Cryopump Research Articles

Cryogenic viscous pump analysis based on hemisphere model

Cryogenic viscous pump (CVP) is also known as fore pump that are mainly designed for the separation of hydrogen isotopes from the helium during the process of regeneration of cryo- pumps. This model will determine the amount of hydrogen which is extracted by supercritical helium cooled pump. It also includes flow rates and inlet conditions that are related to the hydrogen gas flow. This hemisphere model (HM) determines the amount and location which are extracted by the pump as the function of time. During the development of this model the calibration check done for its results, later it has been compared with the measurements of CFP prototype. At the result of this model, it will demonstrate the quantity of hydrogen which is very sensitive to the inlet temperature that is found outside of the Cryopump. Finally, this model will represent the efficient outcome.

The World's First Test Facility That Enables the Experimental Visualization of Cavitation on a Rotating Inducer in Both Cryogenic and Ordinary Fluids

Abstract It is well known that cavitation breakdown, which is a phenomenon in which the pump head suddenly drops with a decrease in the inlet cavitation number, occurs in turbopumps. Especially in cryogenic pumps, cavitation breakdown occurs at a lower inlet cavitation number than that of ordinary fluids such as water. This phenomenon is referred to as a thermodynamic effect, as Stepanoff reported. The thermodynamic properties of the working fluid affect the sizes of the cavitation elements, which affect cavitation breakdown; therefore, experimental flow visualization is an effective approach to realize a more efficient and more reliable cryogenic pump. In 2010, the author and colleagues developed the world's first test facility to enable the visualization of cavitation on a rotating inducer in both cryogenic and ordinary fluids. At that time, only two reports on the flow visualization of a rotating cryogenic impeller had been published: one on flow visualization in liquid hydrogen by NASA in 1967 and the other on flow visualization in liquid nitrogen by the Japan Aerospace Exploration Agency (JAXA) in 2010. The present facility employs a triple-thread helical inducer with a diameter of 65.3 mm and a rotation rate of up to 8000 rpm, with both liquid nitrogen and water available as working fluids. Unsteady visualization experiments for cavitation on an inducer in liquid nitrogen and water have revealed the characteristics of tip vortex cavitation, backflow vortex cavitation, and cavitation element size based on comparisons between cryogenic fluids that exhibit a stronger thermodynamic effect and ordinary fluids such as water.

Leveraging bipolar effect to enhance transverse thermoelectricity in semimetal Mg2Pb for cryogenic heat pumping

Toward high-performance thermoelectric energy conversion, the electrons and holes must work jointly like two wheels of a cart: if not longitudinally, then transversely. The bipolar effect — the main performance restriction in the traditional longitudinal thermoelectricity, can be manipulated to be a performance enhancer in the transverse thermoelectricity. Here, we demonstrate this idea in semimetal Mg2Pb. At 30 K, a giant transverse thermoelectric power factor as high as 400 μWcm−1K−2 is achieved, a 3 orders-of-magnitude enhancement than the longitudinal configuration. The resultant specific heat pumping power is ~ 1 Wg−1, higher than those of existing techniques at 10~100 K. A large number of semimetals and narrow-gap semiconductors making poor longitudinal thermoelectrics due to severe bipolar effect are thus revived to fill the conspicuous gap of thermoelectric materials for solid-state applications.

System scheme design of electric expander cycle for LOX/LCH4 variable thrust liquid rocket engine

With the development of both cryogenic and motor pump technologies, the cryogenic variable thrust liquid rocket engines that using motor pumps have gained considerable attention. However, the heavy battery limits its performance if engine operates for high thrust. To address this challenge, the electric expander cycle system scheme for variable thrust liquid rocket engines is creatively proposed and designed. Subsequently, the system parameters are calculated based on mass and energy conservation with chamber heat transfer considered. As well, the distribution of this novel system state parameters is investigated. Further, a comparison is conducted between the electric expander cycle system, electric pump, and expander cycle systems. The comparison results demonstrate that this innovative system scheme has advantages of simple structure, low battery mass, convenient throttling, and high reusability. The system state parameters distribution indicates that the feed system can achieve the propellants' pressurization requirements throughout the designed 5:1 throttle range, which suggests the feasibility of this system scheme. Moreover, although the proposed system requires more battery power than does the turbine, the turbine power proportion in the entire system increases with thrust. However, the turbine efficiency drops steeply with a decrease in thrust, whereas the double pump efficiency presents a narrow variation range.

