Optimization of the collimation system for CSNS/RCS with the robust conjugate direction search algorithm

The Robust Conjugate Direction Search（RCDS） method is used to optimize the collimation system for the Rapid Cycling Synchrotron（RCS） of the China Spallation Neutron Source（CSNS）. The parameters of secondary collimators are optimized for a better performance of the collimation system. To improve the efficiency of the optimization, the Objective Ring Beam Injection and Tracking（ORBIT） parallel module combined with MATLAB parallel computing is used, which can run multiple ORBIT instances simultaneously. This study presents a way to find an optimal parameter combination of the secondary collimators for a machine model in preparation for CSNS/RCS commissioning.

Design of proton beam collimation system for HIAF-BRing

Background The Booster Ring is further designed to store and accelerate protons up to 2×1012 particles per pulse in the High-Intensity heavy-ion Accelerator Facility project,which was originally designed to accelerate high-intensity heavy ion beams.Purpose and Methods To minimize the uncontrolled proton beam halo loss around the ring in operation,a two-stage collimation system is proposed to provide a well-shielded dump for localizing the proton beam halo loss.Results and conclusion In this paper,the simulation is carried out to evaluate the collimation system which shows a 92.93%collimation efficiency.Finally,several factors that affect the collimation efficiency are taken into consideration,including the physical aperture,the offset and rotation errors of the collimators,the closed orbit distortion,as well as the Betatron tunes.

Systematic study on visible light collimation by nanostructured slits in the metal surface

We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove-groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.

Thermodynamic analysis and simulation for gas baffle entrance collimator of EAST-NBI system based on thermo-fluid coupled method

The world's first full Experimental Advanced Superconducting Tokamak(EAST) is designed with the auxiliary heating method of neutral beam injection(NBI)system. Beam collimators are arranged on both sides of the beam channel for absorbing the divergence beam during the beam transmission process in the EAST-NBI system.The gas baffle entrance collimator(GBEC) is a typical high-heat-flux component located at the entrance of gas baffle. An efficient and accurate analysis of its thermodynamic performance is of great significance to explore the working limit and to ensure safe operation of the system under a high-parameter steady-state condition. Based on the thermo-fluid coupled method, thermodynamic analysis and simulation of GBEC is performed to get the working states and corresponding operating limits at different beam extraction conditions. This study provides a theoretical guidance for the next step to achieve long pulse with highpower experimental operation and has an important reference to ensure the safe operation of the system.

Structured mirror array for two-dimensional collimation of a chromium beam in atom lithography

Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically（in x axis）,and it is 0.55 horizontally（in y axis）.The theoretical model is also simulated,and success of our structured mirror array is achieved.

Methods for Setting up a Three-Dimensional Industrial Surveying System of “Building Blocks Type”

This paper is to advance some relevant techniques to set up a three-dimensional industrial surveying system of “building blocks type”, making use of the electronic theodolite, standard ruler and portable computer.

Another Collimation Mechanism of Astrophysical Jet

The acceleration mechanism of astrophysical jet and the collimation mechanism narrowing down to a long distance have been examined so far. It is a collimation problem of how to narrow the astrophysical jet narrowly. Further, the model of the astrophysical jet acceleration mechanism is required to solve this collimation problem at the same time as well as its acceleration. At the present time, the magnetic force model （magnetic centrifugal force and magnetic pressure） is regarded as the most dominant theory which solves the two problems of astrophysical jet acceleration and collimation at the same time. In addition to the present astrophysical jet narrow collimation mechanism by magnetic tension （pinch） force, in this article, another collimation mechanism which narrows down an astrophysical jet is newly introduced. That is, since a curvature is generated in the space around the astrophysical jet by magnetic field, a kind of pressure equivalent to the gravitational effect is generated in the direction of the interior of astrophysical jet as well as the pinch force from the outer circumferential surface of the astrophysical jet.

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating,accelerating and guiding protons,using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism.In addition,the problems involved are studied by using two-dimensional particle-in-cell simulations.The results show that the proton beam can be collimated,accelerated and guided effectively through this type of target.Theoretically,a formula is derived for the combined electric field of accelerating protons.Compared with a proton beam without a beam collimator,the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10%respectively.Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field,and that the beam collimator plays a role in focusing energy.In addition,the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I.The more prominent point is that the proton number of type II is 2.2 times higher than that of type I.This kind of target has important applications in many fields,such as fast ion ignition in inertial fusion,high energy physics and proton therapy.

