High performance plasma vertical position control system for upgraded MAST

A plasma vertical control system able to control high elongation (～2.5) plasmas at moderate internal inductance (～0.9) is analysed, including both active and passive components in a closed loop system. The analysis is based on the RZIp rigid plasma model and this is extensively validated using present day MAST discharges, especially at the limits of controllability. Special consideration is given to the unusual MAST geometry (coils inside the main vacuum vessel) and general conclusions regarding system design are drawn wherever possible.     

Evolving the JET virtual reality system for delivering the JET EP2 shutdown remote handling tasks

The quality, functionality and performance of the virtual reality (VR) system used at JET for preparation and implementation of remote handling (RH) operations has been progressively enhanced since its first use in the original JET remote handling shutdown in 1998. As preparation began for the JET EP2 (Enhanced Performance 2) shutdown it was recognised that the VR system being used was unable to cope with the increased functionality and the large number of 3D models needed to fully represent the JET in-vessel components and tooling planned for EP2. A bespoke VR software application was developed in collaboration with the OEM, which allowed enhancements to be made to the VR system to meet the requirements of JET remote handling in preparation for EP2. Performance improvements required to meet the challenges of EP2 could not be obtained from the development of the new VR software alone. New methodologies were also required to prepare source, CATIA models for use in the VR using a collection of 3D software packages. In collaboration with the JET drawing office, techniques were developed within CATIA using polygon reduction tools to reduce model size, while retaining surface detail at required user limits. This paper will discuss how these developments have played an essential part in facilitating EP2 remote handling task development and examine their impact during the EP2 shutdown.     

First experimental results with the Current Limit Avoidance System at the JET tokamak

The Current Limit Avoidance System (CLA) has been recently deployed at the JET tokamak to avoid current saturations in the poloidal field (PF) coils when the eXtreme Shape Controller is used to control the plasma shape. In order to cope with the current saturation limits, the CLA exploits the redundancy of the PF coils system to automatically obtain almost the same plasma shape using a different combination of currents in the PF coils. In the presence of disturbances it tries to avoid the current saturations by relaxing the constraints on the plasma shape control. The CLA system has been successfully implemented on the JET tokamak and fully commissioned in 2011. This paper presents the first experimental results achieved in 2011–2012 during the restart and the ITER-like wall campaigns at JET.     

Design,manufacture and initial operation of the beryllium components of the JET ITER-like wall

The aim of the JET ITER-like wall project was to provide JET with the plasma facing material combination now selected for the DT phase of ITER (bulk beryllium main chamber limiters and a full tungsten divertor) and, in conjunction with the upgraded neutral beam heating system, to achieve ITER relevant conditions.The design of the bulk Be plasma facing components had to be compatible with increased heating power and pulse length, as well as to reuse the existing tile supports originally designed to cope with disruption loads from carbon based tiles and be installed by remote handling. Risk reduction measures (prototypes, jigs, etc.) were implemented to maximize efficiency during the shutdown. However, a large number of clashes with existing components not fully captured by the configuration model occurred.Restarting the plasma on the ITER-like Wall proved much easier than for the carbon wall and no deconditioning by disruptions was observed. Disruptions have been more threatening than expected due to the reduced radiative losses compared to carbon, leaving most of the plasma magnetic energy to be conducted to the wall and requiring routine disruption mitigation. The main chamber power handling has achieved and possibly exceeded the design targets.     

Design and operation results of nitrogen gas baking system for KSTAR plasma facing components

A baking system for the Korea Superconducting Tokamak Advanced Research (KSTAR) plasma facing components (PFCs) is designed and operated to achieve vacuum pressure below 5 × 10^?7 mbar in vacuum vessel with removing impurities. The purpose of this research is to prevent the fracture of PFC because of thermal stress during baking the PFC, and to accomplish stable operation of the baking system with the minimum life cycle cost. The uniformity of PFC temperature in each sector was investigated, when the supply gas temperature was varied by 5 °C per hour using a heater and the three-way valve at the outlet of a compressor. The alternative of the pipe expansion owing to hot gas and the cage configuration of the three-way valve were also studied. During the fourth campaign of the KSTAR in 2011, nitrogen gas temperature rose up to 300 °C, PFC temperature reached at 250 °C, the temperature difference among PFCs was maintained at below 8.3 °C, and vacuum pressure of up to 7.24 × 10^?8 mbar was achieved inside the vacuum vessel.     

