Successful FLASH Tests for European XFEL and ILC

The accelerator crew conducting the high current tests at FLASH.

On the way to high beam intensities in superconducting particle accelerators, the collaboration of the DESY FLASH team and International Linear Collider colleagues achieved a decisive milestone. For the first time, pulses of 800 microseconds with an average beam current of six milliamperes at a beam energy of 800 MeV could be achieved in the FLASH accelerator – a free-electron laser and pilot facility for both the European XFEL and the International Linear Collider ILC. For some hours of operation, with shorter pulses between 300 and 500 microseconds, it was even possible to reach the optimum particle current value of 9 milliamperes.

Prior to these experiments, the beam line to the absorber block was remodelled, with upgrades to the vacuum system and the beam diagnostics that ensure a safe dumping of the highly intense electron beam. During the two weeks of high-current tests, the accelerator physicists first used the existing FLASH facility to accelerate pulses of 800 bunches with the highest possible charge. After reaching stable conditions with these parameters, a new photocathode laser was installed in the FLASH photoinjector, which operates with the triple frequency of the present laser, making it possible to produce 2400 pulses in one train. The combination of high electron bunch charges and long pulse trains is planned for further tests to take place after the present FLASH shutdown.
The advantage of the superconducting accelerators used in FLASH, the European XFEL and the ILC is the high beam current, i.e. the number and density of electron bunches to be accelerated. With operation under full load, the accelerators will produce pulses of up to 2400 bunches in 800 microseconds at a beam current of 9 milliamperes. This will generate high collision rates at the ILC, and an amount of up to 30 000 X-ray laser flashes per second at the European XFEL and FLASH. This high frequency of light flashes is only possible at FEL facilities with superconducting technology.