Cryopump Research Articles

The Laplace Project: An integrated suite for preparing and transferring atom probe samples under cryogenic and UHV conditions.

We present sample transfer instrumentation and integrated protocols for the preparation and atom probe characterization of environmentally-sensitive materials. Ultra-high vacuum cryogenic suitcases allow specimen transfer between preparation, processing and several imaging platforms without exposure to atmospheric contamination. For expedient transfers, we installed a fast-docking station equipped with a cryogenic pump upon three systems; two atom probes, a scanning electron microscope / Xe-plasma focused ion beam and a N2-atmosphere glovebox. We also installed a plasma FIB with a solid-state cooling stage to reduce beam damage and contamination, through reducing chemical activity and with the cryogenic components as passive cryogenic traps. We demonstrate the efficacy of the new laboratory protocols by the successful preparation and transfer of two highly contamination- and temperature-sensitive samples—water and ice. Analysing pure magnesium atom probe data, we show that surface oxidation can be effectively suppressed using an entirely cryogenic protocol (during specimen preparation and during transfer). Starting with the cryogenically-cooled plasma FIB, we also prepared and transferred frozen ice samples while avoiding significant melting or sublimation, suggesting that we may be able to measure the nanostructure of other normally-liquid or soft materials. Isolated cryogenic protocols within the N2 glove box demonstrate the absence of ice condensation suggesting that environmental control can commence from fabrication until atom probe analysis.

Transient characteristics and performances of passive recirculation system for liquid rocket engine precooling

This paper presents a numerical study on the transient cooldown process of liquid rocket engine by a passive recirculation precooling system. An unsteady mathematical model is developed by considering the interaction of heat dissipation from solid structure with the time- and location- dependent two-phase flow, and the predicted values show good agreements with experiments. The results demonstrate the roles of boiling regimes, and reveal distinct thermal and flow characteristics from single pipe cooldown and bleed precooling. The liquid rewetting front propagates along the flow direction in the vertical feed line and the turbopump related horizontal pipes, with the exception that opposite propagation appears in the upward recirculation line and causes inverted axial temperature distributions and faster cooling of exit. In terms of the time for meeting the turbopump operation requirement, large-diameter recirculation line and high liquid level in the ullage discharging condition are advantageous to the precooling of cryogenic pump, while subcooled liquid and high liquid level in liquid discharging condition prolong the cooldown process and are undesirable. The dependence of cooldown time on subcooling degree, relative liquid level and recirculation line diameter can be described by linear, cubic and exponential functions, respectively.

Time-dependent simulation of the flow reduction of D2 and T2 in the KATRIN experiment

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the effective electron anti-neutrino mass with an unprecedented sensitivity of 0.2 eV/c2, using β-electrons from tritium decay. Superconducting magnets will guide the electrons through a vacuum beamline from the windowless gaseous tritium source through differential and cryogenic pumping sections to a high resolution spectrometer. At the same time tritium gas has to be prevented from entering the spectrometer. Therefore, the pumping sections have to reduce the tritium flow by at least 14 orders of magnitude. This paper describes various simulation methods in the molecular flow regime used to determine the expected gas flow reduction in the pumping sections for deuterium (commissioning runs) and for radioactive tritium. Simulations with MolFlow+ and with an analytical model are compared with each other, and with the stringent requirements of the KATRIN experiment.

Thermodynamic Analysis on an Integrated Liquefied Air Energy Storage and Electricity Generation System

For an integrated liquefied air energy storage and electricity generation system, mathematical models of the liquefied air energy storage and electricity generation process are established using a thermodynamic theory. The effects of the outlet pressure of the compressor unit, the outlet pressure of the cryogenic pump, the heat exchanger effectiveness, the initial air temperature and pressure before throttling on the performances of the integrated liquefied air energy storage, and the electricity generation system are investigated, using the cycle efficiency and liquid air yield ratio as the evaluation indexes. The results show that if the compressor outlet pressure is raised, both the compression work and the expansion work increase, but because the expansion work increases more slowly, the cycle efficiency of the system gradually decreases. Increasing the cryogenic pump outlet pressure and heat exchanger effectiveness can significantly increase the cycle efficiency of the system; the higher the air pressure and the lower the air temperature before throttling, the greater the liquid air yield after expansion, and the higher the cycle efficiency. The theoretical analysis models and research results can provide a reference for the development of an integrated system of liquefied air energy storage and electricity production, as well as for the development of medium-capacity energy storage technology.

