AVS2001 Session VST-MoP: Developments in Vacuum Technology Poster Session
Monday, October 29, 2001 5:30 PM in Room 134/135
Monday Afternoon
Time Period MoP Sessions | Topic VST Sessions | Time Periods | Topics | AVS2001 Schedule
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VST-MoP-1 Optimization for the Design Parameters of Screw-typed Turbo Vacuum Pumps
R.-Y. Jou (Tung-Nan Institute of Technology, Taiwan, ROC) A rotor configuration design for the new turbo booster pump which is combined a TMP section with a spiral-groove rotor by a specially designed connecting blade and is proposed by Jou et al.1 and this new design is successfully predicted by both of CFD and DSMC methodologies simultaneously. The computed and tested results show that this pump is effective to operate in an inlet pressure range from 10-7Torr to around 10Torr with a maximum pumping speed approximately 1000L/s in free molecular regime. To investigate the inner pressures and to compare the computed data with experimental one, a measurement system also has been constructed.2 Since the aforementioned rotor geometry is composed of three different sections, a TMP section, a connecting section, and a spiral groove section, respectively, it is very difficult or even impossible to efficiently design the rotor geometry and to optimize its performance. In this paper, rotor geometries with characteristics of varied helical angle and groove depth are modeled using two design curves. These curves can be expressed by two appropriate functions, like polynomials, to meet the different pumping requirements in each different regime. The channel of the rotor is then modeled by the rule surface generated from the two characteristic design curves. Through this geometrical representation, pumping speed and compression ratio for this pump also can then be evaluated by the same computational scheme and same design procedure as previous paper. Analyses are conducted to parameters of the curves to show the optimization of the design.
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VST-MoP-2 Two Stage Water Ring Vacuum Pump with Air Ejector Theoretical Analysis and Design Calculation of Gas Flow
C.W.M. Chen (Zibo Water Ring Vacuum Pump Factory Co., Ltd., P.R. China) In this essay, the gas flow state and emergence of excitated liquid inside the ejecting tube of the two stage water ring vacuum pump with air ejector are analysed and calculated by the theories and formulas of unary isentropic flow and the characteristical dimension design calculation formulas for the ejector pump are given in accordance with the test and design experiences. It’s well known that the air ejector has the features such as simple structure, reliable work, light weight, no mechanical moving parts, i.e., no friction, etc. therefore, it’s widely used together with the water ring vacuum pump to form a vacuum air extraction pack to increase the air pumping capacity. For example, when only use the two stage water ring vacuum pump, the work situation point often used is 100-60mbar of suction pressure ,whose lowest pressure is 30~25 mbar (compensation water temperature is 15~20). when used together with the air ejector, the lowest suction pressure is 4~5 mbar. When the suction pressure is 13~15mbar, the air pumping speed is still able to reach 55~60% of the maximum pumping speed of the two stage water ring vacuum pump.this is quite favourable to the work situation which pumps corrosive gas and gas with trace impurity or much steam and requires a larger pumping speed when the suction pressure is 13~15 mbar. Hence, this kind of machine pack is widely used in chemical industry, pharmaceuticals, petrochemical, metallurgy, light industry and so on. Many factories and companies in the world all produce the machine pack formed by two stage water ring vacuum pump with air ejector. The maximum specification has already reached 60~70m3/min. for example, the pumping speed of glrd 3200 type two stage water ring vacuum pump with air ejector produced by general company in U.K. is 60 m3/min (suction pressure is 15 mbar). This essay will theoretically analyse and calcucate the gas flow in the ejector pump of such kind of vacuum air pumping machine pack and introduce the calculation ascertainment of its characteristical dimension. |
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VST-MoP-4 Cryogetter Pumping of the Channel of Neutral Beam Injector
A.N. Dranichnikov, A.A. Ivanov, V.S. Khrestolubov (Budker Institute of Nuclear Research, Russia) In 2000 at the Budker Institute of Nuclear Physics the injector of neutral hydrogen atoms for the RFX device (Padova) was created with equivalent ion beam current up to 2 A, 50 keV energy and 50 ms pulse duration. The pumping of vacuum chamber is provided by two cryogenic priming pumps with pumping speed of 20 m3/s for each of them. At full gas load about 0.53 m3/(Pa*sec) the vacuum at beam channel outlet is provided by the cryogenic pumps at a level of 4*10-4 Pa. Cryosorption by using nitrogen allows to keep up the vacuum between successive injection pulses at 1.5*10-6 Pa. Consequently the helium fluid consumption reduces. Filling liquid helium is carried out completely remotely. The design of the cryogenic pumps and the results of the pumping speed measurements are discussed in this report. |
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VST-MoP-5 Peltier Vacuum Gauge1
