Measurements and removal of cerenkov light generated in scintillating fiber-optic sensor induced by high-energy electron beams using a spectrometer

In this study, we measured scintillating and Cerenkov lights generated in a scintillating fiber-optic sensor using highenergy electron beams and a spectrometer. The spectrum of Cerenkov light generated in a plastic optical fiber was measured with a spectrometer and the intensities of Cerenkov light were measured for irradiated lengths of the plastic optical fiber by integrating the photon counts at every wavelength of the spectrum. The intensities of Cerenkov and scintillating lights were also characterized as a function of the incident angle of an electron beam from a clinical linear accelerator (CLINAC). To minimize or remove Cerenkov light, a subtraction method was employed using a background optical fiber.     

Measurement of therapeutic photon beams-induced Cerenkov radiation generated in PMMA- and PS-based plastic optical fibers

In this study, we characterized Cerenkov radiation generated in polystyrene (PS)- and polymethyl methacrylate (PMMA)-based plastic optical fibers (POFs) to select an adequate optical fiber for producing Cerenkov radiation. To determine the relationship between the absorbed dose and the intensity of Cerenkov radiation, we calculated the energy depositions of photon beams and fluxes of electrons inducing Cerenkov radiation using the Monte Carlo N-Particle eXtended code. Also, intensities of Cerenkov radiation generated in PS- and PMMA-based POFs were measured as functions of dose rate and monitor unit. At last, therapeutic photon beams-induced Cerenkov radiation in PS- and PMMA-based POFs was measured according to depths of solid water phantom.     

填充等离子体的切伦柯夫自由电子激光的理论分析

本文用磁流体理论研究了柱形波导填充等离子体的切伦柯夫自由电子激光器，表明该系统比普通切伦柯夫自由电子激光具有更高的工作频率和线性增长率。发现在入射电流和波导结构一定时，该系统和普通切伦柯夫自由电子激光器的增长率并不是随随电子束与介质的间距的增加而减小，而是存在一个最佳值。     

切伦科夫自由电子激光中自发辐射与受激辐射的关系

本文从单粒子理论出发,导出了切化科夫自由电子激光中自发辐射与受激辐射的关系。结果表明:在切化科夫自由电子激光中也存在着类似于wiggler自由电子激光中的Madey公式的关系。文中还利用得出的结果对倾斜角度受激切伦科夫辐射的增益进行了计算。 关键词：     

High-power and superpower Cerenkov masers

The linear and nonlinear theory of the efficient operation of high-power (gigawatt) and superpower (50 GW) Cerenkov masers is presented. Issues such as breakdown, plasma production, and coupling to the output device are discussed. The relative merits of dielectric Cerenkov masers and plasma Cerenkov masers are considered. The principal design tool is a new particle simulation model that was developed to investigate Cerenkov masers. The novel aspects of this model are briefly described along with a comparison of calculated and experimental results. The agreement between calculations and measurements is generally good. Designs for a high-power and superpower plasma Cerenkov masers are also described     

基于切伦科夫辐射的核素治疗剂量测量可行性分析

针对现有核素治疗中内照射剂量测量缺乏简单、高效方法的问题,基于内照射剂量与切伦科夫辐射之间的关系,提出一种基于切伦科夫辐射的核素治疗内照射剂量测量的新方法。利用蒙特卡罗计算程序Geant4,模拟放射性核素131I在水体模型和甲状腺模型中产生切伦科夫辐射与剂量沉积的分布情况,并定量分析切伦科夫光子数与剂量之间的关系。计算结果表明:在水体模的半径方向上切伦科夫光子数与剂量之间有着相同的变化趋势,且两者有着相同的二维分布规律;核素131I在介质中产生的切伦科夫光子数与剂量两者之间存在一定的线性关系,且这种线性关系与核素的分布情况无关。研究结果证实,将这种放射性核素在介质中产生的切伦科夫辐射应用于内照射剂量学具有非常大的研究潜力和价值。     

Observation of light below Cerenkov threshold in a 1.5 meter long integrating Cerenkov counter

We have observed Cerenkov light, well below threshold, in an integrating Cerenkov counter used to determine particle composition of the secondary hadron beam, which is the source of Fermilab narrow-band neutrinos. The phenomenon can be understood in terms of diffraction effects in a finite length counter caused by radiation emitted by particles traversing the counter even when it is evacuated. At zero pressure, the light can be considered as transition radiation produced when particles enter and leave the counter. A standard Cerenkov diffraction formula describes both the normal Cerenkov radiation and the light emitted below Cerenkov threshold.     

