康普顿背散射技术对贮存环电子束诊断及其应用-II贮存环电子束的极化度测量

简单介绍以激光 电子康普顿背散射原理为基础建立的康普顿背散射极化仪, 采用它能实时、 非破坏性地监测电子束的极化. 该项工作可作为上海激光电子γ源（SLEGS）低能γ束应用研究的内容之一. The Compton backscattering polarimeter is described briefly on the basis of the principle of Compton backscattering in this paper. The polarization of the electron beam can be measured and monitored on time and nondestructively. The project will be one of applications of low energy γ ray beam of SLEGS.     

MeV- and Sub-MeV-photon Sources Based on Compton Backscattering at Spring-8 and KPSI-JAEA

Recently we have constructed two facilities for generating photon beams in the MeV and sub-MeV energy regions by means of the Compton backscattering with a laser and an electron beam at SPring-8 and at Kansai Photon Science Institute of Japan Atomic Energy Agency(KPSIJAEA).The MeV-photon source at SPring-8 consists of a continuous-wave optically-pumped far infrared laser with a wavelength of 118.8 μm and an 8 GeV stored electron beam.Present MeV-photon flux is estimated to be 1.3×10~3 photons/s.On the other hand,the sub-MeV-photon source at KPSI-JAEA consists of a pulse Nd:YAG laser with a wavelength of 1 064 nm and a 150 MeV electron beam accelerated by microtron.In the first trial of the photon production in this source,backscattered photon flux is estimated to be 20 photons/pulse.Both the Compton backscattered photon sources have possibilities to be used for new tools in various fields such as nuclear physics,materials science,and astronomy.     

康普顿背散射技术对贮存环电子束诊断及其应用——I电子束能量的精确测量及光学标准实验站

简单叙述了采用康普顿背散射技术精确测量电子束能量的技术,并指出建立辐射标准实验站对精确电子束能量测量的需求. The technique to measure the electron beam energy accurately with Compton backscattering technique is introduced and requirements for the experimental stations of radiometry are also described in the paper.     

康普顿背散射技术对贮存环电子束诊断及其应用——I电子束能量的精确测量及光学标准实验站

简单叙述了采用康普顿背散射技术精确测量电子束能量的技术,并指出建立辐射标准实验站对精确电子束能量测量的需求. The technique to measure the electron beam energy accurately with Compton backscattering technique is introduced and requirements for the experimental stations of radiometry are also described in the paper.     

Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C

The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it can be used with the 1500MeV electron beam now available from the Mainz microtron MAMI-C. The changes made and the resulting properties of the spectrometer are discussed.     

Verification of terahertz-wave spectrophotometry by Compton backscattering of coherent synchrotron radiation

We developed a continuous-spectrum light beam from Compton backscattering by using coherent synchrotron radiation in an L-band linac at the Kyoto University Research Reactor Institute. The ratio of Compton backscattered photons to background photons when coherent synchrotron radiation was used was three times larger than when coherent transition radiation was used. The transmission spectrum of a polystyrene film in the terahertz-wave region was evaluated by measuring the spectrum of the Compton backscattered photons and it roughly agreed with that measured by a Martin–Puplett-type interferometer. The spectrophotometry using Compton backscattering shows promise as a new tool for investigations in terahertz-wave science.     

上海激光电子γ源

激光具有高强度、 高极化度等优异的性能。 用激光束轰击高能电子束就可以产生高强度、 高极化度的γ射线束。 上海激光电子γ源就是上海同步辐射装置上的这样一条束线站。 预计可以获得能量范围为1—22 MeV的准单色、 高强度（109—1011 s-1）和高极化度（线极化或圆极化）的γ射线束。 介绍了这条束线站目前的进展情况。 Shanghai Laser Electron Gamma Source (SLEGS) is a high intensity,short pulse and compact γ ray source which is based on inverse Compton scattering via interaction between pulsed high power laser beams and picosecond relativistic electron bunches. One of the attractive features of the laser Compton scattering is the easy control of polarization of the produced high energy photons that duplicates polarization of the applied laser beam. The γ ray with energy up to 22 MeV and intensity of 109—1011s 1 are expected to be produced by Compton backscattering of CO2 laser photons on the 3.5 GeV electrons bunches in the Shanghai Synchrotron Radiation Facility (SSRF). In this communication, we report same simulation results and the progressing status of SLEGS.     

