摘要:

The detection of helium in a deuterium gas environment (both mass 4) is an important task in the field of nuclear fusion physics. To fulfill this purpose a detector has been developed which is based on spectroscopic measurement techniques. For the excitation of the helium and deuterium atoms different electron sources have been tested. Most sources had to be rejected because they either produce a disturbingly high background light level or cannot be operated reproducibly after venting or are mechanically not stable enough. The best line emitting light source has been found to be a Penning gauge. The light is collected in an optical fiber bundle, transferred away from the tokamak experiment to an area more easily accessible, split by interference filters intoD&agr;light and the light of a strong He iline, and detected by photomultipliers. Unfortunately broad spectral lines from the deuterium molecule superimpose the strongest He ilines and have nearly the same intensity as the helium lines at a He concentration of about 5%. Therefore, some effort is necessary to deduce the partial pressures of helium and deuterium. A method is described which yields the calibration factors for the observed nonlinear pressure response of the spectral lines. The lower limit for the determination of the helium concentration presently amounts to about 1%–2%; the time resolution of the system is of the order of a few milliseconds.  

ISSN:0034-6748    

DOI:10.1063/1.1142957

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An absolutely calibrated, focusing Laue transmission crystal spectrograph has been developed for inertial confinement fusion (ICF) diagnostics of high‐energy x‐ray continuum at NOVA. A single flat EddT 020 crystal, 500‐&mgr;m thick, provides continuous energy coverage over the 5.5–25 keV energy range. The spectrograph is designed with low dispersion and low resolving powerE/&Dgr;Eof between 10 and 50 for high sensitivity to continuum. Greater resolving power with lower continuum sensitivity is possible by increasing dispersion. The focusing design achieves very low background and provides a compact flat field for coupling to various position sensitive detectors including streak cameras. In addition to EddT, PET 020 has high efficiency in transmission in this energy range and used in the Cauchois geometry achieves high to moderate resolving power that is independent of ICF source size. Initial experiments with gold targets at NOVA with the EddT spectrograph show high sensitivity for single shot recording of continuum and goldLlines on Kodak DEF film. Factors affecting instrument design, resolving power, and sensitivity will be discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143772

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A comparative study on the generation of 2.45‐GHz multicusp electron cyclotron resonance (ECR) plasma is performed. Looped cusp structures such as the ring‐cusp give a low‐power and low‐pressure ignition, and vice versa, indicating an importance to keep the electron trajetory of gradient‐Bdrift motion inside the chamber even in the case of ECR plasmas. The importance of the antenna location in such multicusp fields is elucidated by comparison in two cases of the axial antenna located in the weak magnetic field region, generating a hydrogen plasma of limited density (ne<7.4×1010cm−3), and a radial antenna located in the strong magnetic field region, generating an overdense plasma (ne∼2×1011cm−3).

ISSN:0034-6748    

DOI:10.1063/1.1142961

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Several methods for estimating the plasma potential and density using cylindrical Langmuir probes are compared to the self‐consistent solutions of the Vlasov–Poisson equations calculated by Laframboise (J. G. Laframboise, Ph. D. dissertation, University of Toronto, 1966). Measurements are made during the decay of a magnetic‐field‐free plasma in which the mean‐free path of the electron is shorter than the dimensions of the vacuum vessel (the electrons, therefore, have a Maxwellian velocity distribution). The measurements are made in a parameter range in which exact analytical solutions do not exist for the ion and electron saturation currents, 0.5≤R/&lgr;De≤5, whereRis the probe radius and &lgr;Deis the electron Debye length (kTe/4&pgr;ne2)1/2. An iterative procedure is used to fit the data at probe voltages both above and below the plasma potential while constraining the curves to be continuous at the plasma potential. The measured curves could be represented extremely well by the numerical results. It is therefore assumed that the plasma parameters used to fit the numerical results to the measurements are correct. The systematic errors which result from using several analysis techniques which assumeR/&lgr;De≪1 are also presented, and it is shown that empirical corrections to these errors can be described which compensate for the finite probe radius.