Nonlinear Cerenkov radiation in nonlinear photonic crystal waveguides

We study nonlinear Cerenkov radiation generated from a nonlinear photonic crystal waveguide where the nonlinear susceptibility tensor is modulated by the ferroelectric domain. Nonlinear polarization driven by an incident light field may emit coherently harmonic waves at new frequencies along the direction of Cerenkov angles. Multiple radiation spots with different azimuth angles are simultaneously exhibited from such a hexagonally poled waveguide. A scattering involved nonlinear Cerenkov arc is also observed for the first time. Cerenkov radiation associated with quasi-phase matching leads to these novel nonlinear phenomena.     

铌酸锂质子交换波导中切伦科夫倍频实验研究

报道了质子交换铌酸锂平板波导中切伦科夫倍频蓝绿光输出研究。理论上计算了质子交换波导参数对不同基波波长倍频转换效率的影响。制备出适合于蓝绿光输出的铌酸锂质子交换波导并观测到较高转换效率的倍频光产生,实验中我们测量了倍频转换效率与抽运动率以及抽运波长的关系,实验结果与理论预测吻合。     

Linear Theory of the Beam-Wave Interaction in the Arbitrary Cylindrical Cerenkov Device

The hot dispersion equation in Cerenkov devices has been derived and analyzed numerically using the self-consistent linear theory. In principle, the linear analysis can be applied to efficiently calculating all kinds of beam-wave interaction in various Cerenkov devices composed of axisymmetric slow-wave structures (SWS) with arbitrary periodic profile. Then the results for Cerenkov devices with three typical SWS profiles are presented.     

Analysis of the relationship between neutron dose and Cerenkov photons under neutron irradiation through Monte Carlo method

To theoretically explore the feasibility of neutron dose characterized by Cerenkov photons, the relationship between Cerenkov photons and neutron dose in a water phantom was quantified using the Monte Carlo toolkit Geant4. Results showed that the ratio of the neutron dose deposited by secondary electrons above Cerenkov threshold energy to the total neutron dose is approximately a constant for monoenergetic neutrons from 0.01 eV to 100 eV. With the initial neutron beam energy from 0.01 eV to 100 eV, the number of Cerenkov photons has a good correlation with the total neutron dose along the central axis of the water phantom. The changes of neutron energy spectrum and mechanism analysis also explored at different depths. And the ratio of total neutron dose to the intensity of Cerenkov photons is independent of neutron energy for neutrons from 0.01 eV to 100 eV. These findings indicate that Cerenkov radiation also has potential in the application of neutron dose measurement in some specific fields.     

A New Measurement of Electron Beam Emittance with Cerenkov Radiation “Double Imaging” Method

A new way in electron beam emittance measurement with Cerenkov radiation "double imaging" method is proposed in this paper. In the standard emittance measurements with optical diagnostics such as Cerenkov radiation, OTR (Optical Transition Radiation), fluorescence screen or BMP (beam profile monitor) etc., the emittance is indirectly calculated through quadrupole-scanning technique, with the prior ssumption that the beam phase space density distribution is ellipse, which will certainly induce systematic error when the beam profile is quite irregular or the space-charge effects can not be omitted. In proposed method, the Cerenkov radiation pass through a 1-meter focal-length thin convex lens, and a CCD camera is used to capture two images of Cerenkov radiation at the focal plane and at the image plane of the lens respectively. Then, with image processing technique, we acquire the angular divergence information of the electron beam from the image of the focal plane and the radial distribution information from the image of the image plane, which we call Cerenkov radiation "double imaging" method. Therefore, the emittance can be directly attained according to the definition of the RMS emittance. By this method, we can measure the actual phase space distributions without making any prior assumptions about the density distributions. Compared with other general measurements, this "double imaging" method has advantages of simpler equipment, higher precision and wider application. This paper also presents the computer simulation results of emittance measurement on the DC-SC (DC-Superconducting) photocathode injector of PKU-SCAF (Peking University Superconducting Accelerator Facility) being built at Peking University.     

切伦科夫辐射“双成像法”测量电子束发射度

利用切伦科夫辐射,OTR或荧光靶等光学诊断方法进行发射度测量,国内外绝大部分实验是用CCD相机观测电子束打靶产生的光斑,变化四极透镜的磁场梯度,应用“三梯度法”计算出发射度.文中提出了一种新的“双成像法”测量方法,使切伦科夫辐射光通过一长焦距的消色差薄透镜,分别在焦平面和像平面获取图像.通过图像处理,前者可分析出电子束散角分布,后者可分析出电子束径向分布,从而直接得到均方根发射度.该方法对束流相空间和电荷密度分布无需假设,无需借助“三梯度法”,较其他常规测量方法具有实验装置更简便、测量精度更高和适用性更广等优点.文中给出了该测量方法对北京大学DC?SC光阴极注入器的发射度测量进行计算机模拟实验的结果和分析.     

