Cryopump Research Articles

Thermal Transpiration Behavior of Hydrogen Isotopes in Cryogenic Pump System

Cryogenic pumps are convenient machinery for handling hydrogen isotopes in fusion fuel processing systems. Not only ultra-vacuum pumps working at such as liquid helium or hydrogen temperature but also sorption pumps using liquid nitrogen are applicable. The latter type is suitable to a means of temporary storage and/or transportation between process units. In the cryogenic pumping, there is an issue that the pressure in a pump is not necessarily identical with the pressure measured in its evacuating vessel in equilibrium, because of an effect of thermal transpiration. Thermal transpiration is important in adsorption isotherms which characterize cryo-sorption pumping. In this study, the effect of thermal transpiration was investigated for He, H2 and D2 in a closed system consisting of a volume at room temperature and a volume at cryogenic temperature, connected together by a simple narrow pipe or a pipe containing baffle plates as thermal shield. The effect is here described by an equation of nominal-distribution function with respect to the pressure measured in the hot end volume. Defining an effective inner diameter for the latter pipe, agreement is shown of characteristic curves for geometrically different pipes. The error-functional curves for H2 and D2 are agreed together. The curve for He is also perfectly approximated but with a constant shift. This shift results in the difference of a molecular property among He, H2 and D2.

Collisionless gas flows over a flat cryogenic pump plate

This article concerns collisionless gas flows over a flat cryogenic pump plate with a specific sticking probability. It presents exact density, velocity, temperature, and pressure solutions which are useful in determining the plate sticking probability. At any point off the plate, the local velocity distribution function (VDF) consists of several pieces of Maxwellian VDFs, one is characterized by free stream flow properties and the others by plate surface properties. Integrating the VDFs with different moments leads to these exact solutions, which are further validated by simulations with the direct simulation Monte Carlo (DSMC) method. We use these solutions to derive several useful expressions, based on special measured flow field properties at specific locations off the plate, to evaluate the pump sticking probability. Also, the exact solutions complement past studies of aerodynamic coefficients and heat transfer rate for collisionless gas flowing over a flat plate. They explicitly express the physical and geometrical factors. Evaluations of those solutions are much faster than DSMC simulations. This study can find other useful applications, e.g., cold gas spray for thin film depositions inside a vacuum chamber, and spacecraft plume impingement estimations.

Experimental study on the double-evaporator thermosiphon for cooling HTS (high temperature superconductor) system

A cryogenic thermosiphons is an efficient heat transfer device between a cryocooler and a thermal load that is to be cooled. This paper presents an idea of thermosiphon which contains two vertically-separated evaporators. This unique configuration of the thermosiphon is suitable for the purpose of cooling simultaneously two superconducting bearings of the HTS (high temperature superconducting) flywheel system at the same temperature. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure condition. The interior thermal condition of the double-evaporator thermosiphon was examined in detail during its cool-down process according to the internal thermal states. The double-evaporator thermosiphon has operated successfully at steady-state operation under sub-atmospheric pressure. At the heat flow of 10.6 W, the total temperature difference of the thermosiphon was only 1.59 K and the temperature difference between the evaporators was 0.64 K. The temperature difference of two evaporators is attributed to the conductive thermal resistance of the adiabatic section between the evaporators. The method to reduce this temperature difference has been investigated and presented in this paper. The proper area selection of condenser, evaporator 1, and evaporator 2 was studied by using thermal resistance model to optimize the performance of a thermosiphon. The superior heat transfer characteristic of the double-evaporator thermosiphon without involving any cryogenic pump can be a great potential advantage for cooling HTS bulk modules that are separated vertically.

Tritium gas flow dynamics through the source and transport system of the Karlsruhe tritium neutrino experiment

The source and transport system of the Karlsruhe tritium neutrino experiment (KATRIN) must provide a significant reduction in tritium flow and gas density. It comprises a 10 m long windowless source tube, where the tritium gas is injected, followed by a differential pumping system and a cryogenic pumping system. The primary challenge of the analysis is that the gas flow changes from a viscous flow regime inside the source tube to a transitional flow regime at the first pumping stage, and to a molecular flow regime at the remaining stages of the differential pumping system and further downstream. A strong molecular beaming effect must be considered. This article presents the results of calculations of gas density and flow for the complete source and differential pumping system. It is shown that a total flow-rate reduction factor of 1.4×10−8 can be attained, which is one of the prerequisites to achieve extreme-high vacuum conditions in the spectrometers used in the downstream end of the experiment.

