Magnet Power Supply Research Articles

Status of JT-60SA tokamak under the EU-JA Broader Approach Agreement

JT-60SA is a fully superconducting coil tokamak to be built under the framework of the EU-JA Broader Approach Agreement, and it aims to contribute to the complement of the ITER experiments and to the DEMO reactor design by the study of steady-state high-beta plasma experiments. The conceptual design of the JT-60SA tokamak and the peripheral systems has been carried out in close collaboration of EU and Japan from middle of 2006, and the JT-60SA Conceptual Design Report which involves an analysis of plasma physics and engineering design is summarized in May 2007. This paper intends to present an overall view of the JT-60SA project, and the latest design status of the key engineering issues such as superconducting magnets, divertor target, plasma heating devices, and magnet power supplies.

A novel testing approach for SSRF digital power supply controllers

Digital power supply controller is one of the key parts of SSRF high resolution high stability magnet power supply system. It is very essential to keep any degradation of these excellent properties by any stages as small as possible via careful testing when the controller is developed. In this study, a novel testing approach was presented, with which a novel closed control loop without actual power converter was constructed, and the new developed SSRF Digital Controller can work well in it.

Completion of the KSTAR construction and its role as ITER pilot device

The construction of the Korea Superconducting Tokamak Advanced Research (KSTAR) device has been completed by August 2007. Key achievements in the KSTAR construction are (i) fabrication process establishment in the Nb 3Sn superconducting coils including interface components, (ii) development of magnet structures to resist high magnetic force and thermal loads of TF and PF coils, (iii) accurate assembling of all components using special assembly tools, and (iv) development of ancillary systems including a control system, magnet power supplies, diagnostic systems, heating systems, and cryogenic facility. Device commissioning has been started and the milestone for first plasma discharge is by the end of 2008. The KSTAR operation plan is targeted on the high performance plasma confinement research and long pulse operation achievement using the fully superconducting tokamak device. There is a lot of engineering similarity between KSTAR and ITER, such as using Nb 3Sn superconductor for TF and CS magnets. The experience of the KSTAR device could be an important technical basis for the design, procurement, and initial operation of the ITER device, as a role of a ITER pilot device.

Application of the SMES for the Large Scale Accelerator Magnet Power Supply

Power supply for the large-scale accelerator magnets draws a large amount of power from the utility network. For an example, the new proton accelerator complex for high intensity beam (Japan Particle Accelerator Research Complex, J-PARC) is under construction at the Tokai campus of Japan Atomic Energy Agency (JAEA) as a joint project between KEK and JAEA. The J-PARC 50 GeV proton synchrotron (50 GeV-PS) magnets power supplies are constructed with IGBT and IEGT, then the power factor is almost 100%. However, the swing of an active power becomes almost 170 MW, although the average power is about 50 MW. Such large pulse power will give un-allowed disturbances to an ac power line. A SMES system will be required for compensating such as pulse electric power and reducing the disturbances. Case study on circuit configuration of the power supply with SMES and present status of the R&D for the SMES system will be discussed.

KSTAR 전류전송제어시스템의 원격운전을 위한 EPICS 기반 제어계 구축

KSTAR 전류전송제어시스템은 네트워크기반의 실시간 분산제어시스템으로 EPICS (Experimental Physics and Industrial Control System)를 미들웨어로 채용하여 구축하였다. 전류전송제어시스템은 초전도자석시스템에 전류를 전송하기 위한 시스템으로서 전류전송과 동시에 초전도자석이 초전도상태를 유지하기 위한 냉매의 전송도 담당하고 있다. 주제어실에서의 원격운전을 위하여 EPICS IOC(Input Output Controller) 서버를 현장에 설치하였고 이를 통하여 전류전송제어시스템은 고유의 이름(PV)에 적절한 조작 및 감시 명령을 부여하여 주제어실의 운전화면을 통하여 시스템의 감시 및 조작이 가능하도록 하였다. EPICS와 PLC의 통신을 위하여 ether-ip 드라이버를 이용하여 EPICS IOC를 구축하였으며, 시험 결과 안정성 및 운용성 측면에서 만족할 만한 결과를 획득하였다. The KSTAR Current Lead System(CLS) with network based real-time distributed control system is implemented using an EPICS as a middle-ware software. The current lead system transfers current from magnet power supplies to superconducting magnet system and simultaneously supply the coolant to maintain superconducting state. To control the CLS at main control room an EPICS IOC server is installed in local control area. Using this server, it is able to be controlled and monitored the system in main control room through operator interface(OPI) which uses "caget" to read status and "caput" to write command with a unique name called PV. The EPICS IOC is developed using "ether-ip" driver to communicate with PLC. Also we achieved satisfactory results in operation and stability aspects from a long period commissioning test.

