Beam Transmission Efficiency Research Articles

Characterization of a polycapillary lens for use in micro‐XANES experiments

AbstractPolycapillary lenses permit x‐rays to be focused down to relatively small (<50 µm) beam diameters. A polycapillary device, suitable for focusing of synchrotron radiation, was characterized at beam line L of HASYLAB (Hamburg, Germany). Beam parameters such as beam size, transmission efficiency and gain in flux density were determined as a function of the energy of the primary monochromatic beam entering the polycapillary. At a distance of 4 mm between the lens tip and the sample, the smallest beam diameters were recorded: 30 µm at 7 keV, decreasing to 8 µm at 21 keV. In the energy range from 7 to 15 keV, the transmission efficiency varied between 30 and 45%, while the maximum gain in flux density was calculated to be around 3500. When the energy was changed from 7 to 30 keV, a vertical translation of only 7–8 µm was observed, indicating that this optic is highly suitable for use in µ‐XANES investigations. To illustrate this point, the investigation of paper corrosion due to iron gall inks and the speciation of Ni in environmental particles is described. Copyright © 2003 John Wiley & Sons, Ltd.

Stabilization of the rf system at the SPring-8 linac

Beam energy variation of the SPring-8 linac was 1% or more at the start of beam commissioning. Depending on fluctuation, beam transmission efficiency from the linac to the booster synchrotron was significantly affected, and beam intensity in the booster synchrotron changed 20–30%. This caused delay of optimization of the various parameters in the booster synchrotron. More problematic, the beam intensities stored in each rf (radio frequency) bucket of the storage ring at SPring-8 were all different from each other. The users utilizing synchrotron radiation requested that the beam intensity in each rf bucket be as uniform as possible. It was thus a pressing necessity to stabilize the beam energy in the linac. Investigation of the cause has clarified that the various apparatuses installed in the linac periodically changed depending on circumstances and utilities such as the air conditioner, cooling water and electric power. After various improvements, beam energy stability in the linac of <0.06% rms was attained. Consequently, the beam intensity in each rf bucket required by users was almost satisfactorily improved. This paper describes the processes used to search for the origin of the beam energy fluctuation and the remedy.

Strong-focusing in tandem accelerator with alternating voltage gradient

A new method to obtain low-energy high-intensity beams from a tandem accelerator of a high design-voltage is presented. In this method, the beam undergoes repeated actions of acceleration and deceleration from alternating voltage gradient along the beam axis, so that the beam divergence is minimized. The practical test was carried out at the 10 MV tandem accelerator at Kyushu University, and the beam transmission efficiency at a low operation voltage of 1 MV was found to be an order of magnitude increased. The method also enables the accelerator to stand a high beam load. The necessary changes in the accelerator configuration are quite simple and easily achievable at a low cost.

Numerical simulation of simultaneous acceleration of positive and negative ions in an RFQ

Abstract By means of a numerical method, beam dynamics was analyzed for an RFQ, where mixtures of positive and negative ions were injected into the quadrupole channel. In order to simulate simultaneous bunching of ions with opposite charges, the motion of particles injected into the cavity during two RF periods was traced under consideration of 3D Coulomb forces between particles. Effects of neighbor bunches were also taken into account. In the input region of the structure, the transverse beam divergence due to space charge forces was suppressed by the charge neutralization. However, it was found that the bunch formation in the cavity was disturbed by the attractive forces between positive and negative ions, leading to longitudinal beam loss. Dependence of the beam transmission efficiency on the input beam intensity as well as on the blend ratio of two ion species is reported. These results are compared with those obtained when injecting ions of single species.

Focusing Characteristics of an Optical Head with Superresolution Using a High-Aspect-Ratio Red Laser Diode

The focusing characteristics, when using a superresolution technique, for a high-aspect-ratio laser beam were investigated theoretically. The spot size, sidelobe intensity, and laser beam transmission efficiency were calculated against the shading mask width, fill factor, and optical disc tilt. It was revealed that, for a given transmittance, performing superresolution in the region of fill factors greater than 1 is effective both for reducing the spot size and for increasing the laser beam transmission efficiency. However, since superresolution sharply increases the sidelobe, it must be carried out in a practical range.