D.H. Jung, Y.H. Jeong, C.D. Park, S.M. Chung (POSTECH, S. Korea) The junction of a thermocouple, conventionally used as a temperature sensor, can work as a point heat source or sink if an electric current flows. This characteristic is well known as the Peltier effect. Utilizing the Peltier effect of a thermocouple, we have developed a new type of the vacuum gauge, Peltier vacuum gauge (PVG). PVG is based on thermal conduction by gases, and consists of a single thermocouple that plays roles of the heater and sensor simultaneously. PVG shows the sensitivity similar to, or better than that of the Pirani gauge or convectron gauge in the range between 10-4 torr and atmosphere. However, what distinguishes PVG from these gauges are: (1) it has appreciable sensitivity even above 10 torr due to the fact that it is a point heat source, which allows more effective gaseous conduction spherically in viscous regime, (2) its simple structure offers a way to the miniaturization of a vacuum sensor appropriate for local, and fast probe as the pressure changes, and (3) it operates at a few degrees above the wall temperature with high sensitivity. |
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VST-MoP-6 Total and Partial Pressure Measuring Devices Not to Be Influenced By Charged Particles from External Environments
H. Saeki, T. Aoki (Japan Synchrotron Radiation Research Institute); K. Tatenuma (Kaken Co. Ltd., Japan); T. Momose (Miyagi National College of Technology, Japan) Some B-A gauges in the SPring-8 storage ring have indicated minus pressures or lower pressures due to influx of photoelectrons produced by synchrotron radiation.1,2 Partial pressures using quadrupole mass spectrometers in the ring have not been measured at stored electron beam current of more than 40 mA. It was found that electrons of more than 1 x 10-9 A at the stored beam current of 70 mA flowed into the head of a quadrupole mass spectrometer. It was also found that B-A gauges using in the ring indicated minus pressures due to influx of electrons of more than 2 x 10-10 A. An automatically removal device of charged particles into pressure measuring devices was designed, composed of electrostatic electrodes and an instrument of charged particles. A self-compensating circuit for a mineral insulated gauge cable3 used in a radiation environment was also designed. Using the automatically removal device and the self-compensating circuit, the practical vacuum gauge system with a self-compensator 2 and the quadrupole mass spectrometer will be tested in such a hot vacuum environment and in a radiation environment around accelerators.
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VST-MoP-7 Development of Axial-Emission Ionization Gauge for XHV Measurement
Q.D. Sun (Shanghai Jiao Tong University, P.R. China); J.Z. Chen (Shanghai Lamp Factory, P.R. China) An ionization gauge structure, designed as the "Axial-Emission Gauge (AEG)", with the filament and collector plate located on the opposition ends of a helical grid, has many advantages compared to the BA gauge. This unique arrangement gives higher sensitivity (0.28/Pa) lower limiting pressure (2.7x10-9), less divergence in sensitivity between gauges (5%), and it is easier to degas than BA gauge. In order to further lower the limiting measureable pressure of AEG. Five axial-emission type ionization gauges have been developed: the axial-emission self-modulated ionization gauge, the axial-emission suppressor gauge, the axial-emission bent beam, the axial-emission magnetron ionization gauge and the axial-emission magnetron suppressor gauge. In comparison with the conventional gauges, these five AE type gauges have some advantages also same as AEG. All these points make it more suitable for measurement of UHV and XHV. |
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VST-MoP-8 In situ Pressure Measurement in Small Gettered Volumes
V. Nemanic, M. Zumer, B. Zajec (ITPO, Institute of Surface Engineering and Optoelectronics, Slovenia) In modern small opto-electronic devices like field emitter displays, miniature CRTs, channel photo-multipliers, etc., the vacuum requirements are much more stringent than in conventional electron beam devices. As the pressure should be in the UHV region and the volume is typically a few cm3, a direct measurement is not feasible and is often estimated on the basis of the expected pumping speed of the getter. The present study was arranged to investigate the pressure in small glass tubes (25 - 50 cm3) after the conventional pumping and bake-out procedure, just after the activation of Ba getters and during a period of several months. They were equipped by a spinning rotor gauge (SRG) sphere. Two getter sizes were studied: barium (St15/AM/O/9.5 and St15/AM/O/5), both made by SAES. After the evaporation by the prescribed procedure, the pressure did not drop, but increased from p=1x10-5 mbar up to p=1x10-3 mbar, showing that the pumping speed was completely suppressed by forming of a non-getterable gas. When the same experiments were repeated inside identical glass bulbs connected with a valve to a quadrupole mass spectrometer, formation of methane was observed. The initial rate just after the activation was Q=10-8 mbar l CH 4/s, but even after several hours it was still as high as Q=10-9 mbar l/s. By switching on the hot filament, methane was pumped by the getter after a precedent cracking procedure. The virtual pumping speed was directly related to the heater power, but independent of the getter area. Therefore, within the cathode warm-up period, methane is "pumped" and does not represent a harmful gaseous contaminant in a small electron beam device with a thermionic cathode. |
