RF Control for SRF Cavity Tests

The ERL type accelerator MESA, which is currently under construction at the Institut fuer Kernphysik at the Johannes Gutenberg-Universitaet Mainz, will utilize two modified ELBE type SRF cryomodules with field strengths of 25 MeV each, for achieving electron energies up to 155 MeV. To realize a stable operation of energy recovery, the cryomodules and, in particular, the two 9-cell TESLA type cavities per module need to meet high fabrication standards. They have to be tested and measured prior to installation. This will be done at the HIM facility on the University campus. One key component of the test setup is the RF control, which is realized by a Phase Locked Loop. The PLL compares the phase of two RF signals in order to maintain the driving signal at the resonance frequency of the SRF cavity. This talk will give an insight into the planning and implementation of a RF control that allows high performance operation in a testing environment for SRF structures.