Plasma position and current control system enhancements for the JET ITER-like wall

The upgrade of Joint European Torus (JET) to a new all-metal wall, the so-called ITER-like wall (ILW), has posed a set of new challenges regarding both machine operation and protection. The plasma position and current control (PPCC) system plays a crucial role in minimizing the possibility that the plasma could permanently damage the ILW. The installation of the ILW has driven a number of upgrades of the two PPCC components, namely the Vertical Stabilization (VS) system and the Shape Controller (SC). The VS system has been enhanced in order to speed up its response and to withstand larger perturbations. The SC upgrade includes three new features: an improved termination management system, the current limit avoidance system, and the PFX-on-early-task. This paper describes the PPCC upgrades listed above, focusing on the implementation issues and on the experimental results achieved during the 2011–12 JET experimental campaigns.     

Linux real-time framework for fusion devices

A new framework for the development and execution of real-time codes is currently being developed and commissioned at JET. The foundations of the system are Linux, the Real Time Application Interface (RTAI) and a wise exploitation of the new i386 multi-core processors technology.The driving motivation was the need to find a real-time operating system for the i386 platform able to satisfy JET Vertical Stabilisation Enhancement project requirements: 50 μs cycle time. Even if the initial choice was the VxWorks operating system, it was decided to explore an open source alternative, mostly because of the costs involved in the commercial product.The work started with the definition of a precise set of requirements and milestones to achieve: Linux distribution and kernel versions to be used for the real-time operating system; complete characterization of the Linux/RTAI real-time capabilities; exploitation of the multi-core technology; implementation of all the required and missing features; commissioning of the system.Latency and jitter measurements were compared for Linux and RTAI in both user and kernel-space. The best results were attained using the RTAI kernel solution where the time to reschedule a real-time task after an external interrupt is of 2.35 ± 0.35 μs. In order to run the real-time codes in the kernel-space, a solution to provide user-space functionalities to the kernel modules had to be designed. This novel work provided the most common functions from the standard C library and transparent interaction with files and sockets to the kernel real-time modules. Kernel C++ support was also tested, further developed and integrated in the framework.The work has produced very convincing results so far: complete isolation of the processors assigned to real-time from the Linux non real-time activities, high level of stability over several days of benchmarking operations and values well below 3 μs for task rescheduling after external interrupt. From being the alternative option, RTAI has been finally chosen as the platform for the project. A first stable version of the framework has been integrated on the JET system and is already being commissioned. It will be soon be used on the Vertical Stabilisation Enhancement for the Plasma Control Upgrade (PCU) project at JET.     

光突发交换及其关键技术研究

文章介绍了光突发交换网络的恰量时间协议、网络结构和突发控制分组结构,重点研究了光突发交换网络的竞争解决方案、QoS解决方案和突发会聚机制等关键技术．     

Geometry and expected performance of the solid tungsten outer divertor row in JET

At JET new plasma-facing components for the main chamber wall and the divertor are being designed and built to mimic the expected ITER plasma wall conditions in the deuterium-tritium operation phase. The main wall elements at JET will be made of beryllium and the divertor plasma-facing surface will be made of tungsten. Most of the divertor tiles will consist of tungsten-coated Carbon Fibre Composite (CFC) material. However one toroidal row in the outer divertor will be made of solid, inertially cooled tungsten. The geometry of these solid tungsten divertor components is optimized within the boundary conditions of the interfaces and the constraints given by the electrodynamical forces. Shadowing calculations as well as rough field line penetration analysis is used to define the geometry of the tungsten lamella stacks. These calculations are based on a set of magnetic equilibria reflecting the operation domain of current JET plasma scenarios. All edges in poloidal and toroidal direction are shadowed to exclude near perpendicular field line impact. In addition, the geometry of the divertor structure is being optimized so that the fraction of the plasma wetted surface is maximised. On the basis of the optimized divertor geometry, performance calculations are done with the help of ANSYS to assess the maximum power exhaust possible with this inertially cooled divertor row.     

2—THE SYSTEMATIC OPTIMIZATION OF THE AQUEOUS COMPRESSION-JET WOOL SCOUR. PART II: SCOURING TRIAL FOR OPTIMUM PRODUCTION CAPACITY

A factorial experiment performed on the aqueous compression-jet scour with three independent variables is reported. These variables were the feed-rate of greasy wool, the speed of the layer of wool, and the jetting pressures. The wools were processed to gilled slivers, on which mean-fibre-length determinations were made. The effects of the independent variables on the dependent variables of residual grease and dirt and mean fibre length (the last-named being a measure of the degree of entanglement of the scoured wool) were evaluated. The results obtained indicated the operating conditions to be used to achieve the optimum production capacity.     

