شرح سیستم های تزریق گاز ITER و فعالیت های جاری R & D

The gas injection system (GIS) is an indispensable part of ITER fueling system. It deliveries the necessary gas species from tritium plant to vacuum vessel, pellet injection system or neutral beam for plasma operation and fusion power shutdown. In this paper, the current design status of GIS, including the previous design changes, is briefly described. As the GIS design justification and support, the experimental study on GIS response time is illustrated. The factors delayed the GIS response time are identified, and two kinds of control mode are proved to be effective for improving the GIS response time. The exploration on magnetic shield design shows the discrepancy of shielding performance occurs in the case of the paralleling external magnetic field to the sample cylinder. These R&D works prove the design feasibility in some ways, and support possible solutions for design challenges as alternative design options.

ITER will be the first experimental reactor to produce a ‘burning’ deuterium–tritium plasma [1]. The mixture gases with proportional deuterium and tritium as the fuel of ‘burning’ plasma will be provided by the tritrium plant (TP) and injected into the torus by dedicated fueling system. The gas injection system (GIS) is a major part of the fueling system, it shall provide the fuel gases for plasma initiation, density control and fuel replenishment. Besides that, it also needs to provide the functions of impurity gases injection for radiative cooling and fusion power shut down, supply the working gases for pellet injection system (PIS), neutral beam (NB) and diagnostic neutral beam (DNB) injector and wall conditioning. The GIS, in a simple word, is an actuator to inject the specified gas species and throughput at given time slot following the commands from plasma control system (PCS) via COntrol, Data Access and Communication (CODAC) system to meet ITER project requirement. The GIS and its technical challenges associated have been introduced in many presentations [2], [3], [4] and [5]. And the conceptual design was complemented and changed gradually with the clarifying of physics requirements, boundaries and interfaces. Up to now, the conceptual design of GIS, incorporated previous design changes and corresponding R&D, has been completed. In this paper, the overall description of GIS is briefly presented in Section 2. And Section 3 focuses on some R&D activities, which supports the justification of design feasibility in some ways and provide the potential solutions for design challenging associated.

The GIS is a major part of fueling system to deliver the hydrogenic isotopic gas species to fuel ITER, as well as the impurity gases for divertor protection, detachment control and wall conditioning. The GIS consists of GDS, GFS and FPSS. And the current design status of each sub-system has been briefly introduced, in which the previous design changes have been incorporated: the tubes of gas distribution manifold are resized to meet the requirement of increasing throughput of tritium and flexible control of D/T ratio; the fuel gas supply pressure is reduced to sub-atmospheric pressure to decrease the risk of tritium release; the GVB for NB is removed and an additional tube is required for pure deuterium; three new GVBs and dedicated gas injection lines are reinforced to provide three new gas injection points in divertor level to improve toroidal uniformity of divertor plasma radiation; a dedicated introduction line is added for each FPSS or for pellet propelling. Some possible design changes in future are also mentioned here, which include the removal of guard pipe from fueling manifold, replacing the GVB secondary containment by standard glove box, removal of pure deuterium supply for NB ion source, increasing the total gas quantity from 40 Pa m3 to 1000 Pa m3 at least for FPSS. As the design support, the experimental study on GIS response time and exploration on magnetic shield design have been carried out. The results show the GIS response time is largely influenced by action/settle time of solenoid valve/mass flow controller and the volume of gas injection manifold. Two kinds of control mode, impulse technology and carrier gas technology, are both effective to improve the GIS response time. The residual field inside magnetic shield under 2000 Gs external static magnetic field is discrepant with the original design. When the magnetic field is parallel to the sample cylinder, the value is about one order larger than that in the perpendicular case. That may be caused by the demagnetization effect. The work here can provide justification for design feasibility in some extents and could be the design option or potential solution in the next phase design. Further R&D shall be continued. Though the conceptual design of GIS is completed, the high requirements of reliability, availability, maintainability and inspectability of the safety important component inside GIS, for example, the tritium compatible flow control valve with large throughput, in such strict working conditions (high static stray magnetic field, intricate interfaces and so on) still make the design challenging.