Power handling of the bulk tungsten divertor row at JET: First measurements and comparison to the GTM thermal model

The design of the tile assemblies of the bulk tungsten divertor row in JET was improved in the course of several experiments as far as the power and energy performances are concerned: many prototypes were exposed to high heat fluxes in several electron and ion beam facilities during the development phase. These experiments were carried out in parallel with extensive modelling of the complete tungsten tile assembly in the so-called Global Thermal Model (GTM). The goal was to understand the heat flow from the plasma-facing surface through the supporting structure down to the base plate of the JET MkII divertor sufficiently to be able to later interpret operational data from the torus. Temperatures measured in the torus are in good agreement (?10/+15%) with the model. Some characteristic times show stronger deviations, with no incidence on the highest temperature at all times.     

Process enhanced ultimate safety with the Geyser system

A unique approach to attain enhanced, natural safety at low costs is given with a new, low temperature, low power level, nuclear energy plant of advanced design: the Geyser. The Geyser District Heating Nuclear Energy Plant (GDHNEP) and an ordinary low-temperature steam-cycle, the Geyser Thermal Energy Converter (GTEC), represent together a system possessing of remarkable features. Estimates project, that relatively small district heating plants distributed over a district heating network, or operating autonomously, would be cost effective. As a co-generation device the Geyser system may supply ample heating power and/or electricity opening new alternatives.     

JET and the Physics Basis of ITER

JET has made unique contributions to the physics basis of ITER by virtue of its ITER-like geometry,large plasma size and D-T capability.The paper discusses recent JET results and their implications for ITER in the areas of standard ELMy H-mode,D-T operation and advanced tokamak modes.In ELMy H-mode the separation of plasma energy into core and pedestal contributions shows that core confinement scales like gyroBohm transport.High triangularity has a beneficial effect on confinement and leads to an integrated plasma performance exceeding the ITER Q=10 reference case.A revised type I ELM scaling predicts acceptable ELM energy losses for ITER,while progress in physics understanding of NTMs shows how to control them in ITER.The D-T experiments of 1997 have validated ICRF scenarios for heating ITER/a reactor and identified ion minority schemes (e.g.(^3He)DT) with strong ion heating.They also show that the slowing down of alpha particles is classical so that the self-heating by fusion alphas should cause no unexpected problems.With the Pellet Enhanced Performance mode of 1988,JET has produced the first advanced tokamak mode,with peaked pressure profiles sustained by reversed magnetic shear and strongly reduced transport.More recently,LHCD has provided easy tuning of reversed shear and reliable access to ITBs.Improved physics understanding shows that rational q-surfaces play a key role in the formation and development of ITBs.The demonstration of real time feedback control of plasma current and pressure profiles opens the path towards fully controlled steady-state tokamak plasmas.     

超灵敏小型回旋加速器质谱计旋转式垂直型多样品装置的自动控制系统

介绍用于超灵敏小型回旋加速器质谱计旋转式垂直型多样品装置自动控制系统原理及应用,该系统亦可用于其他多样品自动装置.     

一回路冷却剂净化系统的优化运行

介绍了一回路冷却剂净化系统（KBE）的结构及陛能特点,研究分析了氨对硼酸型态及阴阳树脂的影响,冷却剂贮存系统（KBB）的设计缺陷。整理绘制了机组运行过程中碱金属、溶解氢的趋势图,结合机组在实际运行中出现的阴棚旨排带造成冷却剂氯离子超标、总碱金属偏离、溶解氢浓度下降等实际案例,总结优化了阳树脂氨钾饱和的开始时间、加钾量和氨浓度的控制;以及在不改变KBE初始设计的基础上增加KBE除碱金属功能,优化碱金属偏离的纠正措施。并根据实际运行结果对PUROLITE和BAYER两家公司生产的核级树脂性能进行了对比。     

