Cryocondensation Pump Research Articles

TCV heating and divertor upgrades

The operational range and the reactor relevance of the TCV experiments are being enhanced by two sets of major upgrades. The first includes the installation of neutral beam injection (NBI) and new electron cyclotron (EC) auxiliary heating sources, to reach ITER relevant beta values and vary the electron to ion temperature ratio. A 15–30 keV, 1 MW tangential NBI system has been operational on TCV since 2015. A second beam of 1 MW, 50–60 keV ion energy, also aligned tangentially but opposite to the first beam, is foreseen to approach beta limits, vary the applied torque through zero and probe suprathermal ion physics. For the EC power, two 0.75 MW gyrotrons at the second harmonic have been installed. The next step will add two 1 MW dual frequency gyrotrons, one of which is currently being commissioned. These heating upgrades will increase the total available power for high-density plasmas from 1.25 MW to 5.0 MW. The rest of the upgrade consists of installing an in-vessel structure to form a divertor chamber of increased closure, to reach higher neutral divertor densities and impurity compression and thereby extend TCV divertor regimes toward more reactor relevant conditions for conventional and advanced divertor configurations. Graphite gas baffles will be installed inside the TCV vessel to delineate divertor and main chamber regions. The first set of baffles features 32 tiles on the high and 64 tiles on the low-field side, with geometry guided by simulations performed using the SOLPS-ITER code. The baffles are expected to be effective for a wide range of divertor configurations, including snowflake and super-X divertors, yet maintain plasma close to the inner wall for improved passive stabilization. The baffle dimensions may be varied in the future to modify the divertor closure. Control of the plasma, neutral and impurity densities will be achieved by a combination of toroidally distributed gas injection valves and impurity seeding, and a possible addition of cryo-condensation pumps. Significant diagnostic developments will be undertaken, to better characterize the divertor plasma, measure power and particle deposition at the strike points, and, specifically, improve our physics understanding of the detachment process.

Analysis of the influence of the structure of radiation shield on its transmission probability for a cryo-condensation pump

The cryo-condensation pump used in EAST-NBI is composed of cryo-condensation panels cooled by liquid helium and radiation shields cooled by liquid nitrogen. The transmission probability of radiation shields has great influence on the performance of the cryo-condensation pump. The Monte-Carlo method is applied to simulate the trajectories of the deuterium molecules and to study the effects of the structure of the radiation shields on the transmission probability. By adding imaginary walls, the distribution of positions and flying directions of the molecules is presented. The results indicate that the uniformity of the molecules is the direct factor to influence the transmission probability.

Obtain and study of the Al O condensate with the rough surface during reactive ion deposition

Properties of the surface determine its morphology. There are various methods for obtaining morphological structures on the surface. These methods can make the surface more hard, smooth, rough, slippery. Particular attention deserves the methods of coating in a vacuum environment. They provide the formation of film coatings of with a constant elemental composition, morphological structure and properties on the surface.The paper presents the formation of coatings with rough surface, which can be used in various fields: thermal vacuum, solar energy, gas destroyers, optical coatings, electrolytic capacitors... These coatings were created by depositing aluminum on an aluminum capacitor foil in oxygen environment.The condensate of the aluminum and oxygen compounds can form rough (porous, spongy) structures where there is no crystalline phase of Al2O3, but the amount of oxygen in such condensates corresponds to the oxygen content in Al2O3. The formation of such condensates occurred in a vacuum by means of the thermionic deposition set-up equipped with pre-vacuum and cryo-condensation pumps. The technological chamber of the set-up was pumped out to the pressure of the residual gases of 5×10‑4 Pa. In the process of experiment oxygen was injected into the chamber. The oxygen pressure was supported constant within 10‑1 ‑ 10‑3 Pa. Evaporation of aluminum was carried out from a copper water-cooled crucible using a 10 kW thermocathode electronic gun with a direct incandescent cathode. The water-cooled high-frequency inductor was placed above the crucible to create plasma of vapor of aluminum and oxygen. It was supplied by a high-frequency generator with a pulse duration of 0.5 μs and a repetition rate of 880 kHz. To carry out thermionic deposition, a negative bias voltage of 500 V was applied to the substrate holder. The coatings were deposited on a smooth aluminum capacitor foil with a thickness of 50 μm and a silicon substrate КДБ -10 (100) in same technological cycle. Coatings with a thickness of 3 - 16 microns were obtained in the experiment.The resulting samples were studied using scanning electron microscope, X-ray emission analysis with electronic excitation was carried out and the specific capacity of samples of aluminum foil coated with Al‑O condensate was measured by an electrolytic method.So, coatings of Al‑O condensate were obtained in the work, whose structures were formed to a large extent under the influence of oxygen and depended on its concentration in the process chamber during condensation.The condensate structures varied from the crystalline to large and small-globular with increasing oxygen pressure. The oxygen pressure is the main control parameter in the formation of Al‑O condensate microstructures. Only the diffraction lines of the aluminum phase are recorded on the X-ray diffraction patterns of the condensate films. A decrease in the intensity of the X-ray lines and their significant expansion are observed with increasing oxygen content in the condensate. The Al‑O condensate is a complex mix of the crystalline phase of aluminum and amorphous Al‑O, in which the diffractograms do not observe the oxide-phase lines of Al2O3. Probably, aluminum and oxygen form complex cluster formations on the condensation surface. The specific capacity of samples С0 measured in an electrolyte at a bias voltage equal to zero according to the standard method had a maximum of the parameter PO2/Vk. = 2,1×10‑1 Pa×min./μm, related to the increase in the number of centers of chemical activity that can interact with the electrolyte. At thicknesses of a coating of 3 - 16 microns the specific capacity of a surface has increased in 2 - 10 times, and in some cases in 250, in comparison with a smooth surface of an aluminum capacitor foil.Ref. 7, fig. 5.

