TEMF, TU Darmstadt, Darmstadt, Germany
Energy Recovery Linacs promise superior beam quality: sharper and more intense. To reach these goals, resonance frequency control of the superconducting RF cavities is an important part. In this work, system identification procedures conducted at components of the S-DALINAC (Institute for Nuclear Physics, TU Darmstadt, Germany) are shown. This includes investigations of the piezo tuner’s effect on, e.g., the phase of the accelerating field when a periodic disturbance is applied. The results are compared to simulations of the modelled system and the impact of the applied controller is discussed.
THCOWBS05
IHEP, Beijing, People’s Republic of China
High Energy Photon Source is a 6GeV kilometer-scale synchrotron light source to be built in Beijing. The designed beam emittance is lower than 100pm.rad approaching diffraction limitation with 200mA beam current stored. In order to realize a novel injection scheme and prolong the beam lifetime, a double-frequency RF system has been proposed with 166.6MHz as the fundamental and 499.8MHz as the third harmonic. Both RF system will adopt superconducting cavities. Over the last three years, a 166.6MHz quarter-wave β=1 proof-of-principle SRF cavity has been in-house developed, vertical tested, dressed with helium jacket and ancillaries, and eventually horizontal tested with a success in early 2019. In parallel, the HOM-damped prototype cavity has been designed adopting a hybrid damping scheme. Due to a rather low-frequency HOMs, both HOM couplers and beam-pipe HOM absorbers are to be used to ensure a tight impedance budget.
KPH, Mainz, Germany
MESA is a two pass energy recovery linac (ERL) currently under construction at the Johannes Gutenberg-University in Mainz. MESA uses two 1.3 GHz TESLA type cavities with 12.5 MV/m of accelerating gradient in a modified ELBE type cryomodule in c.w. operation. One potential limit to maximum beam current in ERLs is the transverse beam breakup (BBU) instability induced by dipole HOMs. These modes can be excited by bunches passing through the cavities off axis. Following bunches are then deflected by the HOMs, which results in even larger offsets for recirculated bunches. This feedback can even lead to beam loss. To measure the quality factors and frequencies for the dressed as well as undressed cavities improves the validity of any current limit estimation done.
THCOWBS07
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Superconducting Radio Frequency (SRF) cavities operating with large loaded quality factors is the natural choice for Energy Recovery Linacs which operate at negligible beam loading. While this leads to lower RF power requirements, the stability of the accelerating field is strongly influenced by peak microphonics detuning. In this talk, I will discuss various methods of passively suppressing vibrations used in various facilities using low bandwidth SRF systems, with special reference to CBETA, a multi-turn SRF ERL being commissioned at Cornell University. I will also describe our active microphonics control system based on a modified narrow band Active Noise Control (ANC) algorithm and compare it with schemes being explored in other machines.