气体Cerenkov辐射的量子理论

本文采用量子场论的一级微扰论,建立了气体介质中Cerenkov辐射的量子理论,结果表明,它有与固体、液体Cerenkov辐射不同的特点:线状光谱且轮廓不对称和出现小的红移,辐射角与辐射频率无关,并随入射粒子速度的增大而减小,辐射对入射带电粒子的速度没有阈值限制,激发态与基态原子的Cerenkov辐射几率相等,理论结果与实验基本一致。 关键词：     

Cerenkov losses: a limit for bandgap determination and Kramers-Kronig analysis

Measuring low energy losses in semiconductors and insulators with high spatial resolution becomes attractive with the increasing availability of modern transmission electron microscopes (TEMs) equipped with monochromators, C(s) correctors and energy filters. In this paper, we demonstrate that Cerenkov losses pose a limit for the interpretation of low energy loss spectra (EELS) in terms of interband transistions and bandgap determination for many materials. If the velocity of a charged particle in a medium exceeds the velocity of light, photons are emitted leading to a corresponding energy loss of a few electronvolt. Since these losses are strong for energies below the onset of interband transitions, they change the apparent loss function of semiconductors and insulators, with the risk of erroneous interpretation of spectra. We measured low energy losses of Si and GaAs with a monochromated TEM demonstrating the effect of sample thickness on Cerenkov losses. Angle resolved EELS and energy filtered diffraction patterns (taken without a monochromator) show the extremely narrow angular distribution of Cerenkov losses. The latter experiment provides a method that allows to decide whether Cerenkov radiation masks the very low loss signal in EELS.     

强流短脉冲电子束束剖面的时间分辨测量

 介绍了一套基于切伦科夫辐射的、用于强流短脉冲电子束束剖面测量的装置。装置利用扫描相机记录背面打毛的石英玻璃薄片中产生的切伦科夫光信号。使用该装置，在中国工程物理研究院流体物理研究所的2MeV注入器上进行了切伦科夫光的验证实验和时间分辨的束剖面测量实验。分析表明，测量系统的时间分辨率和空间分辨率分别为1.75ns和0.74mm。     

OBSERVATION OF CERENKOV LIGHT FROM EXTENSIVE AIR SHOWER

The pulse shape and the intensity of Cerenkov light from extensive air shower have been recorded by using two different types of photomultipliers (fast and slow).The distribution of the FWHM of Cerenkov light pulse and the spectrum of Cerenkov photo density have been measured for E>5×10¹⁴eV,at sea level.Comparing the two intensity results from two types of tubes indicate that the system which consists of the slow tubes and the peak ADC is not only simple but also cheap for the Cerenkov light intensity measurement.     

Helical Cerenkov effect, a novel radiation source

The observability of the helical Cerenkov effect as a novel radiation source is discussed. Depending on the value of the index of refraction of the medium, the strength of the uniform magnetic field, and the electron beam energy, helical Cerenkov radiation can occur in the same spectral regions as the ordinary Cerenkov effect, that is, from microwave to visible wavelengths. From the kinematics point of view, I argue that for a microwave wavelength of 10^-1cm this effect should be observable in a medium with an index of refraction of 1.4, with a beam energy of 3 MeV, and a uniform magnetic field of 4 T. On the specific level, however, for the sake of simplicity, I discuss the observability of this effect for visible light with the central wavelength of 5×10^-5 cm which can be achieved with 2 MeV in beam energy, silica aerogel as a medium (with an index of refraction of 1.075), and uniform magnetic fields from 5 to 10 T. For a 10-T magnetic field, I calculate that in the visible region of 250 to 750 nm an electron will produce a photon per 10 cm of traveled length. As to the stimulated helical Cerenkov emission, I estimate that respectable gains are possible even if the beam passes close to the dielectric rather than through it. In addition to being potentially a new radiation source, the helical Cerenkov effect could possibly be used as a detector of radiation by energetic electrons that are trapped in a medium by strong magnetic fields     

Cereukov自由电子激光与Undulator自由电子激光的基本特性的比较

在经过对Cereukov自由电子激光原理分析后，本文将其与Undulator自由电子激光的基本特性进行了比较。     

Coupled mode analysis to study cascading in the QPM Cerenkov regime in waveguides

In this paper we use the coupled mode analysis to study nonlinear phase shifts of the fundamental beam caused by cascaded second order nonlinear effects in the Quasi Phase Matched Cerenkov (QPMC) configuration in waveguides. Under the no-pump depletion approximation which is valid for low conversion efficiencies, we obtain the nonlinear phase shift as a function of length of interaction and grating period. It is observed that the nonlinear phase shift of the fundamental beam can be maximized by choosing a grating period for which the phase matched second harmonic radiation mode is radiated parallel to the film-substrate interface, i.e., for zero Cerenkov angle. Although the phase shifts are smaller than in the case of all guided geometry, QPM Cerenkov configuration is expected to have greater tolerance towards various waveguide parameters and the fundamental wavelength.