Operational characteristics of NBI cryo-condensation pumps

Operational characteristics of NBI cryo-condensation pumps

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.

Thermal Analysis and Optimization for Cryopanel of NBI Cryocondensation Pump

Excellent vacuum performance ensures a high beam transmission efficiency of the neutral beam injector (NBI). The vacuum performance is mainly determined by the cryoperformance of the cryopanel of the cryocondensation pumps which are the main vacuum pumps of NBI. In order to optimize the cryoperformance, the requirements for the temperature distribution and the heat load of the cryopanel are analysed and the factors that affect the cryopanel's temperature distribution are studied. The results indicate that the temperature difference of the cryopanel can be reduced by fabricating the cryopanel with high thermal conductivity material, increasing its thickness and cutting the distance between the two upward cooling pipes. The results may be applied to a cryopanel cooled by forced flow liquid helium.

Engineering of Cryopump for Neutral Beam Injection

Neutrals beam injection (NBI) has proven to be a very effective method for plasma heating. A set of positive-ion-based NBI system is being designed, manufactured and tested at ASIPP. The aim of this study was to ascertain the most effective cryocondensation pump structure for the hydrogen NBI system. The parameter design and mechanical design were made to determine the optimum parameters and structure of the cryocondensation pump. The lowest pressure of 7.2 × 10−6 Pa was achieved in the vacuum chamber, which indicated that this type of liquid helium cryocondensation pump could meet the requirement of the NBI system quite well.

Supercritical helium as a coolant for DIII–D cryopumps

The DIII–D tokamak uses three cryocondensation pumps for plasma density control. Each DIII–D pump consists of a series of concentric stainless steel tubes assembled together. The two phase (TP) helium was chosen for DIII–D because it is available at the DIII–D site and is used for neutral beam (NB) and other applications. The three pumps inside DIII–D have performed as expected for the last several years. Superconducting machines under construction, such as KSTAR and SST-1 have supercritical (SC) helium available on site. The device operator would prefer to use it for cooling the cryocondensation pumps. The design of the DIII–D cryocondensation pump is simple, robust, inexpensive and reliable. This study was undertaken to evaluate if the supercritical helium can be used as a coolant for the GA design of the cryocondensation pump.

Fluorescence spectroscopy of silver clusters formed in rare gas droplets

The Pick Up technique allows continuous formation of high density metal cluster beams in the otherwise hardly accessible size range Me2 to about Me50. With an apparatus based on the use of cryo-condensation pumps, Ar as inert gas for production of the host clusters by adiabatic expansion and silver as metal we demonstrate how the various source parameters influence the composition and mean size of the resulting cluster distributions. The analysis in the gas phase by means fluorescence spectroscopy allows to conclude that an Ar shell encapsulates the metal clusters.