The OPERA Spectrometer Slow Control System

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> OPERA is a long-baseline neutrino experiment at the Gran Sasso underground laboratories (LNGS), to observe <formula formulatype="inline"><tex>$\nu _{\tau} $</tex></formula> appearance in a <formula formulatype="inline"><tex>$\nu _{\mu} $</tex></formula> neutrino beam produced at CERN. The detector is a structure of two super modules, each built-up of a massive lead/nuclear-emulsion target complemented by electronic detectors and a magnetic spectrometer. The two magnets are instrumented by 1000 Resistive Plate Chambers (RPCs) detectors for a total surface of about 3200 <formula formulatype="inline"><tex>${\rm m}^{2}$</tex></formula>. The slow control system has been designed to monitor and control all the critical parameters for the proper functioning of the spectrometers. The different hardware (Magnet and RPC High Voltage power supplies, RPC current meters, Magnet and RPC temperature sensors, RPC timing boards) is read out via CAN bus connections by several distributed clients. The clients write the data to a relational database (PostgresSQL) which is the heart of the system: it gives persistence to the data and allows to perform correlations useful to debug possible system malfunctioning. Among the various tools (histograms and XML Configuration Managers), a controller process checks for possible failures of the system using data from the database and generates warnings/alarms for people on shift. </para>

KSTAR 전류전송계통 진공배기계 구축 및 시운전

KSTAR (Korea Superconducting Tokamak Advanced Research) 전류전송계 (Current Feeder System)는 4.5 K의 저온에서 운전되는 초전도자석과 300 K의 실온에서 운전되는 전원장치 (Magnet Power Supply)를 전기적으로 연결하는 장치이다. 전류전송계는 최대 35 kA의 DC 전류가 인가되는 TF 자석용 및 350초간 20<TEX>$\sim$</TEX>26 ㎄의펄스 전류가 인가되는 PF 자석용으로 분리되어 있으며 리드박스 내부는 전류인입선, 초전도버스라인, 열차폐체 및 냉각라인 등이 설치되어 있다. 리드박스와 초전도버스라인 진공덕트는 KSTAR 주장치와는 별도로 진공배기 시스템이 구축되어있으며, 전체적으로 아령 형상을 하고 있는 진공공간을 효율적으로 진공배기하기 위하여 버스라인 덕트와 주장치 저온용기 사이에 진공 분리막 (Vacuum Separator)이 설치되어 있다. 진공배기를 위한 초벌배기계는 로터리펌프 및 부스터펌프 (Mechanical Booster Pump)로 구축되었으며 고진공 배기계는 4대의 크라이오펌프 (Cryo-pump)로 구축되었다. 진공장치 운전을 위해 PLC 기반의 로컬 제어시스템을 구축하였고 장치 안전을 위한 자체 인터록과 중앙인터록 시스템 및 중앙제어연계시스템이 함께 구축되어 있다. 전류전송계 설치완료 후 진공배기 시운전을 통해 배기시스템의 자가진단 및 리드박스 내부에 설치되어 있는 헬륨배관의 진공누설검사를 완료하였으며, 액체질소를 사용하여 전류인입선 냉각시험을 완료하였다. Current feeder system (CFS) for Korea superconducting tokamak advanced research(KSTAR) project plays a role to interconnect magnet power supply (MPS) and superconducting (SC) magnets through the normal bus-bar at the room temperature(300 K) environment and the SC bus-line at the low temperature (4.5 K) environment. It is divided by two systems, i.e., toroidal field system which operates at 35 kA DC currents and poloidal field system wherein 20<TEX>$\sim$</TEX>26 kA pulsed currents are applied during 350 s transient time. Aside from the vacuum system of main cryostat, an independent vacuum system was constructed for the CFS in which a roughing system is consisted by a rotary and a mechanical booster pump and a high vacuum system is developed by four cryo-pumps with one dry pump as a backing pump. A self interlock and its control system, and a supervisory interlock and its control system are also established for the operational reliability as well. The entire CFS was completely tested including the reliability of local/supervisory control/interlock, helium gas leakage, vacuum pressure, and so on.

