Mariusz Grecki

A Distributed System for Radiation Monitoring at Linear Accelerators

This paper discusses a system for an on-line neutron fluence monitoring at linear accelerators. The system consists of a SRAM-based detector and a radiation-tolerant read-out system. The neutron fluence was measured in several locations of the accelerator. Monitoring of the radiation environment in an accelerator tunnel is necessary to assure reliable long-term operation of electronic systems placed in the tunnel. Monitoring of the chamber is especially important during the design stage of a linear accelerator. The new design of 20 GeV linear accelerator X-ray Free Electron Laser (X-FEL) is currently approved for construction at DESY Research Centre in Hamburg , . The presented paper is based on our research and experimental measurement carried out at 1.2 GeV superconducting electron linac driving the Vacuum UltraViolet Free Electron Laser (VUV-FEL). The application of a pair of TLD-700 and TLD-500 or superheated emulsion (bubble) dosimeters enables the supervision of neutron fluence in accelerators . This process requires continuous and arduous calibration of TLDs, therefore this method is not convenient. Moreover, it is impossible to monitor the radiation environment in real-time. The presented system fills the market niche of real-time neutron monitoring for high-energy accelerators. Neutron fluence and gamma dose measured in this way can be used for the detailed analysis of the VUV-FEL or X-FEL environments. Monitoring of the radioactive area in a linear accelerator tunnel could be helpful to the diagnosis and reduction of beam losses. We have conducted experiments with the distributed system dedicated to neutron flux measurement at the DESY Research Centre in Hamburg. The devices were exposed to a neutron field from an Americium-Beryllium (n,alpha) source 241AmBe. The systems were installed in two accelerators: Linac II and VUV-FEL

The application of a SRAM chip as a novel neutron detector

High-density, fast digital devices, like field programmable gate arrays (FPGAs), microcontrollers, and static random access memories (SRAMs), can be produced by nanotechnology. New technologies allow the design of fast and powerful devices; however, the decreasing dimensions create new problems. Even at ground level, cosmic ray particles arriving from outer space can affect digital devices and provoke single-event effects (SEEs) due to the smaller sensitive volume (SV). In general, for decreasing feature size of memory cells the expected critical charge decreases and the expected sensitivity to radiation increases. High-density SRAM chips were used to design a fast response, highly sensitive neutron detector. We have conducted experiments with SRAMs at the DESY Research Centre in Hamburg, Germany. Memory contents (number of SEU) were recorded as a function of neutron expose time. The chips were exposed to a neutron field from an americium-beryllium neutron source (241AmBe). The second experiment was accomplished in the 450 MeV electron Linac (Linac II) tunnel. Another batch of SRAMs was irradiated with 60Co gamma rays to a dose of about 60 Gy, and no SEU was registered. This shows that gamma radiation has no substantial effect on the production of SEU in the SRAM. The proposed detector could be ideal for the detection of pulsed neutron radiation produced by high-energy electron linear accelerators and synchrotron facilities, which are currently in operation and planned for the near future.

Application of SysML to design of ATCA based LLRF control system

The paper presents the methodology of design of ATCA based LLRF system for XFEL linear accelerators. The LLRF system is used to control RF field in superconducting accelerating cavities regulating amplitude up to 0.03% and phase up to 0.03 deg. It is complex mixed analogue-digital control with latency of order of few tens of nanoseconds. The ATCA architecture was chosen due to high availability and reliability. The system design process is based on systematic and formal approach using SysML language and tools. This modern methodology changes the way of system description from “document centric” to “model centric”. It allows easy communication inside the designers team that is very important in wide international collaboration. In the design process the Use Case description of system functionality was applied. The hierarchical structure and requirements for subsystems was derived from the top level requirements and defined functionality of the system. The functions of various SysML diagrams are presented together with discussion which parts of the system are best described by which diagram type. Both structural and functional views of the system are presented. Since the discussed LLRF system will have distributed architecture the particular effort was put on interfaces description. The SysML tool used in the project was used not only to build SysML model but also allows to estimate project cost using Use Case Points method. This feature is very beneficial in preparation of the project budget.

