摘要:

A compact 15‐channel bolometer array composed of discrete thermistors has been installed on the Princeton Beta Experiment tokamak. The response time, fastest for detectors with low thermal capacities, has been optimized by using ‘‘free‐standing’’ detectors. The detector is supported only by thin electrical leads and no thermal substrate is employed. Overheating due to limited heat dissipation is controlled with careful detector biasing. The sensitivity is limited by the systematic errors in the model of the heat transfer from the detector to the electrodes and leads. A two‐pole cooling model was found to characterize the detector’s thermal decay far better than a simple exponential and resulted in an NEP≊3×10−7W/&sqrt;Hz with a 300‐Hz bandwidth.  

ISSN:0034-6748    

DOI:10.1063/1.1143899

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Spectral‐based signal‐processing techniques for characterizing fluctuation data from plasma discharges in the Advanced Toroidal Facility fusion experiment are described. The analysis process moves from wave form display and spectral analysis of single discharges to coherence filtering and database techniques for identifying coherent fluctuations. These analysis techniques are used to distill large volumes of spectral data from many signals per discharge (for many discharges) into simple forms suitable for comparison with the global variation of plasma parameters.

ISSN:0034-6748    

DOI:10.1063/1.1143900

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A large volume cylindrical radio frequency (rf) plasma source using a magnetic line‐cusp field has been developed for use in large scale plasma processing. In this type of plasma source, a capacitively coupled 13.56 MHz rf plasma is produced in the presence of a magnetic line‐cusp field. Three versions of the plasma source have been constructed and tested. The first version has a pair of peripheral rf electrodes placed outside the ionization chamber and is suitable for preparing a large volume uniform plasma. This plasma source can attain a useful area of plasma with 10% uniformity over a 30‐cm‐diam region. The second version is featured by parallel doughnut‐plate electrodes which form part of the chamber wall and serve as a high current source, where the electron density is proportional to the rf power, being equal to 4×1010cm−3at 400 W. The third version is a slab‐plasma source, which has a rectangular ionization chamber, a pair of rectangular magnetic coils, and a pair of rectangular rf electrodes, yielding an electron density of the order of 109cm−3for a 25 W rf power.

ISSN:0034-6748    

DOI:10.1063/1.1143901

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A Langmuir probe measurement system suitable for characterization of extended, low‐pressure dc or microwave plasmas has been developed around a VAXStation 3200 graphics workstation computer. Both planar and cylindrical probes have been constructed, but the latter has been deemed more satisfactory, and its design developed more fully. A novel interface circuit based on fast high voltage, transformer‐coupled, isolation amplifiers has been constructed to permit probing of regions where the plasma potential is hundreds of volts away from ground, which are typically found in dc glow discharges. This circuit also incorporates a noise suppression feature, using feedback from a second identical probe (compensation probe), which has proven very useful. A great deal of high‐resolution data can be collected quickly using the fast direct memory access (DMA) hardware. Many analysis capabilities and graphical display possibilities are implemented in the FORTRAN control program, but special emphasis has been placed on extracting plasma potentials, electron densities, and electron energy distribution functions (EEDFs) from the first and second derivatives of the probeI‐Vcurve. These are obtained by numerical differentiation techniques that fully correct for ohmic voltage drops across the current sampling resistor. The capabilities of the system will be illustrated with several examples of probe data and EEDFs obtained in a large dc glow discharge system.

