Adam Piotrowski

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 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.

The automatic implementation of Software Implemented Hardware Fault Tolerance algorithms as a radiation-induced soft errors mitigation technique

The radiation-induced soft errors significantly increase the failure rate for advanced electronic components and systems. Rad-sensitive microprocessor-based devices working in the radiation environment are one of the most sensitive parts of the machine. This paper is focusing mainly on the strict software mitigation technique, called Software Implemented Hardware Fault Tolerance (SIHFT). SIHFT methods are based on the redundancy of variables or procedures implemented in compiled project. Sophisticated algorithms are used to check the correctness of control flow in the application. Several articles describe in details theoretical information about software protection algorithms but problem of efficient and error-proof implementation of these methods has always been omitted. Unfortunately, manual implementation of presented algorithms is difficult and can introduce additional problems with program functionality caused by human errors. Presented solution is based on the automatic implementation of SIHFT algorithms during the compilation process. Several modifications of software methods were proposed to make theoretical algorithms possible to the automatic installation.

Integral Interface - Universal Communication Interface for FPGA-Based Projects

During the development process it is very important to assure reliable communication between individual parts of the system. In a special case, when the system is implemented in the FPGA chip, possible solution of communication problem encompass not only ready-made solutions but also especially designed interfaces adapted to specific projects. This paper highlights Integral Interface -universal communication interface for applications in FPGA chip. In addition, presented paper describes specialized program that automatically generates VHDL source code for an interface and supplementary components.

ATCA-based control system for compensation of superconducting cavities detuning using piezoelectric actuators

The linear particle accelerators use superconducting cavities working with high operating gradients. The electromagnetic wave, transferred to the cavity as a set of successive pulses, causes mechanical stresses inside the cavity. Therefore, the resonance frequency of the cavity is significantly modulated, which may lead to cavity detuning in range of hundreds of Hz. The piezoelectric actuators are commonly used for the compensation of the cavity detuning. The paper presents the prototype piezo control system which is capable of compensating 32 cavities simultaneously. Moreover, the first tests of the system in FLASH (Free-Electron Laser in Hamburg) accelerator are presented. The described system is ready to be applied to the next version of LLRF (Low Level Radio Frequency) control system based on ATCA (Advanced Telecommunications Computing Architecture) architecture.

Radtest - Testing Board for the Software Implemented Hardware Fault Tolerance Research

Modern experiments in particle physics are based on advanced and sophisticated electronic systems which have to operate under radiation impact. The problem of designing a hardened system becomes very important, especially in places such as accelerators and synchrotrons where the results of the experiments depend on control system based on digital devices eg. microcontrollers. This paper highlights new solutions of the reliability problem known as the software implemented hardware fault tolerance. That is a strict software approach and could be used with unhardened, commercial off-the-shelf (COTS) components.

Drivers and software for MicroTCA.4

The MicroTCA.4 crate standard provides a powerful electronic platform for digital and analog signal processing. The crate standard is highly configurable and due to an excellent hardware modularity rapid adaption to various different applications is possible. Besides the hardware modularity, it is the software reliability and flexibility as well as the easy integration into existing software infrastructures that will drive the widespread adoption of the new standard.

Real time control of RF fields using a MicroTCA.4 based LLRF system at FLASH

The Free Electron Laser in Hamburg (FLASH) is a large scale user facility, providing highly stable and brilliant laser pulses down to a wavelength of 4.1 nm. Essential for stable and reproducible photon beam is the precision control of the electron bunch parameters. The acceleration principle of the electron bunches at FLASH is based on superconducting RF technology (SRF), in which the RF fields are controlled by a digital low level RF (LLRF) system. This system has been recently upgraded to the Micro Telecommunication Computing Architecture (MicroTCA.4) to improve the performance of the field regulation. This paper presents the first measurements and operation experiences using this new electronic crate standard at a large scale research facility. RF field regulation is carried out by real time fast digital processing on several boards in a MicroTCA.4 crate, and slow automation routines running on a dual core i7 front-end CPU. Scalability and modularity of this system is one of the key parameters to meet the next steps, namely being the platform standard for the European X-ray free electron laser currently build at DESY.

Prototype Control System for Compensation of Superconducting Cavities Detuning Using Piezoelectric Actuators

Pulsed operation of high gradient superconducting radio frequency (SCRF) cavities results in dynamic Lorentz force detuning (LFD) approaching or exceeding the bandwidth of the cavity of order of a few hundreds of Hz. The resulting modulation of the resonance frequency of the cavity is leading to a perturbation of the amplitude and phase of the accelerating field, which can be controlled only at the expense of RF power. Presently, at various labs, a piezoelectric fast tuner based on an active compensation scheme for the resonance frequency control of the cavity is under study. The tests already performed in the Free Electron Laser in Hamburg (FLASH), proved the possibility of Lorentz force detuning compensation by the means of the piezo element excited with the single period of sine wave prior to the RF pulse. The X-Ray Free Electron Laser (X-FEL) accelerator, which is now under development in Deutsche Elektronen-Synchrotron (DESY), will consists of around 800 cavities with a fast tuner fixture including the actuator/sensor configuration. Therefore, it is necessary to design a distributed control system which would be able to supervise around 25 RF stations, each one comprised of 32 cavities. The Advanced Telecomunications Computing Architecture (ATCA) was chosen to design, develop, and build a Low Level Radio Frequency (LLRF) controller for X-FEL. The prototype control system for Lorentz force detuning compensation was designed and developed. The control applications applied in the system were fitted to the main framework of interfaces and communication protocols proposed for the ATCA-based LLRF control system. The paper presents the general view of a designed control system and shows the first experimental results from the tests carried out in FLASH facility. Moreover, the possibilities for integration of the piezo control system to the ATCA standards are discussed.

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.