Abstract
Conventional undulators are used in synchrotron light sources to produce radiation with a narrow relative spectral width as compared to bending magnets or wigglers. The spectral width of the radiation produced by conventional undulators is determined by the number of undulator periods and by the energy spread and emittance of the electron beam. In more compact electron sources like for instance laser plasma accelerators the energy spread becomes the dominating factor. Due to this effect these electron sources cannot in general be used for high-gain free electron lasers (FELs). In order to overcome this limitation, modified undulator schemes, so-called transverse gradient undulators (TGUs), were proposed and a first superconducting TGU was built at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. In this paper simulations of the expected synchrotron radiation spectral distribution are presented. An experimental test with that device is under preparation at the laser wakefield accelerator at the JETI laser at the University of Jena, Germany.
Highlights
In a conventional undulator the fundamental wavelength λ of the emitted radiation is given by λ 1⁄4 λu 2γ2 1 þ K2: 2ð1Þ λu is the period length of the undulator, K e 2πmc λuB~ y the undulator parameter, B~ y the on-axis magnetic flux density amplitude and γ the electron’s Lorentz factor
In order to overcome this limitation, modified undulator schemes, so-called transverse gradient undulators (TGUs), were proposed and a first superconducting TGU was built at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
To facilitate the comparison of the calculation results for different observation distances, photon flux densities are expressed in units of 1=ðs mrad2 0.1% bandwidthÞ. This calculation in principle proves the validity of the concept, both for the ideal linear TGU and for the cylindric SCTGU
Summary
In a conventional undulator the fundamental wavelength λ of the emitted radiation is given by λ 1⁄4 λu 2γ2 1 þ K2: 2ð1Þ λu is the period length of the undulator, K e 2πmc λuB~ y the undulator parameter, B~ y the on-axis magnetic flux density amplitude and γ the electron’s Lorentz factor. The same equation solved for γ describes the resonance condition for a free electron laser (FEL), γr 1⁄4 sffi2λffiffiuλffiffiffiffiffiffi1ffiffiffiffiþffiffiffiffiffiKffi2ffiffi2ffiffiffiffiffi; ð2Þ where γr is the resonance energy of the FEL. If the electron beam has a significant energy spread, the spectrum of the undulator radiation is broadened or, in case of a high gain FEL, the FEL gain is decreased. 10−2, or the bandwidth of the qffiffiffiffiffiffiffi qffiffiffiffiffiffiffi high-gain
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