Tomasz Jezynski

Interfaces and communication protocols in ATCA-based LLRF control systems

Linear accelerators driving Free Electron Lasers (FELs), such as the Free Electron Laser in Hamburg (FLASH) or the X-ray Free Electron Laser (XFEL), require sophisticated Low Level Radio Frequency (LLRF) control systems. The controller of the LLRF system should stabilize the phase and amplitude of the field in accelerating modules below 0.02% of the amplitude and 0.01 degree for phase tolerances to produce an ultra stable electron beam that meets the required conditions for Self-Amplified Spontaneous Emission (SASE). Since the LLRF system for the XFEL must be in operation for the next 20 years, it should be reliable, reproducible and upgradeable. Having in mind all requirements of the LLRF control system, the Advanced Telecommunications Computing Architecture (ATCA) has been chosen to build a prototype of the LLRF system for the FLASH accelerator that is able to supervise 32 cavities of one RF station. The LLRF controller takes advantage of features offered by the ATCA standard. The LLRF system consists of a few ATCA carrier blades, Rear Transition Modules (RTM) and several Advanced Mezzanine Cards (AMCs) that provide all necessary digital and analog hardware components. The distributed hardware of the LLRF system requires a number of communication links that should provide different latencies, bandwidths and protocols. The paper presents the general view of the ATC A-based LLRF system, discusses requirements and proposes an application for various interfaces and protocols in the distributed LLRF control system.

Prototype AdvancedTCA Carrier Board with three AMC bays

The Low Level RF (LLRF) control system of the Free Electron Laser in Hamburg (FLASH) is currently based on the Versa Module EuroCard (VME) standard. However, the application of Advanced Telecommunications Computing Architecture (ATCA) platform, as an alternative to the above mentioned standard, is taken into consideration. ATCA offers most of all improved reliability, because of the integrated management system which controls crucial parameters of the whole platform and provides the operator with control and diagnostics over the system from an external personal computer. Furthermore, implementation of AdvancedTCA architecture results in significant system operability enhancement, due to instant detection of a faulty module and Hot-Swap functionality that enables a swift replacement of the module, without disrupting the whole system. The platform management is under control of the Intelligent Platform Management Interface (IPMI). The paper presents the IPMI software for the Intelligent Platform Management Controller (IPMC) on a prototype Carrier Board. The software covers most of the functionality, defined by AdvancedTCA and IPMI ver. 1.5 standards, including inter alia sensor monitoring, platform event handling, communication with the Shelf Manager and complete activation and deactivation processes not only for the Carrier Board, but also for three attached Advanced Mezzanine Card (AMC) modules. In the future, the software is going to be implemented on the ATCA test boards for LLRF control systems of the FLASH. The application of AdvancedTCA architecture with IPMI functionality in the control system of the X-Ray Free Electron Laser (X-FEL) is considered, as well. Both lasers are situated at Deutsches Elektronen Synchrotron DESY, Hamburg, Germany.

RF backplane for MTCA.4 based LLRF control system

Low-level RF (LLRF) control systems developed for linear accelerator-based free electron lasers (FELs) require real-time processing of thousands of RF signals with very challenging RF field detection precision. To provide a reliable, maintainable, and scalable system, a new generation of LLRF control based on MTCA.4 architecture was started at DESY for the FLASH and European-XFEL facilities. In contrast to previous RF control systems realized in 19-in modules, we could demonstrate field detection, RF generation, RF distribution, DAQ system, and the high-speed real-time processing entirely embedded in the MTCA.4 crate system. This unique scheme embeds ultra-high-precision analog electronics for detection on the rear transition module (RTM) with powerful digital processing units on the advanced mezzanine card (AMC). To increase system reliability and maintainability and to reduce performance limitations arising through RF cabling, we developed and embedded in the MTCA.4 crate, a unique RF backplane for RTM cards. This backplane is used for distribution of high-performance local oscillator (LO), RF, and low-jitter clock signals together with low-noise analog power supply to analog RTM cards in the system. In this paper, we present the design and architecture of the MTCA.4 crate with the RF backplane and successful test results of the LLRF control system.

Prototype real-time ATCA-based LLRF control system

The linear accelerators employed to drive Free Electron Lasers (FELs), such as the X-ray Free Electron Laser (XFEL) currently being built in Hamburg, require sophisticated control systems. The Low Level Radio Frequency (LLRF) control system should stabilize the phase and amplitude of the electromagnetic fields in accelerating modules with tolerances below 0.02% for amplitude and 0.01 degree for phase to produce ultra-stable electron beam that meets the conditions required for Self-Amplified Spontaneous Emission (SASE). The LLRF control system of a 32-cavity accelerating module of the XFEL accelerator requires acquisition of more than 100 analogue signals sampled with frequency around 100 MHz. Data processing in a real-time loop should complete within a few hundred nanoseconds. Moreover, the LLRF control system should be reliable, upgradeable and serviceable. The Advanced Telecommunications Computing Architecture (ATCA) standard, developed for telecommunication applications, can fulfil all of these requirements. The paper presents the architecture of a prototype LLRF control system developed for the XFEL accelerator. The control system composed of ATCA carrier boards with Rear Transition Modules (RTM) is able to supervise 32 cavities. The crucial submodules, like DAQ, Vector Modulator or Timing Module, are designed according to the AMC specification. The paper discusses results of the LLRF control system tests that were performed at the FLASH accelerator (DESY, Hamburg) during machine studies.