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VST-MoP-9 Surface Modification of Chamber Material for Standard Vacuum Pressure Measurement
M. Tosa, M. Goto, A. Kasahara, K. Yoshihara (National Institute for Materials Science, Japan) Main residual gas in a vacuum chamber mainly contains hydrogen molecules in an ultra high vacuum. Reduction of adsorption of hydrogen and other gas molecules is inevitable for standard stable vacuum atmosphere to calibrate standard vacuum pressure g auge. We tried to develop surface modification to reduce adsorption of hydrogen as well as other molecules. Surface modification is developed with surface segregation of hexagonal boron nitride (h-BN) on copper coating film. Copper is excellent in low hyd roge n solution, high thermal conductivity and high vacuum packing but suffers from easy oxidation that becomes large outgassing source. Surface of h-BN is excellent in low gas adsorption but is brittle and preparation of uniform BN layer on the entire sub str ate surface is not easy. Co-sputtering technology using helicon radio frequency wave with a sintered BN disc and a Cu disc deposited mixture of Cu and BN (Cu/B/N) on stainless steel substrates as chamber material. Annealing Cu/B/N film could remove all three main copper spectra peaks with Auger electron spectroscopy, carbon and oxygen peaks largely, then boron and nitrogen peaks increased much higher. Scanning i mage shows perfect uniformity of surface coverage with BN and no element by gas adsorption on the surface after atmospheric exposure. X-ray photoelectron spectroscopy showed π bond shake-up satellite of boron peak peculiar to h-BN. It is concluded that h-BN segregated uniformly on all the surface of the deposited film. Atomic force microscop e shows that the surface of the segregated h-BN layer has same small value of van der Walls' force as that of a sintered h-BN disc. This concludes that h-BN surface segregation layer on the substrate mixed with BN and copper can weaken surface interaction with gas molecules in a vacuum chamber and can much lower gas adsorption on the surface of the chamber wall for steady standard vacuum atmosphere. |
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VST-MoP-10 Outgassing Rate of Newly Titanium Alloy Material
H. Kurisu (Yamaguchi University, Japan); M. Hesaka (Shinko Industrials Co., Japan); T. Muranaka, S. Yamamoto, M. Matsuura (Yamaguchi University, Japan) A low outgassing rate material is required to make an XHV system. Titanium is a new candidate material for use in UHV and XHV. Recently vacuum characteristics of titanium materials were investigated and then it was clarified that the outgassing rate of small samples of chemically polished titanium is smaller by a factor of about 1/3 than that of electropolished stainless steel. (M. Minato and Y. Itoh, 1995) In the present work we pay attention to new titanium alloy material (KOBE STEEL,LTD KS100). In this material very flat surface can be obtained by a polishing and the hardness is larger by a factor about 2 than a titanium. We present outgassing property of the polished new titanium alloy in this paper. To measure the out gassing rate of small samples, we prepared the apparatus employing the orifice method with the orifice conductance is about 2.5x10-3m3/sec (RT, air). In the vacuum system, the vacuum chamber was made of new titanium alloy and the pumping system consists of two turbo molecular pumps. The measurement limit of the outgassing rate is obtained to be 1.6x10-11Pam/sec, when the sample with 160x103m2 area is used, because the pressures of both upper and lower chambers are reached 1x10-8Pa. We prepared the plate samples of polished new titanium alloy materials with the surface roughness of about 1nm. One set of samples consisted of 180 plates with a size of 20x20x1mm (sample area is about 160x103m2). After rough pumping down, samples were kept at 493K and the chamber kept 453K for 48h and then cooled down to room temperature in 48h. Finally out gassing rate was measured. The outgassing rate of the new titanium alloy samples is obtained to be 1.6x10-11Pam/sec, this value is smaller of the order than that of the stainless steel samples under the same measurement condition. On the conference, we will discuss the out gassing property of new titanium alloy materials in details. |
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VST-MoP-11 An Improved Method to Spot-Weld Difficult Junctions
E. Ferrenz, A. Amare, C.R. Arumainayagam (Wellesley College) Recent advances in spot-welding technology such as high frequency direct current (HFDC) inverter welders provide an improved and reproducible method to spot-weld difficult junctions. The importance of removing the oxide layers on metal surfaces, accurately delivering the weld pulse profile, and controlling the force applied to the materials during the welding process are discussed in the context of resistance spot-welding a molybdenum single crystal to a tantalum loop and attaching a tungsten-rhenium thermocouple to the crystal. |
