Continuous Wave Operation of Superconducting Accelerating Cavities With High Loaded Quality Factor

Close to 780 superconducting 1.3-GHz accelerating cavities made of bulk niobium have been installed in the European X-ray free electron laser (E-XFEL) linear accelerator. The linac can operate at a mean gradient (Eacc) of ca. 23 MV/m in the nominal short pulse (SP) operation mode with 1.4-ms pulses and a repetition rate of 10 Hz. An R&D program at Deutsches Elektronen-Synchrotron (DESY) is ongoing since 2011 on the feasibility of a continuous wave (CW) upgrade of the E-XFEL accelerator. In this publication, a modification of the low-level radio frequency (LLRF) control system to the CW mode is presented. Currently, the control system successfully stabilizes accelerating field for the SP mode. The demanding E-XFEL specifications of 0.01% for the field amplitude and 0.01° for the phase stability are required to keep the photon beam quality for all experimental stations. The proposed modification has been implemented and tested to verify the system versatility for SP and CW operation modes. The tests were conducted for a prototype E-XFEL cryomodule XM-3. As for the series cryomodules, this prototype contains eight superconducting 1.3-GHz cavities. The results presented here confirm that the same LLRF system can be used with minor software modifications for either operation mode (CW or SP). However, the CW mode requires a more complex RF-power management and more precise control, especially when cavities operate with very high loaded quality factor (Ql) of the order of 6E7. The achieved stability for such highQl is also presented and discussed

From Pulse to Continuous Wave Operation of TESLA Cryomodules – LLRF System Software Modification and Development

Higher efficiency of TESLA based free electron lasers (FLASH, XFEL) by means of increasedquantity of photon bursts can be achieved using continuous wave operation mode. In orderto maintain constant beam acceleration in superconducting cavities and keep short pulse toCW operation transition costs reasonably low some substantial modification of acceleratorsubsystems are necessary. Changes in: RF power source, cryo systems, electron beam source,etc. have to be also accompanied by adjustments in LLRF system. In this paper challengesfor well established pulsed mode LLRF system are discussed (in case of CW and LP scenarios).Firmware, software modifications needed for maintaining high performance of cavitiesfield parameters regulation (for 1Hz CW and LP cryo-module operation) are described.Results from studies of vector sum amplitude and phase control in case of resonators highQl factor settings (Ql~1.5e7) are shown. Proposed modifications implemented in VME andmicroTCA (MTCA.4) based LLRF system has been tested during studies at CryoModule TestBench (CMTB) in DESY. Results from tests together with achieved regulation performancedata are also presented and discussed

High Level Software Structure for the European XFEL LLRF System

The Low level RF system for the European XFEL is controlling the accelerating RF fields in order to meet the specifications of the electron bunch parameters. A hardware platform based on the MicroTCA.4 standard has been chosen, to realize a reliable, remotely maintainable and high performing integrated system. Fast data transfer and processing is done by field programmable gate arrays (FPGA) within the crate, controlled by a CPU via PCIe communication. In addition to the MTCA system, the LLRF comprises external supporting modules also requiring control and monitoring software. In this paper the LLRF system high level software used in E-XFEL is presented. It is implemented as a semi-distributed architecture of front end server instances in combination with direct FPGA communication using fast optical links. Miscellaneous server tasks have to be executed, e.g. fast data acquisition and distribution, adaptation algorithms and updating controller parameters. Furthermore the inter-server data communication and integration within the control system environment as well as the interface to other subsystems are described

Real-time Estimation of Superconducting Cavities Parameters

Performance of accelerators based on the superconductive cavities including FLASH and XFEL facilities at DESY is affected by cavity parameters variation over time. High gradient electromagnetic field inside cavities causes detuning due to the Lorentz force. In addition the quality factor of cavities can change during the RF field pulse. Currently used method for estimation of those parameters is based on the post-processing of the data recorded during operation of the RF. External servers calculate cavity parameters using cavity equation, forward power and probe signals collected during previous pulse. A novel approach* based on the component implemented in FPGA is presented. In the new method loaded quality factor and detuning are estimated in real-time during the RF pulse for increased reliability and better exception handling. Modified firmware of the LLRF control system based on the Micro Telecommunications Computing Architecture (MTCA) platform has been used for the method verification

FPGA-based Data Processing in the Neutron-Sensitive Beam Loss Monitoring System for the ESS Linac

International audienceThe European Spallation Source (ESS), which is currently under construction, will be a neutron source based on 5 MW, 2 GeV superconducting proton linac. Among other beam instrumentation systems, this high intensity linac requires a Beam Loss Monitoring (BLM) system. An important function of the BLM system is to protect the linac from beam-induced damage by detecting unacceptably high beam loss and promptly inhibiting beam production. In addition to protection functionality, the system is expected to provide the means to monitor the beam losses during all modes of operation with the aim to avoid excessive machine activation. This paper focuses on the FPGA implementation of the real-time data processing in the nBLM system and presents preliminary result of a prototype system installed at LINAC4 at CERN