Axel Neumann

Adapting TESLA technology for future cw light sources using HoBiCaT

The HoBiCaT facility has been set up and operated at the Helmholtz-Zentrum-Berlin and BESSY since 2005. Its purpose is testing superconducting cavities in cw mode of operation and it was successfully demonstrated that TESLA pulsed technology can be used for cw mode of operation with only minor changes. Issues that were addressed comprise of elevated dynamic thermal losses in the cavity walls, necessary modifications in the cryogenics and the cavity processing, the optimum choice of operational parameters such as cavity temperature or bandwidth, the characterization of higher order modes in the cavity, and the usability of existing tuners and couplers for cw.

Status and perspectives of superconducting radio-frequency gun development for BERLinPro

As part of the BERLinPro study, HZB is developing an SRF photoelectron injector. The R&D will be carried out in three stages, the first of which is currently being installed at HZBs HoBiCaT facility. It consists of an SRF cavity with SC solenoid, electron beam diagnosics and drivelaser systems.

Superconducting radio-frequency virtual cavity for control algorithms debugging

Superconducting radio-frequency (SRF) cavities are one of the most important elements in modern particle accelerators as they are used for beam acceleration, bunch manipulation, bunch focusing and defocusing, etc. Nevertheless, the availability of these complex structures prior to their installation in the accelerator is limited, either due to a lack of a real cavity or due to the time needed for the experiment setup (vacuum, cryogenics, cabling, etc.), and thus it can block or delay the development of new algorithms such as low level RF control, quench detection, etc. In this paper, we present a hardware virtual cavity to be used in hardware-in-the-loop simulations. The system implements a cavity electrical model for the transmitted and reflected voltages and more advanced features such as mechanical vibration modes driven by Lorentz-force detuning or external microphonics, hard quenches, and the Q-slope. As viewed from the RF input and output, this virtual cavity acts like a real SRF cavity and can replace such a system in early-stage debugging and operation of ancillary control systems.

First LLRF Tests of BERLinPro Gun Cavity Prototype

The goal of Berlin Energy Recovery Linac Project (BERLinPro) is the generation of a 50 MeV, 100-mA low emittance (below 1 mm mrad) CW electron beam at 2 ps rms bunch duration or below. Three different types of 1.3 GHz SRF modules will be employed: the electron gun, the booster and the main linac. Precise RF amplitude and phase control are needed due to the beam recovery process. In this paper we describe the first tests of the Low Level RF control of the first injector prototype at the HoBiCaT facility, implemented in the digital VME-based LLRF controller developed by Cornell University. Tuner movement control by an mTCA.4 system, together with further plans of using this technology will be also presented. INTRODUCTION The bERLinPro Energy Recovery Linac is a single pass, high average current and all superconducting CW driven ERL currently in construction by Helmholtz Zentrum Berlin (HZB). Its purpose is to serve as a prototype to demonstrate low normalized beam emittance of 1 mm·mrad at 100 mA and short pulses of about 2 ps [1]. bERLinPro will be formed by three 1.3 GHz modules with different characteristics and parameters [2]. The first module is a 1.4-cell gun cavity using a high quantum efficiency (QE) normal conducting multi-alkali cathode, which will deliver 2.3 MeV. The gun module is then followed by the booster module formed by three high power 2-cell booster cavities of Cornell type, where two of them deliver 2.1 MeV each and the third one is operated in zero crossing for bunch compression. The beam is merged into the main linac module consisting in three 7-cell cavities where it is accelerated to 50 MeV in a first pass and decelerated again to 6.5 MeV in a second pass. The beam is finally dumped in a 650 KW beam dump. The gun is one of the most critical components and in order to mitigate risk, it is being developed in several stages. The first one, the so-called Gun0, was a fully superconducting system with a super conducting lead deposited on the back. It allowed beam studies without a complex insert of a high QE normal conducting cathode in a SC environment, [3]. The prototype presented here, called Gun1.0, is a medium power version of the final high power structure and utilizes CW modified TTF-III couplers. It is a beam dynamic optimized design with high QE cathode insert system allowing the generation of a beam up to 4 mA, [4]. It will be used to study bERLinPro bunch parameters and the usage of high QE NC cathode within a SC environment. The last step in the gun development is the Gun2.0, which will feature two modified KEK c-ERL high power couplers [5] to allow 100 mA average current operation. Figure 1: Gun1.0 cavity’s cold mass with fundamental power couplers (left), blade tuner and cathode insert (right). GUN1.0 CAVITY After several vertical and horizontal tests at JLab and HZB where the Q0 specifications were met [2], cold mass assembly and first horizontal tests under module conditions in the horizontal bi-cavity testing facility (HoBICaT) at HZB have been carried out [6]. Table 1: Main Parameters of Gun1.0 Max E0 Max Pf QL 30 (MV/m) 20 KW 3·106 3·107 The cold mass consisting of the magnetic shielding, a blade tuner with a stepper motor and four piezo actuators, and the cathode insertion system, which includes a Petrov filter and a Helium gas cooler, was installed in HZB’s clean room together with the fundamental power couplers. Figure 1 depicts the gun cavity’s cold mass next to the HoBiCaT module. The installed coupler can stand an average input power up to 2 KW, but it is foreseen to equip later with modified warm part to allow 10 kW per coupler [7]. Unfortunately the penetration depth is lower than expected, which led to a higher QL and narrower bandwidth than expected. The last step in the cold mass assembly was to install the blade tuner including the motor and the piezo-actuators, whose pre-stress was adjusted by capacitance measurement. Table 1 shows the expected main parameters for the Gun1.0 cavity. The forward power will be delivered by two power couplers. ___________________________________________ * Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association † pablo.echevarria_fernandez@helmholtz-berlin.de Proceedings of IPAC2016, Busan, Korea TUPOW035 02 Photon Sources and Electron Accelerators A18 Energy Recovery Linacs (ERLs) ISBN 978-3-95450-147-2 1831 C op yr ig ht