A $\hbox{Nb}_{3}\hbox{Sn}$ -Based, Model Superconducting Helical Undulator Fabricated Using a Wind and React Process
A model helical undulator 250 mm in length, with a period of 14 mm, was designed, fabricated and tested. The helical coil was wound with multifilamentary, internal-Sn type Nba3Sn strand. The 0.7 mm OD strand was insulated with S-glass, wound onto the former, and reacted, after which the coil underwent vacuum epoxy impregnation. The beam aperture was 7 mm, the winding bore diameter was 8 mm, and the OD of the complete winding was 18 mm. The helical poles were made from 1016 low carbon steel, and projected slightly above the coil pack, with an OD of 19.06 mm. The coil Ic and the magnetic field in the bore were measured at 4.2 K in a liquid helium bath. The bore field was also measured as a function of position along the length of the undulator.
The TESLA Free Electron Laser -- Concept and Status
The aim of the TESLA Free Electron Laser (FEL) is to develop and realize an Angstrom wavelength, high gain FEL in parallel with the TESLA superconducting e+/elinear collider. As a first step, an FEL for the VUV wavelength regime is now under construction at DESY, making use of the TESLA Test Facility (TTF). The VUV FEL at the TTF comes in two phases, which are both approved. The paper describes the over-all layout of each phase and the status of components. 1 FREE ELECTRON LASERS FOR SHORT WAVELENGTH Over the past 30 years, synchrotron radiation has turned into a most powerful research tool that has been applied in many fields of science ranging from physics, chemistry and biology to material sciences, geophysics, and medical diagnostics. This rapid progress was driven by the development of new, increasingly brilliant sources based on electron storage rings. Due to the recent progress in accelerator technology the possibility has been opened up to complement storage ring based sources by ultra-brilliant Free-Electron Lasers operating in the soft X-ray regime. In a Free Electron Laser (FEL), an electron beam radiates photons at much higher power and better coherence than it does due to spontaneous synchrotron radiation. The key point is that electrons moving in a transverse magnetic field of alternating polarity (undulator) may amplify an existing electromagnetic radiation field (see e.g. [1]). For properly chosen phase and wavelength (see eq. 1) the scalar product of the electron’s velocity vector and the electric field vector does not vanish on average, resulting in an average energy transfer between the electron beam and the radiation field. As a consequence of this interaction, depending on the relative phase, some electrons get accelerated and others decelerated. This results in a longitudinal density modulation of the electron beam at the optical wavelength during the passage through the undulator. With the onset of this “microbunching”, coherent emission at the resonant wavelength sets in which results in an exponential growth of the power in the radiation field (high gain mode), characterized by the gain length L gain : ) / exp( ) ( 0 gain L z I z I ⋅ = Similar to synchrotron radiation sources, there is no fundamental limit in the choice of the photon wavelength. 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 P ea k B ri ll ia n ce [P h ot ./( se c · m ra d 2 · m m 2 · 0. 1% b an d w .)]
Superconducting helically wound magnet for the free-electron laser.
Theoretical and experimental studies conducted by the Stanford Free Electron Laser group have resulted in the first operation of a free-electron laser amplifier and free-electron laser oscillator. Two superconducting helically wound periodic magnetics have been constructed for use with the laser. In this paper we present a discussion of design considerations and test results for the two magnets. The tests included measurement of the magnitude and the variation of the transverse magnetic field with radius in the bore of the magnets, the critical current, and the intensity, angular distribution, and spectrum of the spontaneous radiation emitted by electrons moving through the field.