Recent contribution of JET to the ITER physics

In recent years the JET scientific programme has focussed on addressing physics issues essential for the consolidation of design choices and the efficient exploitation of ITER in parallel to qualifying ITER operating scenarios and developing advanced control tools. This paper reports on recent achievements in the following areas: mitigation of edge localised modes (ELMs), effects of toroidal field (TF) ripple, advanced tokamak scenarios, material migration and fuel retention. Active methods have been developed to mitigate ELMs without adversely affecting confinement. A systematic characterisation of the edge plasma, pedestal energy and ELMs, and their impact on plasma-facing components as well as their compatibility with material limits has been performed. The unique JET capability of varying the TF ripple from its normal low value δB_T = 0.08% up to δB_T = 1% has been used to elucidate the role of TF ripple on confinement and ELMs. Increased TF ripple in ELMy H-mode plasmas is found to have a detrimental effect on plasma stored energy and density, especially at low collisionality. The development of ITER advanced tokamak scenarios has been pursued. In particular, β_N values above the ‘no-wall limit’ (β_N ～ 3.0) have been sustained for a resistive time. Gas balance studies combined with shot-resolved measurements from deposition monitors and divertor spectroscopy have confirmed the strong role of fuel co-deposition with carbon in the retention mechanism through long-range migration and also provided further evidence for the important role of ELMs in the material migration process within the JET inner divertor leg.     

First results from the Lund NMP particle detector system

The design and first results from a Double Sided Silicon Strip Detector (DSSSD) recently installed at the Lund Nuclear Microprobe facility (NMP) are presented. The detector has 64 sector strips and 32 ring strips, which in combination give more than 2000 detector cells, each with characteristics comparable with a standard surface barrier detector (SBD).The detector has been tested both with radioactive sources and with different ion beams and energies. The most striking features are the high rate virtually pile-up free operation and also the possibility of detailed measurement of angular distributions.     

Remote handling installation of diagnostics in the JET Tokamak

The requirement for an upgrade of the diagnostics for the JET ITER Like Wall (ILW) while maintaining personnel exposure to contamination as low as reasonably practicable or ALARP, has necessitated the development of a bespoke set of diagnostic components. These components, by virtue of their design and location, require a versatile yet comprehensive suite of remote handling tools to undertake their in-vessel installation. The installation of the various diagnostic components is covered in multiple tasks. Each task requires careful assessment and design of tools that can successfully interface with the components and comply with the handling and installation requirements. With remote maintenance a requirement, the looms/conduits were designed to be modular with connections which are electrically connected when the module is fitted or conversely disconnected when removed. The shape of each complex and often bulky component is verified during the design phase, to ensure that it can be delivered and installed to its specified location in the torus. This is done by matching the kinematic capabilities of the remote handling system and the path of the component through the torus by using a state of the art virtual reality system.     

Transitional modelling of the neutral gas in the JET neutraliser

Effective understanding of gas flow is important to ensure efficient operation of gas neutraliser systems such as that used at Joint European Torus (JET), which form part of neutral beam heating systems for nuclear fusion experiments. Offering a means of neutralising the charge of initially ionic beams, gas neutralisers permit the injection of beams of neutral particles into the tokamak vessel, which serve to both heat the plasma and drive plasma current. Within the JET neutraliser, gas flow encompasses both the continuum-transition and molecular flow regimes, encouraging the application of novel techniques. The first application of the Augmented Burnett Equations to these systems is presented with results compared to experimental pressure profile data. The results demonstrate that the application of the Augmented Burnett Equations is a valid modelling approach. The strong dependence of accuracy upon outlet Kn is noted and good agreement found with experiment as rarefaction approaches the molecular limit of Kn=1, beyond the theoretical domain of applicability.     

Verification of TOKES simulations against the MGI experiments in JET

The integrated tokamak simulation code TOKES is proposed for estimation of the ITER first wall radiation damage during massive injection of noble gas inside the core for mitigation of the disruptions. Simulations of MGI processes ab initio are almost impossible because of complexity of the problem, but one can get reliable results elaborating the TOKES scenario from JET experiments and applying it for ITER conditions. With this aim the TOKES code is used for simulation of JET shots disrupted with MGI. The TOKES scenario for the thermal quench of MGI at JET and its extrapolation to ITER have been developed basing on analysis of the available JET database and on comparison with the simulations performed.     

