本文選題：質(zhì)子加速器 + 表面μ~+　； 參考：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文

【摘要】：自從在宇宙射線中發(fā)現(xiàn)μ子后,對μ子的研究和應(yīng)用逐漸發(fā)展起來,但是宇宙射線中的μ子強度太低、能量太高且不可控制,這些都限制了對μ子科學(xué)的研究。隨著質(zhì)子加速器的發(fā)展和μ子基本物理性質(zhì)的發(fā)現(xiàn),高強度的μ子束在粒子物理、材料科學(xué)、能源科學(xué)、生命科學(xué)等領(lǐng)域都有重要作用。其中利用自旋極化的μ子束作為磁探針來研究凝聚態(tài)的方法稱為(muon spin rotation/relaxation/resonance)技術(shù)。μSR技術(shù)的基本原理是極化μ子束注入材料后,它的自旋與材料中磁場相互作用,自旋方向會發(fā)生變化,之后衰變產(chǎn)生的正電子傾向于沿著μ子極化方向出射,通過探測正電子的空間和時間信息可以獲得材料中磁場的相關(guān)信息。基于質(zhì)子加器的高強度極化μ子源是通過高能質(zhì)子轟擊石墨靶得到的。質(zhì)子與靶核反應(yīng)產(chǎn)生π介子,由靜止在靶表面附近的π介子衰變產(chǎn)生的μ子,稱為表面μ子,極化率接近100%；飛行中的π介子產(chǎn)生的μ子,稱為衰變μ子,經(jīng)過某一動量篩選可得到極化率約70%的較高能量的μ子束。這兩種類型的μ源能量都在MeV量級,在實驗中測量得到的是體材料性質(zhì)。通過慢化表面μ子得到的慢μ可研究納米材料、薄膜材料、樣品表面等的性質(zhì)。由于μ子慢化效率較低,高強度μ子源是得到可用于實驗的慢μ源的前提；高強度μ子源同時也是通過準直等方法獲得較小束斑或微束μ源的前提。本文主要利用蒙卡模擬軟件和束流矩陣計算軟件開展μ子束流方面的研究。中國散裂中子源(China Spallation Neutron Source, CSNS)經(jīng)過直線和環(huán)形質(zhì)子加速器的加速,最終可得到1.6 GeV的高能質(zhì)子,一期功率100 kW。本文基于CSNS上的高能質(zhì)子束,利用超導(dǎo)螺線管收集和傳輸技術(shù),設(shè)計出我國的高強度脈沖型μ子束線。瑞士PSI (Paul ScherrerInstitute)擁有目前國際上強度最高的連續(xù)型表面μ源和唯一一條能用來做μSR實驗的慢μ束線。微米量級的μ束可以研究小于1 mm2的材料,可以使μSR發(fā)展成為位置靈敏的技術(shù),因此PSI考慮基于高強度表面μ源建設(shè)一個微米束斑的μ子束線。慢μ實驗端外加的電磁場在實驗中對束斑影響很大,本論文研究了這些電磁場對束斑的影響,并給出了減小樣品處束斑大小的辦法。極化率是表面μ子非常重要的特點,本文對超導(dǎo)螺線管磁場對表面μ+極化率的影響進行了詳細計算。本論文主要的研究成果如下：1)基于中國散裂中子源設(shè)計出利用超導(dǎo)螺線管收集系統(tǒng)來獲得高強度脈沖型μ源的束線。首先通過Geant4和Fluka兩種蒙卡模擬軟件計算出低Z和偏高Z靶材的μ子和π介子的能動量分布。使用Geant4計算得到表面μ子和不同能最π介子的產(chǎn)率,以及這些粒子動量方向與初始質(zhì)子束夾角的分布。用Fluka計算了質(zhì)子轟擊四種靶材的能最沉積,綜合分析得到石墨靶是產(chǎn)生μ子和π介子的理想靶材。根據(jù)散裂中子源上高能質(zhì)子應(yīng)用區(qū)的布局,規(guī)劃出超導(dǎo)螺線管收集和傳輸系統(tǒng)的布局。使用G4beamline軟件計算在衰變螺線管之后的表而和衰變μ子相空間分布,將這個相空間分布的參數(shù)作為初始源,應(yīng)用TRANSPORT得到衰變螺線管之后聚焦元件的束流包絡(luò),應(yīng)用TURTLE計算了在實驗端的表而和衰變μ子相空間分布和產(chǎn)率。2)對PSI的πE3束線上考慮建造國際上第一個微米量級連續(xù)型μ子束線的可行性進行了計算。用TRANSPORT和TURTLE兩種模擬軟件首先考慮了束流后端的兩組四極磁鐵組(triplet)對初始束流的聚焦情況,計算結(jié)果表明大角散的束流會明顯減小微米束流的傳輸效率,大的束斑也能減少傳輸效率,但其影響小于角散的影響。計算結(jié)果結(jié)合劉維爾定理表明在兩組triplet之前的束流盡量調(diào)成大束斑的平行束,更利于后端μ子束的聚焦。通過束流光學(xué)模擬優(yōu)化,最終整體束線在200×200μm2范圍內(nèi)的傳輸效率為10-4和10-5最級,因此估算最終經(jīng)過準直后到達微米范圍內(nèi)的μ子強度達到103/s和104/s量級,可以用來進行微束實驗。3)研究了PSI上的低能μ子束在樣品端外加的橫向/縱向磁場和電場對束斑的影響。樣品端外加的磁場用來進行縱向和橫向μSR實驗。外加的平行于μ子動量方向的電場用來將μ子加速到不同能量(0.5～30 keV)來研究不同厚度的樣品。它們會使束斑或偏移或發(fā)散,通過比較實驗測試結(jié)果和使用基于Geant4的musrSim軟件模擬的結(jié)果,發(fā)現(xiàn)可以通過調(diào)整錐形透鏡RA的設(shè)置來極大地減少外加電磁場對束斑的影響,模擬結(jié)果與實驗吻合。當(dāng)前慢μ上的束斑大小σx和σy約為6 mm,使慢μ裝置只能用來測量大于1 cm2的樣品。在慢μ束上考慮了移除觸發(fā)探測器(10 nm碳膜)和縮小慢化體處提取束斑大小來減小實驗端樣品尺寸。移除觸發(fā)探測器時束斑大小可以減小到3.5～4.0 mm。在移除這個探測器的情況下,使用二次慢化體也可以提供μSR實驗測量的時間信號。此外,也模擬研究了在觸發(fā)探測器前和在慢化體前的束流準直方法來減小束斑。4)研究螺線管中表面μ+自旋極化率和產(chǎn)率。μ子在磁場中進行Larmor進動,螺線管中磁場在與μ子極化方向垂直方向上的分量會對極化方向產(chǎn)生影響。使用G4beamline計算了不同靶長、不同螺線管磁場強度、不同靶偏轉(zhuǎn)角度時的表面μ子的自旋極化率和產(chǎn)率的變化。計算結(jié)果表明,螺線管的磁場會對極化率產(chǎn)生一定的影響,但影響并不大,可以忽略。獲得較高產(chǎn)率的最佳靶長在350mm以上,螺線管磁場大于4T,偏轉(zhuǎn)角大于20°。考慮了超導(dǎo)螺線管傳輸系統(tǒng)對表面μ+的聚焦和對極化率的影響,由丁螺線管的縱向分量較小,對表而μ+極化率影響可以忽略；磁場越大,聚焦效果越好,傳輸螺線管的磁場最好大于2T。
[Abstract]:Since the discovery of muon in cosmic ray, the research and application of muon have been developed gradually, but the intensity of muon in cosmic rays is too low, the energy is too high and it is too high, which limits the study of the muon science. With the development of the proton accelerator and the discovery of the basic physical properties of the muon, the high-intensity muon beams are in particle physics. In the fields of material science, energy science, life science and other fields, the method of using the spin polarized muon beam as a magnetic probe to study the condensed state is called (muon spin rotation/relaxation/resonance) technology. The basic principle of the micron SR technique is that the spin of the polarized muon beam is interacted with the magnetic field in the material. The spin direction will change, and the positron produced by the decay tends to go out in the direction of the muon polarization, and