Chr. Day

First operation experiences with ITER-FEAT model pump

Design and manufacturing of the model cryopump for ITER-FEAT have been finished. After acceptance tests at the contractors premises the pump was installed in the TIMO-facility which was prepared for testing the pump under ITER-FEAT relevant operating conditions. The procedures for the final acceptance tests are described. Travelling time, positioning accuracy and leak rate of the main valve are within the requirements. The heat loads to the 5 and 80 K circuits are a factor two better than the designed values. The maximum pumping speeds for H 2 , D 2 , He, Ne were measured. The value of 58 m 3 /s for D 2 is well above the contractual required value of 40 m 3 /s.

Performance tests of the ITER model pump

Abstract To study the pump performance of a sorption cryopump intended for use within the ITER fuel cycle, the test facility TIMO “Test facility for the ITER Model pump” was built at the Forschungszentrum Karlsruhe. After the successful acceptance tests of the model pump in 2000, new components were installed to improve the cooling performance. At the end of the reconstruction activities, the tests with the model pump were continued. During these new test series, all important aspects regarding the changed requirements of the new ITER design were to be checked, such as the pump behavior at high throughputs, the capacities achievable at temperatures higher than 5 K, and the possibility of using the torus cryopumps for the examination of small helium leaks.

New operational aspects of the ITER-FEAT primary vacuum pumping system

At Forschungszentrum Karlsruhe, a special cryosorption vacuum pump system is being developed for ITER-FEAT. The available R&D and design work performed so far originally supported the ITER-FDR machine, but only minor redirection has been needed. However, three new crucial aspects are described and critically discussed in this paper. These are the rather high throughputs per individual pump (which have almost doubled), the poisoning phenomena, and the use of the cryopumps during fine He leak detection. It could be demonstrated that all these aspects generated by the new ITER-FEAT design will not be a limiting factor for cryopump operation.

The ITER vacuum systems

ITER is a large vacuum facility which comprises many service, diagnostic and monitoring vacuum sub-systems as well as three large cryogenic pumping systems for evacuation and maintenance of the required pressure levels. Control of the gas throughput is one of the key issues affecting the performance and achievable burn time of a fusion reactor. The main pumping systems are the torus exhaust pumping, the cryopumps for the neutral beam injection systems for plasma heating, and the cryopumps for the ITER cryostat. All customized cryosorption pumps are force-cooled with supercritical helium and share a similar modular design of cryosorption pumping panels. For regeneration of the cryopumps as well as for roughing down the system volumes prior to operation, four identical sets of forepump trains are used. This paper will focus on the areas of the ITER vacuum systems which require customized developments and cannot rely on commercial solutions. The complex pumps have been tailored for the very specific applications and requirements at ITER, especially characterised by the need to be tritium compatible. An outline of the development path which was needed to come up with a sound design for the ITER cryopumps is given. The way of development is culminating in the manufacturing of 1:1 scale prototypes, which will be extensively tested in dedicated test facilities to ensure compatibility with all design requirements.

Design of the ITER Torus Cryopump

The cryopump concept for the ITER 2001 proposed by ITER-JCT was assessed. Some modifications were recommended. For these modified arrangements, Monte-Carlo calculations were performed to define the pumping probability of the cryopump together with the divertor duct. Results show that the ITER requirement can be fulfilled with small restraints if the pump inlet diameter is enlarged to 1000 mm and the neutron shield in the duct is taken out.

The influence of water on the performance of ITER cryosorption vacuum pumps

A cryopump system is being developed for high vacuum operation of the ITER torus. It is based on combined sorption and condensation of gases at cooled surfaces at about 5 K, coated with activated charcoal. During the operation of ITER water-like species which show strong sorptive interaction with charcoal have to be coped with by the cryopumps. To achieve optimum performance they have to be regenerated from these species at regular, less frequent intervals. The different aspects to be considered when designing this step are reflected in the present paper using water as a typical representative. The poisoning effect is demonstrated to be acceptably moderate. The potentials of both temperature increase and pressure decrease to stimulate water desorption are critically assessed and their specific advantages and drawbacks are discussed.

Component tests on fast heating and cooling with cryopanels for use in the ITER primary vacuum system

Within the framework of the European Fusion Technology Programme, a primary vacuum pump for International Thermonuclear Experimental Reactor (ITER) is being developed. As the tritium inventory accumulated by the pumps must be limited, short pumping cycles are required. At two facilities, different fast heating and cooling techniques of cryosorption panels were investigated. The results for the most advantageous methods are presented. It is shown that fast regeneration of ITER cryopanels is technically feasible.

Initial studies of the divertor dome effect on pumping efficiency in DEMO

In this paper we analyze the gas dynamics effect on the pumping efficiency in the European DEMO 1 ITER-like divertor configuration with and without dome. The achievement of detachment at given upstream heat flux and upstream density under burning conditions depends on the level of neutral pressure in the divertor private flux region (PFR) and on the required throughput at actual pumping speed. The principle effect of the dome on neutral compression in the PFR is assessed by using the DIVGAS code based on direct Monte Carlo simulation [1]. The numerical analysis includes the calculation of neutral density in the PFR and the overall conductance of the sub-divertor structure, which consequently affects the estimation of the effective pumping speed and, ultimately, the achievement of detachment. It is shown that the configuration with dome requires a higher pumping efficiency and that the dome impedes the detachment onset. The dome position can be further optimized to ensure good pumping of impurities and ease detachment onset. DIVGAS is demonstrated to be a most suitable tool to do further parametric and detail studies.

The THESEUS facility — A test environment for the Torus exhaust vacuum pumping system of a fusion power plant

At KIT Karlsruhe, a new vacuum pump concept for fusion power plants is under development. This concept consists of three pump types, namely a vapour diffusion pump as primary pump, a metal foil pump that provides a sharp gas separation of unburnt fuel (pure deuterium/tritium) and a liquid ring pump as backing pump. As special feature, diffusion pump and ring pump apply mercury as working fluid due to its perfect tritium compatibility. All three pump types require a proof-of-principle testing as their performance cannot be predicted easily. For these experiments, a dedicated experimental facility called THESEUS is currently being set up. This facility allows experiments with nitrogen, argon, hydrogen, deuterium and helium as fusion relevant test gases in a pressure range from 103 to as low as 10-9 mbar. Hence, the performance of both primary pumps and backing pumps can be tested. The use of mercury and flammable gases in the facility asks for demanding safety pre-cautions and a well-designed safety system. This paper presents the test facility in full detail. It describes the safety system as well as the Supervised Control And Data Acquisition (SCADA) system, and the gas analysing system that monitors the mercury release and - migration inside the facility.

TRANSFLOW: An experimental facility for vacuum gas flows

The TRANSFLOW experimental facility represents a reliable tool for measuring the conductance of 1:1 scale components as typically used in vacuum systems in a wide range of the Knudsen number (e.g. 10−4≤Kn≤103). The main principle of this facility is the dynamic measurement of the pressure difference upstream and downstream of the duct by setting a constant mass flow rate through the test channel. Many experiments on fully developed and developing flows, based on long and short channels respectively, have been already completed and comparisons with corresponding numerical results have been successfully performed. It has been clearly proven that the TRANSFLOW experimental setup provides conductance results with overall uncertainty between 1 to 10% and it could be used as a benchmark facility for any new proposed scientific numerical method in rarefied gas dynamics and in the whole range of gas rarefaction.