Bernardo B. Carvalho

A fully computerized and distributed VME system for control and data acquisition on the tokamak ISTTOK

Abstract The ISTTOK operation and research programme require a very reliable control and data acquisition system due to the pulsed nature of the tokamak discharges. This system (SCAD) was designed in a distributed, modular, multivendor, integrated and transparent approach, taking advantage of recent improvements in networking, front-end processing and database management. This paper reports some of the most relevant aspects involved in the design of the SCAD current configuration. The computer system is based on personal computers (PCs) and Motorola 68 000 family microprocessors, linked by an ethernet local area network. Control is made by a vacuum controller unit as well as by VME digital I/O, timing and digital-to-analog converter modules. Data acquisition is provided by VME instrumentation as well as by PC based modules and by a digitizing oscilloscope. All VME modules were developed on site. The ISTTOK operation is controlled by a supervisory program. Data from the engineering and physics diagnostics is stored in a central database.

Engineering design of ITER prototype Fast Plant System Controller

The ITER control, data access and communication (CODAC) design team identified the need for two types of plant systems. A slow control plant system is based on industrial automation technology with maximum sampling rates below 100 Hz, and a fast control plant system is based on embedded technology with higher sampling rates and more stringent real-time requirements than that required for slow controllers. The latter is applicable to diagnostics and plant systems in closed-control loops whose cycle times are below 1 ms. Fast controllers will be dedicated industrial controllers with the ability to supervise other fast and/or slow controllers, interface to actuators and sensors and, if necessary, high performance networks. Two prototypes of a fast plant system controller specialized for data acquisition and constrained by ITER technological choices are being built using two different form factors. This prototyping activity contributes to the Plant Control Design Handbook effort of standardization, specifically regarding fast controller characteristics. Envisaging a general purpose fast controller design, diagnostic use cases with specific requirements were analyzed and will be presented along with the interface with CODAC and sensors. The requirements and constraints that real-time plasma control imposes on the design were also taken into consideration. Functional specifications and technology neutral architecture, together with its implications on the engineering design, were considered. The detailed engineering design compliant with ITER standards was performed and will be discussed in detail. Emphasis will be given to the integration of the controller in the standard CODAC environment. Requirements for the EPICS IOC providing the interface to the outside world, the prototype decisions on form factor, real-time operating system, and high-performance networks will also be discussed, as well as the requirements for data streaming to CODAC for visualization and archiving.

The COMPASS tokamak plasma control software performance

The COMPASS tokamak has began operation at the IPP Prague in December 2008. A new control system has been built using an ATCA-based real-time system developed at IST Lisbon. The control software is implemented on top of the MARTe real-time framework attaining control cycles as short as 50 μs, with a jitter of less than 1 μs. The controlled parameters, important for the plasma performance, are the plasma current, position of the plasma current center, boundary shape and horizontal and vertical velocities. These are divided in two control cycles: slow at 500 μs and fast at 50 μs. The project has two phases. First, the software implements a digital controller, similar to the analog one used during the COMPASS-D operation in Culham. In the slow cycle, the plasma current and position are measured and controlled with PID and feedforward controllers, respectively, the shaping magnetic field is preprogrammed. The vertical instability and horizontal equilibrium are controlled with the faster 50-μs cycle PID controllers. The second phase will implement a plasma-shape reconstruction algorithm and controller, aiming at optimized plasma performance. The system was designed to be as modular as possible by breaking the functional requirements of the control system into several independent and specialized modules. This splitting enabled tuning the execution of each system part and to use the modules in a variety of applications with different time constraints. This paper presents the design and overall performance of the COMPASS control software.

ATCA fast data acquisition and processing system for JET gamma-ray cameras upgrade diagnostic

Nuclear reaction gamma-ray diagnosis is one of the important techniques used for studying confined fast-ions. The Joint European Torus (JET) gamma-ray camera diagnostic provides information on the spatial distribution of fast ions. The system is currently being upgraded and should allow gamma-ray image measurements in high power deuterium JET pulses, and eventually in deuterium-tritium discharges. In order to fully exploit the diagnostic capabilities it is mandatory to develop a reliable, maintainable, multi-channel spectroscopy data acquisition and real-time processing (DAQP) system, which shares much of the common development for other specific implementation like Gamma-ray spectroscopy. The DAQP system is based on the Advanced Telecommunications Computing Architecture (ATCA) and contains a 6 GFLOPS x86-based control unit and three transient recorder and processing (TRP) modules, to cope with the two arrays of collimators (10 horizontal + 9 vertical lines of sight), interconnected through PCI Express (PCIe) links. Each TRP module features 8 channels of 13 bit resolution sampling at 250 MHz, 4GByte of local memory and two field programmable gate arrays able to perform complex trigger managing modes and allowing real time analyses (pulse height analyzer and pile-up discrimination), minimizing data storage and transfer issues. The DAQP system aims at overcoming the problem of storing large amount of data during long discharges. A raw/processed mode is being developed where the acquired raw data follows two parallel paths: besides being directly stored in the on-board memory, it is processed and streamed in real-time through PCIe links. This procedure is expected to greatly reduce the amount of data and possible allow continuous operation of the diagnostic. During commissioning and when data validation is required, the 4 GB raw data will be executed on the x86 control unit through a well known algorithm and the result cross checked with the processed data.

Fast feedback control for plasma positioning with a PCI hybrid DSP/FPGA board

The need to control in real-time the plasma parameters in fusion devices leads to the development of algorithms requiring intensive computation and providing results on a few hundred microseconds. The present works objective was the implementation of the current filaments method (CF) to model in real-time the ISTTOK plasma shape and position. The hardware used was the on site developed PCI-TR-256 hardware configurable module, which includes the latest technology in DSP and FPGA. The algorithm estimates the position of the plasma column and generates the control signals for the vertical magnetic field actuators. The main advantage of this system is to provide a digital approach to feedback plasma position control with similar cycle times to those of analog systems but allowing flexible, user defined, algorithms.