the related information of the magnetic field in the material can be obtained by detecting the space and time information of the positron. The high intensity polarized muon source based on proton addition is obtained by bombarding the graphite target through high energy protons. The muon, produced by the decay of the pion decay near the surface of the target, is called the muon, called the surface muon, and the polarizability is close to 100%. The muon produced by the pion in the flight is called the decay muon. After a certain momentum screening, the muon beam of high energy of about 70% of the polarizability can be obtained. These two types of Mu source energy are all in the order of MeV, and are measured in the experiment. The slow micron obtained through slow surface muon can study the properties of nanomaterials, film materials, and sample surfaces. Because of the low efficiency of the muon slows, the high intensity muon source is the prerequisite for the slow Mu source used in the experiment, and the high intensity muon source also obtains small beam spots or microbeams through the collimation and so on. This paper mainly uses the Monte Carlo simulation software and the beam matrix calculation software to carry out the study of the muon beam. The China Spallation Neutron Source (CSNS) is accelerated by a straight line and a ring proton accelerator, and can eventually get 1.6 GeV high energy protons, and the first phase of the power of 100 kW. is based on the height of CSNS. The proton beam, using the superconducting solenoid collection and transmission technology, designs the high intensity pulse muon beam line of our country. The Swiss PSI (Paul ScherrerInstitute) has the highest intensity continuous surface Mu source in the world and the only slow micro beam line used to do the micron SR experiment. The micron magnitude Mu beam can study materials less than 1 mm2. In this paper, the influence of the electromagnetic field on the beam spot is studied in this paper, and the method of reducing the beam spot size of the sample is given. The method of reducing the size of the beam spots at the sample SR is given. The influence of the superconducting solenoid magnetic field on the surface Mu + polarizability is calculated in detail in this paper. The main research results in this paper are as follows: 1) based on the Chinese spallation neutron source, a superconducting solenoid collection system is designed to obtain the beam lines of the high-strength pulse type muon source. First, Geant4 and Fl are used. UKA two Monte Carlo simulation software is used to calculate the energy distribution of the muon and pion of low Z and high Z targets. The yield of the surface muon and the most pions of different energies, and the distribution of the angle between the momentum direction and the initial proton beam are calculated using Geant4. The energy deposition of the proton bombardment targets is calculated by Fluka, and the comprehensive analysis is obtained. To the graphite target is the ideal target for producing muon and pion. According to the layout of the high energy proton application area on the spallation neutron source, the layout of the collection and transmission system of the superconducting solenoid is planned. The G4beamline software is used to calculate the space distribution of the decay solenoid and the decay muon phase, and the parameters of this phase space distribution are taken as the initial. Source, the beam envelope of the focusing element after the decay solenoid is obtained by using TRANSPORT. TURTLE is used to calculate the feasibility of constructing the first micron continuous muon beam line on the PSI PI E3 beam line by using TURTLE to calculate the spatial distribution of the decay muon phase and the yield.2. Two modes of TRANSPORT and TURTLE are used. The proposed