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VST-MoP-12 Estimation of UHV Ball Bearing's Wear by Spectra Analysis of Residual Pressure
E.A. Deulin, V.V. Gerasimov, A.G. Peressadko (Bauman Moscow State Technical University, Russia) The aim of this work is to show correlation between mechanical and vacuum parameters of UHV feedthrough and it's reliability.1 The variation of torque M, outgassing flow in dependence of working cycle's number was investigated. This experiment was carried out on experimental UHV installation with parameters: residual pressure P=7*10-5 Pa, volume of vacuum chamber V=32 l, pumping speed S=150 l/s. The subject of research is a typical ultrahigh vacuum (UHV) mechanism - rotation motion feedthrough. It uses three ball bearings working in UHV. The ball bearings of stainless steel with and without Pb coverage were tested. The analyzed rotary feedthrough was rotating with speed 200 rpm. The diagnosing signals M and Q were storaged every 2000 revolutions of the shaft. The criteria of failure was the achieving by own torque the level of 2 N*m. The correlation level of an average torque Ma, and the maximum torque Mmax parameters with another ones (Q - summarized outgassing flow, Q1 - the spectral power of base frequency) was analyzed. The results show that the longevity of feedthrough based on Mmax parameter with ball bearings covered Pb was 170*103 of working cycles. The average outgassing flow Q for them was about 1*10-4 torr*l/s. The longevity of feedthrough based on Mmax parameter with ball bearings without coverage was 33*103 of working cycles. The average outgassing flow Q for them was about 1*10-5 torr*l/s. During experiment it was shown that the outgassing flow had a periodical charater. The results show that the amplitude of Q1 had a good correlation with Mmax, that's why we could choose it as one of the main diagnosing parameter. |
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VST-MoP-14 Surface Cleaning on Aluminum for Ultra-high Vacuum using Supercritical Fluid CO2 with O2
T. Momose, H. Iki (Miyagi National College of Technology, Japan) Contamination on metals used in ultra-high vacuum equipments causes the degradation of function of the equipments. Therefore, cleaning of metal surface is necessary. Supercritical fluid (SCF) carbon dioxide (CO2) with high solubility for organic compounds was employed for the cleaning.1 However, the cleaning rate using SCFCO2 alone was low.2 Therefore, oxygen gas (O2) was added to SCFCO2. Aluminum (Al) sample is φ5 x t1 mm. Sample was analyzed using x-ray photoelectron spectroscopy (XPS). It is defined that carbon (C) 1s peak in XPS spectra represents contamination. It is also defined that contamination rate is the ratio of area of C1s peak and summation of the area of C1s, O1s, and Al2p peaks. The cleaning rate at 55 °C for 30 minute cleaning was 2 % at 25 mega-Pascal (MPa) in SCFCO2 without O2, and 25 % at 20-30 MPa in SCFCO2 with O2 of 1.5 MPa. The addition of O2 is effective on the cleaning using SCFCO2. Cleaning at the constant ratio of O2 in SCFCO2 showed that cleaning rate is approximately proportional to the oxygen molecule number.
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VST-MoP-15 Influence of Ozonized Water Treatment and Subsequent in situ Sputter Cleaning on Electrical Breakdown Characteristics of Oxygen-free Copper Electrodes of a Vacuum Gap
S. Kobayashi, K. Sekikawa (Saitama University, Japan); K. Asano (Akita National College of Technology, Japan); Y. Saito (High Energy Accelerator Research Organization, Japan) Electrical breakdown characteristics of a vacuum gap depend on the electrode surface conditions, since the breakdown can be initiated by emission of such particles as electrons, ions, gases or clumps. These particles are emitted from contaminant layers of electrode surfaces. To improve breakdown strength removal of contaminant layers is required. Ozonized water treatment is recognized as the process to make surface clean and passivated. It has been exhibited that ozonized water treated oxygen-free copper electrodes can achieve higher breakdown field (breakdown voltage/gap length) after repetitive breakdowns, while the improvement in the breakdown field at the first voltage application (the first breakdown field) is little.footnote1 Electrode suface analysis clarified that the surfaces are slightly contaminated after ozonized water treatment. It was therefore considered that this contamination might cause the first breakdown field stay at the similar level to that for the untreated electrodes. To confirm the effect of the recontamination after ozonized water treatment on the first breakdown field, breakdown fields of electrodes treated with ozonized water alone and treated with ozonized water followed by in situ He ion beam sputter cleaning were compared. Experiments revealed that the additional in situ sputter cleaning is much effective on the improvement in the first breakdown field and the value of the breakdown field achieves 74 MV/m (ozonized water treatment condition : concentration ; 4.8 ppm, treatment hour ; for 60 min), while the value for the electrode treated with ozonized water alone is 69 MV/m. Also revealed is the excellent conditioning effect, that is, after 500 repetitive breakdowns the breakdown field achieves the value of 269 MV/m at 0.3 mm gap length. This value corresponds to the fact that the voltage of about 80 kV can be applied to 0.3 mm gap.. |