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Future rf control systems will require simultaneous data acquisition of up to 100 fast ADC channels at sampling rates of around 100 MHz and real time signal processing within a few hundred nanoseconds. At the same time the standardization of Low-Level RF systems are common objectives for all laboratories for cost reduction, performance optimization and machine reliability. Also desirable are modularity and scalability of the design as well as compatibility with accelerator instrumentation needs including the control system. All these requirements can be fulfilled with the new telecommunication standard ATCA when adopted to the domain of instrumentation. We describe the architecture and design of an ATCA based LLRF system for the European XFEL. The operation of a prototype capable of controlling the vectorsum of 24-cavities and providing measurements of forward and reflected power are presented.

In the paper an RF-gun control system is described. Difficulties caused by the impossibility to observe directly the field gradient are mentioned. Calibration nd measurement procedure is discussed. A mathematical model, which provides a way to calculate the desired signal from the indirect measurements is developed and analyzed. This model is supported by both measurements and simulations discussed in the final part of the paper. Research done with participation of Ph.D. students.

Modern machines used in high energy physics require sophisticated and complex control systems. The complex systems are usually built as distributed systems. Therefore, the connectivity and communication links between distributed subsystems play a crucial role in the control system. The Advanced TelecommunicationComputingArchitecture (ATCA) and Advanced Mezzanine Card (AMC) standards have attracted the attention of physics community because they offer various types of data communication channels with high bandwidth, redundancy, high reliability and availability. The standards allow using different types of communication interfaces like PCIe, Gigabit Ethernet, RapidIO. In real-time systems the data transmission latency is also important. The acquisition of real-time data from hundreds of analogue channels is required for the Low Level Radio Frequency (LLRF) controller of XFEL (X-ray Free Electron Laser) accelerator. The paper presents survey of the communication interfaces of the LLRF controller for XFEL. The discussion includes the properties of interfaces provided by ATCA and AMC standards and summarizes requirements for the data links and protocols required by LLRF controller.

We report results on the performance of a free electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent EUV radiation source have been measured. In the saturation regime the peak energy approached 170 μJ for individual pulses while the average energy per pulse reached 70 μJ. The pulse duration was in the region of 10 femtoseconds and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average EUV power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nanometers the 5th harmonic of the radiation reaches deep into the water window – a wavelength range that is crucially important for the investigation of biological samples.

9 pp. (2007)., Displacement damage caused by fast neutrons in unbiased Gallium Arsenide (GaAs) Light Emitting Diodes (LED) resulted in a reduction of the light output. On the other hand, a similar type of LED irradiated with gamma rays from a 60Co source up to a dose level in excess of 1.0 kGy (1.0 × 105 rad) was found to show no significant drop of the light emission. This phenomenon was used to develop a low cost passive fluence monitor and kerma dosemeter for accelerator-produced neutrons. These LED-dosemeters were used to assess the integrated fluence of photoneutrons, which were contaminated with a strong bremsstrahlung gamma-background generated by the 730 MeV superconducting electron linac of the FLASH (Free Electron Laser at Hamburg) at Deutsches Elektronen-Synchrotron (DESY). The applications of GaAs LED as a routine neutron fluence monitor and displacement damage precursor for the electronic components located in high-energy accelerator environment are highlighted

17 pp. (2007)., Sophisticated electronic devices comprised of sensitive microelectronic components have been installed in the close proximity of the 720 MeV superconducting electron linear accelerator (linac) driving FLASH, the Free Electron Laser in Hamburg, presently in operation at DESY in Hamburg. Microelectronic chips are inherently vulnerable to ionising radiations, usually generated during routine operation of high-energy particle accelerator facilities like FLASH. Hence, in order to assess the radiation effect on microelectronic chips and to develop suitable mitigation strategy, it becomes imperative to characterise the radiation field in the FLASH environment. We have evaluated the neutron and gamma energy (spectra) and dose distributions at critical locations in the FLASH tunnel using superheated emulsion (bubble) detectors, GaAs light emitting diodes (LED), LiF-Thermoluminescence dosimeters (TLD) and radiochromic (Gafchromic EBT) films. This report highlights the application of the passive dosimeters for an accurate analysis of the radiation field in produced by high-energy electron linear accelerators.

