摘要:

Design, hardware, and operating software of a special purpose computer built for the Monte Carlo simulations of a wide class of random Ising spin systems is described. The machine is quite versatile, easy to operate, and executes programs written in a high level C language. It is a 32‐bit bus oriented system, with a very fast, dedicated Monte Carlo processor and a general purpose single‐board computer sharing the 16‐Mbyte address space. The former processor executes the basic Monte Carlo heat bath algorithm, and the latter performs required physical ‘‘measurements’’ on spin configurations and handles communication with a UNIX host machine. The host computer is used to compile and download programs and to receive small quantities of reduced data for permanent storage and further analysis.

ISSN:0034-6748    

DOI:10.1063/1.1138125

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An investigation has been made of the yield of H−ions and electrons extracted from a magnetic multipole, or bucket, ion source as a function of the parameters of the source. Under optimum conditions the H−current density attains a value equal to half of the positive ion current density (H+3) measured at the extraction plane. The experimental results indicate that, while the H−current rises linearly with arc current, the extracted electron current shows a quadratic dependence. There is also a strong dependence of the electron current on the magnetic field applied across the extraction aperture, and source filling pressure. Probe measurements within the plasma volume show considerable axial variation of the fluxes of electrons, H−ions and H+3ions.

ISSN:0034-6748    

DOI:10.1063/1.1138126

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An eight‐channel radiometer for simultaneous measurement of electron temperatures at different radii via electron cyclotron emission is described. It is divided into two parts, the interchangeable front end and the filter section. By replacing the front end, both first and second‐harmonic electron cyclotron emission measurements are possible in the range of 50–180 GHz. The instrument is absolutely calibrated with an accuracy estimated to be within ±10%. The spatial resolution &Dgr;R/Ris of the order 10−3, the temporal resolution 20 &mgr;s.

ISSN:0034-6748    

DOI:10.1063/1.1138127

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A simple technique is demonstrated for measuring strains in an electromagnetically noisy environment using electrical strain gauges. For applications in which strains are produced electromagnetically in current‐carrying structures, the noise signal can be much larger than the strain signal. Furthermore, the noise signal is at precisely the same frequency as the strain signal, making standard methods of synchronous signal detection difficult. This problem has been surmounted by modulating the detection circuit sensitivity. Bridge circuit modulation has been shown to effectively decouple the strain signal from the noise, even at very low strain levels of ∼10−8m/m.

ISSN:0034-6748    

DOI:10.1063/1.1138128

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A problem concerning the velocity distribution standardly assumed in molecular beams is investigated. It is shown, theoretically and experimentally, that the sum of all energy contributions based on the standard assumed velocity distribution function is different from that based on pure thermodynamic energy considerations.

ISSN:0034-6748    

DOI:10.1063/1.1138129

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A large‐area cathode assembly which is capable of continuous, high‐current electron emission is described. The cathode utilizes an indirectly heated lanthanum hexaboride (LaB6) disk as the thermionic electron emitter. The LaB6cathode emits over 600 A of electrons at an average of 20 A/cm2continuously with no observable lifetime limits to date after about 400 h of operation in a plasma discharge. Proper clasping of the LaB6disk is required to avoid impurity production from chemical reactions with the holder and to provide adequate support if the disk fractures during rapid thermal cycling. Modification of the LaB6surface composition due to preferential sputtering of boron by hydrogen and argon ions in the plasma discharge has been observed. The surface appearance is consistent with the formation of LaB4as a result of boron depletion. The electron emission capability of the cathode is not significantly altered by the surface change. This surface modification by preferential sputtering is not observed in hollow cathodes where the ion energy from the cathode sheath voltage is typically less than 50 V. The electron emission by the cathode has not been affected by exposure to both air and water during operation. Utilizing thick disks of this intermediate temperature cathode material results in reliable, high‐current, long‐lifetime electron emitter assemblies.

ISSN:0034-6748    

DOI:10.1063/1.1138130

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A simple scheme for bunching spatially distributed charged particles is described. In the present application, sub‐nanosecond width pulses are obtained from a milliliter volume containing slow (≤2 eV) positrons. The utility of this technique is demonstrated by a qualitative observation of the temperature dependance of the surface state lifetime for positrons on aluminum.

ISSN:0034-6748    

DOI:10.1063/1.1138131

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have completed a finite difference computer simulation of two diverging electrostatic analyzers. In both analyzers, the deflecting plates are cylindrical surfaces which flare out from each other like two arms of a hyperbola. The analyzers are the soft particle spectrometer (SPS) and the spectrographic particle imager (SPI), which correspond, respectively, to an energy spectrometer and an energy spectrograph. The simulation consists of two steps: (1) a finite difference computation of the electrostatic potential field inside the instrument; and (2) a ray‐tracing computation in which many particles are ray traced through the instrument and statistics are gathered on the particles that make it to the collecting region. In both cases, the simulation is two‐dimensional, restricted to the central plane of the instrument. This limitation turns out to be unimportant because the statistics acquired during simulation agree well with experimentally acquired statistics for each instrument. In the case of SPI, the computer simulation has been used to provide information on how variation of geometric parameters affects the quantities that describe a good spectrograph.

ISSN:0034-6748    

DOI:10.1063/1.1138132

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A device to initialize discharges in multisection waveguide lasers is described.High‐voltage pulses from the trigger circuit ionize the laser mixture via electrodes attached to the outside wall of the waveguide. cw discharges have been started in CO2waveguide laser sections for various gas mixtures at operating pressures of up to 450 Torr.

ISSN:0034-6748    

DOI:10.1063/1.1138133

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A simple technique to convert a commercial dye laser into a tunable source of subnanosecond (≤300 ps) pulses with a linewidth of ∼10 GHz (0.01 nm) is described. The technique used is a combination of stimulated Brillouin scattering and optical breakdown. The effectiveness of the system as a spectroscopic tool was demonstrated by using it to record a partial absorption spectrum of iodine.

ISSN:0034-6748    

DOI:10.1063/1.1138134

出版商:AIP    

年代:1985

数据来源: AIP