SEE induced in SRAM operating in a superconducting electron linear accelerator environment

Strong fields of bremsstrahlung photons and photoneutrons are produced during the operation of high-energy electron linacs. Therefore, a mixed gamma and neutron radiation field dominates the accelerators environment. The gamma radiation induced Total Ionizing Dose (TID) effect manifests the long-term deterioration of the electronic devices operating in accelerator environment. On the other hand, the neutron radiation is responsible for Single Event Effects (SEE) and may cause a temporal loss of functionality of electronic systems. This phenomenon is known as Single Event Upset (SEU). The neutron dose (KERMA) was used to scale the neutron induced SEU in the SRAM chips. Hence, in order to estimate the neutron KERMA conversion factor for Silicon (Si), dedicated calibration experiments using an Americium-Beryllium (241Am/Be) neutron standard source was carried out. Single Event Upset (SEU) influences the short-term operation of SRAM compared to the gamma induced TID effect. We are at present investigating the feasibility of an SRAM based real-time beam-loss monitor for high-energy accelerators utilizing the SEU caused by fast neutrons. This paper highlights the effects of gamma and neutron radiations on Static Random Access Memory (SRAM), placed at selected locations near the Superconducting Linear Accelerator driving the Vacuum UV Free Electron Laser (VUVFEL) of DESY.

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.

Radiation monitoring system for X-FEL

Radiation produced during the operation of linear accelerators poses a potential threat to electronic devices installed in the accelerator tunnel. Therefore, a distributed radiation monitoring system was installed at five various spots in the Free electron LASer in Hamburg (FLASH) tunnel. The presented system allows us to measure radiation produced during the operation of a linear accelerator driving FLASH in real time. The system is composed of two modules: radiation-sensitive sensors and a radiation-tolerant readout system constructed with the application of commercial-off-the-shelf (COTS) components. The neutron dosimeter was constructed using an innovative application of a static random access memory (SRAM), whereas a well-known radiation-sensitive RadFET was used for gamma quantification.

The radiation tolerant readout system for srambased neutron detector

Bremsstrahlung gamma radiation and photoneutrons are produced during the operation of high energy linear accelerators. The functionality of electronic devices that are placed inside accelerator tunnels can be jeopardized because of the negative influence of generated radiation. Therefore, a radiation monitoring system able to gauge neutron fluence and gamma dose in real time was constructed. Radiation-sensitive dosimeters cooperate with a readout system. The readout continuously measures both types of radiation and sends quantified data to a main computer. The system is also placed in the tunnel, hence it must be insensitive to radiation or able to tolerate induced malfunctions. A few different readout systems were designed. This work presents the application of different readouts designed using commercial of the shelf (COTS) components. The presented hardware was tested with americium-beryllium neutron source. Finally, the systems were irradiated in a linear accelerator tunnel to estimate their immunity and suitability for a long-term reliable operation in the radioactive field

New method for RF field amplitude and phase calibration in flash accelerator

The paper presents new method for amplitude and phase calibration of the RF field in FLASH accelerator. The concept is based for detection and measurement of transients induced by single bunch. These transients are very small and it is not possible to detect them without special hardware. The paper presents the measurement system developed for a single bunch induced transient detection. The results of measurement obtained with this system are presented proving its correct operation

MOPS - Parallel Environment for Simulation of Electronic Circuits Using Physical Models of Semiconductor Devices

In the paper the parallel environment for simulation of electronic circuits is presented. The proposed solution bases on PVM distributed computing environment software. For semiconductor devices the physical 2-dimensional models can be used instead of lumped ones in order to obtain more precise simulation results and to have a look inside the semiconductor structure. In the paper the architecture of the simulator is discussed and the example of simulation of simple switching circuit containing IGBT device is presented. In the conclusion the future possibilities of extending of the program are presented.

Superconducting cryo-modules characterization for European XFEL - LLRF tests in AMTF

The paper describes achievements in LLRF based tests preparation for superconducting cryo-modules evaluation for European X-ray Free Electron Laser. The software for automatic cryo-modules characterization at the Accelerator Module Test Facility (AMTF) will be presented. In order to identify fundamental working parameters of the eight TESLA cavities cryomodules the scenario of several tests sequence has been proposed and implemented in AMTF. Main parameters like: cavities quenching levels verification, cavities Pi modes identification, slow and fast frequency tuners performance, fundamental power coupler performance, etc are evaluated. Basing on achieved data the decision about module acceptance for work in the linac is done. In this solution the MTCA.4 based LLRF system is used to control and verify cryo-string performance. Middle layer client servers implemented in this environment are responsible for providing tests initial conditions, testing and results archiving in the dedicated data base. Results of described tests are not only vital for module acceptance but are also important for future LLRF system set-up and configuration concerning module work in the accelerator tunnel.