Within the framework of the Stockholm-Uppsala Centre for Free Electron Laser Research, the Manne Siegbahn Laboratory (MSL) collaborates with Deutsches Elektronen Synchrotron (DESY) on magnet development for the European XFEL. The main project concerns fiducialization of the quadrupole magnets for the undulator sections of the XFEL such that the position of the magnetic centre can be related to alignment targets on the magnet yokes with accuracy better than 50 mm. The work also includes magnet characterization of magnetic axis stability and higher order error-field components.
A new project on a precision temperature measurement system for the XFEL undulators started in late 2009. The aim is to adjust the undulator gap to compensate for small changes in temperature rather than keeping a very fixed ambient temperature. The challenge here is to design a sufficiently accurate and precise measurement system to measure a representative temperature for the permanent magnetic material in the undulator.
The MSL-DESY collaboration also includes a previous feasibility study of the use of permanent magnet/electromagnet hybrid dipoles in the XFEL beam dumps.
A rotating coil system has been set up at MSL to measure and characterize the XFEL quadrupole magnets. This device measures the induced voltage from the magnet and allows calculation of the Fourier components of the magnetic field. The ratio between the dipole component and the fundamental quadrupole component gives the position of the magnetic axis relative to the axis of the rotating coil. A coordinate measuring machine is used to relate the rotating axis and thereby the magnetic axis to alignment markers on the magnet. Optical alignment tools (Laser Trackers) utilize these alignment markers to position the quadrupole magnet.
With this system the quadrupole magnets are characterized with respect to:
When available, all quadrupole magnets for the undulators will be measured and fiduzialized with the rotating coil device before installation at XFEL.
Precision temperature measurement of the XFEL undulators
The magnetic properties of the permanent magnetic material in the undulator change with temperature. To maintain wavelength and phase-matching conditions vital for the radiation power output either the ambient temperature must be kept at a very fixed level along the entire length of the undulator (very expensive) or the undulator gap may be changed to compensate for change in temperature. This compensation scheme requires very accurate and precise temperature information of the permanent magnetic material in the undulator. The temperature of the permanent magnetic material can not be measured directly so the challenge here is to design a system to measure a representative temperature.
At the end of the European XFEL the electron beam is separated from the photon beam and directed towards the beam dump with a bending magnet. This dipole magnet is designed to bend 10-25 GeV electrons by 1°/m and is 10 meter long in total. By integrating permanent magnet material (PMM) into a conventional electromagnet, this so called hybrid magnet with a 1 T bias magnetic field consumes no power at the nominal energy of the XFEL, 17.5 GeV.
In case of component failure this dipole magnet also works as a passive safety system, preventing the electrons from reaching the experimental hall.
Magnetic field calculations using OPERA-3D and the Pandira program have been performed to evaluate the possibility of using hybrid dipoles in the XFEL beam dumps. The results are presented in three reports.
Fredrik Hellberg, Manne Siegbahn Laboratory
Anders Hedqvist, Manne Siegbahn Laboratory