Test particle Monte Carlo study of the cryogenic pumping system of the Karlsruhe tritium neutrino experiment

The cryogenic pumping system (CPS) is the last active tritium pumping system of the Karlsruhe tritium neutrino (KATRIN) experiment, in which the neutrino mass will be directly measured from the tritium beta decay. The spectrometer systems downstream to the CPS are required to be tritium-free. The high pumping speed of the CPS is to be provided by condensed argon frost at 3–3.5K on the surfaces of the beamline tubes. In this unique design the beta particles can be simultaneously guided to the spectrometers by the superconducting magnets around the beamline tubes. In addition, nonevaporable getter (NEG) strips or NEG coated tubes are to be used in the last two sections of the CPS to secure this tritium-free boundary in case of a cryogenic failure event. In this article, the properties of the CPS are studied by the test particle Monte Carlo method, in which the effects of the argon frost sticking coefficient, the geometry of the beamline tube and the bend angle between two beamline sections are addressed. The tritium flow rate reduction factor and the adsorption distribution profile are estimated. The performance of the NEG section at different geometries is also presented.

Redesign of Cryogenic Pump in Liquefied Natural Gas Storage Tank Considering Thermal Effect

Redesign of Cryogenic Pump in Liquefied Natural Gas Storage Tank Considering Thermal Effect

First Tritium Results of the KATRIN Test Experiment Trap

The TRAP experiment (TRitium Argon frost Pump) has been built at the Tritium Laboratory Karlsruhe (TLK) as a test rig for the Cryogenic Pumping Section (CPS) of the KArlsruhe TRItium Neutrino Experiment (KATRIN). TRAP employs a heterogeneous layer of pre-condensed argon to adsorb hydrogen isotopes at ~ 4.2 K. This paper presents results obtained in the first three tritium experiments with TRAP.

Recent advances to enhance low Earth orbit space simulation

Accurate ground-based simulation of low Earth orbit (LEO) conditions experienced by a satellite has proven to be a challenge. Recent progress that has been made toward the development of means for simulating portions of the LEO environment will be reviewed. A satellite in LEO has a speed relative to the atmosphere of approximately 8km∕s. The neutral atmospheric molecules exchange momentum upon collision with the surfaces of the satellite, leading to drag, lift, and moments, but ground facilities still have trouble simulating pure beams of ground state atmospheric gases at this speed. The most important atmospheric species, atomic oxygen, collides with ram-direction satellite surfaces with a relative energy of 5eV. The solar UV spectrum in LEO is a composite of many emission lines and continuum, which must be simulated using special lamp systems. Thruster plumes and outgassing molecules result in a contamination atmosphere close to the spacecraft surface. Energetic atomic oxygen atoms in the presence of solar UV radiation and contamination gases can produce synergistic effects that result in many chemical reactions on or in the vicinity of the outer satellite surfaces. These reactions can lead to structural or operational damage to various satellite components, such as a reduction in the effectiveness of thermal control paints, cleanliness of optical lenses, and the reduction of the output of solar cells. Several techniques for generating beams of 5eV atomic oxygen in the ground state will be reviewed as well as special diagnostic instrumentation developed to detect atomic oxygen. These are combined in space simulation chambers for a more complete study of materials degradation. Some electric thrusters exit directly to the vacuum of space. Their exhaust and plume simulation presents unique vacuum chamber pumping problems. Specially designed cryogenic pumps to simulate the conditions that these electric thrusters will experience in orbit will be described. Reference to inventories of space simulation chambers will be given.

The vacuum systems of ITER

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 requested pressure levels. The presence of hydrogen (including the radioactive isotope tritium) and exclusion of other gases defines the parameters of fusion vacuum systems. 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, characterized by high magnetic and radiation fields, excellent availability and maintainability and, especially, 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 and the status of the programme in view of the imminent manufacturing phase is described in this paper.

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.

Application of PLC to dynamic control system for liquid He cryogenic pumping facility on JT-60U NBI system

The control system of the cryogenic facility in the JT-60 NBI system has been replaced by employing the PLC (Programmable Logic Controller) and SCADA (Supervisory Control And Data Acquisition) system. The original control system was constructed about 20 years ago by specifying the DCS (Distributed Control System) computer to deal with ∼400 feedback loops. Recently, troubles on this control system have increased due to its age-induced deterioration. To maintain the high reliability of the cryogenic facility, a new control system has been planned with the PLC and SCADA systems. Their attractive features include high market availability and cost-effectiveness, however, the use of PLC for such a large facility with ∼400 feedback loops has not been established because of insufficient processing capability of the early PLC. Meanwhile, the recent progress in the PLC enables to use the FBD (function block diagram) programming language for 500 function blocks. By optimizing the function blocks and connecting them in the FBD language, the feedback loops have been successfully replaced from DCS to PLC without a software developer. Moreover, an oscillation of the liquid He level, which often occurs during the cooldown mode of the cryopumps, can be automatically stabilized by easily adding a new process program in the PLC. At present, the new control system has worked well.

