Beam Sweep Research Articles

Accurate coplanarity measurement of a network of points, using linear CCD sensors and a sweeping laser beam

A method for a real time remote accurate coplanarity measurement of a network of points is presented. A light surface, generated by a laser and a rotating pentaprism, is used as a reference plane to which the relative positions of a set of CCD sensors, located on the nodes of the network, are determined. Based on this method, a prototype for the alignment of the CMS detector has been built and tested. Position reconstruction algorithms and experimental test results are presented. The obtained position measurement precision was 10 μm up to distances of 6 m.

Fast method for measuring power density distribution of non-circular and irregular electron beams

A fast method for measuring the power density distribution of electron beams has been developed. The method employs a refractory metal disc containing regularly spaced radial slits and a Faraday cup to measure electron beam profiles as the beam is oscillated in a circular pattern over the disc. This beam profiling method can be used for real time focusing along a given beam sweep orientation by monitoring one of the beam profiles. When the focus setting is satisfactory, all of the beam profiles can then be stored for computed tomography (CT) reconstruction. The CT reconstruction renders an image of the powder density distribution and provides beam statistics as a permanent file for process control records. The process (taking ∼1 min to perform in its entirety using a conventional PC) was used to investigate the influence of focus setting on the power density distribution of 5 mA electron beams operating at accelerating voltages of 80 and 140 kv. Results of these tests show the effects of beam astigmatism on the power density distribution and the optimum focus conditions for these non-circular beams. In addition, these results show the ability of the 140 kV beam to focus more precisely and thus produce higher power densities than the 80 kV beam.

Potential profile measurements on compact helical system (CHS) using a 200 keV heavy ion beam probe

A 200 keV heavy ion beam probe system has been prepared to measure potential profiles in the compact helical system. Probing beam trajectory is successfully controlled by a secondary beam sweep system to keep the injection angle of the secondary beam constant during the radial scan. As a result, it was observed that the potential profile changes after the neutral beam heating is applied on electron cyclotron heated plasmas.

The development of curved reflective surfaces for ultrasonic beam redirection in high speed gas flow measurement

Results are presented on the development of curved reflecting surfaces for use in an ultrasonic transit time flowmeter for high speed gas flow measurement. These surfaces were designed to reduce the effects of ultrasonic beam sweep which occur at high (subsonic) flowrates. They reflect the swept ultrasonic beam so as to redirect it towards the receiving transducer. Basic analysis of the effect of the flow on the reflection of beam are included and differential equations for three reflection profiles based on different assumptions about this effect are presented. Numerical techniques used in the solution of these equations are discussed. The effect of the profiles on the ultrasonic transit time is analysed. The design of a reflective ramp based on one of these profiles is presented, and experimental measurements are provided showing an increased meter range without a detectable loss of accuracy.

Targets and target wheel mechanism for APEX

A rotating target wheel system built for the Atlas Positron Experiment (APEX) is described. It is designed so that targets could withstand the heating caused by the energy loss of intense heavy ion beams. A unique feature is the use of a digital encoder to provide logic trigger signals for beam sweeping and event-by-event target location information. Techniques for fabricating targets of tantalum, lead, thorium and uranium and the behaviour of the targets during beam exposure are also discussed.

Total body irradiation with a sweeping 60Cobalt beam

Purpose: This article describe the physical, technical, and dosimetric aspects of total body irradiation (TBI). Methods and Materials: The continuous head swivel motion of a standard 60Cobalt unit has been used to obtain a sweeping beam that encompasses the entire length of the patient in TBI. A perspex beam flattener designed to remove the inverse squarer fall-off in beam intensity along the sweep axis provides a 90% field pair setup permits accurate placement of customized lead compensators to limit the dose to lungs. Results: Measured beam profiles, dose buildup curves, and percentage depth dose for the technique are presented. With compensators in place, the variation in lung dose is shown to be within ± 5% of the prescribed tumor dose. Conclusions: A sweeping beam TBI technique has been advised using a standard 60Cobalt unit. The technique allows the patient to be treated in supine and prone positions, which facilitates the accurate placement of lung compensators to limit the dose to lung tissue.

Uniform target irradiation by circular beam sweeping

A circular sweep of the beam over a large target for making a uniform irradiation zone is suggested. The scan pattern is an untwisted spiral for a continuous beam or a family of concentric circles for a bunched beam. The deflection voltage is provided by RF cavities with orthogonal transverse fields shifted in time by π 2 . The amplitude of the deflection voltage as a function of time and the optimal beam scan frequency with respect to the RF frequency of the accelerator are given. The considered method of target irradiation can be useful in different applications of charged particle beams including microfilters production and transmutation of nuclear wastes where a large amplitude of the deflection voltage and a high uniformity of irradiation are required.

