Zibo Zhou

Engineering Studies on the EAST Tungsten Divertor

Experimental advanced superconducting tokamak device is a D-shaped full superconducting tokamak with actively water cooled plasma facing components. To achieve long pulse and high βH-mode plasma, new plasma position and shape are calculated and optimized during the campaign of 2013-2014. New divertors are designed and developed to fit the plasma and endure the heat flux up to 10 MW/m2. The divertor is International Thermonuclear Experimental Reactor-like. It bases on monoblock and cassette technology and is composed of plasma facing component (PFC) units, cassettes, and support systems. Monoblock structures are just employed on the PFC units of target plates of the divertors, thus W flat tiles are used on the baffles and dome. At the end of monoblocks, end boxes are applied. Cassettes act not only as the supports of the PFC units, but also as manifolds for the cooling channels of the units. The support systems consist of inner support rails, outer support rails, and auxiliary braces. The support systems are installed on the vacuum vessel before cassettes are put on. To dock the cassette with the support system, it is just lifted and pushed forward. To verify and optimize the structure, Research and Development work has carried out for the divertor. The prototypes of PFC units and cassettes are fabricated with different manufacture processes. The total assembly process is also simulated with these prototypes on mockup facility and the vacuum vessel. The results show that the divertor system can be manufactured successfully according to the requirements of drawings and installed conveniently and precisely on the tokamak. All these works certify that the design of the divertor is all right. The batch production of the divertors can be started.

Design, R&D and commissioning of EAST tungsten divertor

After commissioning in 2005, the EAST superconducting tokamak had been operated with its water cooled divertors for eight campaigns up to 2012, employing graphite as plasma facing material. With increase in heating power over 20 MW in recent years, the heat flux going to the divertors rises rapidly over 10 MW m−2 for steady state operation. To accommodate the rapid increasing heat load in EAST, the bolting graphite tile divertor must be upgraded. An ITER-like tungsten (W) divertor has been designed and developed; and firstly used for the upper divertor of EAST. The EAST upper W divertor is modular structure with 80 modules in total. Eighty sets of W/Cu plasma-facing components (PFC) with each set consisting of an outer vertical target (OVT), an inner vertical target (IVT) and a DOME, are attached to 80 stainless steel cassette bodies (CB) by pins. The monoblock W/Cu-PFCs have been developed for the strike points of both OVT and IVT, and the flat type W/Cu-PFCs for the DOME and the baffle parts of both OVT and IVT, employing so-called hot isostatic pressing (HIP) technology for tungsten to CuCrZr heat sink bonding, and electron beam welding for CuCrZr to CuCrZr and CuCrZr to other material bonding. Both monoblock and flat type PFC mockups passed high heat flux (HHF) testing by means of electron beam facilities. The 80 divertor modules were installed in EAST in 2014 and results of the first commissioning are presented in this paper.

Investigation on the Possibility of Tritium Self-Sufficiency for CFETR Using a PWR Water-Cooled Blanket

The neutron wall load (Pn) of Chinese fusion engineering testing reactor (CFETR) will be less than 1 MW/m2. To meet the net tritium breeding ratio (TBR) of the reactor, a new water-cooled blanket concept is considered. The blanket neutronics schemes are performed to explore the local TBR issues in the (Pn) range of 1-5 MW/m2, which aims at the effective design of the blanket concept considering the tritium self-sufficiency. As a result, the calculation results are compared with the local TBR values and the material fraction changes. It is found that the local TBR has the high value at low (Pn) while the blanket size in radial direction is determined. It is mainly because of the total breeding area increasing due to the pipe pitch increasing in the model. This leads to the possibility for CFETR using a simplified blanket interior. In addition, to match the pressurized water reactor (PWR) water-cooled condition, a reduced size of blanket module in toroidal direction is achievable. It can be concluded that a PWR water-cooled blanket has more benefits to CFETR engineering implementation in the future.

The design and R&D work of EAST tungsten divertor

EAST tokamak is one of the advanced full superconducting tokamaks in the world. To achieve better plasma parameters, new plasma position and shape are calculated and optimized in the 2013s update. New divertors should be deigned and developed to endure higher heat flux less than 10MW/m2. The divertor is ITER-like structure. It bases on mono-block and cassette technology. The divertor is composed of PFC units, cassettes and support systems. Mono-block structures are just employed on the PFC units of target plates of the divertors, thus W flat tiles are used on the baffles and dome. Cassettes act as not only the supports of the PFC units, but also the cooling channels of the units. The support systems consist of inner support rails, outer support rails and auxiliary braces. The systems are installed on vacuum vessel before cassettes putting on. When cassette assembly with support system, it is just lifted and pushed forward. To optimize and verify the structure, R&D work has done on the divertor. The prototypes of PFC units in different positions and cassettes with different manufacture processes are fabricated. The assembly process is also simulated with these prototypes on mimic facility and vacuum vessel. The results show that the divertor system can be manufactured successfully according to the drawing requirements. And they can also be installed conveniently and precisely on the tokamak. All R&D work and tests will certify that the design of divertor is all right.

Plasma facing conponents of EAST

EAST plasma facing components (PFCs) have the function of protecting the vacuum vessel, heating systems and diagnostic components from the plasma particles and heat loads, and also additional to this particles and heat loads handling. They are installed in the vacuum vessel together with in-vessel coils, cryopump and diagnostic components. The design, fabrication and assembly have been finished. The PFCs are designed up-down symmetry to accommodate with both double null and single null plasma configuration. All PFCs use graphite tile for plasma facing surfaces affixed to copper alloy heat sink. A special deep hole drilling technology was developed to drill cooling channels directly on heat sink for high efficient heat removal. All Heat sink are installed onto the base alignment rails through stainless steel supports. As the benchmark of assembly for PFCs, the base rails are installed and measured precise based on a new alignment method integrating the optical instruments and a mechanical template. And so is a mechanical check template for checking the surface of first wall. As indicated, all the first wall components were fabricated and assembled successfully and meet the design requirement for the plasma operation.

Analysis of EAST’s New Tungsten Divertor and Cooling System During a Disruption with Halo Currents

Abstract Chinese Academy of Sciences Institute of Plasma Physics (ASIPP) Experimental Advanced Superconducting Tokamak (EAST) has designed and built a new outer divertor with an ITER-like cooling system. As part of a joint collaboration, the Plasma Science and Fusion Center at MIT performed analyses on the EAST design to determine loading, stresses and deflections due to the eddy currents and halo currents occurring during a disruption. The analysis was done using the finite element program COMSOL using techniques developed at MIT to recreate actual tokamak discharges from measured data. This technique has been used successfully to recreate discharges from Alcator C-Mod, a high field tokamak with TZM tiles at the Plasma Science Fusion Center at MIT, and allows us to recreate the fields for any disruption from the EAST data base. For the new divertor, an upward moving disruption was chosen as the design scenario. The plasma filament model predicts fields, eddy currents and loads due to a disruption, but the divertor will also be exposed to halo currents. The new EAST divertor borrows its cooling system design from ITER where the plasma facing tungsten tiles are water cooled by a CuCrZr manifold and pipes attached to the tiles. Halo currents traveling down these tubes and crossing the toroidal field will result in large loads in these components, and COMSOL is used to predict the stresses and deflections. The model predicts that the EAST divertor will survive the combined loading due to the eddy and halo currents.