Research activities of DC superconducting power transmission line in Chubu University

A experiment of a DC Superconducting power transmission line using HTS conductor was started in Chubu University, Japan in autumn 2006. The first cooling down began in October 2006. The coolant is liquid nitrogen, and the cooling system used a cryogenic cooler and cold pump. The operation temperature is the range of 72 K - 80 K. The power cable has a total length of 20 m, and composed of thirty-nine Bi-2223 HTS tape conductors with critical current approximately100 A. The power cable achieved a 2.2 kA. The insulation voltage of the cable is 20 kV. In order to reduce the heat leakage and to avoid the current imbalance in the HTS tapes, we installed the Pelteir Current Lead (PCL) for each of the nineteen HTS tapes of the cable, with remaining twenty HTS tapes connected individually by the usual copper leads (CCL). Depending on the visual observation, and the measurement of temperatures of the current leads, the heat leakage of the PCL is lower than that of CCL. We installed a current transformer for each individual HTS tape conductor circuit, and measured the current of each HTS tape conductor. We measured the critical current of each HTS tape after the cable was installed into the cryostat, and degradation was not observed. Since the variation of the current in each tape is less than 10%, we eliminated the problem of current imbalance. Computational Fluid Dynamics is used to estimate the pressure drop, showing that the straight-tube cryostat has the advantage against the bellows- and corrugated-tube cryostats to reduce the pressure drop of the circulation of coolant. We proposed further to use the siphon for circulating the coolant in order to reduce the circulation losses and costs. We proposed that the voltage of the system be kept below 30 kV in order to use low cost power inverters. This choice can increase the storage energy of the power transmission line itself if we do not use a co-axial cable system because of it allows use of large current. And the magnetic energy of power grid is estimated to 4.5MJ/km for ±30 kA.

TRAP—a cryo-pump for pumping tritium on pre-condensed argon

The TRitium Argon frost Pump experiment (TRAP) has been built at the Tritium Laboratory Karlsruhe (TLK) as a test rig for the Cryogenic Pumping Section (CPS) of the KArlsruhe TRItium Neutrino Experiment (KATRIN). TRAP employs a heterogeneous layer of pre-condensed argon to adsorb hydrogen isotopes at ∼ 4.2 K . This article covers the technical setup of the TRAP experiment and presents first results obtained in a commissioning run with deuterium.

Bismuth Hollow Cathode for Hall Thrusters

B ISMUTH has several qualities that make it well suited for development as a Hall-thruster propellant. When compared with more conventional propellants such as xenon, bismuth holds significant advantages from both an energetics (lower ionization energy) [1] and cost standpoint. In addition, there are significant ground-test-facility cost savings, because bismuth does not require the use of cryogenic pumps. Unlike traditional propellants, bismuth is solid at room temperature; thus, the exhausted bismuth solidifies on the room-temperature vacuum chamber walls, and consequently the entire vacuum chamber becomes an effective pumping surface. With this in mind, operating a high-power bismuth Hall thruster would require only enough pumping speed to keep up with facility outgassing and minor vacuum leaks. However, there are some difficulties that need to be addressed when using a condensable propellant. Some of the issues include sustaining elevated temperatures for bismuth evaporation, regulating bismuth mass flow, mechanical limitations inherent with using refractory metal components, and bismuth plating of thruster and spacecraft components. Recently, there have been three new programs to develop bismuth Hall thrusters, with the first successful demonstration occurring in the spring of 2005 [2–4]. In this work, the bismuth thruster was operated using a xenonLaB6 cathode. The encouraging results of the bismuth thruster motivated a study to examine the feasibility of an all-bismuth system using a bismuth cathode. In addition to all of the physical and economical gains, it would be advantageous to incorporate a bismuth cathode to eliminate the need for multiple propellant supplies on an eventual flight unit. In 2005, a functioning prototype bismuth cathode was developed and a limited number of operating characteristics were reported [5]. The primary goals of the present research were to evaluate the operating characteristics of a bismuth LaB6 cathode at different mass flow rates, compare bismuth data with xenon and krypton performance, and to reduce the amount of power required for cathode operation.