光学极化度测量仪的研制及弱光Stokes参数的测量

极化电子束在物理学及其相关领域应用十分广泛,要深入研究这些应用必须对电子束的极化度进行精确测量,通常测量电子束极化度的仪器有两种：Mott极化度测量仪和光学极化度测量仪。因光学极化度测量仪与Mott极化度测量仪相比有许多优点而倍受关注。文章首先阐述了光学极化度测量仪的理论基础和实验原理,然后介绍了所研制光学极化度测量仪的设计方案和物理结构,最后给出了用该光学极化度测量仪测量弱光的Stokes参数的结果。     

Measurement of spin polarizabilities of the proton

Spin polarizabilities are as-yet experimentally unknown fundamental structure constants that describe the response of the nucleon spin to the action of a changing electromagnetic field. The A2 Collaboration at the Institute for Nuclear Physics in Mainz (Institut für Kernphysik, Mainz) performed the first measurements of the energy and angular dependences of spin asymmetries of the cross section for doubly polarized (polarized-photon beam incident to a polarized proton target) Compton effect in the Δ-resonance region, these asymmetries being sensitive to values of the spin polarizabilities. The preparation of spin-asymmetry measurements at energies below the pion-production threshold with an active (scintillating) polarized target is in progress. These measurements will make it possible to determine individual spin polarizabilities of the proton in a model-independent way.     

Probing a nucleon spin structure at TESLA by the real polarized gamma beam

The recent proposals concerning the usage of the real polarized gamma beam, obtained by Compton backscattering of the laser photons off the electron beams from either the linear or circular accelerators were considered. The heavy quark photoproduction process, which gives a unique opportunity to measure the polarized gluon distribution, was investigated. Received: 22 March 1999 / Revised version: 17 June 1999 / Published online: 14 October 1999     

Statistical simulation of multiple Compton backscattering process

A number of laboratories are currently developing monochromatic sources of X-rays and gamma quanta based on the Compton backscattering (CBS) of laser photons by relativistic electrons. Modern technologies are capable of providing a concentration of electrons and photons in the interaction point such that each primary electron can emit several hard photons. In contrast to the well-known nonlinear CBS process, in which an initial electron “absorbs” a few laser photons and emits a single hard one, the above-mentioned process can be called a multiple CBS process and is characterized by a mean number of emitted photons. The present paper is devoted to simulating the parameters of a beam of back scattered quanta based on the Monte Carlo technique. It is shown that, even in the case of strong collimation of a resulting photon beam, the radiation monochromaticity may deteriorate because of the contribution coming from the multiple photon emission, which is something that must be considered while designing new CBS sources.     

Signatures of the Unruh effect via high-power, short-pulse lasers

The ultra-high fields of high-power short-pulse lasers are expected to contribute to understanding fundamental properties of the quantum vacuum and quantum theory in very strong fields. For example, the neutral QED vacuum breaks down at the Schwinger field strength of 1.3×10¹⁸ V/m, where a virtual e⁺e^- pair gains its rest mass energy over a Compton wavelength and materializes as a real pair. At such an ultra-high field strength, an electron experiences an acceleration of a_S=2×10²⁸g and hence fundamental phenomena such as the long predicted Unruh effect start to play a role. The Unruh effect implies that the accelerated electron experiences the vacuum as a thermal bath with the Unruh temperature. In its accelerated frame the electron scatters photons off the thermal bath, corresponding to the emission of an entangled pair of photons in the laboratory frame. While it remains an experimental challenge to reach the critical Schwinger field strength within the immediate future even in view of the enormous thrust in high-power laser developments in recent years, the near-future laser technology may allow to probe the signatures of the Unruh effect mentioned above. Using a laser-accelerated electron beam (γ～300) and a counter-propagating laser beam acting as optical undulator should allow to create entangled Unruh photon pairs (i.e., signatures of the Unruh effect) with energies of the order of several hundred keV. An even substantially improved experimental scenario can be realized by using a brilliant 20 keV photon beam as X-ray undulator together with a low-energy (γ≈2) electron beam. In this case the separation of the Unruh photon pairs from background originating from linearly accelerated electrons (classical Larmor radiation) is significantly improved. Detection of the Unruh photons may be envisaged by Compton polarimetry in a 2D-segmented position-sensitive germanium detector.     

Measurement of the proton spin polarizabilities at MAMI

The spin polarizabilities of the nucleon are fundamental structure constants which describe the response of the nucleon spin to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is the Compton scattering with polarization degrees of freedom. Three Compton scattering asymmetries on the proton were measured in the Δ(1232) region using a polarized incident photon beam and a polarized (or unpolarized) proton target at the Mainz Microtron (MAMI). These asymmetries are sensitive to values of the spin polarizabilities. Fits to asymmetry data were performed using a dispersion model calculation, and a separation of all four proton spin-polarizabilities in the multipole basis was achieved. The values of the proton spin polarizabilities are presented.     

