摘要:

An electrostatic probe for ion temperature and density measurements was built and tested in the scrape‐off region of the TBR‐1 small tokamak. The main parameters involved in the design and details of the construction of the probe are presented. The electron discrimination and the probe efficiency for ion detection were checked by measuring the probe current as a function of the collector retraction length for a constant voltage. The results for the ion temperature and density obtained from the characteristic curves are discussed and compared with previous measurements.

ISSN:0034-6748    

DOI:10.1063/1.1138683

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The development of a microcomputer‐controlled electrostatic probe as a diagnostic technique is described. The technique uses cylindrical probes and the definitive theory of Laframboise to give rapid measurements of the plasma parameters in a medium density (1010to 1012cm−3) plasma including the fast electron density and temperature. The iterative technique described overcomes many of the problems associated with established methods of Langmuir probe analysis.

ISSN:0034-6748    

DOI:10.1063/1.1138684

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A computer code has been developed which simulates a Thomson scattering measurement, from the counting statistics of the input channels through the mathematical analysis of the data. The scattered and background signals in each of the wavelength channels are assumed to obey Poisson statistics, and the spectral data are fitted to a Gaussian curve using a nonlinear least‐squares fitting algorithm. This method goes beyond the usual calculation of the signal‐to‐noise ratio for the hardware and gives a quantitative measure of the effect of the noise on the final measurement. This method is applicable to Thomson scattering measurements in which the signal‐to‐noise ratio is low due to either low signal or high background. Thomson scattering data from the S‐1 spheromak have been compared to this simulation, and they have been found to be in good agreement. This code has proven to be useful in assessing the effects of counting statistics relative to shot‐to‐shot variability in producing the observed spread in the data. It was also useful for designing improvements for the S‐1 Thomson scattering system, and this method would be applicable to any measurement affected by counting statistics.

ISSN:0034-6748    

DOI:10.1063/1.1138685

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The optics of the 160‐keV deuterium neutral beam injection for the Joint European Torus–plug‐in neutral injector (JET‐PINI) have been studied in a single beamlet, using the test stand ligne d’etudes d’optiques (LEO). The beamlet optical features, that is perveance‐divergence relationships, beam profiles, and steering angle by aperture offset, have been measured. Computations have been compared with the experimental results obtained both in this monobeamlet experiment and in the multibeamlet system of the 160‐keV PINI injector.

ISSN:0034-6748    

DOI:10.1063/1.1138686

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report on a fast framing camera designed to image imploding foils driven by inductive storage drivers. The camera has several front ends which are disposable, they allow for imaging in either the visible, UV, or x‐ray regions; it also has very large dynamic range which allows it to record sequences of events where the brightness changes by many orders of magnitude.

ISSN:0034-6748    

DOI:10.1063/1.1138687

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Production of electron‐beam pulses with a 700‐ps FWHM duration, using laser‐photoelectron emission from a cold trioxide cathode in a 3‐MV Van de Graaff accelerator has been demonstrated. At 70‐kW laser power (&lgr;=337.2 nm) a current of about 1 mA has been measured which means a cathode quantum efficiency of 10−7. An electron transit time jitter of about 40 ps has been measured, to be attributed to voltage fluctuations on the accelerator tube electrodes resulting from the charging belt system. The results are discussed with respect to the feasibility to produce short pulses with a 1‐nC total charge, taking into account the quantum efficiency of 10−4measured in a test setup for the cold trioxide cathode. Larger quantum efficiency for the accelerator cathode and decrease of the transit time jitter are the main goals set for development of the Van de Graaff accelerator as a radiation source for very high time‐resolution experiments in radiation chemistry and physics.

ISSN:0034-6748    

DOI:10.1063/1.1138688

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A simple photocathode for electron injection into high‐density gas is described. Relatively large electronic current pulses have been obtained by using a commerical low‐power xenon flash lamp. The photocathode efficiency has been studied as a function of the metal film thickness. The device has been used in swarm experiments at pressures up to 10 MPa in the temperature range 40–300 K.

ISSN:0034-6748    

DOI:10.1063/1.1138689

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A number of different, rf‐excited 3‐W cw CO2waveguide lasers have been built. Four of these lasers, after continuously working for 15 000–30 000 h, still yield about 70% of their original power output. The design variations cover N2‐ and CO‐bearing gas mixtures, as well as internal‐ and external‐capacitively coupled excitaton electrodes. A similar laser survived 50 000 5‐min‐ON/5‐min‐OFF cycles without significant mirror damage. We have not been able to find suitable cold cathodes that allow the building of longitudinally dc‐excited cw CO2waveguide lasers that work for such extended periods of time.

ISSN:0034-6748    

DOI:10.1063/1.1138690

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A compact, solid‐state radio frequency oscillator of low‐power consumption is described which allows quantitative measurement of the optogalvanic effect in low‐pressure gas discharges. The oscillator has been used to record a portion of the 2‐0 overtone band of nitric oxide at a pressure of ∼1 Torr using a tunable color‐center laser operating at 2.65 &mgr;m.

ISSN:0034-6748    

DOI:10.1063/1.1138691

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A magneto‐optic Faraday rotation diagnostic was implemented on aZ‐pinch driven flux‐compression generator to measure line‐averaged, megagauss, axial‐magnetic fields up to 1.6 MG with rise times of 30 kG/ns. The axial‐magnetic field rotated the plane of polarization of a 2‐W argon laser beam in a 0.725‐mm‐diam, fused silica quartz fiber mounted coaxial with theZpinch. The rapid rise time and the high radiation environment presented by theZ‐pinch plasma caused a high‐pressure impulse <100 kbar, to be coupled into the quartz‐fiber probe disrupting the polarization‐preserving properties of the fiber. The time scale for disruption was characteristic of a shock propagating radially through the fiber to its core. This paper will describe the response of the Faraday diagnostic under these conditions and present a simple model that describes the effects of fiber depolarization that is consistent with previous observations of stress‐induced depolarization in optical fibers.

ISSN:0034-6748    

DOI:10.1063/1.1138692

出版商:AIP    

年代:1986

数据来源: AIP