A cryocondensation pump for a high-density atomic hydrogen jet target

A large cryocondensation pump for an intense atomic hydrogen beam was designed, fabricated, and tested; its compact design allowed a total copper cryopanel area of about 15 m 2. The cryopanels operated at about 2.6 K. For an atomic hydrogen beam of up to 3.2 × 10 18 atoms s −1, the measured pumping speed was about 1.2 × 10 7 l s −1, which is 4.2 × 10 26 atoms Torr −1 s −1.

Development of cryosorption pump for neutral beam injector

Abstract A high speed gas pumping system is required to minimize the reionization loss of neutral beams in a neutral beam injector; until now the beam line design has made use of a condensation cryopump system. The system becomes more expensive as size increases and needs high maintenance and has a high operation cost. Instead of the cryocondensation pump a cryosorption pump is considered for the beam line. This paper describes the development of a high speed cryosorption pump for a neutral beam injector. A module test has been carried out to have a fundamental data base. A cryosorption pump with a pumping speed of about 300 m3 s−1 has been designed on the basis of the result of the module test and has been applied on the neutral beam injector of JIPP T-IIU Tokamak. In this paper, the design and the experimental results are discussed.

Particle Exhaust Characteristics of an In-Vessel Cryopump Used in DIII-D Diverted Plasmas

A particle exhaust scheme, employing a cryocondensation pump in the outboard divertor region under a baffle, has been installed and operated in the DIII-D tokamak. The cryopump provides toroidally symmetric pumping at a rate of 30000 to 40000 l/s for D{sub 2} in the pressure range of 1 to 4 mTorr. Pressures in the 2 to 3 mTorr range are routinely observed under the baffle. This translates to particle exhaust throughputs of nearly 100 Torr l/s. The exhaust throughput could be controlled by selecting the position of the plasma strike region with respect to the opening to the baffle chamber. The pump has been used quite effectively for plasma density control. 19 refs., 9 figs., 1 tab.

Pumping characteristics of a cryopump with Ar sorbent in He and in a D2/He mixture

The He generated as a result of D/T burn in a fusion reactor must be exhausted from the plasma to avoid fuel dilution effects. In view of this, transport and exhaust studies of He in fusion plasmas are getting increasing attention in recent years. In fusion plasmas, the exhaust gas will be a combination of D2 and He, with He forming only a small fraction (about 10%). The cryosorption pumping characteristics of pure He and a mixture of D2 and He (90% D2) have been investigated using a cryosorption pump with condensed layers of Ar as sorbent. A cryocondensation pump cooled by liquid He at 4.3 K, and located in the outboard divertor region of the DIII‐D tokamak, was used for the experiment. The investigation was conducted in a pressure regime that is relevant for particle exhaust from fusion plasmas. The experiment revealed that (1) the cryosorption pumping speed of pure He drops precipitously if the Ar/He ratio falls below about 20; (2) the pumping speed for He in a D2/He mixture decreases in an exponential manner with the amount of D2 pumped; (3) increasing the thickness of Ar in the range of 1–12 μm had little effect on the pumping speed for He in a D2/He mixture; and (4) for a pumping surface coated with a thick (≳2 μm) layer of Ar, surrounded by a radiation shield having a transparency factor of about 6, a He pumping speed in the range of 15–25 m3 s−1 m−2 in the mTorr pressure range for a pulse duration of about 5 s can be obtained after pumping about 80 Torr l of D2.

Effect of low density H-mode operation on edge and divertor plasma parameters

We present a study of the impact of H-mode operation at low density on divertor plasma parameters on the DIII-D tokamak. The line-average density in H-mode was scanned by variation of the particle exhaust rate, using the recently installed divertor cryo-condensation pump. The maximum decrease (50%) in line-average electron density was accompanied by a factor of 2 increase in the edge electron temperature, and 10% and 20% reductions in the measured core and divertor radiated power, respectively. The measured total power to the inboard divertor target increased by a factor of 3, with the major contribution coming from a factor of 5 increase in the peak heat flux very close to the inner strike point. The measured increase in power at the inboard divertor target was approximately equal to the measured decrease in core and divertor radiation.

Conceptual design of a neutral beam system for a next step tokamak

Abstract The conceptual design of a neutral injector for ITER(EDA) presented here is based on a combination of established technology and the European negative ion development programme. The injector is based on negative ions as the energy required is more than 250 keV, above which the production of neutral beams from positive ions becomes unrealistic on grounds of efficiency. It is proposed to have a negative ion source at a high negative potential, with the ions accelerated up to the ground potential of the neutralizer via a SINGAP electrostatic accelerator. In the initial design a gas neutralizer is proposed, but a future upgrade using a plasma neutralizer is clearly possible. The charged fraction of the beam emerging from the neutralizer will be deflected electrostatically onto conventional water-cooled dump plates, and the neutral beam will fall onto a long pulse copper calorimeter downstream of the residual ion dump during beamline commissioning. The necessary low gas pressure in the beamline is maintained by cryo condensation pumps, which will require overnight regeneration.

Two phase liquid helium flow testing to simulate the operation of a cryocondensation pump in the DIII-D tokamak

A liquid helium-cooled cryocondensation pump has been installed in the DIII=D tokamak fusion energy research experiment at General Atomics. The pump is located within the tokamak vacuum chamber beneath the divertor baffle plates and is utilized for plasma density and contamination control. Two-phase helium flows through the pump at 5 to 10 g/s utilizing the beat transfer and constant temperature characteristics of boiling liquid helium. The pump is designed for a pumping speed of 32,0001/s. Extensive testing was performed with a prototypical pump test fixture. Several pump geometries (simple tube, coaxial flow plug, and coaxial slotted insert) were tested, in an iterative process, to determine which was the most satisfactory for stable cryocondensation pumping. Results from the different tests illustrating the temperature distribution and flow characteristics for each configuration are presented.

Particle Exhaust Scheme Using an In-Vessel Cryocondensation Pump in the Advanced Divertor Configuration of the DIII-D Tokamak

A particle exhaust scheme using a cryocondensation pump in the advanced divertor configuration of the DIII-D tokamak is described. In this configuration, the pump is located inside a baffle chamber...

A Cryocondensation Pump for the DIII-D Advanced Divertor Program

A cryocondensation pump was designed for the baffle chamber of General Atomics DIII-D tokamak and will be installed in the fall of 1992. The purpose of the pump is to study plasma density control by pumping of the divertor. The pump is toroidally continuous, approximately 10 m long and located in the lower outer corner of the vacuum chamber of the machine. It consists of a 1 m2 liquid helium-cooled surface surrounded by a liquid nitrogen-cooled shield to limit the heat load on the helium-cooled surface. The liquid nitrogen-cooled surface is surrounded by a radiation/particle shield to prevent energetic particles from impacting and releasing condensed water molecules. A thermal enhancement coating was applied to the nitrogen shell to lower the maximum temperature of the shell. The coating is non-continuous to keep the toroidal electrical resistance high. The whole pump is supported off the water-cooled vacuum vessel wall. Supports for the pump were designed to accommodate the thermal differences between the 4K helium surface, the 77 K nitrogen shells, and the 300 K vacuum vessel supporting the pump and to provide a low heat leak structural support. Disruption loading on the pump was analyzed and a finite element structural analysis of the pump was completed.A testing program was completed to evaluate coating techniques to enhance heat transfer and emissivity of the various surfaces. Fabrication tests were performed to determine the best method of attaching the liquid nitrogen flow tubes to their shield surfaces and to determine the best alternative to fabricating the different shells of the pump. A prototype sector of the pump was built to verify fabrication and assembly techniques.

Cryopumping of atomic hydrogen

The pumping speed for the cryopumping of an atomic hydrogen beam was measured. Measurements were made for cryocondensation, cryosorption, and differential pumping. The pumping speed for atomic hydrogen was observed to be much smaller than the pumping speed for molecular hydrogen. It is believed that this is due to the energy released during the recombination of the atomic hydrogen.

Conceptual design of a closed vacuum pumping system using turbomolecular pump for fusion reactor

Abstract As a vacuum pumping system for a D—T fusion reactor, a closed type of pumping system which does not exhaust DT fuel gas and removes only impurity gas including helium ash is proposed. The closed system is defined as a closed vacuum circuit in which only DT fuel gas can be circulated and refueled to the reactor. The basic components in the system consist of turbomolecular pumps, dry vacuum pumps, cryocondensation pumps and gas reservoirs. Helium ash removal is affected by use of getter materials for DT gas. Other impurity gas is pumped with 50 K cryocondensation pumps, and at the regeneration phase the pumped gas is dealt with by a tritium clean-up system. The detailed design of the system is described and the possibility of the system for practical use is discussed.