BEPCⅡ激光丝系统探测器模拟研究(英文)

BEPCⅡ上正在进行激光丝系统的研究。基于GEANT4对激光丝系统探测器进行了模拟。首先模拟了康普顿散射信号在探测器材料中电磁簇射的分布,确定了探测器初始尺寸。之后模拟了不同尺寸下探测器的输出,根据模拟结果确定了探测器的最终尺寸,使得探测器在所确定的尺寸有较大的信号输出。还进行了不同康普顿散射位置时探测器的响应模拟,结果表明束流管道的影响是不可忽略的,是探测器响应非线性的主要原因,预计该结果对束流截面测量有重要意义。最后简要介绍了BEPCⅡ几种可能的束流能量时,探测器信号输出和能量泄漏的模拟结果。     

在BEPC上建造γ束线站的分析

考虑电子的反冲并利用康普顿散射,研究了激光同步辐射光源(LSS)辐射的光子波长、光子能量。结果表明,对于不同的γ,LSS辐射的光子波长和能量有不同的近似公式。当γ<<λ1/4λe时,LSS辐射的光子波长λ2≈λ1/4γ2,能量(εc2≈4γ2εc1;当γ>>λ1/4λe时,LSS辐射的光子波长λ2≈λe/γ,能量cε2≈m0γc2;结果表明,LSS辐射的条件是种子激光的波长λ1大于电子的物质波波长λm;LSS辐射的极值波长是λ2m ax=h/m0γv,极值能量是cε2m ax=βeε;本文后半部分提出了利用北京正负电子对撞机的强流高亮度电子束与激光的康普顿背散射产生单色γ射线的建议。     

New methods for precision Møller polarimetry<Superscript>⋆</Superscript>

Precision electron beam polarimetry is becoming increasingly important as parity violation experiments attempt to probe the frontiers of the standard model. In the few GeV regime, M?ller polarimetry is well suited to high-precision measurements, however is generally limited to use at relatively low beam currents (< 10 μA). We present a novel technique that will enable precision M?ller polarimetry at very large currents, up to 100μA.     

Uncertainty of the beam energy measurement in the e~+e~- collision using Compton backscattering

The beam energy is measured in the e+e-collision by using Compton backscattering. The uncertainty of this measurement process is studied by virtue of analytical formulas, and the special effects of variant energy spread and energy drift on the systematic uncertainty estimation are also studied with the Monte Carlo sampling technique. These quantitative conclusions are especially important for understanding the uncertainty of the beam energy measurement system.     

Polarimetry of short-pulse gamma rays produced through inverse Compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse gamma rays based on the fact that gamma rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original gamma rays. Polarized, short-pulse gamma rays of (1.1+/-0.2)x10(6)/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse gamma rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the gamma-ray intensity is in good agreement with the simulated value of 1.0x10(6). Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29+/-0.12)%, which is also consistent with the expected value of 1.3%.     

Perspectives in nuclear physics

We discuss some of the many important questions in modern subatomic physics that have been addressed over the past two decades at Mainz. These achievements range from precision studies of nucleon form factors, to nucleon spectroscopy, novel probes of nucleon structure such as virtual Compton scattering and fundamental tests of quantum chromodynamics. In the future one may expect to see this effort expanded to precision tests of physics beyond the Standard Model.     

Prüfung der Quantenelektrodynamik durch Compton-Streuung und Paarvernichtung

In view of the present experimental efforts, Compton scattering and pair annihilation in flight are analysed as purely electrodynamic processes to test quantum electrodynamics at small distances. After a short discussion of the introduction of the form factors we consider the possibility of a (partial) cancellation between elctrodynamic and nucleon structure effects. There is also the possibility of a partial cancellation of the non local effects in Compton scattering and wide angle bremsstrahlung because of the opposite action of spacelike and timelike form factor arguments. We calculate the Compton and the two photon pair annihilation cross sections with form factors and illustrate the result with several numerical diagrams. Two photon pair annihilation turns out to be especially favourable for a first test of quantum electrodynamics because there is no cancellation of possible non local effects and the necessary very high energy can be circumvented by a colliding beam experiment. With a 10% experimental error the planned colliding beam experiment at Stanford with 500 MeV could test the electron propagation function down to 0.6 · 10^?14cm. After that, Compton scattering can be used to investigate the electron propagation function also for time-like arguments.