ISSN:0034-6748    

DOI:10.1063/1.1143902

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A gas chromatographic system for the analysis of gas species to be collected from the JET torus and to be processed in the JET active gas handling plant during the active operation phase with deuterium and tritium plasmas was designed and built by CFFTP under contract with JET. The gas‐chromatograph consists of a compression/injection stage and of two parallel, analytical stages, one for the detection of helium, hydrogen, oxygen, nitrogen, methane, carbon monoxide, and the six hydrogen molecules by means of a thermal conductivity detector (TCD) and one for the detection of carbon monoxide, methane, carbon dioxide, and higher hydrocarbons by means of a flame ionization detector (FID). A flow proportional counting detector (FPCD) is placed in series to TCD and FID for the specific analysis of tritiated gas compounds. A detailed description of the system and of its performance will be given which was evaluated using several calibrated gas mixtures including test runs with tritiated species at JET. The gas species mentioned above can be detected in the concentration range from ppm levels to 100%. The estimated error is about 20% at very low concentrations and 1% at high concentrations. The required minimum detection limit for the TCD can be achieved by the injection of large samples and the use of large filament currents. In addition, neon or helium can be chosen as carrier gas. The use of Ne increases the sensitivity for hydrogen and allows the detection of He, whereas He carrier gas gives superior TCD results for all other gases. Due to the high sensitivity of the FPCDs ppb levels of tritiated gas species can be detected.

ISSN:0034-6748    

DOI:10.1063/1.1143903

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thin scintillators used as detectors of escaping fusion products in the TFTR tokamak are studied with Van de Graaf beams of 3‐MeV protons and 3.5‐MeV alphas. ZnS scintillators are found generally adequate for the D–D experiments performed up to now, marginal for near‐term D–T experiments because the emitted light saturates at alpha fluxes greater than 1010cm−2 s−1, and totally inadequate for future ignited plasmas. Other scintillators have been tested that have lower light efficiencies but much better properties at high fluxes. In particular, the P46 scintillator appears to be an excellent choice for future experiments.

ISSN:0034-6748    

DOI:10.1063/1.1143904

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new type of low‐energy ion accelerator has been developed. It includes an eight‐storied Disktron generator, newly developed accelerating tubes which hold up to 4 MV/m, both single and tandem acceleration capability, and a compound negative ion source. The Disktron generates 3.2 MV with a dummy load and 2.2 MV with ion beams, and has a voltage stability better than 10−3at around 1 MV with a corona feedback stabilizer or a generating voltmeter feedback stabilizer only. The highly stabilized voltage of the Disktron has particularly been allowed to form an ion microbeam of about 1‐&mgr;m diameter.

ISSN:0034-6748    

DOI:10.1063/1.1143905

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have developed an improved technique to increase the stability of single‐frequency lasers by employing a scanning Fabry–Perot interferometer and a stabilized helium neon laser. Our instrument surpasses earlier devices in several key areas. The laser frequency can now be stabilized while scanned across its inherent single‐frequency tuning range. The frequency stability is long term with an increased frequency correction rate of nearly 500 Hz. The laser frequency can be scanned repeatedly with a repetition accuracy equal to the frequency stability. Also, the electronics permit the laser frequency to be swept externally while synchronized with other instruments. Our stabilizer reduced the frequency drift of a commercial ring dye laser to ±1 MHz relative to the reference laser.

ISSN:0034-6748    

DOI:10.1063/1.1143906

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

As power levels of industrial lasers increase, effective determination of beam profiles over extended operational regimes becomes problematic, due to dynamic range limitations of available detectors. To address this deficiency, a variable coupling rotating wand was developed for on‐line monitoring of output radiation from high average power CO2lasers. The concept features real‐time beam sampling adjustment, activated by wand rotational speed change. An associated controller provides appropriate speed regulation of the wand motor drive, via a computer generated setpoint. Design parameters thereby ensure optimal sensor operation at all power levels. A safety override prevents sensor damage by terminating laser operation, if wand speed decreases below a safe value.

ISSN:0034-6748    

DOI:10.1063/1.1143907

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The incorporation of a retroreflecting, pseudoconjugating cone as a folding element in a double‐pass unstable resonator of a high‐power carbon dioxide oscillator–amplifier is presented. The concept, when implemented with a truncated cone, has yielded significant improvements in optical energy extraction efficiency, beam quality, and alignment stability. The performance of such a modified clear aperture cone resonator, in comparison with a standard roof prism cavity geometry, is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143908

出版商:AIP    

年代:1993

数据来源: AIP