KSTAR 전류인입선 및 헬륨냉매 제어시스템 제작 및 설치

KSTAR (Korea Superconducting Tokamak Advanced Research) current lead system (CLS) has a role to interconnect magnet power supply (MPS) in room temperature (300 K) and superconducting (SC) bus-line, electrically. For the first plasma experiments, it should be assembled 4 current leads (CL) on toroidal field (TF) current lead box (CLB) and 14 leads on poloidal field (PF) CLB. Two current leads, with the design currents 17.5 kA, and SC bus-lines are connected in parallel to supply 35 kA DC currents on TF magnet. Whereas, it could supply to each pairs of PF magnets during more than 350 s. At the cold terminals of the leads, there are joined SC bus-lines and it was constructed helium coolant control system, aside from main tokamak system, to protect heat flux through current leads and enhanced Joule heat due to supplied currents. Throughout the establishment processes, it was tested the high vacuum pumping, helium leak of the helium lines and hardwares mounted between the helium lines, flow controls for CL, and liquid nitrogen cool-down of possible parts (current leads, CL helium lines, and thermal shield helium lines for CLB), for the accomplishment of the required performances.

Iterative EM Design of an MRI Magnet Using HTS Materials

Conventional superconducting MRI magnet electromagnetic (EM) design involves the critical parameters of the magnet field and dimensional requirements, plus the low temperature superconductor (LTS) wire properties. When using HTS material for an MRI magnet, in addition to the conventional characteristics of a superconductor, the wire and the joint resistance need also to be considered. This is mainly due to the relatively low n-values of the BSCCO tape when compared to that of a conventional LTS wire, and it is also due to the more resistive joint nature for HTS joints. This paper discusses an iterative EM design procedure that calculates the resistance of the HTS wire/tape for the entire magnet, which is a strong function of the magnetic fields at different locations in the coils. The resistance is fed back to the regular MRI EM design for optimization, in order to meet resistance target and the ordinary MRI design goals. This iterative design process results in an optimized HTS MRI design with overall low resistance for magnet drifting and power supply requirements.

Measurement and Analysis of kHz Orbit Fluctuations in the Pohang Light Source

In this article, we report on the orbit stability in the kHz frequency range of the Pohang Light Source (PLS). Fluctuations of the stored beam positions in the PLS storage ring were measured using a digital beam position monitor (BPM) at a fixed location in the ring. Fourier analysis of the measured beam position revealed fluctuation frequencies in the kHz range. The current ripples of the corrector magnet power supplies (MPSs) are suspected to be the sources of these position fluctuations. We surveyed the current ripples of 140 corrector MPSs in the ring to obtain their frequency distribution. The distribution, weighted by the response-matrix elements for each correctors and the BPM, was found to have a strong correlation with the spectrum of the beamposition fluctuations, which substantiates the suspicion.