209 PIVを用いた多翼ファン翼間内流れの可視化および速度分布計測

Visualization and velocity measurement of flow through impeller of a multi blade fan have been carried out with PIV technique. Tracer particle image was taken by a still camera. Test section was illuminated by dual laser beam sweep method. The obtained double exposured photograph was low density particle image. It was analyzed by auto-correlation method with personal computer. Reconstructed vector diagram shows a good agreement with that obtained by a particle tracking method.

Recombination correction factors for an ionization chamber exposed to discrete patterned pulsed swept beams.

An equation for a recombination correction factor for a pulsed swept beam of electrons was derived by Boag. This equation is based on an integration technique, which assumes that a large number of spot beams cover the radiation field, that the field size is much larger than the spot beam size, and that the spot beam size is much larger than the chamber size. However, for computer-controlled pulsed swept beams of electrons, the spot beam pattern can be altered, may not cover all of the field area, and the locations are reproducible. In this report, a summation method is proposed for this type of beam. Calculations for two such beams are demonstrated with the chamber located in the center of the field, and with the chamber half-way to and at the edge of the field for a linear accelerator. The results lie between the integration pulsed swept and pulsed beam curves. Moving the ionization chamber from the center toward the edge of the field produces curves closer to the pulsed swept beam curve. Increasing spot beam size produces curves closer to the pulsed beam curves. It is therefore concluded that the pulsed swept beam cannot be characterized by a single recombination correction factor curve. The actual curve will be bounded by the integration pulsed swept and pulsed beam curves.

The design of an atmospheric pressure ionization/time-of-flight mass spectrometer using a beam deflection method

A novel time-of-flight (TOF) mass spectrometer configuration has been designed which can be interfaced to a continuous ion beam source produced by atmospheric pressure ionization. The TOF device uses a beam deflection method to sweep the ion beam past a slit placed near the ionization source in order to generate a start pulse for TOF detection. The beam sweep technique is modeled by computer simulation and optimized for the various experimental parameters. Nonvolatile samples are injected into the TOF device using liquid injection into a glow discharge atmospheric pressure ionization source in helium. A resolution of at least 519 at m/z 311 is obtained, which is limited by the experimental parameters available in our experiment. The mass resolution is computer modeled and it is shown that as the mass increases, the experimental constraints become less important, and the resolution will increase. It is predicted that using the correct experimental conditions and with the addition of an ion reflector that resolution of well over 1000 should be obtained.

二次イオン質量分析法によるシリコン結晶中の炭素と酸素の分析において定量性に影響する因子

The purposes of this study were to evaluate the influences of the primary ion beam current and the primary ion beam sweep area on the quantitative analyses of carbon and oxygen in silicon single crystals by secondary ion mass spectrometry (SIMS). The influences of them were examined in consideration of the slope of calibration curves and the form of craters. Five different (100) silicon single crystals, whose carbon and oxygen concentrations were determined by Fourier Transformation infrared spectrometry (FT-IR), were used as samples.The best analytical conditions of carbon and oxygen obtained were 0.6 μA and 1.0 μA for the primary ion beam current and 200 μm×200 μm and 100 μm×100 μm for the primary ion beam sweep area, respectively. The high primary ion beam current density was suitable for the oxygen analysis, and the medium primary ion beam current density for the carbon analysis. The reason of the difference of suitable primary ion beam current density is explained with a difference of mechanism of adsorption of carbon-containing molecules and oxygen-containing molecules under the ion bombardment. Adsorption of carbon-containing molecules on the sample surface is enhanced under the ion bombardment, whereas that of oxygen-containing molecules is not enhanced. So, the high primary ion beam current density is not suitable for the carbon analysis since the background intensity is increased by adsorption of carbon-containing molecules.At the best analytical condition of oxygen obtained, the sputtering rate was 15 nm/s and the form of crater after ion sputtering became like a corn. Therefore, the depth resolution was wrong and sensitivity is not compatible with depth resolution on SIMS analysis.

Femtosecond optical gating with a traveling-wave amplifier

A traveling-wave amplifier, pumped by high-power femtosecond pulses, operates as an optical gate, providing a gate window of 100 fs and a gain of greater than 109. This property is applied for femtosecond pulse generation from the cw output of a Kr+ laser. The required signal input level is as small as 1 photon/fs. The temporal properties of the traveling-wave amplifier can be fairly well described by a simple rate-equation system that takes into account gain competition between the signal and amplified spontaneous emission. The gate width is determined by the time mismatch between the transit of the signal through the amplifier and the sweep of the pump beam across the active volume.

Implant dose uniformity simulation program

A two-dimensional implant dose uniformity simulation code consisting of two programs named SCAN and MAP has been developed. The code can take account of the effects of beam sweep waveform, beam sweep frequency, beam size, and wafer rotation speed. The result of the calculations can be plotted in a two-dimensional contour map similar to a wafer uniformity map.

