Design and optimization of an electromagnet undulator

In this paper we discuss the design and optimization of an electromagnet undulator. A short period electromagnet undulator has been reported and used for free electron laser experiment under the approximation of infinite permeability of the lamination core. Here we remove this approximation and present analytical expressions for an alternate design concept on the electromagnet undulator.     

Hard undulator radiation in an inverse medium

X-ray radiation from fast electrons in undulators filled with an inverse medium is studied. A formula for the spectral density of the number of photons is derived. The intensity zeroth harmonics, as well as the intensity of radiation in zero undulator field, are described by the Tamm-Frank formula for Cherenkov radiation. It is shown that the spectral density of emitted photons in a wavelength range of λ ? 0.4–2.0 Å in such a medium can be increased by four orders of magnitude as compared to the radiation intensity in a vacuum undulator. The energy of emitted electrons in the former case must be in an interval of 5-2 GeV, while electrons with an energy of 14-6 GeV are required in vacuum undulators.

     

First results of investigation of radiation from positrons in a crystalline undulator

Radiation emitted by positrons moving in a periodically deformed crystal has been experimentally observed for the first time. Radiation spectra have been measured in a wide energy range. Experimental evidence has been obtained for an undulator peak in a radiation spectrum, which is qualitatively consistent with calculations. Crystalline undulators ensure an equivalent magnetic field of 1000 T and a period in the submillimeter range and can therefore be used to generate x-ray and gamma radiation that is a hundred times harder than radiation in usual undulators.     

The prototype of new variable period undulator for Novosibirsk free electron laser

To improve the parameters of the second stage Novosibirsk free electron laser we plan to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles. Both these advantages will be realized in the new undulator under development in Budker INP. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.     

Influence of a constant magnetic field on the radiation of a planar undulator

The influence of a constant magnetic field on the radiation of a planar undulator is studied analytically with the use of generalized Bessel functions. The behavior of on-axis radiation intensity in the undulator and the influence of a magnetic field on off-axis radiation are investigated. The critical magnitude of the constant component of the magnetic field, which has a significant effect on the motion of electrons in the undulator, is calculated analytically. The examples of several planar undulators are discussed, and the influence of the Earth’s magnetic field on their spectrum is evaluated.     

On the radiation of a planar undulator with constant magnetic field on its axis taken into account

The intensity of undulator radiation, distortion of the spectrum, and the broadening of spectral lines of a planar undulator with a constant component of the magnetic field on its axis are studied using the technique of generalized special functions. Based on the obtained mathematical solutions, it is shown how the choice of certain values of the undulator parameters makes it possible to decrease the distortions of its radiation spectrum. The dependence of distortion of the spectral lines on the number of periods, the magnetic field, and other undulator parameters is determined analytically. The broadenings of the spectral lines caused by homogeneous and inhomogeneous effects produced by the constant-field components in undulators are compared. The possibility of the influence of the Earth’s magnetic field on the radiation of an undulator with a large number of periods is analyzed.     

横向聚焦波荡器磁场的计算与分析

横向聚焦波荡器可用于电子束能量较低、函数较小的情况。在现有横向聚焦波荡器设计方案的基础上,通过倾斜磁块端面和磁极面提出了几种不同结构的横向聚焦波荡器方案。利用三维磁场模拟程序Radia,对这些波荡器的聚焦场特性进行了模拟计算,对其聚焦特性与主要参数的关系进行了研究,并与现有其他横向聚焦波荡器的聚焦特性进行了对比。对弱聚焦和强聚焦两种情况,分别给出较好的结构方案。对于弱聚焦,平均聚焦梯度随中心场强的增大而略有增大,变化不明显;对于强聚焦,平均聚焦梯度随中心场强的增大而明显增大,呈高次曲线关系。     

Calculation and analysis of the magnetic field of a linearly tapered undulator

There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator.In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula.The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments.Therefore, for a linearly tapered undulator,we can use the empirical formula to design the variation of the undulator gap.For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period.     

A model for analytical description of magnetic field effects and losses in a planar undulator radiation

We analyze the influence of constant magnetic constituents on the radiation of high energy electrons in a planar undulator. Broadening and spectrum shift effect of the constant field is compared with other common spectrum distortions in UR sources. Analytical formulation of the effect of the constant magnetic field enables us to obtain and study exact expressions for the UR intensity. They reveal the possibilities to influence off-axis effects and give practical recommendations for the undulators with radiation properties, best profitable for free electron lasers. Several examples of undulators are considered, recommendations specific for each case are given.     

Design and analysis of a laser micrometer for undulator gap measurement applications

In this paper we report the design of a laser micrometer for undulator gap measurement studies. In this scheme, the parallel light emerging from the rotating polygon mirror passes through an F-theta lens makes a vertical line on the image plane. When an object intercepts the line, the interrupted and the uninterrupted light is detected in a DSO through a detector. The beam spot size and the linear velocity of the beam spot on the scan line are the two important parameters of the laser micrometer. The beam spot size measurements show that it is constant along the scan line for a number of RPMs. It measures a constant value at ±3 mm to the effective focal length of the F-theta lens. The measurements are verified for two types of objects i.e. solid object and a circular hole and also for an electromagnet undulator. The electromagnet undulator is measured with an accuracy of 3–5 µm.     