Power supply systems for rapid cycling synchrotron

AbstractJAEA and KEK are jointly constructing the high‐intensity proton accelerator project J‐PARC. Its main accelerator is a 3‐GeV rapid cycling synchrotron (RCS). Two types of resonant excitation systems, parallel and cascade, are introduced to excite DC biased 25‐Hz AC currents through its main magnets. The parallel excitation is adopted for the dipole magnet power supply system, and the cascade excitations are adopted for the seven family quadrupole magnets system. In this paper, the two systems are investigated and analyzed, and an explanation is given as to why the different types are adopted in each system. The authors believe that such hybrid exciting systems are most suitable for a high‐power RCS. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 49–60, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20535

The Power Supply System for HL-2A Tokamak's Magnetic Field

The highpower pulsed power supply system for the magnetic field ofthe HL-2A Tokamak is described in this paper. The total output powerof its eight magnetic field power supply units of nearly250 MW. Their highest DC output voltage and current are 3510 Vand 45 kA, respectively. All the units are operated in a pulsedmode. The pulse duration is 5 s, and the cyclic period is15 min. The power supply system consists mainly of pulsedflywheel motor generators, rectifying transformers, thyristorconverters, diode rectifiers and switches. The system incorporatesmany key technologies—supply equalization with two generators andfour diode bridges, constant-angle phase triggers with a widefrequency range, current equalization, a status detector for thehigh current 6-phase converter, and advanced monitoring based on aprogrammable logic computer and engineering parameter measurement.The experimental results show that the performance of the powersupply systemsatisfies the requirements of HL-2A experiments very well.

Current Control of 12-Pulse Regenerative Converter for High Current Magnetic Power Supply

High current magnetic power supply for superconductivity coil of tokamak requires fast dynamic performance of di/dt and smooth change over of current direction. To meet these specifications, high performance DSP-based controller is designed for 12-pulse thyristor dual converter with inter-phase transformer (IPT). Not only the total current of Y- and Delta-converter units, but also the difference for those, should be regulated fast and accurately. Proportional and integral controller is designed for difference current control and the controller output is compensated to Delta-converter. A new algorithm for the calculation of the initial firing angle is proposed for the minimization of non-ideal effect during the change over of dual converter currents.

Plasma current start-up experiments without the central solenoid in the TST-2 spherical tokamak

Several techniques for initiating the plasma current without the use of the central solenoid are being developed in TST-2. While TST-2 was temporarily located at Kyushu University, two types of start-up scenarios were demonstrated. (1) A plasma current of 4 kA was generated and sustained for 0.28 s by either electron cyclotron wave or electron Bernstein wave, without induction. (2) A plasma current of 10 kA was obtained transiently by induction using only outboard poloidal field coils. In the second scenario, it is important to supply sufficient power for ionization (100 kW of EC power was sufficient in this case), since the vertical field during start-up is not adequate to maintain plasma equilibrium. In addition, electron heating experiments using the X–B mode conversion scenario were performed, and a heating efficiency of 60% was observed at a 100 kW RF power level. TST-2 is now located at the Kashiwa Campus of the University of Tokyo. Significant upgrades were made in both magnetic coil power supplies and RF systems, and plasma experiments have restarted. RF power of up to 400 kW is available in the high-harmonic fast wave frequency range around 20 MHz. Four 200 MHz transmitters are now being prepared for plasma current start-up experiments using RF power in the lower-hybrid frequency range. Preparations are in progress for a new plasma merging experiment (UTST) aimed at the formation and sustainment of ultra-high β ST plasmas.

Synchrotron magnet power supply network with normal and common modes including noise filtering

We study theoretical aspects of power supply network for synchrotron magnets, particularly the Heavy Ion Medical Accelerator Complex (HIMAC) system that operates with good stability. We introduce a simplified electric circuit model, which uses a thyristor rectifier power supply, a noise filter, and synchrotron magnets, to introduce the concept of the normal and the common modes. The normal and common modes become decoupled when all the electric loads are placed symmetrically around the ground line for a three line circuit system. This construction makes the normal mode the dominant control of the magnetic fields of the accelerator magnets. It is then found that the connection of the ground (common) line to the middle point of the thyristor power supply is essential to make the common mode stable. These two arrangements can remove the noise at high frequency in the normal mode by the noise filter and hence the noise in the magnetic fields, resulting in stable performance of the synchrotron network.

