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Electric space propulsion is a technology that is used in a continuously increasing number of spacecrafts. The qualification of these propulsion systems has to run in ground-based test facilities which requires long testing times and powerful pumping systems. In these usually large test facilities, high pumping speeds are achieved with cryopumps. Cryopump operation is very expensive with respect to electrical energy and cooling water consumption. Therefore, being able to optimize pump shape, cold plate material, and pump placement in a chamber is beneficial. Pump design and tuned operating strategies can reduce costs and increase intervals between regeneration. Testing different pump configuration setups in a large facility is mostly prohibitive due to high costs and long testing times. Optimization via modelling is a better choice for design and also, later, for operation. Therefore, having a numerical model and proven guidelines at hand for optimization is very helpful. This paper describes a new model developed at DLR for the optimization of cryopump layout and operation. Model results are compared with cryopump operational and warm-up data. This validation is the basis for further optimization actions like multi-layer insulation layouts and pump cold plate upgrades, and helps in understanding and mitigating the detrimental effect of water condensates on the cryopump cold plates. [ABSTRACT FROM AUTHOR]

Electric space propulsion is a technology that is used in a continuously increasing number of spacecrafts. The qualification of these propulsion systems has to run in ground-based test facilities which requires long testing times and powerful pumping systems. In these usually large test facilities, high pumping speeds are achieved with cryopumps. Cryopump operation is very expensive with respect to electrical energy and cooling water consumption. Therefore, being able to optimize pump shape, cold plate material, and pump placement in a chamber is beneficial. Pump design and tuned operating strategies can reduce costs and increase intervals between regeneration. Testing different pump configuration setups in a large facility is mostly prohibitive due to high costs and long testing times. Optimization via modelling is a better choice for design and also, later, for operation. Therefore, having a numerical model and proven guidelines at hand for optimization is very helpful. This paper describes a new model developed at DLR for the optimization of cryopump layout and operation. Model results are compared with cryopump operational and warm-up data. This validation is the basis for further optimization actions like multi-layer insulation layouts and pump cold plate upgrades, and helps in understanding and mitigating the detrimental effect of water condensates on the cryopump cold plates.

Abstract This study investigated the inflow angle and capture coefficient є using numerical simulation, and then validated the inferred relation by experimentation. The inflow angular dependent capture coefficient є (θ) of a cylindrical cryopump used to create a high-vacuum environment for electric propulsion tests was calculated from a three-dimensional particle trajectory simulation. Results show that є (θ) is 0.25–0.83 as a function of the inflow angle of particles to the pump surface. A total capture coefficient є total is obtained by integration of the є (θ) multiplied by the flux distribution of particle to the pump surface. For the thermal inflow flux, є total is calculated as 0.55 for the cylindrical cryopump alone and 0.70 for a cylindrical cryopump with a duct for a gate valve. The analytically estimated є total was evaluated by pressure distribution measurements taken in a φ2.0 × 3.0 m vacuum chamber evacuated by two cylindrical cryopumps. The numerically simulated pressure shows good agreement with the measured pressure within ±6%. Further investigation of the improvement of the є total when the particles flow directly to a pump demonstrates that є total increases 16% when particles flow directly to a pump. Highlights • We assessed inflow angular dependence of capture coefficient є of a cryopump. • That angular dependence is greater on a cryopump with a duct for a gate valve. • When the inflow angle is normal to the cryopump surface, є has a peak value of 0.75. • Simulated є was validated using pressure measurement experiments. [ABSTRACT FROM AUTHOR]

