V. Hauer

Computational and experimental study of gas flows through long channels of various cross sections in the whole range of the Knudsen number

A computational and experimental study has been performed for the investigation of fully developed rarefied gas flows through channels of circular, orthogonal, triangular, and trapezoidal cross sections. The theoretical-computational approach is based on the solution of the Bhatnagar-Gross-Krook kinetic equation subject to Maxwell diffuse-specular boundary conditions by the discrete velocity method. The experimental work has been performed at the vacuum facility “TRANSFLOW,” at Forschungszentrum Karlsruhe and it is based on measuring, for assigned flow rates, the corresponding pressure differences. The computed and measured mass flow rates and conductance are in all cases in very good agreement. In addition, in order to obtain some insight in the flow characteristics, the reference Knudsen, Reynolds, and Mach numbers characterizing the flow at each experimental run have been estimated. Also, the pressure distribution along the channel for several typical cases is presented. Both computational and experime...

Outgassing rate measurements of stainless steel and polymers using the difference method

This paper presents a new outgassing test facility based on the difference method, which is a rarely used modified throughput technique. Furthermore, the experimental approach presented is validated based on new measurement data for three relevant materials. The facility allows to measure at a good resolution thermal outgassing rates at variable temperatures between room temperature and 300 °C. The measurement approach is discussed, the facility is described, and the measurement uncertainty is evaluated. Three materials were measured to demonstrate the new experimental approach and to compare the results obtained for stainless steel 316L and two polymers, Viton® and Vespel®. For stainless steel 316L, the influence of different pretreatments was analyzed. It was found that by baking in vacuum as well as in air (400 °C, 100 h), the outgassing rate can be reduced by almost a factor of ten, in line with predictions based on outgassing theory. The polymers were investigated, as they represent materials with qu...

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.

R&D progress for the ITER vacuum pumping system

Within the frame of the European Fusion Programme Forschungszentrum Karlsruhe is charged to develop the vacuum systems for ITER. These activities comprise the high vacuum systems for the torus exhaust gas, the neutral beam injectors and the cryostat, as well as the mechanical forepump trains for all of these systems. This paper describes the several systems and gives an overview about the underlying R&D work performed to provide a design basis for large vacuum pump systems. Most of the presented cryosorption results have been measured in the TIMO test bed, which houses an approximately 1:2 scale model of the torus cryosorption pump. In TIMO, almost all ITER relevant conditions can be replicated (like operational times, coolant flows, gas flows, temperatures, pressure), except of the pumping of tritium. The latter issue will be dealt with in a dedicated experiment during the 2003 trace tritium campaign in JET. It is shown that cryosorption vacuum pumping is an efficient and robust technique to be employed for ITER. Concepts for an appropriate forepump train for the high vacuum pumps are also discussed.

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.

A Novel Sorbent Material Test Device at Variable Cryogenic Temperatures

The knowledge of accurate performance data of porous materials is an essential need for investigation of new candidate sorbent materials for use in cryosorption devices. The temperature range between 5 K and 20 K is foreseen to be used in order to exploit the cryosorption mechanism in cryovacuum pump systems for nuclear fusion. But direct experimental data at cryogenic temperatures are very scarce in the open literature, especially at temperature levels other than LHe or LN.Thus, a novel device was developed to measure sorption characteristics of porous materials under variable temperature cryogenic conditions (3.5 K to 100 K). The COOLSORP facility is based on a commercially available pore‐analyser, upgraded by a heatable, closed He cycle, two‐stage Gifford McMahon refrigerator. This facility is characterised by its wide range of accessible pressures, from ambient down to 10−4 Pa.The paper describes the facility set‐up and and presents typical examples of low temperature sorption data on different gases ...

Outgassing behavior of different high-temperature resistant polymers

In vacuum applications, polymers often need to be used in spite of their relatively high outgassing rates, e.g., as sealing or spacer material. For some polymers—like Viton®, which is used for O-rings—data on outgassing rates can be found in literature, while for others, in particular, the most relevant ones that can be used at higher temperatures, only few results are available. Therefore, different high-temperature resistant polymers were measured at the Outgassing Measurement Apparatus, which uses the difference method. These polymers were polyimides like Kapton®, Vespel®, and Meldin®, as well as a polyetheretherketone and a polybenzimidazole. In order to investigate the temperature behavior of the outgassing of the polymers, the measurements were performed at room temperature, 100 °C, and 200 °C. The outgassing species were determined by a mass spectrometer. In addition, the dependence of the outgassing on the material thickness was analyzed. The paper shows that the outgassing rates of the examined p...

Experimental investigation on charcoal adsorption for cryogenic pump application

Fusion reactors are generating energy by nuclear fusion between deuterium and tritium. In order to evacuate the high gas throughputs from the plasma exhaust, large pumping speed systems are required. Within the European Fusion Programme, the Karlsruhe Institute of Technology (KIT) has taken the lead to design a three-stage cryogenic pump that can provide a separation function of hydrogen isotopes from the remaining gases; hence limiting the tritium inventory in the machine. A primary input parameter for the detailed design of a cryopump is the sticking coefficient between the gas and the pumping surface. For this purpose, the so-called TIMO open panel pump experiment was conducted in the TIMO-2 test facility at KIT in order to measure pumping speeds on an activated carbon surface cooled at temperatures between 6 K and 22 K, for various pure gases and gas mixtures, under fusion relevant gas flow conditions, and for two different geometrical pump configurations. The influences of the panel temperature, the gas throughput and the intake gas temperature on the pumping speed have been characterized, providing valuable qualitative results for the design of the three-stage cryopump. In a future work, supporting Monte Carlo simulations should allow for derivation of the sticking coefficients.

Operation space of divertor detachment in DEMO

In the paper we consider the operation window of DEMO divertor detachment expected under DEMO I operation conditions for various external impurity levels, particle throughput and pumping conditions, envisaged for fusion reactor. The operation region is defined in terms of upstream heat flux and the upstream density and is bounded by the burn conditions and by the transition threshold between L and H mode. It is also restricted by the density and upstream heat fluxes required for detach operation in DEMO divertor. The transition from the attached to the detached state is simulated in the frame of a simple model which includes the pumping efficiency dependence on density, recombination at the divertor plate and particle throughput. The model was benchmarked with JET experiment and reproduced global features of the transition. The neutral pressure in the divertor chamber and the particle flux to the cryo-and diffusion pump are estimated for detached divertor conditions as well as the number of required pumps.

The European Supplied Components of the ITER Vacuum Pumping Systems

Abstract The ITER Vacuum Pumping systems are designed to pump hydrogen isotopes, including tritium, helium and impurities. The EU is responsible for the in-kind supply of 8 torus-, 2 cryostat-, 3 Heating Neutral Beam-(HNB) and 1 Diagnostic Neutral Beam-(DNB) cryopumps, their 14 Cold Valve Boxes (CVBs) and the cryolines between them as well as the Leak Detection and Localization (LD&L) systems. The design of these systems has progressed well in the past with the exception of LD&L, where the results of a significant R&D program are required to define the design. The torus and cryostat cryopumps incorporate an inlet vacuum valve capable of controlling the pumping speed and require to be sufficiently instrumented for performance and inventory control. In order to fully define the related Procurement Arrangements (PA) and minimize any technological, programmatic or cost risks, a 1:1 Pre-Production cryopump (PPC) has been planned to be built and tested as well as a series of necessary R&D activities will need to be performed. These activities will address all technological challenges, specify the instrumentation needs of these Vacuum Pumping systems and analyze their performance, incorporating also all safety provisions and remote handling requirements.