Сравнение методов повышения всасывающей способности в криогенном насосе методом численного моделирования

Сравнение методов повышения всасывающей способности в криогенном насосе методом численного моделирования

Research on a Superconducting Magnetic Bearing System for Submerged Cryogenic Disk Motor-Pump

There are some disadvantages in conventional cryogenic liquid pumps (CLPs) with mechanical bearings, such as difficult lubrication and short working life. In this paper, we propose a new structure of CLP-submerged cryogenic disk motor-pump with superconducting magnetic bearing (SMB). The impeller and the rotor of the disk motor are combined as the suspension rotor of the disk motor-pump. The suspension rotor which is supported by SMB system, rotates frictionlessly with self-stabilized. The SMB system includes a radial-type SMB, an axial-type permanent magnet bearing, and an axial flux disk motor. Theoretical calculations and experimental measurements of levitation forces in the SMB system are carried out. The levitation force of radial-type SMB is calculated by using H -formulation finite-element model in COMSOL. The kinetic model of the suspension rotor is established to ensure the force balance and torque balance. The results demonstrate the feasibility of the proposed submerged cryogenic disk motor-pump with SMB.

Assessment of the JT-60SA divertor cryopump performance

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 D2 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.

Investigation on the lubricity of self-lubricating ball bearings for cryogenic turbine pump

Abstract The lubricity of newly designed self-lubricating 70-mm-bore angular contact ball bearings was tested using a special bearing tester under thrust load of about 20 kN and speed of about 20000 r/min in liquid nitrogen. The test bearing was characterized with the pure polytetrafluoroethylene (PTFE) retainer coupled with the Ag-based lubricant film initially deposited on bearing raceways. After running for 1200 and 2400 s respectively, the states of the PTFE transfer films on the surfaces of the balls and raceways as well as the wear state of the Ag-based solid lubricant film for each tested bearing were analyzed mainly by scanning electron microscopy and X-ray photoelectron spectroscopy. The results indicated that good lubricating conditions were obtained for all tested bearings. The newly designed self-lubricating ball bearing could run steadily for more than 2400 s under high speed, heavy load and at cryogenic temperature conditions. The formation and the evolution of PTFE transfer films with bearing operation are mainly discussed according to the relevant analysis.

Quantitative measurement of outgassing and degassing rate for various materials used in cryogenic pumps

Outgassing from materials is a principal impediment for creating and maintaining clean and ultrahigh-vacuum environments. Data about out-gassing rates of different materials is very important for designing any vacuum system operating in ultra- high vacuum regime. Gas load due to outgassing from different materials determines the size (capacity) of pumps and order of vacuum that can be achieved in the system. Data on outgassing rates of materials are available in literature but not for all materials especially cryogenic pump materials at the required temperature of operation. To know the outgassing and degassing rate of such materials an experimental system was set up. The facility is having base outgassing rate of ∼ 5x10-12 mabr-l/s-cm2 measured through American Vacuum Society (AVS) recommended standard practices. The ultimate vacuum achieved was ∼5 x10-9 mbar having a sample chamber volume of 8 liters. Development of cryogenic pump involves selection of many materials like sorbents, black coatings, adhesive, sealant and support materials. They are selected based on their performance under UHV conditions especially minimum out-gassing during pre-evacuation and known degassing rate while regeneration. During reactivation and regeneration the cryo-surface carrying the adsorber bed is heated up to temperatures in the range of ∼150 deg C to activate the sorbent for the better cryoumping effect. Thermal outgassing studies of various samples including activated carbons, Al2O3-TiO2 coating, indigenous cryo-adhesives, indium wire and G-10 were carried out and are discussed in the paper. The measurements were quantitative and will be helpful for estimating outgassing and degassing gas loads during pumping and bake-out conditions.