Design and operation of the in-vessel cryopump for the new upper divertor in ASDEX Upgrade

To study alternative divertor configurations in the ASDEX Upgrade (AUG) tokamak a new upper divertor, Div-IIo, with two in-vessel coils and a cryopump (CP) will be installed in 2022. For efficient density control in the new divertor configuration during plasma discharges, the CP has to guarantee an effective pumping speed for deuterium (D2) of at least Seff = 15 m3/s. The CP will be installed behind the inner divertor with a toroidal pumping gap of width 30 mm between the inner and outer divertor plates. It consists of 7 modules with a major radius of R = 1.2 m and a total active length of 5.4 m.To investigate reactor relevant D2-He gas mixtures during upper single null discharges, the liquid helium cryo-panels are coated with activated charcoal as cryosorbent.For quick regeneration of the charcoal from the accumulated gases, heating wires on the cryo-panels are installed.To reduce the pumping speed during high density discharges, an in-vessel cryo valve between two modules is installed. The pumping speed can be reduced by 35%.The cryo-panels operate with saturated liquid helium (LHe) at a temperature of 4.4 K. The thermal radiation shield consisting of reflector and chevron-baffle operate with saturated liquid nitrogen (LN2) at 80 K. To supply the new upper CP with LHe and LN2 the existing LHe-LN2-supply of the lower CP will be used. Therefore, an additional distributor box and a multi-channel transfer line to the upper CP have been installed in 2019.

Adoption of the ASDEX Upgrade pumping to hydrogen released by an in-vessel cryopump

Detached divertor scenarios at ASDEX Upgrade (AUG) need high gas fluxes, which are mainly pumped with the gas binding in-vessel cryopump (CP). To cope with the large quantities of hydrogen released from the CP during regeneration, a hydrogen compatible pumping system (HCPS), which is built to comply with safety regulations for explosion protection, has been built up in parallel to the already existing gas transfer pumping system (TPS). The amount of gas injected in the vacuum vessel (VV) is limited by an additional volume added to the gas inlet system. A fully automated procedure has been implemented for comprise with safety regulations. This includes daily tests of the components and communications with other relevant systems.

Simulation study of pressure change between cryogenic reservoir and pump

Supercritical hydrogen storage tanks are one of the most promising hydrogen storage technologies. When liquefied hydrogen is pressurized by a cryogenic high-pressure reciprocating pump, supercritical hydrogen is produced. The most important element for supercritical hydrogen production is the management of the net positive inlet pressure (NPIP) of the cryogenic high-pressure reciprocating pump. This paper presents a numerical analysis model for predicting the NPIP of cryogenic high-pressure reciprocating pump systems using liquid nitrogen instead of hydrogen as a medium for the preliminary study of supercritical hydrogen production. An algorithm was developed to compute the pressure of a two-phase fluid in a cryo-reservoir, where boil-off gas is generated and liquid nitrogen is reduced via a pump. The waiting time to guarantee the initial pressure and the available time of the pump were simulated, and an available pump flow rate depending on the initial pressure has been confirmed.

Vibration and speed envelope analysis of cryogenic pumps induced during cavitation

Vibration and speed envelope analysis of cryogenic pumps induced during cavitation

Neutral tritium gas reduction in the KATRIN differential pumping sections

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the effective electron anti-neutrino mass with an unprecedented sensitivity of $0.2\,\mathrm{eV}/\mathrm{c}^2$, using $\beta$-electrons from tritium decay. The electrons are guided magnetically by a system of superconducting magnets through a vacuum beamline from the windowless gaseous tritium source through differential and cryogenic pumping sections to a high resolution spectrometer and a segmented silicon pin detector. 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 more than 14 orders of magnitude. This paper describes the measurement of the reduction factor of the differential pumping section performed with high purity tritium gas during the first measurement campaigns of the KATRIN experiment. The reduction factor results are compared with previously performed simulations, as well as the stringent requirements of the KATRIN experiment.