Guidelines for setting the useful range of pulse plating parameters

Guidelines are developed in this paper, based on a presentation to the 8th European Pulse Plating Seminar, Vienna, 2018, to facilitate the choosing of appropriate pulse plating parameters for different applications, taking into account electrochemical limiting factors. These guidelines take the form of a selection tool consisting of a self-checking Excel table.     

Fusion

Fusion works. It powers the Sun and the other stars, and the Joint European Torus (JET) at Culham in the UK has produced 16 MW of fusion power. Fusion has many potential advantages, including essentially limitless fuel, no carbon dioxide or other emissions, and intrinsic safety. Recent progress has been good and the outlook is promising. Several steps are needed before a prototype (demonstration) power station (‘DEMO’) can be brought into operation. These steps are: (1) build a power-station-size experimental device (an international tokamak experimental reactor (ITER)) and a materials test facility (i.e. an international fusion materials irradiation facility (IFMIF)), which will take 10 years; (2) run these facilities and incorporate the results into the design of DEMO—up to a further 10 years; and (3) build DEMO—up to another 10 years. DEMO could therefore be in operation within 30 years. Fusion power could follow on a significant scale, 10 or more 1.5 GW power stations, before the middle of this century. In the second part of the century, fusion could power large centres of population and perhaps be used to produce hydrogen fuel. Meeting growing energy demand (primarily driven by needs in developing countries) while reducing carbon emissions is a large and growing challenge. A portfolio approach is needed—there is no magic bullet. Given fusion's potential, it is essential that it is developed as rapidly as is reasonably possible (even if success is not 100% certain) as one of very few options available for large-scale production of base-load power.     

The JET real-time plasma-wall load monitoring system

In the past, the Joint European Torus (JET) has operated with a first-wall composed of Carbon Fibre Composite (CFC) tiles. The thermal properties of the wall were monitored in real-time during plasma operations by the WALLS system. This software routinely performed model-based thermal calculations of the divertor and Inner Wall Guard Limiter (IWGL) tiles calculating bulk temperatures and strike-point positions as well as raising alarms when these were beyond operational limits.Operation with the new ITER-like wall presents a whole new set of challenges regarding machine protection. One example relates to the new beryllium limiter tiles with a melting point of 1278 °C, which can be achieved during a plasma discharge well before the bulk temperature rises to this value. This requires new and accurate power deposition and thermal diffusion models.New systems were deployed for safe operation with the new wall: the Real-time Protection Sequencer (RTPS) and the Vessel Thermal Map (VTM). The former allows for a coordinated stop of the pulse and the latter uses the surface temperature map, measured by infra-red (IR) cameras, to raise alarms in case of hot-spots. Integration of WALLS with these systems is required as RTPS responds to raised alarms and VTM, the primary protection system for the ITER-like wall, can use WALLS as a vessel temperature provider.This paper presents the engineering design, implementation and results of WALLS towards D-T operation, where it will act as a primary protection system when the IR cameras are blinded by the fusion reaction neutrons. The first operational results, with emphasis on its performance, are also presented.     

Fusion yield measurements on JET and their calibration

The power output of fusion experiments and fusion reactor-like devices is measured in terms of the neutron yields which relate directly to the fusion yield. In this paper we describe the devices and methods used to make the new in situ calibration of JET in April 2013 and its early results.The target accuracy of this calibration was 10%, just as in the earlier JET calibration and as required for ITER, where a precise neutron yield measurement is important, e.g., for tritium accountancy.We discuss the constraints and early decisions which defined the main calibration approach, e.g., the choice of source type and the deployment method.We describe the physics, source issues, safety and engineering aspects required to calibrate directly the Fission Chambers and the Activation System which carry the JET neutron calibration. In particular a direct calibration of the Activation system was planned for the first time in JET. We used the existing JET remote-handling system to deploy the ²⁵²Cf source and developed the compatible tooling and systems necessary to ensure safe and efficient deployment in these cases.The scientific programme has sought to better understand the limitations of the calibration, to optimise the measurements and other provisions, to provide corrections for perturbing factors (e.g., presence of the remote-handling boom and other non-standard torus conditions) and to ensure personnel safety and safe working conditions. Much of this work has been based on an extensive programme of Monte-Carlo calculations which, e.g., revealed a potential contribution to the neutron yield via a direct line of sight through the ports which presents individually depending on the details of the port geometry.     

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.