Portable two linearly polarized beams absorption biometric system

The purpose of this paper is to design a portable two linearly polarized beams absorption biometric system (PTLPBABS) that measures the amount of absorption of the visible collimated beam passing by the sample to know the absorbance of the sample. The measured object in the system is the gold colloid that the sample produces after a biochemical reaction. After measuring the absorbance of the gold colloid we can obtain the concentrations of the waiting-measured sample and further obtain the concentration of chemical solution contained in the sample. The two linearly polarized beams device can be used to enhance rejection of ambient light and causes PTLPBABS to have excellent data stability measured. The process of the double optical path method increases the opportunities that the visible collimated beam is absorbed, which raise the detection sensitivity of the system to a sensitivity of 0.1%.

Neutron Radiography System Collimator Design via Monte Carlo Calculation

Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron radiography system that utilizes 241Am-Be neutron source. Many different arrangements have been simulated to obtain a neutron flux with higher amplitude and more uniform distribution in the collimator outlet, next to image plane. In the final arrangement the specifications of neutron filter, Gamma-ray shield and beam collimator has been determined. Simulations has been carried out for a 5Ci 241Am-Be neutron source. In this case 43.8 n/cm2s thermal neutron flux has been achieved at a distance of 35 cm from neutron source.

瓦里安21EX直线加速器多叶准直器维护与维修

0引言 配备多叶准直器（mulli-leaf collimator,MLC）系统的直线加速器能使照射野最大限度地接近肿瘤形状,从而达到最大限度地杀死肿瘤细胞,同时最小程度影响正常组织的目的[1]。由于MLC比挡铅的操作方法更简单快速[2],目前配有MLC的直线加速器在全国各地的放疗科应用越来越广泛[3]。因多叶准直器被安装在医用电子直线加速器的照射机头上,所以部件受辐射比较严重,

医科达Precise医用直线加速器多叶准直器(MLC)维修2例

随着计算机技术的飞速发展和加速器设备的改进,三维适形放射治疗逐渐得到普及,使得靶区和邻近的危及器官的剂量分布有了较大的改善,最大限度地将照射剂量集中到病变（靶区）内,杀灭肿瘤细胞,使周围正常组织和器官减少或免受照射,从而提高了放射治疗的治疗增益比[1]。采用多叶准直器（multileaf collimator，MLC）的调强适形放射治疗（intensity modulated radiation therapy．IMRT）是当前放疗的主流技术之一^[2]。

医科达Synergy直线加速器光学系统故障分析与维修

采用多叶准直器（multileaf collimator,MLC）的调强适形放射治疗（intensity modulated radiation therapy,IMRT）是当前放射治疗的主流技术之一,其通过光学监视系统来影响多叶准直器的控制,最大精度将照射剂量集中到病变内,移除肿瘤细胞,且周围正常组织和器官减少或免受照射。

CT机Collimator详析

X -CT的品牌、型号较多,但不管是什么厂家什么型号的CT ,其Collimator的结构都是大同小异,本文将详细剖析单层CT机的Collimator的结构,讨论一些常见故障,并提出相应解决方法。

铅适形挡块、手动多叶光栅——谁更适合临床适形放疗？

适形放疗是目前开展最活跃的一种放射治疗方法。它可以有效提高肿瘤的靶区剂量．明显减轻靶区周围正常组织的放射性损伤。要实现适形照射野放疗主要有两种方法：利用低熔点铅制作符合肿瘤投照形状的适形铅挡块（Block）．或使用多叶准直器（multi leaf collimator—MLC）形成适形照射野。MLC又分为手动MLC和电动MLC两种。由于电动MLC价格昂贵，维修复杂，目前国内难以普及。作为电动MLC的过渡产品，手动MLC使用手工操作叶片．省去了驱动操作叶片的电子设备，大大降低了成本。近年来手动MLC的使用日渐广泛．有逐渐取代铅挡块技术的趋势。笔者通过实际工作比较认为手动MLC不具备电动MLC的迅捷方便的操控性，也不具备铅块的良好重复性．并存在难以克服的缺陷。

