Tomasz Kozak

Real-time IPMI protocol analyzer

The Advanced Telecommunications Computing Architecture (ATCA) is a modern platform, which gains popularity, not only in telecommunication applications, but also in others fields like High Energy Physics (HEP) experiments. Computing systems based on ATCA provide high performance and efficiency and are characterized by significant reliability, availability and serviceability. ATCA offers these features because of an integrated management system realized by the Intelligent Platform Management Interface (IPMI) implemented on dedicated Intelligent Platform Management Controller (IPMC). IPMC is required on each ATCA board to fulfill the ATCA standard and is responsible for many vital procedures performed to support proper operation of ATCA system. It covers, among others, activation and deactivations of modules, monitoring of actual parameters or controlling fans. The commercially available IPMI implementations are expensive and often not suited to demands of specific ATCA applications and available hardware. Thus, many research centers and commercial companies decide to develop their own version of IPMC software. Despite precise IPMI specification of communication requests and responses, these implementations are often incompatible with each other, which leads to incorrect in-system behavior of devices equipped with IPMCs from various vendors. ATCA specifies the I2C protocol as a physical layer of IPMI. There are many devices able to monitor the I2C bus such as logic analyzers or specialized oscilloscopes. However, there is no available equipment capable of debugging IPMI as a higher level protocol. The article compares available methods of IPMI debugging and describes a custom made device prepared to monitor in realtime up to eight IPMI lines and analyze the IPMI protocol. Accessibility of this kind of equipment allows to discover errors and find the reasons of faulty behavior of the IPMC under development, greatly reduce the time to market factor and decrease costs of ATCA system development.

Design and Operation of the Integrated 1.3 GHz Optical Reference Module with Femtosecond Precision

In modern Free-Electron Lasers like FLASH or the European XFEL, the short and long-term stability of RF reference signals gains in importance. The requirements are driven by the demand for short FEL pulses and low-jitter FEL operation. In previous publications, a novel, integrated Mach-Zehnder Interferometer based scheme for a phase detector between the optical and the electrical domain was presented and evaluated. This Laser-to-RF phase detector is the key component of the integrated 1.3GHz Optical Reference Module (REFM-OPT) for FLASH and the European XFEL. The REFMOPT will phase-stabilize 1.3GHz RF reference signals to the pulsed optical synchronization systems in these accelerators. Design choices in the final hardware configuration are presented together with measurement results and a performance evaluation from the first operation period in the European XFEL.

Fast intra bunch train charge feedback for FELs based on photo injector laser pulse modulation

Bunch charge variations in free electron lasers such as the free electron laser (FEL) in Hamburg (FLASH) or the European X-ray FEL (E-XFEL) impact the longitudinal phase space distribution of the electrons resulting in different bunch peak currents, bunch durations, and bunch shapes. The electron bunches are generated by short ultraviolet (UV) laser pulses impinging onto a photocathode inside a radio frequency (RF) accelerating cavity. At FLASH, bursts of bunches up to 800 pulses with an intra train repetition rate of 1 MHz are used and even higher repetition rates (up to 4.5 MHz) are planned at the E-XFEL. Charge variations along these bunch trains can be caused by variations of the laser pulse energies, instabilities of the accelerating fields in the RF cavity, and time-dependent effects in the photoemission process. To improve the intra bunch train charge flatness and to compensate train-to-train fluctuations, a dedicated digital control system, based on the Micro Telecommunication Computing Architecture (MicroTCA.4) standard, was designed, implemented, and successfully tested at FLASH. The system consists of a bunch charge detection module which analyzes data from a toroid system and provides the input signal for the controller which drives a fast UV Pockels cell installed in the optical path of the photocathode laser. The Pockels cell alters the laser polarization and thus the transmission through a polarizer. The modulation of UV laser pulse energy with an iterative learning feedforward minimizes the repetitive errors from bunch train to bunch train. A fast feedback algorithm implemented in a field-programmable gate array allows for fast tuning of bunch charge inside the bunch train. In this paper, a detailed description of the system and the first preliminary measurement results are presented.