Experimental investigation and numerical calculation of the cryogenic ejector in a liquid nitrogen system

A cryogenic ejector is designed, which can pump liquid from cold plates by high-pressure nitrogen gas. The pressure of primary flow ranges from 300 kPa to 700 kPa and the mass flow rate of jet flow is between 2 g/s and 8 g/s in the experiment. The ejector coefficient and exergy efficiency are calculated for different working conditions. Entrainment ratio reaches up to 1.8 and the maximum exergy efficiency is 0.7. The interdependence of the inlet pressure and flow rate ratio is theoretically evaluated. A model is built to obtain the thermal properties at different parts of the ejector. The errors of pressure, temperature and flow rate between computational results and experimental results are less than 3%, 1% and 15%, respectively. The cryogenic pump box systems are introduced. The exergy analyses are implemented to compare the efficiencies of traditional immersed pumps and the newly proposed cryogenic ejector. When the temperature of primary flow is less than 20 K, the exergy efficiency of the ejector pump is higher than the immersed pump, which is about 0.826. This research effectively settles the problems of the cryogenic liquid extraction and is also significant for the hydrogen energy regasification and utilization.

Long discharges in a steady state with D2 and N2 on the actively cooled tungsten upper divertor in WEST

Nitrogen (N2) will be used in ITER to enhance the radiative fraction to ∼90%, thereby cooling the edge plasma and preventing damage to the plasma-facing components. However, the reactivity of N2 with hydrogen isotopes can lead to the formation of tritiated ammonia (NT3). This should be considered in terms of the in-vessel tritium inventory, the regeneration of the cryo pumps, and the processes in the ITER de-tritiation plant. In the ‘W’ Environment in Steady-state Tokamak (WEST), a series of long L-mode discharges (∼50 s), with a constant N2 seeding from the outer strike point region has been performed on the upper actively cooled divertor. In the absence of active pumping, the N2 balance shows steady-state retention during plasma discharge, and is partially (∼35%) released in between discharges. Although a significant amount of N2( 18.65 Pa m3) has been injected, the wall still exhibited N2 pumping capabilities. Under these conditions, as long as this N2 reservoir is not saturated, there is not enough N available for the detectable threshold of ND3 formation to be reached. In these WEST experiments, no ammonia is detected during the pulse or after the pulse in the outgassing phase. These results are consistent with and complementary to the N2 seeded experiments performed in the Joint European Torus (JET) with its ITER-like wall and in the Axially Symmetric Divertor Experiment (ASDEX) upgrade.

Water pumping performance of a Cryo–TMP combination pump

There is an increasing need to systematically investigate the performance of commercial Cryo–TMP [in-line Cryogenic Water Pump (CWP) + Turbo Molecular Pump (TMP)] combination pumps. In this study, the factors affecting the pumping speed of water in a Cryo–TMP, such as the number of cold rings, dimensions, shape, etc., are systematically analyzed by Monte Carlo simulation. We constructed a test dome and a Cryo–TMP500 based on the simulation results to measure the strict effective pumping performance of the Cryo–TMP. In addition, we established a systematic measurement method for pumping performance using the Cryo–TMP500 in three experimental modes: TMP-only mode, CWP-off mode, and CWP-on mode. The results show that the water pumping speed of the Cryo–TMP500 with only one cold ring is ∼76% of that of a standalone cryopump (∼30 000 L/s) with the same opening inlet diameter; this speed is 22 550 L/s, which is in good agreement with the simulation result of 23 276 L/s. The pumping speeds for non-condensable gases (H2, N2) are 8%–19% higher than expected.

Fabrication of 128Te thin target for nuclear levels lifetime measurements

Measuring nuclear level lifetimes of pico-seconds and femto-seconds order is important for understanding typical nuclear shapes. To extract such short lifetimes, specially designed thin targets are needed. A thin isotopically enriched 128Te target of thickness ∼ 1.2 mg/cm2 on the thick backing foil of natural gold of thickness ∼ 9.8 mg/cm2 has been prepared for the Doppler shift attenuation method (DSAM) lifetime measurement. The target was made by vacuum deposition technique using the cryogenic pump based Ultra High Vacuum (UHV) chamber available at the Inter University Accelerator Centre (IUAC), New Delhi. In this activity, a specially designed indigenously developed graphite crucible with 1 mm opening was used to minimize material loss and to improve the deposition efficiency of the material. To get the desired thickness of the target, only 20 mg of isotopically enriched 128Te material was used. The quality check of the prepared foil was done by the Energy Dispersive X-ray fluorescence (EDXRF) technique.