Novel load ripple voltage-controlled parallel DC active power filters for high performance magnet power supplies

The cooling storage ring of the heavy ion research facility in Lanzhou (HIRFL-CSR) is one of the five mega-science projects undertaken by Chinese Academy of Science within its ninth and tenth five-year plan period. The HIRFL-CSR facility can providing heavy ion beams in wide energy range, manifold and with high quality. This paper presents a hybrid filter structure consisting of a passive filter and a parallel dc active power filter (DCAPF) for a sample magnet power supply in HIRFL-CSR. The configuration of the power system with the DCAPF is introduced. Then a novel feedback control scheme for the DCAPF is proposed with detecting the output ripple voltage across the magnet load. For detailed discussion, a simple model of the whole system has been derived and the stability characteristic is analyzed. Through simulation and experiment investigation, the DCAPF is successfully applied in a 120-kW magnet power supply in HIRFL-CSR finally. The ripple factor and tracking accuracy of the output current through the load achieve 8.87 ppm and 100 ppm, respectively. Therefore, the rigor requirements of low output current ripple and fast ramp rate are both satisfied with the DCAPF proposed.

Characteristics of a HTS Persistent Current Switch System Considering the n-Value

This paper deals with characteristics of a High-Tc superconductor (HTS) persistent current switch (PCS) system considering the n-value. I also present its operational characteristics through experiments. A HTS PCS system mainly consists of a PCS, a HTS magnet load, and a magnet power supply (MPS). The HTS magnet load was made-up of two double pancake coils in series. In order to measure the persistent current with respect to the magnet flux changes, a hall sensor was installed at the center of the magnet load. In the experiments, the initial current dropped rapidly in the persistent current mode. In order to analyze current decay, we introduced a new electrical equivalent model considering the n-value. Experimental results of the HTS PCS system have been compared with the theoretical results. It has been concluded that the characteristics of initial current decay were mainly determined by the voltages generated in the pancake load due to n-value and joint resistance

Voltage Rating Reduction of Magnet Power Supplies Using a Magnetic Energy Recovery Switch

A new concept of magnet power supplies that can reduce voltage ratings of the power supplies is proposed. Circuit diagram and operation principles of magnetic energy recovery switch (MERS) are described. MERS consists of a capacitor and four semi-conductor devices such as MOSFETs and IGBTs. It is connected in series to a power supply and a coil. MERS is a switch module and it has no power supply in itself. Because MERS generates a voltage required for the inductance of the coil, the power supply only has to supply a voltage required for the resistance of the coil. Therefore, using MERS can reduce voltage rating and capacity of the power supply. Two types of power supply using MERS and voltage rating reduction are discussed. Comparatively small power supplies for high-repetition pulsed magnets and alternating magnetic field coils can be designed. Some experiments were carried out and confirmed that MERS can reduce voltage ratings of power supplies

Power supply and quench protection for the MICE cooling channel magnets

This report discusses the power supply and quench protection system selected for the MICE superconducting coupling and focusing magnets. First, the MICE focusing and coupling magnet parameters are presented. Second, the report describes passive quench protection systems for these focusing and coupling magnets. Thermal quench-back from the magnet mandrel, which is a key to the MICE magnet quench protection system, is also discussed. A system of diodes and resistors is used to control the voltage to ground as the magnet quenches. Third, the report presents the magnet power supply parameters for MICE magnets.

A SMES-Based Power Supply for Accelerator Magnets

As particle accelerator technology advances, rapid cycling machines become more common. An increase in ramping speed of the magnets will draw more pulsed power from the utilities grid up to non acceptable levels. An intermediate storage of active and reactive power with fast reaction times and excellent cycling capabilities becomes more and more important. A study has been performed for the conceivable replacement of the existing magnet power supply of the PS (Proton Synchrotron) of CERN. A possible solution is a SMES-based modular compensator system, which allows a step-by-step build-up of the system in turn with test operations during regular shut-down phases while continuing operation of the existing power supply