Highlights • One complete cryopump unit of JT-60SA and a detailed 3D model of 1757 components. • 6400 CPUs in supercomputer Marconi-Fusion, 1010 test molecules and high precision. • The pumping speeds and the heat loads to the condensation pipes are obtained. • The present design can meet the requirement of pumping, cooling and regeneration. Abstract The cryogenic pumping system is one of the key components that define the operational window of JT-60SA. It is envisaged to utilize condensation pumps that work at 3.8 K, and proper thermal shields cooled with water and 80 K gaseous helium are necessary to allow having them installed at short distance to the torus in order to exploit high pumping speeds. In this paper, one complete divertor cryopump unit in a 40° sector is studied by Monte Carlo simulation. The pumping speeds of one cryopump unit for D 2 were found to be between 14.8 m3/s and 18.1 m3/s depending on the assumptions taken. In addition, the heat loads to the cryopump condensation pipes during steady state nominal operation, as well as the heat loads and transient behavior after massive gas injection events are assessed. The present design can fulfil the requirement of pumping, cooling and regeneration. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Closed cycle refrigerators for cryogenic temperatures (cryocoolers) provide a convenient solution in a wide range of applications, from low temperature physics to cryopumping, superconducting magnets or low noise infrared sensing. Understanding in detail the physical mechanisms underlying cryocooler operation is then of practical and fundamental interest. This paper deals with the analysis as a linear dynamical system of a GM cryocooler operation, considered over a limited range of temperature around a setpoint. The method is interesting as a way to model the thermal behavior of the refrigerator that can be effective in systematic analysis of cryocoolers thermal behaviour and design of temperature controllers. [ABSTRACT FROM AUTHOR]

The cryo-vacuum pump (CVP) system controls the plasma density by condensing undesirable gases together with a set of turbo molecular pumps. One CVP will be installed under each of the ten units of the actively cooled divertor in Wendelstein7-X for the long-pulse operation up to 30-min duration. Each CVP is operated with supercritical Helium (ScHe) at 4 K and liquid nitrogen (LN2) at 80 K fed by a plug-in, which is installed inside a W7-X port of the plasma vessel (PV). The plug-in made of stainless steel provides for the vacuum boundary between the plasma chamber and the torus hall atmosphere. Four transfer lines ( $12 \times 1$ mm) are positioned inside the plug-in: two for the inlet/outlet of ScHe and two for the inlet/outlet of LN2, respectively. The design has to guarantee the feeding at the specified temperature of ScHe and LN2 while minimizing thermal losses and thermal interactions between pipes. Inside the plug-in the vacuum level is $10^{\mathrm {-3}}$ Pa at room temperature (RT) and $10^{\mathrm {-5}}$ Pa during operation. The pipes of the ScHe are shielded with a multilayer superinsulation. The cryogenic feed lines are protected with a cryo shield against thermal loads in the port as well as in the PV. The thermal analysis confirmed the efficiency of the thermal shielding design, which keeps temperatures of ScHe and LN2 pipes within operation limits. During baking, the PV is heated to 150 °C while the cryostat remains close to RT. The port and transfer lines are equipped with bellows to accommodate this situation. But the plug-in is rigid and the resulting bend induces mechanical loads on the flanges between port and plug-in. The mechanical analysis confirmed that the selected bolts and pretension conditions guarantee the tightness of the flange during baking. [ABSTRACT FROM AUTHOR]

The cryopump will be installed for the high power and long pulse operation up to 30 min of Wendelstein 7-X (W7-X). In total there are 10 independent and identical cryopumps, one cryopump for each of the 10 discrete divertor units. The cryopump is located along the pumping gap in the toroidal direction below the divertor target modules and close to the location where field lines hit the divertor target surface. Each pump has a design envelop of ∼400 mm diameter and ∼4 m length. During a fast discharge event of the W7-X superconducting coils, the changing magnetic field will induce eddy currents on the metallic cryopump components, especially on the low resistance copper parts. The combination of the eddy current and the background magnetic field will generate mechanical forces and moments on the cryopump structure. The electromagnetic analysis provided the eddy current and Lorentz force distribution as an input for the mechanical analysis. These analyses showed no possible resulting damages on the structure of the cryopump. [ABSTRACT FROM AUTHOR]