Behavior of Misaligned Beams in a High-Intensity Proton RFQ

Motion of off-centered beams in an RFQ for basic researches on nuclear transmutation was analyzed by using a beam optics computer code. In this analysis not only higher-order harmonics in the intervane potential but also 3D beam-generated forces including image effects were taken into account. Beam loss property and transmission efficiency were investigated for different input beam currents as well as for different injection angles. Results are compared with predictions by the PARMTEQ code. Enhancement of beam displacement at the exit of the cavity as well as increase in transverse beam loss was observed as effects of the image charge force. In any case beam loss due to the image effects was less than 3% of the injected particles. For beam injection angles larger than 1°, the beam transmission efficiency decreased owing to non-linear terms in the intervane potential. Tolerance for the error in beam injection angle into the RFQ cavity is also discussed.

Behavior of Misaligned Beams in a High-Intensity Proton RFQ.

Motion of off-centered beams in an RFQ for basic researches on nuclear transmutation was analyzed by using a beam optics computer code. In this analysis not only higher-order harmonics in the intervane potential but also 3D beam-generated forces including image effects were taken into account. Beam loss property and transmission efficiency were investigated for different input beam currents as well as for different injection angles. Results are compared with predictions by the PARMTEQ code. Enhancement of beam displacement at the exit of the cavity as well as increase in transverse beam loss was observed as effects of the image charge force. In any case beam loss due to the image effects was less than 3% of the injected particles. For beam injection angles larger than 1°, the beam transmission efficiency decreased owing to non-linear terms in the intervane potential. Tolerance for the error in beam injection angle into the RFQ cavity is also discussed.

Doppler-shifted neutral beam line shape and beam transmission

Analysis of Doppler-shifted Balmer-α line emission from the Tokamak Fusion Test Reactor’s (TFTR) neutral beam injection systems has revealed that the line shape, which is a direct measure of the velocity distribution function, is well approximated by the sum of two Gaussians, or, alternatively, by a Lorentzian. For the sum of two Gaussians, the wide-divergence part of the distribution contains 40% of the beam power and has a divergence five times that of the narrow part. Assuming a narrow 1/e-divergence of 1.3° (based on fits to the beam shape on the calorimeter), the wide part has a divergence of 6.9°. The entire line shape is also well approximated by a Lorentzian with a half-maximum divergence of 0.9°. Up to now, most fusion neutral beam modelers have assumed a single Gaussian velocity distribution, at the extraction plane, in each direction perpendicular to beam propagation. This predicts a beam transmission efficiency from the ion source to the calorimeter of 97%. Waterflow calorimetry data, however, yield a transmission efficiency of ∼75%, a value in rough agreement with predictions of the two Gaussian or Lorentzian models presented here. The broad wing of the two Gaussian distribution also accurately predicts the loss in the neutralizer. An additional factor in determining the power density at the surface of beam absorbers is the angle at which the particles arrive. Angles are different for particles emitted from different locations on the ion source. To treat this situation, the average angle of incidence is calculated. For beam loss at the exit of the neutralizer, the average angle of incidence is 2.2°, rather than the 4.95° subtended by the center of the ion source. This average angle of incidence is found to be a function of beam divergence.

Effects of 3D image charge force on the motion of off-centered beams in an RFQ

Behavior of misaligned ion beams in an RFQ was analyzed by using a 3D beam dynamics computer code. In order to take the image force into account, a 3D Dirichlet's boundary problem defined by the electrode surface and the off-centered beam space charge was solved at every time-integration step. This method was applied to analysis of the beam dynamics in an 80-MHz RFQ. Compared with the result obtained without image charge effects, no marked change was observed for the beam transmission efficiency. However, it has been found that the amplitude of transverse beam oscillation can be amplified by the image charge force.

Beam characteristics and preliminary applications of the tandem based AMS at Peking University

A dedicated tandem based AMS facility was constructed and put into operation at Peking university. Preliminary applications to the carbon dating of archaeological samples are performed at a background level of 10 −14 with an accuracy better than 1.7%. The designed features of the system as well as the measured beam emittance and transmission efficiency are presented. The suppression of background and fractionation effect and the precision of the measurements are discussed.

The Daresbury tandem. A review 1970-92

A review of the technical developments which were made for the design of the Daresbury 20 MV tandem with particular emphasis on those ideas which were new and innovative is presented. The topics discussed include the high current inductive charging system or laddertron, the shielding of insulators and resistors from voltage surges, the hard vacuum ceramic/titanium accelerator tube, screening of sensitive electronics and the control system. The developments made to these systems over the years of full time operation from 1983 to 1992 are described and the most recent additions to the accelerator to improve the ion bunch stability and to improve the operational beam transmission efficiency using specially developed computer software are also described.