Improved framework for the maintenance of the JET intershot analysis chain

At the JET experiment data from routine diagnostics is analysed automatically by a suite of codes within minutes after operation. The maintenance of these interdependent codes and the provision of a consistent state of the physics database over many experimental campaigns against a backdrop of continuous hardware and software updates, requires well defined maintenance and validation procedures. In this paper, the development of a new generation of maintenance tools using distributed version control and a work-flow following the principle of continuous integration [1] is described.     

Physics of the conceptual design of the ITER plasma control system

The ITER plasma control system (PCS) will play a central role in enabling the experimental program to attempt to sustain DT plasmas with Q = 10 for several hundred seconds and also support research toward the development of steady-state operation in ITER. The PCS is now in the final phase of its conceptual design. The PCS relies on about 45 diagnostic systems to assess real-time plasma conditions and about 20 actuator systems for overall control of ITER plasmas. It will integrate algorithms required for active control of a wide range of plasma parameters with sophisticated event forecasting and handling functions, which will enable appropriate transitions to be implemented, in real-time, in response to plasma evolution or actuator constraints.In specifying the PCS conceptual design, it is essential to define requirements related to all phases of plasma operation, ranging from early (non-active) H/He plasmas through high fusion gain inductive plasmas to fully non-inductive steady-state operation, to ensure that the PCS control functionality and architecture will be capable of satisfying the demands of the ITER research plan. The scope of the control functionality required of the PCS includes plasma equilibrium and density control commonly utilized in existing experiments, control of the plasma heat exhaust, control of a range of MHD instabilities (including mitigation of disruptions), and aspects such as control of the non-inductive current and the current profile required to maintain stable plasmas in steady-state scenarios. Control areas are often strongly coupled and the integrated control of the plasma to reach and sustain high plasma performance must apply multiple control functions simultaneously with a limited number of actuators. A sophisticated shared actuator management system is being designed to prioritize the goals that need to be controlled or weigh the algorithms and actuators in real-time according to dynamic control needs. The underlying architecture will be event-based so that many possible plasma or plant system events or faults could trigger automatic changes in the control algorithms or operational scenario, depending on real-time operating limits and conditions.     

Thermo-mechanical calculations on operation temperature limits of tungsten as plasma facing material

Tungsten is a candidate material as a plasma facing material in the next step fusion devices. The material surface will be exposed to transient heat loads as well as steady-state heat loads. The present work describes the thermo-mechanical analysis of tungsten by finite element calculation. It is shown that tungsten has a strict operational temperature limit under transient heat loads. For the ITER-grade W, the operation limit of the base surface-temperature was calculated to be in a range of 400-780 °C under an applied transient heat load of 0.2 GW/m² for 0.5 ms in order to avoid plastic deformation of W.     

Overview of the SNS target system testing and initial beam operation experience

The Spallation Neutron Source (SNS) construction project has been completed including initial beam operation with the mercury target, moderators and associated systems. The project was initiated in 1999, with groundbreaking in December of 1999. Final integrated system testing for the mercury target, cryogenic moderators, shutter systems, water and other utility systems and all control and safety systems were completed in April 2006 and first beam on target was delivered April 28, 2006. This paper will give an overview of the system testing conducted in preparation for beam operation and initial operating experience with low power beams. One area of testing was extensive remote handling testing in the target service bay to demonstrate all key operations associated with the target and mercury loop. Many improvements were implemented as a result of this experience. Another set of tests involved bringing the supercritical cryogenic moderator systems on line. Again, lessons learned here resulted in system changes. Testing of the four water loops was very time consuming because of the complexity of the systems and many instrumentation issues had to be resolved. A temporary phosphor view-screen was installed on the front of the target which has been extremely useful in evaluating the beam profile on the target. Initial profile results will be presented. Target system performance for initial beam operation will be discussed. In general, all systems performed well with excellent availability. There were some unexpected findings. For example, xenon spallation gas products are believed to have deposited on a downstream gold amalgamation bed designed to remove mercury vapor and this disposition increased the local dose rate. A summary of findings and plans for ramping up in power will be given.