A technique of measuring and correcting emittance dilutions due to accelerator structure misalignments

This paper describes a method of reducing the transverse emittance dilution in linear colliders due to transverse wakefields arising from misaligned accelerator structures. The technique is a generalization of the Wake-Free [T.O. Raubenheimer, Nucl. Instr. and Meth. A 306 (1991) 61] correction algorithm. The structure errors are measured locally by varying the bunch charge and/or bunch length and measuring the change in the beam trajectory. The structure errors can then be corrected by varying the trajectory or moving the structures. The results of simulations are presented demonstrating the viability of the technique.     

A method for measuring the high voltage of a low energy Van de Graaff accelerator

A simple method for measuring the operating high voltage of a small positive ion Van de Graaff accelerator was developed. It is based on the determination of the end-point energy obtained from the X-ray radiation spectra. The accuracy of the proposed method is better than 1%. Most of these accelerators have an associated magnetic beam analyzer and/or generator voltmeter gauges that require calibration. The proposed method can be used to calibrate these instruments.     

A new dynamic technique for the measurement of hemispherical total emittance

A new dynamic technique for the measurement of thermal conductivity under development at the IMGC requires accurate values of heat capacity and of hemispherical total emittance at high temperature. Until recently, these data were provided by subsecond pulse heating experiments performed on the same specimens in the same apparatus. The pulse heating technique is the most accurate method for the determination of heat capacity at high temperatures, but because of various experimental problems, the accuracy of hemispherical total emittance determinations is limited to 5%. A new method for a more accurate determination of hemispherical total emittance is proposed, which uses the same experimental data available from thermal conductivity experiments. An analysis of the temperature profiles measured during the free cooling indicates that regions with high-temperature gradients (toward the ends of the specimen) are the best regions for thermal conductivity measurements, while regions with low-temperature gradients (at the center of the specimen) are the best regions for hemispherical total emittance determinations. The new measurement method and some preliminary results are presented and discussed.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

一种新的测量半球全波发射率的动态技术

本章介绍了一种用于半球全波发射率测量的动态技术 .它需要已知热容量和热传导率的准确的资料 .对在自然冷却过程中所测量的样品的温度分布的分析表明 ,高温度梯度区域 (样品的两端部分 )是测量热传导率的最好区域 ,而低温度梯度区域 (样品的中间部分 )是测量半球全波发射率的最佳范围 .讨论了这种新的测量方法及一些初步的实验结果 .     

Investigating the TEPC radiation quality factor response for low energy accelerator based clinical applications

The use of a tissue equivalent proportional counter (TEPC) filled with propane based tissue equivalent gas simulating a 2 microm diameter tissue sphere has been investigated to estimate the radiation quality factor of the neutron fields used in in vivo neutron activation measurements at the McMaster University 3 MV Van de Graaff accelerator. The counter response to estimate the effective quality factor based on the definitions of Q(L) provided in ICRP 26 and 60 as a function of neutron energy has been examined experimentally using monoenergetic and continuous neutron spectra in the energy range of 35 to 600 keV. In agreement with other studies, the counter failed to provide a flat R(Q) response and showed a sharp drop below 200 keV neutron energy. Development of an algorithm to evaluate the quality factors using measured dose-mean lineal energy, yD, and comparison of the algorithm with other reported algorithms and analytical methods developed for the improvement in TEPC dose equivalent response has been reported.     

Temperature dependence of the band emittance for nongray bodies

The general problem of obtaining correct emittance values from broadband IR radiometric measurements on nongray samples is discussed. If the spectral emittance has structure in a band, the emittance, averaged over that band, will be temperature dependent, even if the spectral emittance is insensitive to the temperature change. We point out that a widely used expression, with correction for radiance from the surroundings reflected by the sample, is valid only if the spectral emittance is temperature and wavelength independent, i.e., gray. If the spectral emittance is nongray, the conventional emission factor, as determined by a broadband radiometer, is temperature dependent and the numerical value is significantly different from the averaged band emittance sought. Two algorithms are suggested to extract the correct band-averaged emittance from the temperature-dependent radiometric emission factor obtained with the conventional expression. The algorithms are demonstrated with a step model for the spectral emittance, and it is shown that the agreement with the correct average band emittance is significantly improved.     

