Design of FPGA based high-speed data acquisition and real-time data processing system on J-TEXT tokamak

Tokamak experiment requires high-speed data acquisition and processing systems. In traditional data acquisition system, the sampling rate, channel numbers and processing speed are limited by bus throughput and CPU speed. This paper presents a data acquisition and processing system based on FPGA. The data can be processed in real-time before it is passed to the CPU. It provides processing ability for more channels with higher sampling rates than the traditional data acquisition system while ensuring deterministic real-time performance. A working prototype is developed for the newly built polarimeter–interferometer diagnostic system on the Joint Texas Experimental Tokamak (J-TEXT). It provides 16 channels with 120 MHz maximum sampling rate and 16 bit resolution. The onboard FPGA is able to calculate the plasma electron density and Faraday rotation angel. A RAID 5 storage device is adopted providing 700 MB/s read–write speed to buffer the data to the hard disk continuously for better performance.     

Architecture of SPIDER control and data acquisition system

The ITER Heating Neutral Beam injectors will be implemented in three steps: development of the ion source prototype, development of the full injector prototype, and, finally, construction of up to three ITER injectors. The first two steps will be carried out in the ITER neutral beam test facility under construction in Italy. The ion source prototype, referred to as SPIDER, which is currently in the development phase, is a complex experiment involving more than 20 plant units and operating with beam-on pulses lasting up to 1 h. As for control and data acquisition it requires fast and slow control (cycle time around 0.1 ms and 10 ms, respectively), synchronization (10 ns resolution), and data acquisition for about 1000 channels (analogue and images) with sampling frequencies up to tens of MS/s, data throughput up to 200 MB/s, and data storage volume of up to tens of TB/year. The paper describes the architecture of the SPIDER control and data acquisition system, discussing the SPIDER requirements and the ITER CODAC interfaces and specifications for plant system instrumentation and control.     

EAST ion cyclotron resonance heating system for long pulse operation

Radio frequency (RF) power in the ion cyclotron range of frequencies (ICRF) is one of the primary auxiliary heating techniques for Experimental Advanced Superconducting Tokamak (EAST). The ICRF system for EAST has been developed to support long-pulse high-β advanced tokamak fusion physics experiments. The ICRF system is capable of delivering 12 MW 1000-s RF power to the plasma through two antennas. The phasing between current straps of the antennas can be adjusted to optimize the RF power spectrum. The main technical features of the ICRF system are described. Each of the 8 ICRF transmitters has been successfully tested to 1.5 MW for a wide range of frequency (25–70 MHz) on a dummy load. Part of the ICRF system was in operation during the EAST 2012 spring experimental campaign and a maximum power of 800 kW (at 27 MHz) lasting for 30 s has been coupled for long pulse H mode operation.     

FPGA-based embedded Linux technology in fusion: The MAST microwave imaging system

A cutting-edge standalone data acquisition system has been developed using Field Programmable Gate Arrays (FPGAs). It has 16 ADC channels operating at 250 MSPS, at 14-bit resolution acquiring continuously at 8 GB/s for 0.5 s. The system uses the Virtex 6 FPGA running embedded Linux on the MicroBlaze^TM soft processor. We propose the development of a standard FPGA architecture, based on a methodology which has enabled us to develop this system using commercial-off-the-shelf (COTS) components. This architecture can easily be modified for a variety of applications, both high and low performance at a competitive cost in terms of hardware, engineering and development.     

Progress in control and data acquisition for the ITER neutral beam test facility

SPIDER, the ion source test bed in the ITER neutral beam test facility, is under construction and its operation is expected to start in 2014. Control and data acquisition for SPIDER are undergoing final design. SPIDER CODAS, as the control and data acquisition system is referred to, is requested to manage 25 plant units, to acquire 1000 analogue signals with sampling rates ranging from a few S/s to 10 MS/s, to acquire images with up to 100 frames per second, to operate with long pulses lasting up to 1 h, and to sustain 200 MB/s data throughput into the data archive with an annual data storage amount of up to 50 TB. SPIDER CODAS software architecture integrates three open-source software frameworks each addressing specific system requirements. Slow control exploits the synergy among EPICS and Siemens S7 programmable controllers. Data handling is by MDSplus a data-centric framework that is geared towards the collection and organization of scientific data. Diagnostics based on imaging drive the design of data throughput and archive size. Fast control is implemented by using MARTe, a data-driven, object-oriented, real-time environment. The paper will describe in detail the progress of the system hardware and software architecture and will show how the software frameworks interact to provide the functions requested by SPIDER CODAS. The paper will focus on how the performance requirements can be met with the described SPIDER CODAS architecture, describing the progress achieved by carrying out prototyping activities.     

