摘要:

The effect on H−production by injecting primary electrons with different energies into the three regions of a magnetically filtered multicusp source has been investigated. A substantial increase in H−yield occurs only when very low‐energy electrons (E≊1 eV) are added to the plasma in the filter or extraction chamber region. The measured increases were about 50% and 25%, respectively. This increase may indicate that the H−ions are formed by dissociative attachment of vibrationally excited H2. In that case, the low‐energy electron injection scheme could maintain a low average H−ion energy which in turn could improve the brightness of the extracted beam.

ISSN:0034-6748    

DOI:10.1063/1.1138938

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An electron impact ion source using a solid charge was interfaced with A/D and D/A units which are connected to a microprocessor control unit. A PID (proportional, integral, and derivative) control algorithm was implemented to control the ion source. The power fed to the ion source filament and furnace filament are controlled so as to keep both the discharge voltage and current constant. With this controlled ion source, the result shows a steady ion current. For example, with Pb+ions, an initial ion current of 13 &mgr;A stayed within ±1.5 &mgr;A for 60 min; with no control, the ion current fell steadily and had to be manually reset three times every 20 min over a 60‐min run. Similar results have been obtained with Mg+, Al+, Zn+, and Sn+ions.

ISSN:0034-6748    

DOI:10.1063/1.1138939

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A beam delivery system for large uniform dose fields suitable for cancer radiotherapy has been constructed for the TRIUMF pion treatment facility using discrete step beam scanning in three dimensions. The patient on a couch is scanned laterally relative to a pencil beam in a raster fashion. At each spot, the depth dose profile is delivered by range modulations using a range shifter. The operations of the scanning couch and range shifter are synchronized by the use of beam monitor pulses from a beam intensity integrating system. The system is hence versatile enough to handle treatment volume of highly irregular shape and yet is immune to fluctuations in accelerator output.

ISSN:0034-6748    

DOI:10.1063/1.1138940

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The design, construction, and operational characteristics of a continuous3He–4He dilution refrigerator specifically built for use in muon spin relaxation ( &mgr;SR) measurements at LAMPF are described in this paper. The refrigerator is unique in that it makes an angle of 30° with respect to horizontal—a requirement imposed by the previously existing physical constraints of the &mgr;SR spectrometer. Additionally, the refrigerator and associated gas handling units are portable so as to facilitate ease of movement into and out of the muon beam. Typical parameters describing refrigerator performance are 60‐mK base temperature with 22‐&mgr;W cooling capacity at 100 mK.

ISSN:0034-6748    

DOI:10.1063/1.1138941

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A diagnostic technique for measuring beam emittance is developed for electron beams with diverging envelopes under strong space‐charge forces. Radial profiles of current density, local temperature, and divergence angle are measured by the slit–pinhole method for axisymmetric beams. The particle distribution function in transverse phase space is then constructed and the rms emittance is obtained by numerical integrations. A 5‐kV, 200‐mA, 3‐&mgr;s, and 60‐pps electron beam is used in the comparison between theory and this experimental diagnostic method.

ISSN:0034-6748    

DOI:10.1063/1.1138942

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A novel experimental method to measure both the velocity distribution and the relativistic factor &ggr; of intense guided electron beams is described. The method is based on the use of a magnetic hill to discriminate the electrons with different transverse velocity components. Analysis of the current reflected by the hill as a function of the height of the hill yields the above mentioned beam characteristics.

ISSN:0034-6748    

DOI:10.1063/1.1138943

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The absolute detection efficiencies of detectors consisting of two microchannel plates (MCP) in a chevron arrangement, were experimentally determined for 0.1–2.3‐keV electrons and 2.1–4.4‐keV Mg+ions. Both detectors tested included a grid with 92.5% transmission in front of the first MCP. For the measurements, the observed detector count rates were compared to the corresponding particle currents collected in a Faraday cup and measured with a vibrating reed electrometer. The electron detection efficiency of the MCP detector, including the grid, decreases from 0.82 at 0.1 keV to 0.65 at 2.3 keV for electrons incident normal to the surface. The Mg+ion detection efficiency for the same arrangement, but with 43° incidence angle, increases from 0.49 at 2.1 keV to 0.81 at 4.4 keV.

ISSN:0034-6748    

DOI:10.1063/1.1138944

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The output energy distribution of microchannel plates with different output electrode structures has been studied experimentally. It is shown that the penetration depth of the output electrode into the microchannel plates &ohgr; is a very important factor affecting both the output energy spread and the gain. When &ohgr; becomes twice the length of a channel diameter, the unfavorable tail component in the energy distribution can be suppressed. Improvement in the output energy spread, however, results in a considerable gain reduction. These characteristics are clarified by the internal current behavior in MCPs inferred from two operating dynode currents at the input and output ends.

ISSN:0034-6748    

DOI:10.1063/1.1138945

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new type of molecular‐dissociation furnace has been developed for producing thermal beams of H and O atoms to be used as targets for fast atomic projectiles in various scattering experiments. Target‐particle densities in the beam from the furnace of about 1011cm−3have been achieved with molecular‐dissociation fractions in excess of 0.7 for each species. The techniques used are described and compared with more traditional furnace designs.

ISSN:0034-6748    

DOI:10.1063/1.1138946

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

This paper is complementary to a recent work [Kumaretal., Rev. Sci. Instrum.54, 463 (1983)] that described a simple, inexpensive technique for correcting laser‐induced, pulsed signals for fluctuations of the individual laser excitation pulses. This inexpensive pulse‐by‐pulse correction technique, based on analog circuitry, exhibits an improved time‐constant characteristic and is applicable to both linear and nonlinear processes. Circuit details are presented here and the versatility of the technique is illustrated by laser optogalvanic spectroscopy of the iodine molecule.

ISSN:0034-6748    

DOI:10.1063/1.1138947

出版商:AIP    

年代:1986

数据来源: AIP