Sucessfully tested: More energy for FLASH prototype

The newest accelerator module for the FLASH free-electron laser has successfully passed the test. Now it is possible to increase the FLASH energy towards 1.2 GeV. This means that even shorter wavelengths down to 4.5 nanometers will be available for experiments starting next year. The module is a prototype for the European XFEL and it was partly manufactured in China. Later on, China will supply part of the modules needed for the XFEL as a contribution in kind.

For this extension of FLASH an additional module with eight accelerating structures is needed. The desired accelerating gradient of the module was specified to be 25 megavolt per metre so that – after the installation of the module at the end of the current FLASH accelerator - the electron beam energy will safely reach 1.2 GeV. In parallel the manufacturing of this additional module allows to crosscheck the last small technical changes needed for the European XFEL. For this reason, the accelerating unit, the so-called cavity string, was adapted to the XFEL module design and mounted into the first prototype from China. It was was built in China on behalf of the IHEP institute in Beijing. It consists of the outer vacuum tank and the inner support structure for the cavity string called the ‘cold mass’.

The prototype PXFEL1 was assembled at DESY from April to June 2009, with the participation of the CEA Saclay where series production is to take place. Then it was directly installed into DESY’s cryomodule test bench (CMTB)and cooled down to -271°C. In mid-July, after successful tests of the RF couplers, a gradient average of up to 30 MV/m was reached. At PXFEL1, all cavities reached the gradients that were expected on the basis of the previous results from the individual cavity test bench tests.

Currently, the modules are tested for heat losses, and the integrated superconducting magnets for their performance according to plan. First results confirm the expectations. on the. This is especially true for the mechanical behaviour at cooling down from room temperature to -271°C: the observed shrinkage and movements of the whole structure are all within the allowed tolerances.

The successful assembly of the module PXFEL1 underlines the good collaboration of the institutes IHEP/Beijing, CEA-IRFU/Saclay, IN2P3-LAL/Orsay, INFN/Milano, CIEMAT/Madrid and DESY within the framework of the XFEL accelerator consortium.