The ITER vacuum system will use first of a kind cryopumps to provide high vacuum conditions to the torus vacuum vessel, the cryostat, and the neutral beam injectors. In order to evacuate the high gas flows required by the plasma scenarios, the cryopumps will need sequential regeneration with unprecedented high frequencies. The Front-End Cryopumps Distribution System, made of 12 cold valve boxes and 1 warm regeneration box, will provide helium to each of the cryopumps at the required pressure, temperature and mass flowrate, with dynamic synchronization with plasma pulses, in order to control the pumps behaviour during pumping and regeneration. A model of the cryopumps and their cryogenic distribution system is being developed, with the purpose of simulating the cryogenic process in dynamic scenarios and optimize the final design and the control of the system. This paper presents the dynamic model of the torus subsystem, made of 6 torus cold valve boxes, and the connected cryopumps, during operation and 100 K regeneration scenarios. The preliminary simulation results will be presented, giving useful information for a refined setting of parameters like pressures, mass flow rates, and valves control. These results are suitable to be used to optimize the distribution system final design and commissioning. [ABSTRACT FROM AUTHOR]

A molecular pump is always used as the main pump of the vacuum leak detection system because of its strong ability for pumping helium. But the pumping speed of a molecular pump is not enough for large vacuum chamber. A cryopump is a clean, oil-free and high pumping-speed vacuum pump. If a cryopump is used as the main pump of the vacuum leak detection system, the number of the pumps will decrease. This paper describes the experiments on vacuum leak detection system with cryopump as a main pump, and analyses the phenomena in the experiments. The results show that the cryopump decreased the vacuum pressure of the system significantly, but it had nearly no influence to the system sensitivity. The response time and the clean-up time of the leak detection system with only molecular pump were both 3 min. But the response time of the leak detection system with both molecular pump and cryopump was 10 min–20 min, and the clean-up time of the system was longer than an hour. [ABSTRACT FROM AUTHOR]

The ITER main vacuum system consists of six torus exhaust pumps integrated in the Cryostat through dedicated housings at the building B1 level. The Port Cell area outside the cryopump plug is affected by neutrons streaming through the housing structure and diagnostics penetrations. The aim of the study presented in this paper is to perform a complete assessment of the nuclear responses in the Cryopump Port Cell #12 by means of the MCNP-5 Monte Carlo code in a full 3-D geometry. The results of the neutronic analyses provide guidelines for the design and maintenance of the embedded components, ensuring their structural integrity and proper operation. Radiation transport calculations have been carried out to determine the radiation field inside the Port Cell through 3-D neutrons and gamma maps. Nuclear heating induced by neutrons and photons and the absorbed dose during the ITER lifetime on steel and silicon have been estimated in the Port Cell area, in order to assess the nuclear loads that the diagnostics and related electronic components have to withstand. Furthermore, the impact of the gamma-rays emitted by neutron-activated water circulating in the Primary Heat Transfer System have been evaluated on the Port Cell environment: 3-D maps of the gamma flux, nuclear loads on steel/silicon during plasma operation are provided. [ABSTRACT FROM AUTHOR]

A 10 m s-pulsed NBI (Neutral Beam Injection) system for VEST (Versatile Experiment Spherical Torus) plasma heating is designed to provide a beam power of more than 0.6 MW with 20 keV H° neutrals. The VEST NBI injector is composed of 2 sets of 20 keV/25A magnetic cusp type bucket ion source, neutralizer ducts, residual ion dump, NB vessel with a cryopump, and rotating calorimeter. The position and size of these beamline components are roughly determined with geometric calculation of beam power transmission: the overall length of beamline is 1.8 m, spacing between ground grid and neutralizer of 1.0 m, and position of residual ion dump is 0.8 m downstream from the neutralizer exit. Optimizing the gas feed between ion source and neutralizer can leads to a neutralization efficiency of ∼76%. Finally, the beam power of maximum 0.6 MW can be delivered to the VEST plasma with a beam loss of 10%. [ABSTRACT FROM AUTHOR]