Erratum to “Thomson scattering upgrade on Tore Supra” [Fusion Eng. Des. 85 (2010) 335–339]

The Thomson scattering diagnostic supplies the electron temperature and density of Tore Supra plasmas from the spectrum analysis of scattered light of a very short laser pulse. A new spectrometer has been realized to improve the signal to noise ratio. In order to obtain an efficient noise reduction, a real time calculation is necessary. The current analogue integration of the signal is inadequate. A fast digitalization must be used with a sampling rate of 1 GSamples by second, a bandwidth of 150 MHz and a 12 bit dynamic range. In a first step, fast analogue data acquisition boards for 4 channels were added in 2009 to the VME acquisition system in place. A MATACQ (Matrix for acquisition) board was chosen for sampling analogue data up to 2 GSamples/s over 4 channels with a large bandwidth of 300 MHz and a 14 bit dynamic range. This solution offers a low cost acquisition system that is not available in any other commercial board with this dynamic range. The first results will be obtained on calibration period with a light emitted diode before the summer 2009. This article will present the new data acquisition system and the coming first results.     

Assessment of tritium levels in rivers and precipitation in north-western Greece before the ITER operation

The project ITER aims to demonstrate that fusion is the energy source of the future. The prototype Tokamak machine is intended to start operation at about 2019 and tritium is one of the major contaminants that can be accidentally released in the environment. Nowadays environmental tritium levels are of natural origin except in the vicinity of nuclear facilities. The evaluation of background tritium levels is essential in the context of a future possibility of accidental tritium releases. For this purpose and also because of the lack of relevant information, an extended programme of river and rain water sampling was implemented in north-western Greece. Water samples from six major rivers in this area and rain water samples were analysed for tritium content. The rivers under investigation were Aliakmonas River, Pinios River, Arachthos River, Kalamas River, Aoos River and Louros River, which originate from the central Greek mountain range Pindos, and flow to Aegean and Ionian Sea.The tritium concentrations were determined by the Liquid Scintillator Analyser Tri-Carb 3170TR/SL. The statistical analysis of data revealed that there is a seasonal variation of tritium concentration in rain samples and a less pronounced seasonal variation in river samples. The weighted mean tritium concentration for rain samples was determined equal to 0.90 ± 0.08 Bq L^?1 (7.6 ± 0.7 TU) and the respective mean value for river samples was 0.94 ± 0.04 Bq L^?1 (7.9 ± 0.3 TU). Further analysis has demonstrated that river waters tend to show lower tritium concentrations than the concurrently measured tritium concentrations in rain samples, during spring and summer (at 47% and 71% of the sampling stations, respectively), while this observation is reversed during autumn and winter (at 44% and 35% of the sampling stations, respectively). This may be attributed to rain water remaining underground for a long period allowing tritium to decay and when it reappears as river water, the tritium concentration values are lower when compared to the rain water concentrations. Rough estimates of the residence time of underground waters in the study area provided values, which ranged from 0.5 to 11.7 years, with a mean value of 5.2 ± 0.9 years.     

Numerical analysis of MD events and preliminary thermal calculation for KTX vacuum vessel

KTX is a new reversed field pinch (RFP) magnetic confinement device which is under design in ASIPP and USTC. Major disruption (MD) events may occur in future operating process, which is simulated with the finite element (FE) method. The results present that the peaks of eddy currents on vessel and conductor shell are respectively 11.791 kA and 68.637 kA with maximum stress 67.1 MPa due to high transient electromagnetic (EM) force. It is confirmed that the structure is still strong enough to bear the electromagnetic loads even if the worst case. Besides, as KTX vacuum vessel will take the method of natural cooling for heat dissipation during plasma discharge (0.5–1.0 MA), a preliminary thermal calculation was implemented in normal condition to decide suitable time parameters such as duration and interval. It is suggested that the discharge interval should be no less than 5 min for the complete 1 MA plasma with 100 ms duration, which can guarantee the temperature of vacuum vessel below 200 °C.     