Effect of beam energy spread on cascade optical klystron undulator radiation

In this paper we analyze the effect of beam energy spread on cascade optical klystron undulator radiation. The analysis suggests that stronger dispersion strength needs a better beam quality in both single stage and cascade optical klystron undulator radiation.     

Radiation from Elliptical Undulators with Magnetic Field Harmonics

Journal of Experimental and Theoretical Physics - We analyze undulator radiation in some multiperiodic magnetic fields. We consider undulators with planar, helical, and elliptical axisymmetric...     

CAEPXFEL波荡器束线初步物理设计

中国工程物理研究院计划开展XFEL光源的研制,主要通过电子束在波荡器中的辐射特性产生硬X射线。根据理论分析和数值模拟,在电子束最高能量可达12GeV的实际条件下,初步设计了一条间隙可调的真空外波荡器束线,波荡器分为25段,每段长3.86m,间隙7~10mm,周期长度25.4mm,磁场0.636~1.03T,束线总长120m左右,辐射光子能量为3~25keV。     

Diagnostic technique applied for FEL electron bunches

Diagnostic technique applied for FEL ultrashort electron bunches is developed at JINR-DESY collaboration within the framework of the FLASH and XFEL projects. Photon diagnostics are based on calorimetric measurements and detection of undulator radiation. The infrared undulator constructed at JINR and installed at FLASH is used for longitudinal bunch shape measurements and for two-color lasing provided by the FIR and VUV undulators. The pump probe experiments with VUV and FIR undulators provide the bunch profile measurements with resolution of several femtosecond. The new three microchannel plates (MCP) detectors operated in X-ray range are under development now in JINR for SASE1-SASE 3 European XFEL.     

Effect of the correction of the motion of relativistic electrons in a magnetic undulator on the properties of undulator radiation

The properties of undulator radiation of electrons in a planar undulator with an arbitrary number of periods of the magnetic field and with correcting sections along the ends of the undulator are investigated. It is shown that in setups with relatively large number of periods of the field, the emission of particles in the correcting sections has a large effect on the general characteristics of undulator radiation of electrons in the setup. The experiment confirmed the basic assumptions of the theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 52–58 November, 1981.     

Refurbishment of a used in‐vacuum undulator from the National Synchrotron Light Source for the National Synchrotron Light Source‐II ring

The National Synchrotron Light Source (NSLS) ceased operation in September 2014 and was succeeded by NSLS‐II. There were four in‐vacuum undulators (IVUs) in operation at NSLS. The most recently constructed IVU for NSLS was the mini‐gap undulator (MGU‐X25, to be renamed IVU18 for NSLS‐II), which was constructed in 2006. This device was selected to be reused for the New York Structural Biology Consortium Microdiffraction beamline at NSLS‐II. At the time of construction, IVU18 was a state‐of‐the‐art undulator designed to be operated as a cryogenic permanent‐magnet undulator. Due to the more stringent field quality and impedance requirements of the NSLS‐II ring, the transition region was redesigned. The control system was also updated to NSLS‐II specifications. This paper reports the details of the IVU18 refurbishment activities including additional magnetic measurement and tuning.     

Neutrino analog of undulator radiation

The neutrino analog of the undulator radiation of ultrarelativistic electrons is studied theoretically. A new source of electron neutrino pairs based on electronic accelerators and single crystals as the undulator is proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 69–74, April, 1985.     

Spatial undulator of finite length

The spectral-angular and polarization properties of undulator radiation, generated by relativistic electrons in a spatially periodic magnetic system (undulator), are studied. The possibility of obtaining radiation with a different spectral form and different polarization is demonstrated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 7–11, August, 1984.     

波荡器谐波场增强效应对电子自发辐射谱的影响

 有效利用电子束在波荡器中运动时产生的谐波辐射,是获得更短波长辐射最直接的方法之一。提高波荡器磁场的谐波分量可以提高电子束的谐波辐射光场强度。分析了一种改进Halbach型波荡器结构,计算了其磁场的构成,分析表明这种结构可以使磁场的三次谐波分量提高至基波分量的25%左右。以合肥光源的电子束参数为例,计算了波荡器磁场谐波分量增强后对电子束自发辐射谱的影响。计算结果表明,波荡器磁场谐波分量增强至25%时,可以使电子束自发辐射的三次谐波辐射增强至基波辐射光子通量的67%左右。     

Studies of classical radiation emission from plasma wave undulators

The authors examine the characteristics of the classical radiation emitted by a relativistic electron beam that propagates perpendicularly through a large amplitude relativistic plasma wave. Such a study is useful for evaluating the feasibility of using relativistic plasma waves as extremely short wavelength undulators for generating short wavelength radiation. The electron trajectories in a plasma wave undulator are obtained using perturbation techniques and are then compared to numerical simulation results. The frequency spectrum and angular distribution of the spontaneous radiation emitted by a single electron and the stimulated radiation gain are obtained analytically, and are then compared to 3-D numerical simulations. The characteristics of the plasma wave undulator are compared to the AC free-electron laser (FEL) undulator and the conventional FEL