software first considers the focusing of the initial beam by the two group of quadrupole magnet groups (triplet) in the back end of the beam. The calculation results show that the large angular beam will obviously reduce the transmission efficiency of the micron beam flow. The large beam spot can also reduce the transmission efficiency, but its influence is less than the influence of the dispersion. The calculation results show that the two groups of T are combined with the Liu Ville theorem. The beam flow before riplet is adjusted to the parallel beam of the large beam spot, which is more conducive to the focus of the muon beam in the back end. Through the beam optics simulation, the transmission efficiency of the whole beam in the range of 200 * 200 mu M2 is 10-4 and the 10-5 level. Therefore, the estimation of the micron intensity within the micron range after the collimation is up to 103/s and 104/s. The effect of the transverse / longitudinal magnetic field and electric field on the beam spot on the sample end of the low energy muon beam on the sample is studied for the micro beam experiment.3. The external magnetic field applied to the sample end is used to carry out the longitudinal and transverse micron SR experiments. The applied electric field parallel to the direction of the muon momentum is used to accelerate the muon to different energy (0.5 to 30 keV) to study the difference. The thickness of the samples. They make beam spots or offset or diverge. By comparing experimental results and using the results of Geant4 based musrSim software simulation, it is found that the effect of the applied electromagnetic field on the beam spot can be greatly reduced by adjusting the configuration of the conical lens RA. The simulation results are in agreement with the experiment. The sigma y is about 6 mm so that the slow unit can only be used to measure the sample larger than 1 cm2. In the slow beam, the removal of the trigger detector (10 nm carbon film) and the reduction of the size of the beam spot at the slower reduce the sample size of the experimental end. The size of the beam spot can be reduced to 3.5 to 4 mm. when the detector is removed, so that the detector is removed, so that the detector is removed. The two slowers can also provide time signals measured by the experimental measurement of SR. In addition, the study of the beam collimation method before the trigger detector and the beam collimation before the slow body to reduce the beam spot.4) studies the micron spin polarization and yield of the surface of the solenoid. The Larmor precession in the magnetic field is carried out in the magnetic field, and the magnetic field in the solenoid is in the direction of the muon polarization in the solenoid. The components in the vertical direction will affect the polarization direction. Using G4beamline, the spin polarization and yield of the muons on the surface of the different targets, different solenoids and different target deflection angles are calculated. The results show that the magnetic field of the solenoid will have a certain influence on the polarizability, but the influence is negligible. The best target length of high yield is above 350mm, the magnetic field of the solenoid is greater than 4T and the deflection angle is more than 20 degrees. The effect of the superconducting solenoid transmission system on the focus of surface Mu + and the influence on the polarizability is considered. The longitudinal component of the solenoid is smaller and the influence of the meter and the polarization rate can be ignored. The greater the magnetic field, the better the focusing effect, the transmission screw is better. The magnetic field of a line tube is better than 2T.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O571.53

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