加速器質量分析による｀１０´Ｂｅと｀２６´Ａｌの測定

The technical details of accelerator mass spectrometry (AMS) developed at the University of Tokyo tandem facility are described for 10Be and 26Al measurements. Using a unique techique called the “internal beam monitor method”, isotopic ratios of 10Be/9Be and 26Al/27Al are determined without sequentially accelerating each isotope. 10Be and 26Al are injected to the accelerator in forms of negative ions, 10Be16O- and 26Al-, accompanied by the pilot beams of 9Be17O- and 10B16O-, respectively. The accelerated negative ions are converted to positively charged atomic ions by passing through a thin Ar gas in the stripping canal at the high voltage terminal of the accelerator. The triply charged ions, 10Be3+ and 26Al3+, are selected and counted by a heavy ion detector, while the currents of 9Be3+ and 16O2+, decomposed ions from the pilot beams, are simultaneously monitored with Faraday cups at the focal plane of the magnetic analyzer. The monitor beam currents allow the determination of the beam transmission efficiency through the accelerator. The data are presented to show an ability of precise measurement. The reproducibilities for repeated measurements in 24 hours were 1~3% and 2~5% and the sensitivities were 5×10-14 and 1×10-13, for 10Be and 26Al, respectively.

Geometrical effects on the beamlet optics of a two-stage ion accelerator

The effects of geometrical parameters (aspect ratio, aperture size, gaps) and electrical parameters (voltage distribution, beam energy) on single-beamlet profiles are investigated theoretically and experimentally on a two-stage ion accelerator over both a broad range of beam conditions and a wide range of angles (0 to ±11.5°). In general, the intensity distribution is non-Gaussian. Under optimum conditions, divergence angles half-width at half maximum less than 0.5° could be achieved even with large holes (0.9 mm). Shaping the plasma grid reduced the non-Gaussian wings and improved the beam transmission efficiency.

Magnetic compression and electrostatic reflection of very high /spl upsi/ γ electron beams

High current sub-ohm electron-ion diodes are produced in the highly converging fringe fields at one end of a magnetic solenoid. With these diodes, the magnetic compression of a very high /spl upsi/γ electron beam is investigated with and without the formation of a virtual cathode at the peak magnetic field. The magnetically focused beam transmission efficiency, area compression, and fluence gain are documented for up to 10:1 mirror ratios. When a virtual cathode is formed at the mirror peak, efficient electron beam reflexing is induced - thereby increasing the effective fluence through thin foils by a factor of six (or twice the optimum gain with conventional magnetic compression). Up to 3 MJ/g deposition in 0.1 mil copper foil is deduced from this data.

Optical Engineering Aspects of Laser Surgical Instrumentation

At the Laser Laboratory of the Medical Center of the University of Cincinnati for more than 11 years detailed studies have been done with laser surgery in animals and in clinical investigative studies in a large series of patients. It is evident that the optical engineering phase of current laser surgical instrumentation requires considerably more research and development. Reliable high-output lasers, preferably CW, Md-YAG, CO2 are argon are required. Optical engineering requirements include flexibility and efficiency of beam transmission through small, sterilizable precise operating probes capable of incision, coagulation or fulguration. Probes must be adaptable for use with operating microscopes and for laser surgery in body cavities.

Some theoretical considerations of ion optics of the mass spectrometer ion source: II. Evaluation of ion beam transmission efficiency

The mathematical theory of the motion of ions in the ion source has been applied to evaluate the ion beam transmission efficiency. In the absence of any repeller field, ions from a narrow horizontal strip of width equal to that of the exit slit are withdrawn. On the other hand, in the presence of a repeller field the ion withdrawal space consists of two star-shaped figures connected by a narrow canal. The dimensions of the star-shaped figures are comparable with the width of the entrance slit, which is about ten times the width of the exit slit. When the ion withdrawal space is a maximum, the transmission efficiency is a maximum. The repeller field for a maximum ion withdrawal space is about 0·32 per cent of the accelerating field. The mass discrimination for heavy ions due to a weak source magnetic field (a few hundred gauss) is negligible.