Developing Control of Cryo-Pump Test Cold-Box System: Some Investigations

Tokamak, a leading contender of practical fusion reactor, is a popular system using powerful superconducting magnets to confine plasma in a toroidal space to conduct controlled thermo-nuclear reactions required for fusion power research. Tokamak uses state-of-the-art superconducting magnet system requiring specialized cryogenic cooling, which is achieved and maintained by a forced-flow of helium at supercritical state. Supercritical helium mass flow rate as high as 2.21 kg/s at the cryogenic temperature of ~ 4.6 K is necessary not only to obtain cryogenic conditions required for these toroidal superconducting magnet system, but also to regulate cryo-conditions against severe thermal shocks and disturbances due to exothermic plasma reactions and other operational variations. In prior work, the largest cryogenic centrifugal pump was developed to meet and obtain such special cryogenic conditions with various normal and off-normal operating modes. However, such special cryo-pump needs to be tested first rigorously in a special, custom-designed cryogenic test set-up before using them in actual Tokamak systems. A dedicated test-system, called Test Cold-Box, is proposed and developed to test such large cryogenic centrifugal pump. The test-system consists of a liquid helium sub-cooler bath, heat-exchangers, control valves, heaters, etc. In our work, a suitable multi-loop control scheme for the Test Cold-Box is also proposed. Classic multi-loop PID control scheme with classic Ziegler-Nichols and modern IMC tuning have been evaluated using ASPEN HYSYS® simulation environment. The paper describes this Test Cold-Box system including cryo-pump along with suitable controls, and its operational analysis in ASPEN HYSYS® simulation environment.

Levitation and rotation characteristics of bearingless motor at cryogenic temperature and pump application

Levitation and rotation characteristics of bearingless motor at cryogenic temperature and pump application

Correction of Dynamic Characteristics of SAR Cryogenic GTE on Consumption of Gasified Fuel

When the gas turbine engines (GTE) NK-88 were developed for liquid hydrogen and NK-89 for liquefied natural gas, performance of the systems with a turbo-pump unitary was improved and its proved without direct regulation of the flow of a cryogenic fuel, which was supplied by a centrifugal pump of the turbo-pump unit (TPU) Command from the “kerosene” system. Such type of the automatic control system (SAR) has the property of partial “neutralization” of the delay caused by gasification of the fuel. This does not require any measurements in the cryogenic medium, and the failure of the centrifugal cryogenic pump does not lead to engine failure. On the other hand, the system without direct regulation of the flow of cryogenic fuel has complex internal dynamic connections, their properties are determined by the characteristics of the incoming units and assemblies, and it is difficult to maintain accurate the maximum boundary level and minimum fuel consumption due to the influence of a booster pressure change. Direct regulation of the consumption of cryogenic fuel (prior to its gasification) is the preferred solution, since for using traditional liquid and gaseous fuels this is the main and proven method. The scheme of correction of dynamic characteristics of a single-loop SAR GTE for the consumption of a liquefied cryogenic fuel with a flow rate correction in its gasified state, which ensures the dynamic properties of the system is not worse than for NK-88 and NK-89 engines.

Improvement of Superconducting Linear Motor for Cryogenic Pump

Improvement of Superconducting Linear Motor for Cryogenic Pump

A highly reliable cryogenic mixing pump with no mechanical moving parts

This paper presents the design and preliminary test results of a novel cryogenic mixing pump based on magnetocaloric effect. The mixing pump is developed to enable long-term cryogenic propellant storage in space by preventing thermal stratification of cryogens in storage tanks. The mixing pump uses an innovative thermodynamic process to generate fluid jets to promote fluid mixing, eliminating the need for mechanical pumps. Its innovative mechanism uses a solid magnetocaloric material to alternately vaporize and condense the cryogen in the pumping chamber, and thus control the volume of the fluid inside the pumping chamber to produce pumping action. The pump is capable of self-priming and can generate a high-pressure rise. This paper discusses operating mechanism and design consideration of the pump, introduces the configuration of a brassboard cryogenic pump, and presents the preliminary test results of the pump with liquid nitrogen.

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.

SNS Cryogenic Test Facility Kinney Vacuum Pump Commissioning and Operation at 2 K

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) has built and commissioned an independent Cryogenic Test Facility (CTF) in support of testing in the Radio-frequency Test Facility (RFTF). Superconducting Radio-frequency Cavity (SRF) testing was initially conducted with the CTF cold box at 4.5 K. A Kinney vacuum pump skid consisting of a roots blower with a liquid ring backing pump was recently added to the CTF system to provide testing capabilities at 2 K. System design, pump refurbishment and installation of the Kinney pump will be presented. During the commissioning and initial testing period with the Kinney pump, several barriers to achieve reliable operation were experienced. Details of these lessons learned and improvements to skid operations will be presented. Pump capacity data will also be presented.

