低能传输段空间电荷补偿效应

近些年来,随着基础科学和应用科学对强流加速器需求的日益增加,强流加速器得到了很大推广和发展.在强流加速器的低能段,空间电荷效应会导致束流发射度的增长,束流品质的变坏.这样的束流通常需要空间电荷补偿来控制空间电荷效应.空间电荷补偿是指束流可以通过吸收与束流电性相反的粒子从而减少束流空间电荷发散力的一种效应.北京大学自主开放了PIC-MCC空间电荷补偿模型,该模型被应用在H+和H-束流的空间电荷补偿模拟当中,且得到了与实验符合得比较好的结果.     

New progress on beam availability and reliability of PKU high intensity CW proton ECR ion source

The stability and reliability of an ion source and its beam availability are extremely significant for any accelerator,especially for those high current long term CW operation ones like ADS. Although the first high quality 306-hours continuous wave(CW) operating curve at 50 m A@35 ke V has been successfully obtained with a standard compact 2.45 GHz ECR ion source at Peking University(PKU), but the uncertainties that caused beam trips before are unacceptable during an accelerator real operation and should be eliminated. Meanwhile, no permission will be given when the beam power is upgraded from 50 m A@35 ke V to 50 m A@50 ke V. To improve the PKU CW proton source quality, several upgrades were done recently. After those improvements, a new long term CW proton beam experiment at 50 m A@50 ke V was carried out in June 2016. The total running time is 300.5 hours, including near 6 hours ion source preparation and 294 hours non-disturb continuous operation. Within the continuous 13 days operation, no beam-off happened, no spark was observed,no beam drop appeared, no interrupting action was needed, and only a few beam fluctuations caused by the air conditional failure occurred. Beam availability and reliability within the 294 hours is 100%. The root-mean-square(RMS) emittance of this 50 m A@50 ke V CW proton beam is about 0.186 π.mm.mrad. A careful inspection of the ion source was done after this long term operation and no obvious damage was found. The restart experimental results obtained after the ion source inspection prove the high repeatability of PKU PMECRIS. In addition, a 130-m A H+beam was obtained at 50 k V with duty factor of 10%(100 Hz/1 ms) with this source. Details will be presented in this paper.     

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Optical emission spectroscopy(OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance(PMECR) ion source at Peking University(PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance(ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.     

低能强流离子注入丁腈橡胶的表面改性(英文)北大核心CSCD

丁腈橡胶是一种广泛使用的合成橡胶,目前应用于各种非轮胎制品。离子注入被认为是一种提高丁腈橡胶表面特性的有效手段,比如降低摩擦系数、提高耐抗性等。最近,为了理解辐照效应对于硫化橡胶的功能特性如摩擦系数和硬度等的影响,利用北京大学离子源测试平台将N^+和H^+注入丁腈橡胶表面进行研究。离子注入完成以后,对丁腈橡胶表面的摩擦系数、硬度、耐热老化性能、摩擦特性以及耐磨损性能进行了分析。     

A fast emittance measurement unit for high intensity DC beam

A combined unit, which has the ability to measure the current and emittance of the high intensity direct current(DC)ion beam, is developed at Peking University(PKU). It is a multi-slit single-wire(MSSW)-type beam emittance meter combined with a water-cooled Faraday Cup, named high intensity beam emittance measurement unit-6(HIBEMU-6). It takes about 15 seconds to complete one measurement of the beam current and its emittance. The emittance of a 50-mA@50-kV DC proton beam is measured.     