RTM RF Backplane for MicroTCA.4 crates

We developed a new Rear Transition Module (RTM) Backplane for MicroTCA.4 crates that is compliant with the PICMG standard and is an optional crate extension. The RTM Backplane provides multiple links for high-precision clock and RF signals to analog μRTM cards. Usage of an RTM Backplane allows to significantly simplify the cable management, and therefore to increase the reliability of electronic controls when multiple analog RF front-ends are required. In addition, the RTM backplane allows also to add so called extended RTM (eRTM) and RTM Power Modules (RTM-PM) to a 12-slot MicroTCA crate. Up to four 6 HP wide eRTMs and two RTM-PMs can be installed behind the front PM and MCH modules. An eRTM attached to the MCH via Zone 3 connector is used for analog signal management on the RTM backplane. This eRTM allows also installing a powerful CPU to extend the processing capacity of the MTCA.4 crate. Remaining three eRTMs provide additional space for analog and digital electronics that may not fit on the standard RTM cards. The RTM-PMs deliver managed low-noise (separated from front crate PMs) analog bipolar power (+VV, -VV) for the μRTMs and an unipolar power for the eRTMs. This extends functionality of the MicroTCA.4 crate and offers unique performance improvement for analog front-end electronics. This paper covers a new concept of the RTM Backplane, a new implementation for the real-time LLRF control system and performance evaluation of designed prototype.

Distributed versus Centralized ATCA Computing Power

The RF Control for the European XFEL requires powerful data processing capability for many algorithms including feedback, calibration, diagnostics and low and high level applications needed for field control. While central processing architecture will be easier to manage and develop, it will also increase the requirements for the communication links connecting the boards. On the other hand, a distributed system improves performance and reliability but result in higher complexity. The trade-offs between the two architecture will be discussed and examples will be presented.

Interfaces and Communication Protocols in ATCA-Based LLRF Control Systems

Linear accelerators driving Free Electron Lasers (FELs), such as Free Electron Laser in Hamburg (FLASH) or X-ray Free Electron Laser (XFEL), require a sophisticated Low Level Radio Frequency (LLRF) control system. The controller of the LLRF system should stabilize the phase and amplitude of the field in accelerating modules below 0.02 % of amplitude and 0.01 degree for phase tolerances to produce ultra stable electron beam that meets required conditions for Self-Amplified Spontaneous Emission (SASE). Since the LLRF system for XFEL must work for the next 20 years, it should be reliable, reproducible and upgradeable. Having in mind all the requirements of LLRF control system, the Advanced Telecommunications Computing Architecture (ATCA) was chosen to build a prototype LLRF system for FLASH accelerator that is able to supervise 32 cavities of one accelerating section. The LLRF controller takes advantage of the features offered by the ATCA standard. The LLRF system consists of a few ATCA carrier blades, Rear Transition Modules (RTM) and several Advanced Mezzanine Cards (AMCs) that provide all necessary digital and analogue hardware components. The distributed hardware of the LLRF system requires a number of communication links that should provide different latencies, bandwidths and protocols. The paper presents the general view of the ATCA-based LLRF system, discusses the requirements and proposes application for various interfaces and protocols in the distributed LLRF control system.

Control and measurement system for high quality superconducting cavities

The measurements of superconducting cavity parameters before module assembly stage are very important, because they allow to evaluate critical properties (resonant frequency, quality factor of accelerating mods) of individual resonating cavities. Such measurements are performed in Vertical Test Stand facilities. One of such setups is Vertical Test Stand II (VTS II) at DESY. It is used for conditioning and characterization of cavities for FEL (Free Electron Laser) experiments (especially for FLASH and European XFEL). In the previous set-up cavities in VTS II were operated in Continuous Wave mode using analog control system. The core of the system was analog Phase Lock Loop used to lock phases of incident wave and transmitted wave. All measurements were done using external equipment such as oscilloscopes, spectrum network analyzers, etc. The main disadvantage of such system was lack of flexibility - each small modification required precise system tuning, no new functionality could be added and automation of measurements was hard to achieve. The paper presents new solution of the control system for VTS II based on digital hardware. It allows to overcome most of disadvantages of previous analog system. All measurements and control functions are integrated on a single (FPGA based) computation board, which is fully integrated with external control system. The usage of such system offers functionality such as long term data acquisition (due to Continuous Wave operation of the cavity), special modes of operation (like Self Excited Loop or Digital PLL - due to low bandwidth of measured resonator) and possibility of measurement process automation. Additionally developed user interfaces allow remote access to the system parameters and flexible configuration. The paper discusses each sub-system, presents measurement results and overall system performance evaluation together with some views for future functionality development.