On-site developed components for control and data acquisition on next generation fusion devices

Publisher Summary This chapter discusses the main requirements, principles and technical issues to be taken into account in the conceptual design of the control and data acquisition systems of new fusion experiments. The control and data acquisition system of a new generation fusion device should be conceived in a distributed, integrated, hierarchical, manufacturing independent, and user-friendly approach, taking advantage of the most recent improvements in networking, front-end processing, and database management. Data acquisition is performed by several dedicated subsystems designed in a function oriented structure and linked by fast networks. This architecture allows to develop the subsystems independently, to minimize the data traffic in the network, and to increase the system safety. It also provides upgrading capacity to meet new experimental requirements during the life of the experiment and flexibility to include new technologies.

HDL based FPGA interface library for data acquisition and multipurpose real time algorithm processing

The inherent parallelism of the logic resources, the flexibility in its configuration and the performance at high processing frequencies makes the field programmable gate array (FPGA) the most suitable device to be used both for real time algorithm processing and data transfer in instrumentation modules. Moreover, the reconfigurability of these FPGA based modules enables exploiting different applications on the same module. When using a reconfigurable module for various applications, the availability of a common interface library for easier implementation of the algorithms on the FPGA leads to more efficient development. The FPGA configuration is usually specified in a hardware description language (HDL) or other higher level descriptive language. The critical paths, as the management of internal hardware clocks, that require deep knowledge of the module behavior shall be implemented in HDL to optimize the timing constraints. The common interface library should include these critical paths, freeing the application designer from hardware complexity and able to choose any of the available high-level abstraction languages for the algorithm implementation. With this purpose a modular Verilog code was developed for the Virtex 4 FPGA of the in-house Transient Recorder and Processor (TRP) hardware module, based on the Advanced Telecommunications Computing Architecture (ATCA), with eight channels sampling at up to 400 MSamples/s. The TRP was designed to perform real time Pulse Height Analysis (PHA), Pulse Shape Discrimination (PSD) and Pile-Up Rejection (PUR) algorithms at a high count rate (few MHz). A brief description of this modular code is presented and examples of its use as interface with end user algorithms, including a PHA with PUR, are described.

FPGA Remote Update for Nuclear Environments

In recent years there has been a growing interest to use reconfigurable modules, based on field-programmable gate array (FPGA) devices, in nuclear environments. One of the requirements for these types of modules, when operating in complex future nuclear power experiments, is their remote update capability. The operational needs of pulsed fusion reactors will lead to a large production of very high energy neutrons (MeV range). The current procurement policies for nuclear installations do not allow exposure of electronics to radiation, except following very strict rules. However, considering the “as low as (is) reasonably achievable” (ALARA) principle with respect to human exposure to radiation, the access to cubicles might be restricted, requiring the remote update of FPGA codes. FPGAs are volatile devices, and their programming code is usually stored in dedicated flash memories for proper configuration during module power-on. This paper presents an alternative method for FPGA remote update, capable to store new FPGA codes in inboard Serial Peripheral Interface (SPI) flash memories. The new method, based on the Xilinx Quick Boot application note and adapted to PCIe protocol, was developed with the KC705 Evaluation Kit from Xilinx and successfully tested in the in-house Advanced Mezzanine Card (AMC) prototype, installed on the ATCA-PTSW-AMC4 carrier module from the ITER Fast Plant System Controller catalogue.

A 100 MHz VME data acquisition system

Abstract A VME based 100 MSPS data acquisition system with four independent input channels and timing capability is presented. Data describing the performance of the system is also shown. Discussion is focused on the use of recently delivered devices, flash ADCs and high speed FIFO memories, configured in a data acquisition architecture, which takes advantage of the features inherent to those new devices.

A real-time architecture for the identification of faulty magnetic sensors in the JET tokamak

In a tokamak, the accurate estimation of the plasma boundary is essential to maximise the fusion performance and is also the first line of defence for the physical integrity of the device. In particular, the first wall components might get severely damaged if over-exposed to a high plasma thermal load. The most common approach to calculate the plasma geometry and related parameters is based in a large set of different types of magnetic sensors. Using this information, real-time plasma equilibrium codes infer a flux map and calculate the shape and geometry of the plasma boundary and its distance to a known reference (e.g. first wall). These are inputs to one or more controllers capable of acting on the shape and trajectory based in pre-defined requests. Depending on the device, the error of the estimated boundary distance must usually be less than 1 centimetre, which translates into very small errors on the magnetic measurement itself. Moreover, asymmetries in the plasma generated and surrounding magnetic fields can produce local shape deformations potentially leading to an unstable control of the plasma geometry. The JET tokamak was recently upgraded to a new and less thermally robust all-metal wall, also known as the ITER-like wall. Currently the shape controller system uses the output of a single reconstruction algorithm to drive the plasma geometry and the protection systems have no input from the plasma boundary reconstruction. These choices are historical and were due to architectural, hardware and processing power limitations. Taking advantage of new multi-core systems and of the already proved robustness of the JET real-time network, this paper proposes a distributed architecture for the real-time identification of faults in the magnetic measurements of the JET tokamak. Besides detecting simple faults, such as short-circuits and open-loops, the system compares the expected measurement at the coil location and the real measurement, producing a confidence value. Several magnetic reconstructions, using sensors from multiple toroidally distributed locations, can run in parallel, allowing for a voting or averaging scheme selection. Finally, any fault warnings can be directly fed to the real-time protection sequencer system, whose main function is to coordinate the protection of the JETs first wall.