A method to produce lithium pellets for fueling and ELM pacing in NSTX-U

A device for producing small, high frequency spherical droplets or pellets for lithium or other liquid metals has been developed and could aid in the controlled excitation or pacing of edge-localized plasma modes (ELMs). The Liquid Lithium/metal Pellet Injector (LLPI) could also be used to replenish lithium coatings of plasma-facing components (PFCs) during a plasma discharge. With NSTX-U having longer pulse lengths (up to 5 s), it is desirable to be able to inject lithium during the discharge to maintain the beneficial effects. Using a nozzle injector design and a surrogate to lithium, Wood's metal, the LLPI has achieved droplet diameters between 0.6 mm < d_drop < 1 mm in diameter and frequencies up to 1.5 kHz with argon gas driving the formation. This paper presents the LLPI being developed with initial results mainly using Wood's metal and some lithium, using high pressure argon to force the liquid lithium through the nozzle.     

基于PXI Express的托卡马克同步数据采集系统设计

随着J-TEXT装置的发展,原有的数据采集系统在稳定性、模块化、采样率等方面已不能满足装置运行的需要,所以需建立一套新的数据采集系统来满足实验需求。本文介绍了基于PXI Express的托卡马克分布式高速同步数据采集系统的设计与实现。系统的采集单元由PXIe机箱NI PXIe-1062Q、PXIe控制器NI PXIe-8133和高速同步数据采集卡NI PXIe-6368组成,兼容ITER CODAC最新标准,具有良好的机械封装性、模块化程度高和高采样率等优点。系统采用同步差分采集方式采集实验数据,并将数据存储于核聚变领域通用的MDSplus数据库中。测试和使用结果表明,系统能在2 MSps采样率下连续稳定工作,可较好地满足装置运行的需要。     

Development of high voltage power supply for the KSTAR 170 GHz ECH and CD system

A 3.6 MW (66 kV/55 A) DC power supply system was developed for the 170 GHz EC H&CD system in KSTAR. The power supply system consists of a cathode power supply (CPS), an anode power supply (APS) and a body power supply (BPS). The cathode power supply is capable of supplying a maximum voltage of ?66 kV and a current of 55 A to the cathode with respect to the collector using pulse step modulation (PSM). The high voltage switching system for the cathode is made by a fast MOS-FET solid-state switch which can turn off the high voltage to the cathode within 3 μs in the occurrence of gyrotron faults. The APS is a voltage divider system consisting of a fixed resistor and zener diode units with the capability of 60 kV stand-off voltage. The anode voltage with respect to the cathode is controlled in a range of 0–60 kV by turning the MOS-FET switches connected in parallel to each zener diode on and off. For high frequency current modulation of the gyrotron, the parallel discharge switch is introduced between the cathode and anode in order to clamp the charged voltage in the stray capacitance. The BPS is a DC power supply with the capability of 50 kV/160 mA. The nominal operation parameter of BPS was 23 kV and 10 mA, respectively, and the voltage output is regulated with a stability of 0.025% of the rated voltage. The series MOS-FET solid-state switch is used for on/off modulation in the body voltage sychronizing with anode voltage. The parallel discharge switch is also introduced between the body and collector for high frequency RF modulation. This paper describes the key features of the high voltage power supply system of the KSTAR 170 GHz gyrotron as well as the test results of the power supply.     

