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AVS2004 Session VT-TuP: Poster Session

Tuesday, November 16, 2004 4:00 PM in Room Exhibit Hall B

Tuesday Afternoon

Time Period TuP Sessions | Topic VT Sessions | Time Periods | Topics | AVS2004 Schedule

VT-TuP-1 Mathematic Simulation of Processes in Flow Parts of Hybrid Turbomolecular Vacuum Pumps M.G. Sapeshinsky (Bauman Moscow State Technical University, Russia) Mathematical models of process of carry of molecules are developed the channel, allowing to optimize a flowing part hybrid turbomolecular the vacuum pump (TMP) in a wide range speeds. Interaction of steps and flowing is investigated parts turbomolecular the vacuum pump with various constructive schemes. The design procedure of parameters is developed ТМР with axial-radial a stream of gas. The algorithm is developed optimization flowing part ТМР with axial and axial-radial stream gas, laws of change of geometrical parameters are received on to steps of a compound flowing part. Theoretical researches were carried out with use of a method of statistical tests and a method of angular factors. Experimental researches were carried out in laboratory conditions on models and experimental samples. Algorithm of optimization at presence nonlinear functional restrictions on controlled parameters uses algorithm sliding the admission and a method of absolute penal functions under condition of maintenance set speed of action of the pump on the chosen gas, and also on several gases. The problem of optimization is put as variational. Therefore the absolute penalty function is used, if in current optimization step S_real will be less than S: F(x,ρ) =Φ(x)+ρ \|(S_real - S) < 0\| , where ρ- penalty parameter, the upper value of which is restricted by bad dependence F(x,ρ). After calculation of evacuation characteristic at current values of controlled parameters it is possible the situation, when P is less, than the limit rest pressure P_min. In this case the value S_real is taken 0, and the target function is formed as follows: F'(x, ρ, ρ ₁)=Ф(x)+ρ \|(S_real - S) < 0 \|+ ρ ₁ \|{(lg (P)- lg(P_min)}< 0\| , ρ is chosen equal 10⁵. Minimization of flow part volume of TMP with axial and, the more, with axial-radial gas flow with given technical conditions for nitrogen (N₂) does not guarantee the required operation rate for light gases (H₂, He) due to nonlinear character of dependence S_max of axial and axial-radial rotors on round velocity when U/V <1. Therefore, if, for example, it is needed to minimize the flow part's volume of a TMP with given evacuation rate S at P for nitrogen N₂ and given evacuation rate S at P for hydrogen H₂, the absolute penalty function is formed as follows: F''(x, ρ, ρ ₁ , ρ ₂ , ρ ₃)= Ф(x)+ρ\|(S_real - S) < 0\|+ ρ ₁\|{lg(P)-lg(P_min)} < 0\|+ ρ ₂ \|(S_real, Н- S) < 0\|+ρ ₃ \|{lg (P) - lg(P_min, Н)} <0\| , where P_min, H - limit rest pressure for H₂. Naturally, it is necessary to calculate the discrete evacuation characteristic for H₂.Often in technical conditions are included different restrictions on other outgoing and optimization parameters, e.g. rotation frequency f, external diameter D₂ etc.
VT-TuP-2 Measurements of Photon Stimulated Desorption from a Copper Beam Chamber wall During Four Years of Synchrotron Radiation Exposure¹ C.L. Foerster, C. Lanni (Brookhaven National Laboratory) Photon Stimulated Desorption (PSD) has been continuously measured from a copper beam chamber for more than four years. Vacuum surface oxide had been completely removed prior to the start of measurements in order to reduce the initial PSD. Desorption rates were found to decline uniformly during the long-term exposure. Measurements of PSD and specular photon reflection were performed on NSLS beamline U9a at Brookhaven National Laboratory. It is well known that PSD causes a pressure rise in accelerator and storage ring vacuum, which limits their commissioning and performance. A copper beam chamber from a previous experiment was chemically etched and chemically cleaned prior to installation on beamline U9a. Previous PSD measurements on other chambers have shown that this chemical treatment removes any memory of prior exposure or conditioning. After installation, the copper chamber and end stop were vacuum baked to 250°C for more than a week to completely remove vacuum surface oxides. The chamber was exposed to more than 3x10²⁵ photons direct from the source having a critical energy of 595 eV and striking at an incident angle of 100 mrad. The major PSD yields for hydrogen, carbon monoxide, carbon dioxide, and methane are reported as a function of accumulated photon flux and preparation. The initial PSD yields for the copper chamber after oxide removal were greatly reduced compared to previous measurements at this laboratory and those reported from other laboratories. The PSD component gases remained the same during the long exposure and all were significantly reduced. Carbon dioxide and methane were reduced much more than hydrogen and carbon monoxide. Specular photon reflection did not change significantly during the extended exposure.¹ Work performed under the auspices of the U.S. Department of Energy, under contract DE-AC02-98CH10886.