22 pp. (2006)., The electromechanical model of the TESLA cavity has been implemented in FPGA technology for real-time testing of the control system. The model includes Lorentz force detuning and beam loading effects. Step operation and vector stimulus operation modes are applied for the evaluation of a FPGA cavity simulator operated by a digital controller. The performance of the cavity hardware model is verified by comparing with a software model of the cavity implemented in the MATLAB system. The numerical aspects are considered for an optimal DSP calculation. Some experimental results are presented for different cavity operational conditions.

17 pp. (2006)., A digital control of superconducting cavities for a linear accelerator is presented. FPGA-based controller, supported by Matlab system, was applied. Electrical model of a resonator was used for design of a control system. Calibration of the signal path is considered. Identification of cavity parameters has been carried out for adaptive control algorithm. Feed-forward and feedback modes were applied in operating the cavities. Required performance has been achieved; i.e. driving on resonance during filling and field stabilization during flattop time, while keeping reasonable level of the power consumption. Representative results of the experiments are presented for different levels of the cavity field gradient.

This report contains a comprehensive technical description of a new international research infrastructure, the European X-Ray Free-Electron Laser (XFEL) Facility. It was written between October 2005 and June 2006 and provides a realistic cost estimate and a compelling assessment of the scientific pay-off. The report has been prepared with the contribution of hundreds of people from many laboratories in Europe and even beyond. Their contributions have been harmonised and merged by many editors, and the whole effort has been coordinated by the European Project Team, generously supported and hosted by the Deutsches Elektronen-Synchrotron (DESY) laboratory.

15 pp. (2005)., Aim of the control system development for TESLA cavity is a more efficient stabilization of the pulsed, accelerating EM field inside resonator. Cavity parameters identification is an essential task for the comprehensive control algorithm. TESLA cavity simulator has been successfully implemented using high-speed FPGA technology. Electromechanical model of the cavity resonator includes Lorentz force detuning and beam loading. The parameters identification is based on the electrical model of the cavity. The model is represented by state space equation for envelope of the cavity voltage driven by current generator and beam loading. For a given model structure, the over-determined matrix equation is created covering long enough measurement range with the solution according to the least-squares method. A low-degree polynomial approximation is applied to estimate the time-varying cavity detuning during the pulse. The measurement channel distortion is considered, leading to the external cavity model seen by the controller. The comprehensive algorithm of the cavity parameters identification was implemented in the Matlab system with different modes of operation. Some experimental results were presented for different cavity operational conditions. The following considerations have lead to the synthesis of the efficient algorithm for the cavity control system predicted for the potential FPGA technology implementation.

Nowadays the designer of a new rf control system has access to a wealth of powerful digital, analog, and rf circuitry. The requirements for the rf control system have changed from only controlling the amplitude and phase of the accelerating field to the required degree to stability. Additional tasks include exception handling and extensive build-in diagnostics while pursuing issues related to reliability, operability, and maintainability. Also operation close to the performance limit must be supported while maximizing the availability of the accelerator. With many accelerator projects in planning or under construction several state-of-the art rf control designs have evolved. This paper will present an overview of this new technology and discuss its performance.

3 pp. (2004)., Dynamic detuning of the superconducting rf cavities due to Lorentz force induced mechanical excitation is a critical concern since the magnitude can approach the cavity band- width and require significant additional rf power for field control. In this paper, the influence of high accelerating fields on the resonance frequency in superconducting TES- LA cavities is discussed. Cavities at the TESLA Test Facil- ity [1] have been operated at the design operating gradient close to 25 MV/m. It is shown that Lorentz force detuning constant factors are different for different cavities, signifi- cant spread have been observed.