摘要:

Techniques developed for the alignment of high‐energy accelerators have been applied to the alignment of the Tara tandem mirror magnetic confinement device. Tools used were: a transit/laser surveyor’s system for establishing an invariant reference; optical scattering from ferromagnetic crystallites for establishing magnetic centers in the quadrupole anchor/transition modules; an electron‐optical circle‐generating wand for alignment of the solenoidal plug and central cell modules; and four differently configured electron emissive probes, including a 40‐beam flux mappingegun, for testing the alignment of the coils under vacuum. Procedures are outlined, and results are given which show that the magnetic axes of the individual coils in the Tara set have been made colinear with each other and with the reference to within ±1.0 mm over the length of the machine between the anchor midplanes.

ISSN:0034-6748    

DOI:10.1063/1.1138019

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A slow wave antenna has been designed to propagate Alfve´n waves unidirectionally in the Texas Tech Tokamak. The antenna receives 30‐kW rf pulses at 4–20 MHz, directly from a 50‐&OHgr; transmission line, without matching circuitry. Unidirectional Alfve´n waves are successfully excited in the tokamak over a wide range of frequencies. Power coupling is approximately 36% with a little higher coupling during excitation of a pronounced toroidal eigenmode.

ISSN:0034-6748    

DOI:10.1063/1.1138020

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Thermal imaging cameras sensitive to 3–5 &mgr; radiation are routinely used to measure heat flow to the main limiter, to the vacuum vessel wall behind the main limiter, and to the divertor plate limiters. The cameras are equipped to provide either a standard television image, one frame per ∼16.7 ms, or a surface temperature profile on one line of the image with a time resolution of ∼125 &mgr;s. In the former mode, we can determine both the location and the intensity of the heating on the main limiter during multimegawatt neutral‐beam injection into plasma; in the latter mode, we can measure heat pulses striking the limiter from plasma processes occurring on fast timescales (e.g.,D&agr;spikes of ∼500 &mgr;s duration). Data is stored in both video image and digitized forms. In the latter, a ‘‘peak‐sample‐hold’’ circuit electronically records the maximum signal of each line sweep and stores this data in digitized form on magnetic tape. This facilitates later comparisons of infrared camera data with other diagnostic signals using plotting packages on the DEC‐10.

ISSN:0034-6748    

DOI:10.1063/1.1138021

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A detector setup with three LN‐cooled Si(Li) diodes is used to measure soft x‐ray spectra (0.8–20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. The setup is part of a pulse‐height‐analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is very much increased during the neutral beam heating, with an enhancement factor of at least 10 over the OH wall radiation. Since we measure the plasma and the wall radiation at the same time, the measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g.,Ti‐K&agr;) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x‐ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation, for example, charge particle bombardment of the wall.

ISSN:0034-6748    

DOI:10.1063/1.1138022

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A bent quartz‐crystal spectrometer of the Johann type with a spectral resolution of &lgr;/&Dgr;&lgr;= 10000–25000 is used on the Tokamak Fusion Test Reactor (TFTR) to determine central plasma parameters from the spectra of helium‐like and lithium‐like metal impurity ions (Ti, Cr, Fe, and Ni). The spectra are observed along a central radial chord and are recorded by a position‐sensitive multiwire proportional counter with a spatial resolution of 250 &mgr;. Standard delay‐line time‐difference readout is employed. The data are histogrammed and stored in 64 K of memory providing 128 time groups of 512‐channel spectra. The central ion temperature and the toroidal plasma rotation are inferred from the Doppler broadening and Doppler shift of the K&agr; lines. The central electron temperature, the distribution of ionization states, and dielectronic recombination rates are obtained from satellite‐to‐resonance line ratios. The performance of the spectrometer is demonstrated by measurements of the Ti xxiK&agr; radiation.

ISSN:0034-6748    

DOI:10.1063/1.1138023

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A proton space charge having multi‐MeV kinetic energy was injected through a thin ground plane to extract electrons and produce a time‐dependent autoneutralization space potential. An electron‐emitting floating‐potential resistive divider was used to measure the space potential during 20 ns of the proton current pulse. During this time, proton kinetic energy fell from 10.6 to 8.5 MeV and thus the space potential (taken as 1.09× the floating potential) fell from 5.8 to 4.6 kV.

ISSN:0034-6748    

DOI:10.1063/1.1138024

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A repeating pneumatic pellet injector has been developed for plasma fueling applications. The repetitive device extends pneumatic injector operation to steady state. The active mechanism consists of an extruder and a gun assembly that are cooled by flowing liquid‐helium refrigerant. The extruder provides a continuous supply of solid hydrogen to the gun assembly, where a reciprocating gun barrel forms and chambers cylindrical pellet from the extrusion; pellets are then accelerated with compressed hydrogen gas (pressures up to 125 bar) to velocities ≤1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steady‐state rates of 2 s−1have been obtained with 2.1‐ , 3.4‐ , and 4.0‐mm‐diameter pellets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 s−1for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large present‐day fusion devices such as the Tokamak Fusion Test Reactor (TFTR). Experimental results are presented, including effects of propellant pressure and barrel length on gun performance.

ISSN:0034-6748    

DOI:10.1063/1.1138025

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The characteristics of operating an extended‐area, triple‐layer microchannel‐plate assembly are described in detail. The assembly has an anode array to produce 120 channels of information. When run in the pulse‐counting mode, gains of up to 5×108are obtained with very low levels of dark current. A number of special features and problems have been observed during operation. These include unexpectedly high count rates for each channel and severe gain variation along the length of the plate. A model distribution function for a pulse is derived and it is shown that this gain variation is due to space‐charge effects that occur in the interstage gaps. This effect, although previously discounted, can consistently explain the data presented here and earlier by other authors. One assembly was rebuilt and now exhibits much greater uniformity in gain. Its pulse‐height spectrum also has the unusually small, full‐width at half‐maximum: gain ratio of typically 50%.

ISSN:0034-6748    

DOI:10.1063/1.1138026

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A microchannel‐plate photomultiplier (MCP‐PMT) has been applied to the time‐correlated single‐photon counting technique. Electrical and timing characteristics were investigated for the two types of MCP‐PMT’s, nonproximity type (Hamamatsu R1264) and proximity type (R1564), which are different in distance between the photocathode and MCP. In the proximity type, the transit‐time spread was found to be 60 ps, i.e., a factor of 4 shorter than that in conventional photomultipliers with a dynode string. It was concluded that both types of MCP‐PMT’s are fully applicable to the single‐photon counting method and that the proximity type MCP‐PMT in particular leads to further improvements in the cathode transit‐time difference and the wavelength effect of the timing properties. Some examples of experimental results are shown for fluorescence decay curves and picosecond time‐resolved spectra.

ISSN:0034-6748    

DOI:10.1063/1.1138027

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Raman measurements on ethanol containing rhodamine 6G have been carried out by a single‐photon counting technique with highly repetitive (∼82 MHz), short‐duration (∼5 ps) laser pulses using a time gate as narrow as 31 ps. The Raman‐to‐fluorescence intensity ratio and the signal‐to‐noise ratio have been improved by factors of 129 and 4.2, respectively. These values are in good agreement with numerical estimations. This method has also been found to be very effective in reducing dark counts and interfering plasma lines from the laser tube. The optimum width and position of the gate to attain the best signal‐to‐noise ratio for a given fluorescence decay time and a response function of the experimental system are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1138028

出版商:AIP    

年代:1985

数据来源: AIP