Calculated photonic structures for infrared emittance control

Using an available program package based on the transfer-matrix method, we calculated the photonic band structure for two different structures: a quasi-three-dimensional crystal of square air rods in a high-index matrix and an opal structure of high-index spheres in a matrix of low index, epsilon = 1.5. The high index used is representative of gallium arsenide in the thermal infrared range. The geometric parameters of the rod dimension, sphere radius, and lattice constants were chosen to give total reflectance for normal incidence, i.e., minimum thermal emittance, in either one of the two infrared atmospheric windows. For these four photonic crystals, the bulk reflectance spectra and the wavelength-averaged thermal emittance as a function of crystal thickness were calculated. The results reveal that potentially useful thermal signature suppression is obtained for crystals as thin as 20-50 microm, i.e., comparable with that of a paint layer.     

CAMAC control system for the unilac injector

A computer control system for the UNILAC injector has been developed. To study the problems of injector operation under real conditions, a test bench was built which would generate nearly the same load on the control system as the injector. The control problems of source operation, ion beam extraction, focusing, beam diagnostics and spectra optimization have been studied intensively.     

Density measurements of diamond-like coatings using a low energy accelerator

With the aid of nuclear physical methods based on the use of a low energy accelerator it is shown that the density of even a small, uneven and rough diamond-like coating prepared by mass-separated ion beam deposition can be determined reliably. The density of the coating corresponds to that of diamond. Outlines of the used methods, i.e. Rutherford backscattering and/or nuclear resonance shift combined with the use of a profilometer and Doppler shift attenuation, are presented.     

A new form of accelerator for charged particles

A new form of accelerator is proposed which employs an electric field of constant magnitude rotating in a plane perpendicular to a static magnetic guidance field.     

A design for a 280-kV ion accelerator

The innovative design features for a 280-kV ion accelerator are described. These features include a versatile in-line ion injector which was modelled after a commercial ion gun and an acceleration tube and power-transfer system that were made, economically, in-house. The accelerator is capable of generating a mass-filtered ion beam of solid or gaseous species. Maximum beam current observed during initial trials with N₂⁺ was 0.6 μA at an acceleration potential of 50 kV, rising as acceleration potential was increased to 1.5 μA at 280 kV. Spot size remained invariant at approximately 3 mm diameter.     

HL-2A中性束注入器送气实验

为满足HL-2A中性束加热的需求,我们为HL-2A的NBI注入器研制了脉冲送气回路及其控制系统,系统的核心流量控制部件为PEV-1压电晶体阀,主要是根据气压测量结果调整压电阀电源输出脉冲电压波形来控制压电阀的流导.为克服了压电阀性能参数离散,对不同离子源的送气回路进行了单独标定.送气实验结果表明,离子源放电室气压控制精度达到了0.05Pa,通过调整不同压电阀电源输出波形,减小了束线4个离子源送气回路之间相互影响,得到了平稳的离子源工作气压.     

An “emittance conserving” chopper for particle beams

The principle and the construction of the emittance conserving chopper at the Munich tandem laboratory will be presented as well as its performance and first operation with beam. The chopper is installed at the high energy side of the MP tandem and consists of two resonant circuits. The first circuit is the actual beam deflector, while the second circuit, which is operated at a higher harmonic frequency of the first one, corrects for both the transversal and longitudinal spreading of the beam caused by the applied fields of the first circuit.     

Heavy ion injector for the CERN Linac 1

An injector system has been constructed to provide heavy ion beams for the CERN accelerators. In the initial step, an ECR (electron cyclotron resonance) source produces an O⁶⁺ ion beam, which is accelerated in an RFQ (radiofrequency quadrupole) structure from 5.6 keV/u to 139.5 keV/u. The specifications of this preaccelerator are described and results of test measurements at GSI are presented, as well as first experience at CERN. Oxygen ions have been accelerated in the CERN machines to 200 GeV/u. An upgrading program for the acceleration of sulphur or calcium is presented.     

A compact railgun accelerator for millimeter-sized dielectric solid armatures

Millimeter-sized dielectric solid armatures have been accelerated in a compact railgun system. It is shown that application of an external pulsed magnetic field can solve the problem of catastrophic erosion of electrodes at the initial stage and accelerate small armatures up to a velocity of about 6 km/s.     

A simple unified physical model for a reluctance accelerator

In this paper, we develop an illustrative, physically unified model for treating a solenoidal reluctance linear accelerator. A simplified field-based physical model is developed from basic principles and cast in a variational (Lagrangian) form. The equations of motion are presented in a convenient form for computation, from which a fast and compact numerical model is constructed that also accounts for the effects of core saturation as well as the energy exchange between the field and armature motion. The results of this model are then compared with experimental results obtained from a small-scale mass launcher apparatus. Good agreement between experimental and computed behavior has been observed.     

A study on low magnetic permeability gas tungsten arc weldment of AISI 316LN stainless steel for application in electron accelerator

Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel.