Cryopump Research Articles

Solutions to mitigate heat loads due to electrons on sensitive components of ITER HNB beamlines

The operation of neutral beam injectors for plasma heating and current drive in a fusion device provides challenges in the thermal management of beamline components. Sensitive components such as the cryogenic pumps at beamline periphery shall be protected from the heat flux due to stray electrons. These are emitted by the negative ion accelerator or generated along the beamline by interaction of fast electrons, ions or atoms with background gas and surfaces. In this article the case of the ITER Heating Neutral Beam (HNB) and its test facility MITICA is discussed, for which the beam parameters and the required pulse length of one hour is a major leap forward with respect to the present experience with neutral beam systems. The engineering solutions adopted for effective cryopump protection against the heat load from electrons are described. The use of three-dimensional numerical simulations of particle trajectories in the complex geometry of the beamline was needed for the quantitative estimations of the heat loads. The presented solutions were optimized to minimize the impact on gas pumping and on the functionality of other components.

Experimental and Numerical Research on the Diversion Effect of a Conic Flame Deflector for a Lunar Module Ascent Stage

AbstractThe diversion effect of a conic flame deflector for a lunar module ascent stage is investigated experimentally and numerically. Eighteen tests were performed in a vacuum chamber mounted with a liquid helium cryogenic pump using a scaled engine and models. The experimental results indicate that the conic flame deflector can guide the exhaust gas away from the ascent stage model more effectively than a plate; meanwhile, the conic flame deflector can create a reverse torque, which helps to correct the deflection of the ascent stage model. Finally, the experimental results show that the reverse torque changes with the distance and angle between the ascent stage model and the conic flame deflector model. Numerical simulations have been done with the computational fluid dynamics and direct simulation Monte Carlo (CFD/DSMC) method, and the numerical results are in good agreement with the experimental results. The numerical results reveal that the reason for the above phenomena is shock waves. An expansio...

Process Design of Cryogenic Distribution System for CFETR CS Model Coil

The superconducting magnet of Central Solenoid (CS) model coil of China Fusion Engineering Test Reactor (CFETR) is made of Nb3Sn/NbTi cable-in-conduit conductor (CICC), and operated by forced-flow cooling with a large amount of supercritical helium. The cryogenic circulation pump is analyzed and considered to be effective in achieving the supercritical helium (SHe) circulation for the forced-flow cooled (FFC) CICC magnet. A distributed system will be constructed for cooling the CFETR CS model coil. This paper presents the design of FFC process for the CFETR CS model coil. The equipment configuration, quench protection in the magnet and the process control are presented.

Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces

Global gas balance experiments at ASDEX Upgrade (AUG) and JET have shown that a considerable fraction of nitrogen injected for radiative cooling is not recovered as N2 upon regeneration of the liquid helium cryo pump. The most probable loss channels are ion implantation into plasma-facing materials, co-deposition and ammonia formation. These three mechanisms are investigated in laboratory and tokamak experiments and by numerical simulations. Laboratory experiments have shown that implantation of nitrogen ions into beryllium and tungsten leads to the formation of surface nitrides, which may decompose under thermal loads. On beryllium the presence of nitrogen at the surface has been seen to reduce the sputtering yield. On tungsten surfaces it has been observed that the presence of nitrogen can increase hydrogen retention. The global nitrogen retention in AUG by implantation into the tungsten surfaces saturates. At JET the steady state nitrogen retention is increased by co-deposition with beryllium. The tokamak experiments are interpreted in detail by simulations of the global migration with WallDYN. Mass spectrometry of the exhaust gas of AUG and JET has revealed the conversion of nitrogen to ammonia at percent-levels. Conclusions are drawn on the potential implications of nitrogen seeding on the operation of a reactor in a deuterium–tritium mix.

B-19 極低温ポンプ開発のための超電導コイルを用いた能動型磁気軸受の特性評価

B-19 極低温ポンプ開発のための超電導コイルを用いた能動型磁気軸受の特性評価

A compact cryogenic pump

A centrifugal cryogenic pump has been designed at Argonne National Laboratory to circulate liquid nitrogen (LN2) in a closed circuit allowing the recovery of excess fluid. The pump can circulate LN2 at rates of 2–10L/min, into a head of 0.5–3m. Over four years of laboratory use the pump has proven capable of operating continuously for 50–100days without maintenance.

Fuel cycle for a fusion neutron source

The concept of a tokamak-based stationary fusion neutron source (FNS) for scientific research (neutron diffraction, etc.), tests of structural materials for future fusion reactors, nuclear waste transmutation, fission reactor fuel production, and control of subcritical nuclear systems (fusion–fission hybrid reactor) is being developed in Russia. The fuel cycle system is one of the most important systems of FNS that provides circulation and reprocessing of the deuterium–tritium fuel mixture in all fusion reactor systems: the vacuum chamber, neutral injection system, cryogenic pumps, tritium purification system, separation system, storage system, and tritium-breeding blanket. The existing technologies need to be significantly upgraded since the engineering solutions adopted in the ITER project can be only partially used in the FNS (considering the capacity factor higher than 0.3, tritium flow up to 200 m3Pa/s, and temperature of reactor elements up to 650°C). The deuterium–tritium fuel cycle of the stationary FNS is considered. The TC-FNS computer code developed for estimating the tritium distribution in the systems of FNS is described. The code calculates tritium flows and inventory in tokamak systems (vacuum chamber, cryogenic pumps, neutral injection system, fuel mixture purification system, isotope separation system, tritium storage system) and takes into account tritium loss in the fuel cycle due to thermonuclear burnup and β decay. For the two facility versions considered, FNS-ST and DEMO-FNS, the amount of fuel mixture needed for uninterrupted operation of all fuel cycle systems is 0.9 and 1.4 kg, consequently, and the tritium consumption is 0.3 and 1.8 kg per year, including 35 and 55 g/yr, respectively, due to tritium decay.

An experimental study on heat transfer between supercritical carbon dioxide and water near the pseudo-critical temperature in a double pipe heat exchanger

Supercritical carbon dioxide (SCO2) is a promising working fluid for the cryogenic refrigeration, air-condition and heat pump systems. The present study sets up a SCO2–water test loop to study the heat transfer performance of SCO2 in a double pipe heat exchanger. The effects of SCO2-side pressure, mass flux and buoyancy force as well as water-side mass flux are investigated. It is found that the total and SCO2-side heat transfer coefficients reduce as the SCO2-side pressure increases. The peak total and SCO2-side heat transfer coefficients appear at a higher temperature than the pseudo critical temperature. The water-side mass flux has a larger effect on the total heat transfer coefficient compared to the SCO2-side mass flux in the studied cases. The contribution of buoyancy force to the heat transfer performance is large at the small SCO2-side mass flux and it becomes smaller as the SCO2-side mass flux increases. The SCO2-side pressure and water-side mass flux have little effect on the buoyancy force. A heat transfer correlation that includes the effect of buoyancy force is obtained by fitting the experimental data with genetic algorithm.

Experimental and CFD analyses of a thermal radiation shield dimple plate for cryogenic pump application

Large customized cryogenic pumps are used in fusion reactors to evacuate the plasma exhaust from the torus. Cryopumps usually consist of an active pumping surface area cooled below 5 K and shielded from direct outer thermal radiation by plates cooled at 80K. In nuclear fusion applications, cryopumps are exposed to excessively high heat fluxes during pumping operation, and follow-up regeneration cycles with rapid warm-up and cool-down phases. Therefore, high cryogenic operational mass flows are required and thus pressure drop and heat transfer characteristics become key issues for the design of the pump cryogenic circuits. Actively cooled dimple plates are a preferred design solution for the thermal radiation shield. A test plate with a rhomb pattern of dimples has been manufactured and tested in terms of pressure drop with a dedicated test facility using water. In the present work, computational fluid dynamics (CFD) models of the test dimple plate have been performed, and computed pressure drops have been compared to experimental results. Despite the complexity of the geometry, a good agreement with the experimental results was found. Then, the validated CFD approach has been further extended to relevant operation conditions, using gaseous helium at cryogenic temperature as working fluid. The resulting pressure drop and heat transfer characteristics are finally presented.

Transmission of electrons inside the cryogenic pumps of ITER injector.

Large cryogenic pumps are installed in the vessel of large neutral beam injectors (NBIs) used to heat the plasma in nuclear fusion experiments. The operation of such pumps can be compromised by the presence of stray secondary electrons that are generated along the beam path. In this paper, we present a numerical model to analyze the propagation of the electrons inside the pump. The aim of the study is to quantify the power load on the active pump elements, via evaluation of the transmission probabilities across the domain of the pump. These are obtained starting from large datasets of particle trajectories, obtained by numerical means. The transmission probability of the electrons across the domain is calculated for the NBI of the ITER and for its prototype Megavolt ITer Injector and Concept Advancement (MITICA) and the results are discussed.

A pump-free boosting system and its application to liquefied natural gas supply for large ships

This study proposes a new boosting system that is capable of increasing the pressure of a low-temperature liquid such as LNG (liquefied natural gas) and supplying it continuously to a ship engine without using cryogenic pumps. The system consists of two boosters, each of which is equipped with a mini-vaporizer and regulating valves. The two boosters operate alternately to ensure a continuous supply of the low-temperature pressurized liquid. The operating philosophy is that the mini-vaporizer of the first booster increases the internal pressure and supplies the pressurized liquid to the engine while the other booster is filled with the low-pressure fresh liquid, waiting for its turn to supply the liquid to the engine. This boosting system is applied to an LNG fuel gas supply system. Dynamic process simulation is conducted to demonstrate its operational feasibility. Assessment of operation availability and life-cycle cost analysis are also conducted to show that the proposed system offers better reliability and cost-effectiveness than the conventional pump system.

Fabrication of enriched 174Yb2O3 thin targets on carbon and tantalum backings

Making multiple thin targets by the evaporation method, without breaking the vacuum of the chamber minimizes the time and the amount of the enriched target material. In the present work the making of two thin isotopic 174Yb2O3 targets: one of thickness ~763μg/cm2 on a tantalum backing foil (thickness ~3.25mg/cm2) and the other of ~125μg/cm2 on carbon backing foil (thickness ~25μg/cm2) are reported. The targets were made by the evaporation method using a cryogenic pump based Ultra High Vacuum (UHV) chamber available at the Inter University accelerator center (IUAC), Delhi. In this activity only 49mg of 99.9% enriched 174Yb2O3 target material has been used.

TECHNEX & FIVES CRYOMEC: ПОСТАВКИ ЭФФЕКТИВНЫХ НАСОСОВ ДЛЯ ЖИДКИХ КРИОПРОДУКТОВ

Cryogenic pumps are widely used in a variety of cryogenic systems. From their quality and reliability of depend on indicators systems in which they belong. A renowned manufacturer of high-efficiency pumps and safety is the company «Fives Cryomec AG» (Allschwil, Switzerland). Given the characteristics of five main series of pumps. In these use innovative developments company, for example, helps to prevent the occurrence cavitation. Explains the experience of cooperation of this company with a multi-specialty an engineering company «Technex Ltd.» (Kiev, Ukraine), which has supplying pumps a number of consumers in the CIS and other countries. Pumps included in cryogenic systems, constructed «Technex Ltd.». In this company have a group of mechanical engineers, certified «Fives Cryomec AG» for the installing of pumps and service work at customer sites.

A Dimensionless Scaling Parameter for Thermal Effects on Cavitation in Turbopump Inducers

To characterize cryogenic pump performance, at least one parameter in addition to flow coefficient and cavitation number is required. This parameter arises because the heat of vaporization and other physical parameters change along the saturation line of liquids and results in a thermal effect on cavitation that has been observed and studied by previous researchers over a range of operating conditions and working fluids. These previous efforts have defined both dimensionless and dimensional parameters governing thermal effects in pumps. In the present work, a dimensionless parameter (DB) scaling thermal effects in a cavitating pump across different tip diameters, rotational speeds, and working fluids is derived using a model of bubble growth in a time-varying pressure field. Although the derivation is somewhat different than others have used, the result is similar and in some cases identical to that of others. Careful testing is carried out to experimentally validate this parameter with (deaerated) variable temperature water and with variable pump speed. The results show that within the accuracy of the data, the same head fall-off curve is obtained when either the water temperature or the pump speed is used to set the DBs. This suggests the proposed parameter can thermally scale cryogenic pumping conditions for suction performance when testing in hot water. Also examined is the effect of thermodynamics on inducer cavitation instabilities. The quasi-steady, dynamic environments at the pump inlet are compared in cold and superheated water. The cavitation instabilities of the test inducer are found to be dramatically changed by thermal effects. These findings emphasize the importance of considering both fluid mechanical and thermal scaling when designing a test program to evaluate the suction performance of a cryogenic pump.

Design, fabrication, and testing of fiber Bragg grating sensors for cryogenic long-range displacement measurement

It is essential to measure the shrinkage/expansion and positioning/aligning of magnets and to control valve displacement which plays a vital role in experiments like the Karlsruhe tritium neutrino experiment beam tube and Cryo pumps. Hence, a displacement sensor which, over a long working range, can be operated under extreme environmental conditions needs to be developed. Fiber Bragg gratings (FBG) have been considered to be excellent sensor elements useful for a variety of applications. This paper will discuss a long range displacement sensors based on fiber Bragg gratings for cryogenic temperature applications. The cryo pump inlet valve control requirements have been taken as example specifications for sensor design. To achieve the development goal, a proper signal transducer and sensor package were designed. A study of the strain transmission of surface-bonded FBG was conducted. The influence of bonding thickness and bonding length was reported. The design, fabrication, and performance were tested at low temperature of around 77K. The sensor performance was found to be satisfactory at both room temperature and 77K and linearly for long-range displacement of 550mm with 14pm/mm sensitivity and 0.142mm accuracy.

Integration of cryopump instrumentation for SST-1 NBI

A positive ion neutral injector (PINI) capable in delivering 5MW (55kV, 90A) ion beam power is being operated for SST-1 neutral beam injection (NBI). The production and neutralization of the ion beams in the injector require a gas throughput of 20 torr I/s in the plasma box and 50–100 torr I/s in the neutralizer section. It is necessary to maintain operating pressure of vessel at 10−5 torr to reduce the re-ionization loss of beam within tolerable limits. Conventional Turbo molecular pumps cannot maintain this vacuum level at required gas feed rate so two cryo condensation pumps are being operated to achieve require vacuum in vessel. In order to monitor and optimize the performance of cryopumps, it is necessary to measure the temperature at various locations in LN2 and LHe path. It is also required to monitor the level of LHe and LN2 in cryopumps. Several temperature and level sensors are mounted at various places in cryopumps and integrated with PLC and SCADA based control system.

An economic evaluation of operating expenditures for LNG fuel gas supply systems onboard ocean-going ships considering availability

This paper proposes a methodology for economic evaluations of liquefied natural gas fuel gas supply (LNG–FGS) systems. To evaluate the economics of various LNG–FGS systems, expected operating expenditures during long-term voyages were compared, including the loss from venting boil-off gas (BOG) to prevent overpressurisation of the fuel tank, penalties for venting BOG, expenses for consuming marine diesel oil when LNG–FGS systems are unavailable, and expenses for electricity consumption. A secondary objective was to compare the economics of various LNG–FGS systems for large-sized ships. An analysis demonstrated that the comparative operational expenditures vary considerably within various design options. Three LNG–FGS systems were compared. As a case study, an Aframax tanker (a highly popular crude carrier) was chosen, and the actual voyage scenario between Ulsan and Antwerp was used for calculating expenses. The results indicated that group FP-P (fully pressurised-type storage tank with cryogenic pump) provides a profit of approximately 7 MUS$ per 25 yrs compared to group UP-P (unpressurised-type storage tank with cryogenic pump); conversely, group FP-P incurs a loss of approximately 5.4 MUS$ per 25 yrs compared to group FP-N (fully pressurised-type storage tank with vapour-generating unit). Nevertheless, group FP-N is valuable for small-sized tanks because the vapour-generating unit requires high energy consumption during an extended initial time to raise pressure. In conclusion, group FP-P is the most economical system if it can compensate for approximately 5.4 MUS$ in capital expenditure and maintenance costs. The proposed methodology reflects the availability of necessary equipment and the results of process dynamic simulation in an actual voyage scenario.

Characteristics of the positive ion source at reduced gas feed.

The neutral beam injector of steady state superconducting tokamak (SST1-NBI) at IPR is designed for injecting upto 1.7 MW of neutral beam (Hº, 30-55 keV) power to the tokamak plasma for heating and current drive. Operations of the positive ion source (PINI or Plug-In-Neutral-Injector) of SST1-NBI were carried out on the NBI test stand. The PINI was operated at reduced gas feed rate of 2-3 Torr l/s, without using the high speed cryo pumps. Experiments were conducted to achieve a stable beam extraction by optimizing operational parameters namely, the arc current (120-300 A), acceleration voltage (16-40 kV), and a suitable control sequence. The beam divergence, power density profiles, and species fractions (H(+):H2(+):H3(+)) were measured by using the diagnostics such as thermal calorimetry, infrared thermography, and Doppler shift spectroscopy. The maximum extracted beam current was about 18 A. A further increase of beam current was found to be limited by the amount of gas feed rate to the ion source.

Feasibility analysis and application design of a novel long-distance natural gas and electricity combined transmission system

This paper proposed a novel long-distance combined transmission system, in which LNG (liquefied natural gas) is transported in the pipeline and electricity is transmitted through a high-temperature superconducting cable refrigerated by LNG. Through this system, electricity and LNG could be transmitted simultaneously with high efficiency. This paper analyzed the theoretical feasibility of the proposed system and studied the effects of several key parameters on energy transmission loss. The analysis results show that the loss rate of LNG transportation system decreases with the increase of pipe diameter. There is an economic flow velocity with which the minimum loss rate of the LNG transportation system could be achieved. The total loss rate of the combined system decreases with the increase of the transmission capacity ratio of electricity to LNG. Through an application computation, it is found that the transmission efficiency of the combined system can reach up to 96%, and the loss rate is just 58% of that of the conventional systems. Moreover, the power wasted induced by the heat leakage occupies 85.2% of the total power wasted at the cryogenic refrigeration and pump station, which may suggest improving the insulation performance is significant to the transmission efficiency of the combined system.

Recursive approach of EEG-segment-based principal component analysis substantially reduces cryogenic pump artifacts in simultaneous EEG–fMRI data

Electroencephalography (EEG) data simultaneously acquired with functional magnetic resonance imaging (fMRI) data are preprocessed to remove gradient artifacts (GAs) and ballistocardiographic artifacts (BCAs). Nonetheless, these data, especially in the gamma frequency range, can be contaminated by residual artifacts produced by mechanical vibrations in the MRI system, in particular the cryogenic pump that compresses and transports the helium that chills the magnet (the helium-pump). However, few options are available for the removal of helium-pump artifacts. In this study, we propose a recursive approach of EEG-segment-based principal component analysis (rsPCA) that enables the removal of these helium-pump artifacts. Using the rsPCA method, feature vectors representing helium-pump artifacts were successfully extracted as eigenvectors, and the reconstructed signals of the feature vectors were subsequently removed. A test using simultaneous EEG–fMRI data acquired from left-hand (LH) and right-hand (RH) clenching tasks performed by volunteers found that the proposed rsPCA method substantially reduced helium-pump artifacts in the EEG data and significantly enhanced task-related gamma band activity levels (p=0.0038 and 0.0363 for LH and RH tasks, respectively) in EEG data that have had GAs and BCAs removed. The spatial patterns of the fMRI data were estimated using a hemodynamic response function (HRF) modeled from the estimated gamma band activity in a general linear model (GLM) framework. Active voxel clusters were identified in the post-/pre-central gyri of motor area, only from the rsPCA method (uncorrected p<0.001 for both LH/RH tasks). In addition, the superior temporal pole areas were consistently observed (uncorrected p<0.001 for the LH task and uncorrected p<0.05 for the RH task) in the spatial patterns of the HRF model for gamma band activity when the task paradigm and movement were also included in the GLM.