Manipulation and optimization of electron transport by nanopore array targets

The transport of sub-picosecond laser-driven fast electrons in nanopore array targets is studied.Attributed to the generation of micro-structured magnetic fields,most fast electron beams are proven to be effectively guided and restricted during the propagation.Different transport patterns of fast electrons in the targets are observed in experiments and reproduced by particle-in-cell simulations,representing two components:initially collimated low-energy electrons in the center and high-energy scattering electrons turning into surrounding annular beams.The critical energy for confined electrons is deduced theoretically.The electron guidance and confinement by the nano-structured targets offer a technological approach to manipulate and optimize the fast electron transport by properly modulating pulse parameters and target design,showing great potential in many applications including ion acceleration,microfocus x-ray sources and inertial confinement fusion.

Glycerol effects on optical,weight and geometrical properties of skin tissue

Complex study of glycerol effects on the skin tissue was performed.The change in optical,weight and geometrical parameters of the rat skin under the action of the glycerol solutions was studied ex vivo.Possible mechanisms of the skin optical clearing under the action of glycerol solutions of different concentrations were discussed.The results can be helpful for refinement of models developed to evaluate the effective diffusion coefficients of glycerol in tissues.

Dosimetric evaluation of VMAT radiation therapy technique for breast cancer after conservative surgery based on three different types of multileaf collimators

Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The purpose of this study was to investigate the dosimetric effects of different multileaf collimators(MLC) on VMAT radiotherapy plans for treating breast cancer.Methods Fifteen breast cancer patients who were treated using a conventional technique in our department were selected to participate in this retrospective analysis. VMAT plans based on three types of Elekta MLCs [Beam Modulator(BM) with 4-mm leaf width, Agility with 5-mm leaf width and MLCi2 with 10-mm leaf width] were independently generated for each patient. Plan comparisons were performed based on dose-volume histogram(DVH) analysis including dosimetric parameters such as the homogeneity index(HI), conformity index(CI), Dmax, Dmin, and Dmean for the planning treatment volume(PTV), in addition to dose-volume parameters for the organs at risk(OARs). The delivery efficiency of the three types of MLCs was compared in terms of the beam delivery time and the monitor units(MUs) per fraction for each plan. Results Both target uniformity and conformity were improved in plans for Agility and BM MLC compared with the plan using MLCi2. The mean HI decreased from 1.14 for MLCi2 to 1.13 for BM and 1.10 for Agility, while the mean CI increased from 0.68 for MLCi2 to 0.73 for BM and 0.75 for Agility. Furthermore, at both low and high dose levels, smaller volumes of ipsilateral lung, heart, contralateral lung, and breast were irradiated with Agility MLC than with the other two types of MLCs. The delivery time with Agility MLC was reduced by 10.8% and 32.1%, respectively, compared with that for MLCi2 and BM.Conclusion Our results indicate that the Agility MLC exhibits a dosimetric advantage and a significant improvement in delivery efficiency for the treatment of breast cancer using VMAT.

Coherent beam combination of adaptive fiber laser array with tilt-tip and phase-locking control

We present an experimental study on tilt-tip（TT） and phase-locking（PL） control in a coherent beam combination（CBC） system of adaptive fiber laser array.The TT control is performed using the adaptive fiber-optics collimator（AFOC）,and the PL control is realized by the phase modulator（PM）.Cascaded and simultaneous controls of TT and PL using stochastic parallel gradient descent（SPGD） algorithm are investigated in this paper.Two-fiber-laser-,four-fiber-laser-,and six-fiber-laser-arrays are employed to study the TT and PL control.In the cascaded control system,only one high-speed CMOS camera is used to collect beam data and a computer is used as the controller.In a simultaneous control system one high-speed CMOS camera and one photonic detector（PD） are employed,and a computer and a control circuit based on field programmable gate array（FPGA） are used as the controllers.Experimental results reveal that both cascaded and simultaneous controls of TT using AFOC and PL using PM in fiber laser array are feasible and effective.Cascaded control is more effective in static control situation and simultaneous control can be applied to the dynamic control system directly.The control signals of simultaneous PL and TT disturb each other obviously and TT and PL control may compete with each other,so the control effect is limited.