Behaviors of Axial and Radial Electromagnetic Force for Cryogenic Disk Motor

There are axial and radial electromagnetic forces between the stator and rotor of axial flux disk motor besides the useful torque. The electromagnetic forces act on the rotor and are crucial to the stable operation in magnetic levitation applications driven by disk motor. This article concerns the behaviors of axial and radial electromagnetic forces of disk motor using for cryogenic submersible pump. It is measured experimentally that the electromagnetic properties of motor materials, including the electrical conductor and magnetic conductor materials, in room temperature (RT) and liquid nitrogen (LN2) environment. Then, the 3D finite element model (FEM) of the three-phase asynchronous disk motor in RT environment is built which is also validated by the RT experimental tests. Finally, the behaviors of axial and radial electromagnetic forces in LN2 environment are investigated using the modified FEM taking account of the effect of cryogenic environment on the motor material. It is concluded that the axial electromagnetic force decreases monotonously with the increasing air-gap thickness or the decreasing rotating speed. When the rotor exhibits radial eccentricity, there is a restoring radial electromagnetic force, trying to pull the rotor back to the central position. The radial electromagnetic force increases with the increasing rotational speed and radial eccentric displacement.

Structural-phase junctions in the system of Pt–Si during rapid thermal treatment

In recent years the interest to silicides significantly rose relating to their huge potentialities as the material of the low-Ohm contacts and interconnections of metallization of the silicon integrated circuits. In view of this the necessity appeared to consider more extensively the thermal dynamic, electric and structural peculiarities of their formation. Purpose of the work was in investigation of influence of the rapid thermal treatment on the structural –phase junctions in the system of Pt–Si during formation of platinum silicide. As samples, the Pt films were used, 43.7 nm thick and applied on the substrates of the mono-crystal silicon KEF КЭФ 0.5 with orientation (111) by means of the magnetron sputtering of the platinum target with purity of 99.95 % on the unit MRS 603 with the cryogenic pumping to the pressure not worse, than 5 · 10–5 Pa. As the operating medium, argon was used, whose purity constituted 99.933 %. Rapid thermal treatment was performed in the nitrogen medium within the temperature range from 200 to 550 °С with a step of 50 °С and the time period of 7 s. The process of interaction of platinum with silicon during treatment of the Pt–Si system was evaluated by means of the analysis of the RBS spectra. It is demonstrated, that within the temperature range of 200 °С ≤ Т ≤ 300 °С during 7 s of the rapid thermal process on the boundary of the metal film with the substrate, formation takes place of the Pt2Si layer owing to diffusion of the Pt atoms into silicon via the layer of the growing silicide. The temperature Т = 300 °С is peculiar for the complete application of the Pt film during 7 s in process of the silicide formation of the single phase system of Pt2Si. At 350 °С ≤ Т < 450 °С formation is registered of the double phase system of Pt2Si → PtSi, starting from the inter-phase boundary of Si/Pt2Si predominantly owing to the opposite diffusion of the Si atoms into the layer of Pt2Si. The temperature of the rapid thermal treatment Т = 450 °С marks formation of the thermally stable balanced structure of PtSi along the entire silicide thickness, which is 50–100 °С lower and considerably more rapid, than during the long-term balanced thermal treatment.

Electron-microscope investigations of the Pt-Si system during its rapid thermal treatment

The paper is dedicated to investigation of the influence of rapid thermal treatment on the microstructure of platinum silicide. The Pt films 43.7 nm thick were applied on the substrates of the monocrystal silicon by means of the magnetronic sputtering of platinum with the purity of 99.95 % on the МРС 603 set-up with the cryogenic pumping to the pressure not worse than 5*10-5 Pa. As an operating medium, argon was used with the purity of 99.933 %. Rapid thermal treatment of samples was performed in the thermal balance conditions by irradiating the non-working side of the wafer with the incoherent light flow in the nitrogen atmosphere during 7 s at the temperatures of 200-550 °C. The irradiation source in the set-up was represented by the quartz halogen incandescent lamps. The comparative analysis was done through the traditional long thermal treatment of the platinum films at a temperature of 550 о С for 30 min in the nitrogen atmosphere. Investigations of the platinum silicide microstructure were performed by means of the transmission electron microscopy which demonstrated that the increase in the RTT temperature initiates first the annealing of defects on the inter-grain boundaries, which is evident from the more distinct contrast from the grains, and then one can observe their growth reflecting the forming of the new phase (silicide one). Such progress of changes of the platinum silicide microstructure and of the size of the grains with the increase in treatment temperature is determined by the heat of its forming. As the Pt2Si phase forming heat is minimum and constitutes 10.4-16.8 Kkal/atom of metal, and for PtSi - 15.7-25.5 Kkal/atom of metal, then the forming of a stable PtSi structure requires a higher temperature. The authors carried out calculations of the activation energy of the diffusion synthesis of platinum silicide during rapid thermal treatment. The calculations show that it is 0.37 eV smaller, than during the long thermal treatment. This means that in this case this process is subject to acceleration related to the rupture of the silicon-silicon bonds and electron excitation in silicon under the influence of the photon flow.

