摘要:

A CsI salt‐based cathode which is capable of producing a modest perveance, 10 s of A/cm2electron beam for several microseconds pulse lengths, and has little susceptibility to diode closure has been experimentally characterized. This explosive field‐emission CsI‐coated carbon fiber cathode has operated in modest 10−5Torr vacuums at voltages up to 160 kV, and can easily be configured to provide space‐charge‐limited solid or annular electron beams in arbitrarily large diameter configurations. The CsI cathode has demonstrated negligible closure for 2 &mgr;s pulses, and has operated for 200 shots with no degradation in cathode performance. Data on the operating performance of this salt cathode, including effective gap time history and streak photographs demonstrating uniformity of the current density, are presented. A comparison of CsI cathode performance with a velvet explosive field emitting cathode used in electron‐beam production is also presented. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146504

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The electron and negative ion densities and temperatures are reported for a large volume hybrid multicusp negative ion source. Based on the scaling laws an analysis is made of the plasma formation and loss processes. It is shown that the positive ions are predominantly lost to the walls, although the observed scaling law isn+∝I0.57d. However, the total plasma loss scales linearly with the discharge current, in agreement with the theoretical model. The negative ion formation and loss is also discussed. It is shown that at low pressure (1 mTorr) the negative ion wall loss becomes a significant part of the total loss. The dependence ofn−/neversus the electron temperature is reported. When the negative ion wall loss is negligible, all the data onn−/neversus the electron temperatures fit a single curve. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145654

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An intense negative hydrogen ion source has been developed, which has a strong external magnetic filter field in the wide area of 35 cm×62 cm produced by a pair of permanent magnet rows located at 35.4 cm separation. The filter strength is 70 G in the center and the line‐integrated filter strength is 850 G cm, which keeps the low electron temperature in the extraction region. Strong cusp magnetic field, 1.8 kG on the chamber surface, is generated for improvement of the plasma confinement. These resulted in the high arc efficiency at the low operational gas pressure. 16.2 A of H−ion current with the energy of 47 keV was obtained at the arc efficiency of 0.1 A/kW at the gas pressure of 3.8 mTorr in the cesium‐mode operation. The magnetic field in the extraction gap is also strong, 450 G, for the electron suppression. The ratio of the extraction current to the negative ion current was less than 2.2 at the gas pressure of 3 mTorr. The two‐stage acceleration was tested, and 13.6 A of H−ion beam was accelerated to 125 keV. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145655

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A single channel microwave interferometer has been developed for a tokamak with an improved detection that uses an heterodyne configuration and is based on a differential quadrature phase concept. With the new detection very sensitive and accurate direct phase measurements are obtained due to the elimination of the spurious variations of the detected signals resulting from the nonideal behavior of the output mixers. As a result, the line integrated density along the vertical central chord of the vacuum chamber can be determined during the whole plasma discharge. Fast density variations occurring both at the formation phase of the plasma and during sawtooth cycles could also be measured. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145656

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The basic feasibility of a proposal to simplify the conventional low energy rf electron linear accelerator (linac), is considered. The design suggested foresees replacement of the traditional high power systems of external rf generator and modulator by a more passive switched energy storage system. The proposed conception of a compact linac is based on known rf energy compression techniques and an efficient self‐excited oscillation in a special accelerating/oscillating linac structure. The principal relations, performance estimations, and one‐dimensional time‐dependent simulation results for such a linac are presented. The possibility of self‐excited oscillation by an unbunched low voltage beam in a waveguide linac section is proved and investigated experimentally. The common features and differences compared with a conventional backward‐wave tube are analyzed. An application of this effect is proposed for impedance and group velocity measurements in slow‐wave structures. Since the rf energy commutation may be one or two orders faster than the electric high voltage energy commutation (conventional modulator), combining the structure proposed and rf energy compression system can give high levels of the average beam power (10–100 kW). The linac facility would have considerably reduced weight and sizes (more than 2.5 times) as compared to similar industrial linacs. The power supply required is in 40–120 kV range dc source, and an estimated overall wall plug efficiency is a few percent. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145657

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Metrology requirements for optical components for third‐generation synchrotron sources are taxing the state of the art in manufacturing technology. We have investigated a number of error sources in a commercial figure measurement instrument, the Long‐Trace‐Profiler II, and have demonstrated that, with some simple modifications, we can significantly reduce the effect of error sources and improve the accuracy and reliability of the measurement. By keeping the optical head stationary and moving a penta prism along the translation stage, as in the original pencil‐beam interferometer design of von Bieren, the stability of the optical system is greatly improved, and the remaining error signals can be corrected by a simple reference beam subtraction. We illustrate the performance of the modified system by investigating the distortion produced by gravity on a typical synchrotron mirror and demonstrate the repeatability of the instrument despite relaxed tolerances on the translation stage. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145658

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The x‐ray transmission properties of a very thin polyimide window in the range 7–310 A˚ have been investigated. The window is nominally 0.24 &mgr;m thick and is supported by a hexagonal polyimide grid. Transmission of over 60% and 80% at the oxygenK&agr; and carbonK&agr; lines, respectively, have been achieved. The use of such windows as the entrance window of a gas scintillation counter (GSPC) operating as a broadband spectrometer at XUV wavelengths is discussed. Overall detector efficiencies of greater than 10% for wavelengths less than 150 A˚ are possible to achieve. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145659

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The University of Wisconsin‐Madison Accredited Dosimetry Calibration Laboratory has designed and constructed an Attix style variable‐length free‐air ionization chamber for application in mammographic energy x‐ray beams. The chamber is designed to enable absolute in‐air exposure measurements. A unique feature of this design is that the variation in plate separation is accomplished by use of two stepping motor controlled translation stages. This paper details the characterization of this instrument and presents some preliminary exposure measurement results. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145590

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The sinter density of small superconducting BSCCO samples (Bi2Sr2Can−1CunOy;n=1, 2, or 3;yabout 7) was determined by hydrostatic weighing using a special technique to correct the mass data for penetration of immersion liquid. A discontinuity in the reevaporation curve permits one to distinguish between liquid, penetrated into the sample, and that adhering to the surface of the specimen. This allows one to calibrate by wiping away of excess liquid without fluid extraction out of sample pores. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145591

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The present paper presents a new experimental method developed for obtaining, simultaneously, the thermal conductivity and thermal diffusivity of nonmetallic materials. The method is based on signal treatment in the frequency domain. Two fast, high sensitivity heat flux transducers and two surface thermocouples measure the heat flux and temperatures, respectively. Time dependent temperature and heat flux signals at the boundaries define the equivalent complex impedanceZ. Fourier transform is applied to these signals and the impedanceZis obtained in the frequency domain. The difference between the experimental values and the values ofZestimated using a theoretical model is then minimized. The result is the simultaneous estimation of the thermal diffusivity and thermal conductivity. The use of both the modulus and the phase of an equivalent complex impedance promotes a separation of parameters, which assures the obtained values of &lgr; and &agr; to be unique. Error analysis and a comparison with the steady‐state method are also presented. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145592

出版商:AIP    

年代:1995

数据来源: AIP