 10–15 J ofK‐shell radiation into 4&pgr; with the hydrogenlike and heliumlike alpha lines totaling 55%–65% of the total spectral emission. The x‐ray emission of the DPF device was studied as a function of discharge current and anode diameter.

ISSN:0034-6748    

DOI:10.1063/1.1143489

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have built a five‐channel, x‐ray detector array based on diamond photoconducting detectors (PCDs). The diamond elements have dimensions of 3 mm × 1 mm × 1 mm (or 0.5 mm). We use diamond PCDs for their stability, flat spectral response, and low leakage currents. The good time response of diamond PCDs is due to the 100‐ps electron/hole recombination time. Filters were designed to give information in the 1–10‐keV spectral region. Calibration of the diamond PCDs showed sensitivities between 4 and 7 × 10−4A/W for a bias of 100 V. We shall present data fromz‐pinch experiments on Saturn.

ISSN:0034-6748    

DOI:10.1063/1.1143490

出版商:AIP    

年代:1992

数据来源: AIP