Uptake of deuterium in partially D-depleted residual codeposits left on DIII-D tiles after laboratory thermo-oxidation experiments

Recent evidence has shown that tokamak carbon-based codeposits may become partially or fully depleted of hydrogen through thermo-oxidation, as the hydrogen content of the codeposits is removed more rapidly than the carbon content. In this study we examine the ability of such partially-depleted residual DIII-D divertor codeposits to uptake deuterium upon subsequent exposure to deuterium gas or deuterium plasmas. The partially D-depleted specimens used here were obtained from a previous study where DIII-D codeposits were oxidized for 2 h at 623 K (350 °C) and 267 Pa (2 Torr) O₂ [J.W. Davis et al., Thermo-oxidation of DIII-D codeposits on open surfaces and in simulated tile gaps, J. Nucl. Mater. 415 (2011) S789–S792]. In the present study some of these specimens, having undergone prior oxidation, were exposed to D₂ glow discharge plasmas or D₂ gas at 20 kPa (150 Torr) at 300 or 523 K. In the case of plasma exposure, no uptake of D was observed, while an increase in D content was seen following D₂ gas exposures. When the gas exposure took place at 300 K, heating the specimens in vacuum to 623 K for 15 min led to the release of all of the increased D content. For the gas exposure at 523 K, the increase in D content was found to require longer (8 h) vacuum baking to remove. However, in a reference codeposit specimen (from a closeby location on the tile), which had not been previously oxidized, there was a similar increase in D content following D₂ exposure at 523 K, but it could not be released even following 8 h vacuum baking at 623 K.     

Lithium technologies for edge plasma control

We have investigated two new modes of operation been in T-10 limiter tokamak experiments with a novel rotary feeder of lithium dust. Quasi steady-state mode I and pulse mode II of dust delivery were realized in both OH and OH + ECRH disruption free plasmas at the lithium flow rate up to 2 × 10²¹ atoms/s. A higher flow rate in mode II with injection rate of ～5 × 10²¹ atoms/s caused a series of minor disruptions, which was completed by discharge termination after the major disruption. The observed decreases of bolometer and D_β signals, with increase of the electron density during the lithium dust injection, reveal the effects of the first wall conditioning. The lithium technology may provide inherent safety pathway for major disruption mitigation in a tokamak reactor, which requires demonstration in contemporary tokamak experiments.     

The performance test and analysis of ITER Main and Correction Busbar conductor

The first ITER Main Busbar (MBCN1) and Correction Busbar (CBCN1) conductor samples were manufactured in ASIPP and tested in the SULTAN facility. This paper introduces the sample manufacture, including strand, cabling, jacketing and sample preparation, and discusses the performance of MBCN1 and CBCN1 conductors. The testing results show that both samples have high T_cs, and meet the ITER requirement.Due to the ITER acceptance standard T_cs of MB conductor was changed to 6.7 K at 45.5 kA/3.9 T. The performance of MBCN1 conductor after cyclic load fits the ITER requirement, but the sample was only tested at 57 kA/2.75 T before cycling test. Using some hypothesis and equation to extrapolate the T_cs performance of MBCN1 conductor before cycling test, the result also fits the ITER requirement.For CBCN1 conductor, the central line of the central cooling spiral shifted about 1.3 mm during the cabling. The deviation causes an increase of the max self-field by about 0.005 T, which could not influence the CBCN1 conductor real T_cs performance at peak field.     

A digital long pulse integrator for EAST Tokamak

A digital integrator has been developed to be compatible with the long pulse plasma discharges on the Experimental Advanced Superconductor Tokamak (EAST), in which the induced signal is modulated by a chopper, and a field programmable gate array (FPGA) in the 16-bit digitizer is used to realize the digital integration in real time. After rectification and integration, the drift is almost linear and stable in controlled temperature, so a period of 50 s is used to determine the linear drift rate for drift compensation. The integration data can be directly transferred to the reflective memory (RFM) card, which is installed in the same PCI eXtensions for Instrumentation (PXI) chassis, so the data transmission can be also done in real time. The test results show that the real time data transmission rate is up to 10 kHz, the integration drift is typically less than 0.4 uVs/s and drift performance is a little worse in real long pulse discharge, which can be reduced further by using more precise data acquisition.     