Tritium migration along the cryopumping section

The transport section of the Karlsruhe Tritium Neutrino experiment (KATRIN) must provide the dramatic reduction of tritium flow and gas density from the end of a 10-m-long windowless gaseous tritium source throughout several stages of a differential pumping system. The final stage of this section, the cryogenic pumping section (CPS) based on pumping of tritium on argon frost at 4.5 K, should provide the flow ratio between inlet and outlet in the range of 107. Cryosorbed tritium may decay, emitting a few keV electrons. These electrons in their turn cause the electron-stimulated desorption of cryosorbed argon and tritium, which is redistributed along the CPS (migration process). This effect was modeled with the use of the method of angular coefficients. The main result is that the tritium migration process does not affect the CPS performance at KATRIN for a given inlet flow. Meanwhile, if the flow chosen is larger, the migration effect could be dominant.

A circulating hydrogen ultra-high purification system for the MuCap experiment

The MuCap experiment is a high-precision measurement of the rate for the basic electroweak process of muon capture, μ −+p→n+ ν μ . The experimental approach is based on an active target consisting of a time projection chamber (TPC) operating with pure hydrogen gas. The hydrogen has to be kept extremely pure and at a stable pressure. A Circulating Hydrogen Ultra-high Purification System was designed at the Petersburg Nuclear Physics Institute (PNPI) to continuously clean the hydrogen from impurities. The system is based on an adsorption cryo pump to stimulate the hydrogen flow and on a cold adsorbent for the hydrogen cleaning. It was installed at the Paul Scherrer Institute (PSI) in 2004 and performed reliably during three experiment runs. During several months long operating periods the system maintained the hydrogen purity in the detector on the level of 20 ppb for moisture, which is the main contaminant, and of better than 7 and 5 ppb for nitrogen and oxygen, respectively. The pressure inside the TPC was stabilized to within 0.024% of 10 bar at a hydrogen flow rate of three standard liters per minute.

액체질소를 이용한 터보펌프 인듀서의 수력성능시험

A cryogenic test facility has been developed to perform inducer and pump tests using liquid nitrogen. Performance tests of a turbopump in the maximum 50ton-thrust class can be performed with cryogenic fluid in the facility which operates at a temperature around -l96℃ with the rotational speed up to 30,000rpm To verify the reliability of the cryogenic pump test facility, hydraulic performance tests of an inducer were accomplished, and their results were compared with the result from a water test. The results confirm the reliability of the cryogenic test facility, and it is expected to contribute for on-going development of a turbopump for liquid rocket engines.

Diagnosis of cryogenic pump-motor systems using vibration and current signature analysis

In general, to send out natural gas via a pipeline network across the nation in LNG terminal, high-pressure cryogenic pump supply highly compressed LNG to high-pressure vaporization facilities. The Number of cryogenic pumps determined the send-out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high vibration at cryogenic pumps-motor system in LNG terminal, vibration spectrum analysis and motor current signature analysis have been performed together. Through the analysis, motor rotor bar problems are estimated by the vibration analysis and confirmed by the current analysis. So, it is demonstrated through the case study in this paper, how performing vibration analysis and current signature analysis together can reliable diagnosis rotor bar problems in pump-motor system.

Development of a method for liquid xenon purification using a cryogenic centrifugal pump

We are developing a new type of photon detector for an experiment to search for muons decaying into a positron and a gamma ray. In this experiment, the photon detector will utilize liquid xenon (Xe) as the scintillation material. Good transparency of the liquid Xe is required in order to gain the highest performance out of the detector. Impurities like water and oxygen must be removed efficiently for this purpose. We have developed a new purification system, dedicated to removing water from liquid Xe, by employing a cryogenic centrifugal pump and molecular sieves. The performance of the system is described in this article.

Optimization Calculations for the KATRIN Magnet System

The Karlsruhe Tritium Neutrino experiment aims to measure the neutrino mass to extreme high precision by measuring the energy spectrum of the electrons of the tritium decay. A highly specialized magnet system is needed to transport the electrons from tritium beta decay along a more than 70 meter long path with differential and cryogenic pumping sections, pre- and main spectrometer to the detector plane. Each magnet group does not only provide a guiding field for the electrons but also serves additional purposes. The intermediate sections between magnet groups as well as the magnet design itself needs to be analyzed very carefully in order to work properly in the whole KATRIN experiment. This paper describes optimization calculations performed to achieve this goal