Practical 2.45-GHz microwave-driven Cs-free Hˉ ion source developed at Peking University

A practical 2.45-GHz microwave-driven Cs-free Hˉ source was improved based on the experimental Hˉ source at Peking University(PKU). Several structural improvements were implemented to meet the practical requirements of Xi'an Proton Application Facility(XiPaf). Firstly, the plasma chamber size was optimized to enhance the plasma intensity and stability. Secondly, the filter magnetic field and electron deflecting magnetic field were enhanced to reduce co-extracted electrons. Thirdly, a new two-electrode extraction system with farther electrode gap and enhanced water cooling ability to diminish spark and sputter during beam extraction was applied. At last, the direct Hˉ current measuring method was adopted by the arrangement of a new pair of bending magnets before Faraday cup(FC) to remove residual electrons. With these improvements, electron cyclotron resonance(ECR) magnetic field optimization experiments and operation parameter variation experiments were carried out on the Hˉ ion source and a maximum 8.5-mA pure Hˉ beam was extracted at 50 kV with the time structure of 100 Hz/0.3 ms. The root-mean-square(RMS) emittance of the beam is 0.25 Π·mm·mrad. This improved Hˉ source and extraction system were maintenance-free for more than 200 hours in operation.     

A miniaturized 2.45 GHz ECR ion source at Peking University

A miniaturized 2.45 GHz permanent magnet electron cyclotron resonance(PMECR) ion source, which has the ability of producing a tens-m A H+beam, has been built and tested at Peking University(PKU). Its plasma chamber dimension is Φ30 mm×40 mm and the whole size of the ion source is Φ180 mm×130 mm. This source has a unique structure with the whole source body embedded into the extraction system. It can be operated in both continuous wave(CW) mode and pulse mode. In the CW mode, more than 20 m A hydrogen ion beam at 40 k V can be obtained with the microwave power of 180 W and about 1 m A hydrogen ion beam is produced with a microwave power of 10 W. In the pulse mode, more than50 m A hydrogen ion beam with a duty factor of 10% can be extracted when the peak microwave power is 1800 W.     

考虑缝间流量不对称的裂缝井干扰试井分析方法

考虑压裂缝间的相互干扰作用,采用有限差分方法耦合地层与裂缝渗流方程,建立压裂井邻井干扰试井模型,绘制试井典型图版.分析裂缝表面线流量分布,由于存在缝间干扰,压裂井裂缝表面线流量呈非对称分布.同时,由于干扰井裂缝的高导压能力,模型中干扰信号将更快传导至观察井井底,压力导数曲线提前出现干扰过渡阶段.研究了观察井与干扰井布井方位的影响,当观察井与干扰井裂缝位于同一直线时,裂缝高导压作用最显著,其中裂缝半长的影响效果远大于裂缝导流能力.通过与商业软件数值试井模型对比,验证了模型的正确性.使用建立的模型解释了现场实例,曲线拟合效果好,解释结果合理,为判断井间连通性及制定开发调整措施提供了重要依据.     

论汉语无主句的英译

汉语有很多无主句,这符合汉语意合的思维习惯。而英语则重形合,句子里一般都需要有主语。汉语的无主句译成英语时,往往需要确定并补出主语或改变句型,使句子结构符合英语语法的规范。本文探讨了如何理解汉语无主句、译文主语的确定及英译时可运用的几种方法。     

Surface enhancement of molecular ion H_2~+ yield in a 2.45-GHz electron–cyclotron resonance ion source

High current hydrogen molecular ion beam is obtained with a specially designed stainless steel liner permanent magnet2.45-GHz electron–cyclotron resonance(ECR) ion source(PMECR II) at Peking University(PKU). To further understand the physics of the hydrogen generation process inside a plasma chamber, theoretical and experimental investigations on the liner material of the plasma chamber in different running conditions are carried out. Several kinds of materials, stainless steel(SS), tantalum(Ta), quartz, and aluminum(Al) are selected in our study. Experimental results show that stainless steel and tantalum are much better than others in H~+_2 generation. During the experiment, an increasing trend in H~+_2 fraction is observed with stainless steel liner after O_2 discharge inside the ion source. Surface analyses show that the roughness change on the surface after O_2 discharge may be responsible for this phenomenon. After these studies, the pure current of H~+_2 ions can reach 42.3 mA with a fraction of 52.9%. More details are presented in this paper.