Currently, the pulsed linac at EuXFEL, operated at DESY, according to the design parameters can deliver up to 2700 electron bunches during an RF flat-top time of 600μs. The user community is interested to have more electron bunches that can be done only by increasing RF pulse duration. The RF flat-top length at the linac is limited by several factors, primarily the RF pulse length in the existing photoinjector. The new RF gun is currently under development and testing and will enable beam pulses of up to 800μs. The second limiting factor could be the stability of the RF power sources, the klystrons, which must handle longer high-voltage and RF pulses. Another very important part are the accelerating cavities and RF fundamental couplers, which must handle increasing power during cavity filling and a longer RF flat-top time. Initial investigations into extending the RF flat-top length began in 2022. Recently, various measures have been developed and implemented to increase the RF flat-top length while keeping power consumption low without compromising linac performance. These include optimizing the high-power RF shape, the HV shape of the klystrons, and the coupling factors of the accelerator cavities. The latest results from development and tests of several RF stations with a flat-top length of 800μs are presented.
Фогель et al. (Wed,) studied this question.