Commissioning of cryogenic system for China Spallation Neutron Source

China Spallation Neutron Source(CSNS) cryogenic system provides supercritical cryogenic hydrogen to neutron moderators, including a helium refrigerator, hydrogen loop and hydrogen safety equipment. The helium refrigerator is provided by Linde with cooling capacity of 2200 W at 20 K. Hydrogen loop system mainly includes cryogenic hydrogen pipes, hydrogen circulator cold-box and accumulator cold-box. Cryogenic hydrogen pump, ortho-para convertor, helium-hydrogen heat-exchanger, hydrogen heater and accumulator are integrated in hydrogen circulation cold-box, and accumulator cold-box. Hydrogen safety equipment includes safety valves, rupture disk, hydrogen sensor, flame detector and other equipment to ensure that cryogenic system in dangerous situations will go down, vents, or takes other measures. The cryogenic system commissioning work includes four steps. First, in order to test the refrigerating capacity of refrigerator, when acceptance testing, refrigerator internal heater was used as thermal load. Second, using simulation load as heat load of moderator, hydrogen loop use helium instead of hydrogen, and cooled down to 20 K, then re-warming and test the leak detection of hydrogen loop system. Third, base on the step 2, using hydrogen as working medium, and optimized the control logic. Forth, cryogenic system with the moderators joint commissioning. Now, cryogenic system is connected with the moderators, and the forth step will be carried out in the near future.

Experimental investigation of passive thermodynamic vent system (TVS) with liquid nitrogen

Thermodynamic vent system (TVS) is an attractive technology to maintain an allowable pressure level of a cryogenic propellant storage in a spacecraft under micro-gravity condition. There are two types of TVS; active or passive. In this paper, the passive TVS which does not utilize a cryogenic liquid circulation pump is experimentally investigated with liquid nitrogen and numerically analyzed by thermodynamic and heat transfer model. A cylindrical copper tank, which is 198 mm in inner diameter and 216 mm in height, is utilized to suppress a thermal-stratification effect of inside cryogenic fluid. A coil heat exchanger, which is 3 m in length and 6.35 mm in outer diameter, and a fixed size orifice of which diameter is 0.4 mm are fabricated to remove heat from the stored fluid to the vented flow. Each vent process is initiated at 140 kPa and ended at 120 kPa with liquid nitrogen fill levels which are 30%, 50% and 70%, respectively. In the numerical model, the fluid in the tank is assumed to be homogeneous saturated liquid-vapor. Mass and energy balance equations with heat transfer conditions suggested in this research are considered to calculate the transient pressure variation in the tank and the amount of heat transfer across the heat exchanger. We achieve the average heat rejection rate of more than 9 W by TVS and conclude that the passive TVS operates satisfactorily. In addition, the prediction model is verified by experimental results. Although the model has limitation in providing accurate results, it can surely predict the tendency of pressure and temperature changes in the tank. Furthermore, the model can suggest how we can improve the heat exchanger design to enhance an overall efficiency of passive TVS. Moreover, the performance of passive TVS is compared with other cryogenic vent systems (direct vent system and active TVS) by suggested performance indicator.

Исследование кавитационных явлений в криогенном насосе методом численного моделирования

Исследование кавитационных явлений в криогенном насосе методом численного моделирования

Results of the first Cool-down of the KATRIN Cryogenic Pumping Section

The Karlsruhe Tritium Neutrino (KATRIN) experiment uses the kinematics of tritium β-decay to determine the effective neutrino mass with a sensitivity of mν = 200meV/c2 (90% C.L.). In order to measure the decay electrons it is important to guide them adiabatically from the source to the spectrometer. In addition the diffusion of tritium into the spectrometers from the source has to be reduced by 14 orders of magnitude as tritium inside the spectrometers would induce additional background. For these two tasks the transport and pumping section were constructed. The last part of this section is the Cryogenic Pumping Section (CPS), which aims to reduce the residual gas flow by more than seven orders of magnitude. For this a cold argon frost surface, with a ≈ 2 m2) area that is maintained at 3 K, will be prepared to adsorb the incoming tritium molecules.Before the whole KATRIN setup will be connected together the performance of CPS will be tested on its own. This poster presents the measurement results of the first cool-down of the CPS.This work was supported by the GRK1694 and the Helmholtz Association.