Cryogenic pumps of mobile machinery

Cryogenic pumps are of particular importance in mobile machinery, in particular in wheeled and tracked vehicles. This is due to the development of hydrogen energy. In the nearest future, we will see hydrogen powered mobile cars. In this regard, it would be useful to have an up-to-date overview of modern cryogenic pumps. This article discusses the main types of cryogenic pumps, identifies problems encountered in the design and operation of pumping units and formulates the requirements for these devices. A brief overview of the most common designs of cryogenic pumps of foreign and Russian production is presented.

System scheme design for LOX/LCH4 variable thrust liquid rocket engines using motor pump

With the development of both cryogenic and motor pump technologies, the cryogenic variable thrust liquid rocket engine that uses a motor pump is becoming an advanced power system for use in various aerospace missions. In the present study, this kind of engine system scheme is originally developed. The technical metrics of the engine system are primarily obtained based on the time history of the thrust for the descent engine in the lunar process as the mission profile. Subsequently, to satisfy the general mission requirements, the system schematic diagram is designed, followed by the design of the according subassemblies. The design highlights the pressure-drop models of the pipe and the cooling channels, and the mass model of the chamber. These models may improve computation precision. In this design scheme, based on the theoretical models and derivations, the state and structural parameter distributions for the system scheme are first proposed. Moreover, the influences of the tank material type, the battery type, and other parameters on the system scheme are analyzed. The results demonstrate that the pressurization system, due to its heavy battery and motors, constitutes the largest portion of the dry mass of the entire system, which may weaken the advantages compared with the conventional turbine pump system. The second-largest portion of the dry mass is composed of the propellant tanks, due to the restricted minimum wall thickness and the use of cryogenic materials. It is reported that, during the throttling process, there is a linear relationship between the route pressure losses of the cooling channels along with pipes and the 1.75 power of the chamber pressure. Based on this analysis, a better understanding of the proposed system scheme of the LOX/LCH4 variable thrust rocket engine that uses a motor pump can be obtained.

Study of Cavitation Characteristics of a Cryogenic Pump by Computational Fluid Dynamic Methods

This article is devoted to the study of cavitation characteristics of a centrifugal cryogenic pump. Hydrodynamic simulation of the fluid flow in the wet part of the pump was carried out in order to determine the output parameters of the pump. A critical increase in the temperature of liquid helium, corresponding to the beginning of cavitation in the pump, was determined. A cavitation performance of the pump was built under given operating conditions and a critical NPSH was determined.

Dynamic simulation of ITER cryogenic system under D-T operation

Co-simulation of Cryoplant and Tokamak superconducting magnet system (referred to as Magnet) has been performed to characterize operating condition associated with control strategies. Cryoplant model, developed by EcosimPro®, consists of three identical refrigerators connected with integrated Cryoplant Termination Cold Box (CTCB) which distributes the coolant to five Auxiliary Cold Boxes (ACB) for Magnet and CryoPump (CP) cooling. Meanwhile, Magnet model, developed by Visual Modeler®, consists of Toroidal Field (TF) coil, Central Solenoid (CS), TF STructure (ST) and Poloidal Field (PF)/Correction Coil (CC). Magnet model computes thermo-hydraulic behavior of a forced-flow Supercritical Helium (SHe), with specified thermal energy deposition along the conductor in the case of Deuterium-Tritium (DT) operation as well as plasma disruption followed by the fast energy discharge of CS and PF. Global simulation of ITER cryogenic system provides its operating characteristics for complex cryogenic processes. The paper discusses the coupling of Cryoplant and Magnet models and the control strategy for Cryoplant to manage substantial dynamic heat loads.