ISSN:0034-6748    

DOI:10.1063/1.1142743

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The present article describes the constructional aspects of an 85‐kJ capacitor bank at 20 kV for the production of pulsed high magnetic fields. The discharge current magnitude is 56 kA at a ringing frequency of 1.1 kHz. The bank employs 8 double‐mode trigatrons in parallel which are triggered into conduction by the application of 16 simultaneous low jitter high voltage pulses generated by a multiple trigger pulse generator. The performance of the bank with double‐mode trigatrons is compared with that obtained by conventional single‐mode trigatrons. The waveforms of discharge current in time domain and fast fourier frequency spectrum for single‐ and double‐mode trigatrons are presented and analyzed for performance evaluation. The performance with double‐mode trigatrons is characterized by distinctly superior synchronization in the closing of trigatron switches over a wide range of operating voltage resulting in high peak discharge current and low waveform distortion.

ISSN:0034-6748    

DOI:10.1063/1.1142762

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A production technique for sheet plasma with a dc magnetron discharge source is proposed. The magnetron discharge was realized by a cross field of permanent magnets and a rectangular‐typed hollow cathode, which enhances the production of high‐density plasma. The plasma produced was introduced into a low‐pressure region where an axial magnetic field was applied through a slit anode to form the sheet plasma, of high electron density of 4.5×1010cm−3, electron temperature of 2.8 eV for low discharge current (0.3 A) and low magnetic field (0.18 kG). The thickness of the sheet plasma is found to be almost the same as the ion cyclotron diameter. This plasma production technique would be useful for thin‐film preparation on large‐area substrates.

ISSN:0034-6748    

DOI:10.1063/1.1142727

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An apparatus has been constructed to analyze the particle flux of positive ions on surfaces from dry etching reactors. The particle flux can emerge from a great variety of reactive ion etching systems or from reactive ion beam etching sources. The particle beam passes through a small orifice with a diameter of 100 &mgr;m. A differentially pumped quadrupole mass spectrometer with a specially designed ion transfer optics performs the energy analysis of positive ions. The energy range can be varied between 0 and 500 eV with a resolution of 1%. The angular distribution measurements of the particle flux are carried out varying the inclination of the mass analyzer by ±20° with the vertex lying centrally in the sampling orifice. The angular resolution is about 1°. Rotation of the source on top of the apparatus and translation over ±10 cm inxydirection and 15 cm inzdirection perpendicular to it is provided in order to assure fully local resolution. The electrical properties of the orifice‐ion optics system is discussed with respect to their influence on ion trajectories. The purpose of the apparatus is to provide data on particle fluxes relevant for microelectronic processing.

ISSN:0034-6748    

DOI:10.1063/1.1142741

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A 1400‐kg five‐mode bar detector has been constructed and tested at room temperature. Detailed calculations and computer simulations have been performed to optimize the design and study the dynamics of the system. The tests have confirmed the analytical prediction that a large fraction (67% in this experiment) of the energy deposited into the bar is transferred to the last resonator. The rise time of the energy at the last resonator is short (&bartil;2 ms), and corresponds to an effective detector bandwidth of &bartil;500 Hz.

ISSN:0034-6748    

DOI:10.1063/1.1142708

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A general microwave electron gun (rf gun) theory and some new ideas about further reducing the emittance of electron beams are reviewed and introduced briefly. Experimental results are presented from a thermionic cathode rf gun which has been developed for Beijing Free‐Electron Laser Project (BFELP) at Institute of High Energy Physics (IHEP), Academia Sinica as the injector of 30 MeV constant gradient linac. LaB6is used as the thermionic emitter with 100 crystal surface and the temperature around 1620 °C. Back bombardment heating effect and another effect connected with the cathode surface temperature was observed. An electron beam with macropulse length 4 &mgr;s, repetition rate 12.5 Hz, greater than 500 mA beam current during macropulse and around 1 MeV maximum energy has been obtained. In the last section of this article, two useful formulas used to determine electric field distribution near the cathode surface and coupling coefficient &bgr; of a rf gun are introduced.

ISSN:0034-6748    

DOI:10.1063/1.1142680

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A highly efficient multi‐joule output TE‐CO2laser has been developed using a spiker‐sustainer excitation method. With helium‐free laser gas mixtures 5‐J laser pulses have been produced at a pressure of 400 mbar with an energy output efficiency of 22.6%. The addition of small amounts of hydrogen to the gas mix has been found to enhance laser performance.

ISSN:0034-6748    

DOI:10.1063/1.1142645

出版商:AIP    

年代:1992

数据来源: AIP