The Nissin NH-20SP medium-current ion implanter

The NH-20SP medium-current ion implanter has been developed to meet the needs of advanced ULSI fabrication processes. The NH-20SP has the following features: (1) parallel-beam implantation, (2) 8 in. wafer compatible, (3) precise dose-uniformity control, (4) in-situ parallelism and uniformity monitor, (5) large-tilt-angle implantation, (6) step wafer-rotation during implantation. The NH-20SP employs a hybrid scan system. The horizontal parallel-beam sweep is accomplished with two sets of electrostatic electrodes. A wafer is scanned vertically by a swing-arm scan mechanism. A digital beam sweep system controls the dose uniformity across the wafer. Implant dose uniformity is achieved by adjusting the speed of the vertical wafer motion. The swing-arm scan mechanism provides a large-tilt-angle implantation and stepwise rotation of the wafer during implantation. In this paper an overview of these features will be given and performance data will be presented.

Status of the Alcator C-MOD scanning two-dimensional Thomson scattering diagnostic

The detailed study of noncircular tokamak discharges will require measurements of local Te and ne over a two-dimensional region. A novel scanning Thomson scattering system is under construction for use on the Alcator C-Mod device. A multipulse (50 Hz pulse rate) Nd:YAG laser (1 J, 15 nS) will be used to scan the plasma major radius within a 14 cm range during a 160 mS period with a spatial step size of 2 cm. The laser beam sweep, which is limited by the size of the diagnostic ports, will cover ∼50% of the plasma discharge cross section. The scattered laser light spectra at various positions along the vertical laser beam path will be analyzed by a set of up to 11 (initial operation is planned for six) Wadsworth spectrometers. A prototype spectrometer with associated light collection optics has been tested and the total Thomson system optical transmission has been measured to be ∼12–15%. System details and performance measurements will be presented.

Pattern selection in thermal convection in an annulus

We report an analysis of the selected wave vector, as a function of the Rayleigh number, in thermal convection in annular geometry. The patterns have been studied by means of shadowgraph and, more quantitatively, with a sweeping laser beam. The selection processes have been investigated in cells of different sizes. We find that the wavevector increases for radial aspect ratios less than 2, whereas it decreases for larger aspect ratios. The thresholds for time-dependent regimes have also been measured.

The Laser Beacon: A survey system for the torsion-free alignment and monitoring of the L3 Muon Spectrometer octants

Given the small sagitta of a few millimeters of high energetic muons in the L3 Muon Spectrometer at LEP (CERN) and the enormous dimensions (75 m 2 × 14 m) of this instrument, it is evident that alignment is the most critical task for its proper evaluation. In the chambers of each of the sixteen modules (“octants”), which form the spectrometer, wire planes are precisely positioned with respect to the front side and the rear side centerlines. A novel system - the Laser Beacon System - allows to make these centerlines coplanar within 25 μ rad by the aid of a reference plane defined by a sweeping laser beam. This restricts a possible torsion induced systematic momentum error for a 50 GeV/ c muon to 0.25%. The main design and production features of the Laser Beacon System are described. Results of measurements in test assemblies and in the octants are given.

流路壁に近接する柱状物体周りの馬蹄渦の可視化

The flow around a circular cylinder or a rectangular column placed at various spacing to a flat plate has been investigated experimentally by making use of visualization technique. An open channel is used for the experiment, and the column is placed vertically to the bed. The method of flow visualization used in this report is the beam sweep laser speckle photography. The plane of observation is illuminated by periodical sweeps of a laser beam scanned by a galvanometer mirror, and multi-exposure photographs of speckle pattern of the flow seeded with tracer particles are recorded.Visualization results clearly show the change of horseshoe vortex system with the spacing between the end face of column and the bed of the channel.

Dynamic errors of a two-coordinate ADC of displacements with a circular light beam sweep

Dynamic errors of a two-coordinate ADC of displacements with a circular light beam sweep

ビームスィープ・レーザスペックル写真法による定量的可視化法の開発

The speckle photography has been established as a method of velocity measurement in two-dimensional flow field at the same instance. This method is based on taking a double exposure photograph (specklegram) of measuring field, seeded with tracer particles and illuminated by pulsed light sheets. If a pulsed light source combined a low-power CW-laser with a beam chopper is used for this method, the intensity of light sheet is not sufficient to obtain a fine specklegram of the flow suspending with small tracer particles following up the flow.In this report, a new technique that the flow field is swept by a laser beam generated from a He-Ne laser source (15mW) is developed and named as the beam sweep laser speckle velocimetry. This method is applied to velocity measurement of a flow with a horseshoe vortex produced by a triangular column placed into a laminar boundary layer developed in a water channel flow suspending TiO2 particles (mean dia. 5μm). As the result, the fine specklegram is obtained for quantitative flow visualization.