Development of an integrated sampler based on direct 222Rn/220Rn progeny sensors in flow-mode for estimating unattached/attached progeny concentration

A flow-mode integrated sampler consisting of a wire-mesh and filter-paper array along with passive solid state nuclear track detectors has been developed for estimating unattached and attached fraction of ²²²Rn/²²⁰Rn progeny concentration. The essential element of this sampler is the direct ²²²Rn/²²⁰Rn progeny sensor (DRPS/DTPS), which is an absorber-mounted-LR115 type nuclear track detector that selectively registers the alpha particles emitted from the progeny deposited on its surface. During sampling at a specified flow-rate, the unattached progeny is captured on the wire-mesh; while the attached progeny gets transmitted and is captured on the filter-paper. The alpha particles emitted by the deposited progeny atoms are registered on the sensors placed at a specified distance facing the wire-mesh and the filter-paper, respectively. The various steps involved in the development of this flow-mode direct progeny sampler such as the optimization of the sampling rate and the distance between the sensor and the deposition substrate are discussed. The sensitivity factor of the DTPS-loaded sampler for ²²⁰Rn progeny deposited on the wire-mesh and filter-paper is found to be 23.77 ± 0.64 (track cm^?2 h^?1) (Bq m^?3)^?1 and 22.30 ± 0.18 (track cm^?2 h^?1) (Bq m^?3)^?1, respectively; while that of DRPS-loaded sampler for ²²²Rn progeny deposition, is 3.03 ± 0.14 (track cm^?2 h^?1) (Bq m^?3)^?1 and 2.08 ± 0.07 (track cm^?2 h^?1) (Bq m^?3)^?1, respectively. The highlight of this flow-mode sampler is its high sensitivity and that it utilizes the passive technique for estimating the unattached and attached progeny concentration, thus doing away with the alpha counting procedures.     

Design of a MGy radiation tolerant resolver-to-digital convertor IC for remotely operated maintenance in harsh environments

During future ITER maintenance operations, sensors and their embarked electronics will be exposed to a hostile and radioactive environment. This paper presents the design of a MGy radiation tolerant 16 bit resolver-to-digital converter (RDC) in 130 nm CMOS technology. The RDC features a Type II digital tracking loop, able to track resolvers with speeds up to 300 rps, and excitation frequencies up to 4 kHz. The RDC uses two integrated ΔΣ-analog-to-digital converters (ADCs) to digitize the resolver outputs. The 16 bit, 10 kHz ADCs utilize a correlated double sampling technique to remove radiation induced offset and 1/f-noise. The front-end features a static angular resolution of 16 bits (4.2 arcsec_rms) and a resolution of 10 bits (6 arcmin_rms) at a rotor speed of 100 rps. The circuit has a simulated radiation tolerance exceeding 1 MGy. It has the ability to operate under temperatures up to 125 °C, and to allow multiplexing with signals from other conventional sensors for compact, robust read-out architectures.     

Design of neutral beam injection system for KSTAR tokamak

The neutral beam injection (NBI-1) system has been designed for providing a 300 s deuterium beam of 120 kV/65 A as an auxiliary heating and current drive system of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak. The deuterium beam is produced from a long pulse ion source composed of a bucket-type plasma generator and a multi-aperture tetrode accelerator with the help of discharge power supplies and high voltage (HV) power supplies. The beamline components (BLCs) include a neutralizer with an optical multi-channel analyzer (OMA) section, a bending magnet (BM), an ion dump assembly, a movable calorimeter, beam scrapers, and a cryo-sorption pump system in a rectangular vacuum tank. A beam duct equipped with bellows and a voltage break is placed between the NBI vacuum tank and the KSTAR vacuum vessel. All data and parameters of the NBI system are controlled by a control and data acquisition (CODAQ) system through the EPICS based Ethernet interface.     

Cluster storage for COMPASS tokamak

The COMPASS tokamak is expected to produce several gigabytes of data per shot in near future. A new storage system is needed to accommodate and access all the data. It should be scalable, fault-tolerant, and parallel. It should not be based on proprietary solutions to maintain independence from hardware and software manufacturers and preferably it should be built on inexpensive commodity hardware. One of the promising distributed parallel fault-tolerant file systems, GlusterFS, was selected for testing. The aim of the work was to make initial tests of a particular small GlusterFS setup to confirm its aptitude for the COMPASS storage system. Aggregated reading throughput from multiple NFS clients was one of the most important figures that were benchmarked, it scaled well with the number of clients, starting just above 60 MiB/s¹ for 1 client and going slightly over 300 MiB/s for 6 clients.