VT-TuP-3 Continued Vacuum Pump Oil Testing at the National Synchrotron Light Source to Minimize Oil Waste¹ C.L. Foerster, J.-P. Hu, E. Haas (Brookhaven National Laboratory) An oil-testing project was established to determine if synthetic vacuum pump oil could be used effectively to reduce the large amount of oil waste produced during normal operation of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL). More than two hundred oil-sealed rotary vane pumps are used at the NSLS facility, such that a longer oil change interval would greatly reduce maintenance costs as well as oil waste. Initial pump oil waste was approximately 75 gallons per year. Two basic types of vacuum pump oils, mineral and synthetic, are being tested for a direct comparison. Three of the same size two-stage mechanical pumps were set up and run simultaneously having the same gas load. Convectron gauges, cold cathode gauges, and isolation valves were connected to a central vacuum chamber having a common inlet pressure control and a sampling valve for residual gas analysis. To simulate oil degradation produced by long-term mechanical pump operation, the system air load was manually controlled, with an air bleed valve in a common vacuum chamber, which was periodically adjusted, to run the pumps at a 500 mTorr inlet pressure. Vacuum pump oil suppliers to expedite the oil viscosity change, acid buildup, and pump-wear debris production suggested the pressure for mechanical pump testing. At this inlet pressure, the testing time is reduced and any oil back streaming is minimized. After one and a half years of running there have been no significant changes in either of the oil types. The detailed test data for the resulting oil properties, oil degradation, visual comparison, vacuum conditions, and pump characteristics will be presented for comparison of the pump oils used at NSLS and for estimation of the resulting oil waste reduction.¹ Work performed under the auspices of the U.S. Department of Energy, under contract DE-AC02-98CH10886.
VT-TuP-4 Adsorption System Controlled with Surface Roughness for Smooth Sliding in a Vacuum A. Kasahara, M. Goto, Y. Pihosh, M. Tosa (National Institute for Materials Science, Japan) Friction measurement was measured out on typical vacuum materials as Copper sheets and type 304 austenitic stainless steel sheets after such surface treatments as chemical polishing or electrochemical buffing. We have shown that the materials with surface roughness around 100nm can offer as smooth sliding in a vacuum as at an atmospheric pressure with a developed vacuum friction measurement system based on Bowden-Leben type system. This smooth sliding may arise from absorption gas layer as lubricant kept in hollows of surface nanoscopic asperities. We accordingly estimated adsorption gases for lubrication by decrease in sliding load with the friction measurement system to study the effect of surface roughness on the adsorption gases. We found existence of low friction coefficient about 0.03 on a Cu sample with surface roughness about 90nm under the load of 0.1N at an atmospheric pressure. The load with over about 0.2N and under about 0.05N also showed increasing friction coefficient at an atmospheric pressure. We can understand change of friction coefficient by using Stribeck-Diagram. The diagram shows the existence of regions indicating solid lubrication, boundary lubrication, mixture lubrication and hydrodynamic lubrication by assuming adsorption layer as lubricant on nano surface roughness. It is therefore concluded that the surface with 100nm roughness exhibiting similarly low friction in a vacuum as at an atmospheric pressure is ideal modified surface for residual adsorbed gases layer system to act as fluid lubricant.
VT-TuP-5 New Approach to the Calibration of 10 torr Precise Vacuum Gauges S.Y. Woo, I.M. Choi, B.S. Kim (Korea Research Institute of Standards and Science, Korea) Capacitance diaphragm gauges (CDG) are electromechanical pressure sensors in which the displacement of a stretched thin metal diaphragm is detected by a capacitance measurement. These are very accurate gauges and frequently used as transfer gauges. In order to calibrate such accurate vacuum gauges, precise mercury manometers have been used. However, complexity, harmfulness of mercury vapor, and cost of mercury manometers made it difficult to use in many calibration laboratories. As a substitute, a gas-operated piston gauges can be used for calibration of such vacuum gauges. But it is difficult to use them for low pressure measurements, because the pressure must be balanced against the weight of the piston, which generally corresponds to a pressure of several kilopascals. To reduce this minimum operating pressure, we adopted a variable bell-jar pressure method. We also developed a new home-made automatic mass loading apparatus which makes it possible to add or remove weights easily without breaking the vacuum during the calibration. Our calibration system can be used to measure pressures from 100 Pa to 2 kPa in the absolute mode. In this paper, practical calibration results are given for two different CDGs in the range of 10 torr full scale.
VT-TuP-6 A Real Time Quantitative Diagnostic Technique for Measuring CVD Precursors J. Yun, B. Ahn, J. Kim, Y. Shin, K. Chung (Korea Research Institute of Standards and Science, South Korea) We present a technique for monitoring the precursor consumption in a chemical vapor deposition (CVD) system. CVD involves chemical reactions that transform gaseous precursors into a solid material in the form of thin film or powder on the surface of a substrate. Precursor costs are a significant factor, and therefore, methods for monitoring precursor consumption are desirable. One diagnostic solution is to use an ultrasonic sensor to determine the precursor liquid level in the CVD containers. This method has advantages in being a noncontact and inexpensive method. It includes an ultrasonic sensor, an ultrasonic generator/receiver, and a computer system that includes an A/D board. The time between the sending of the ultrasonic signal and the return of an echo is used to determine the CVD precursor level in the container. The level of liquid (d) in the container is given by d = V.{(1/2)t}, where v is the velocity of the ultrasonic pulse, and t is the time of flight of the ultrasonic pulse reflected from the surface of the liquid. We got the results obtained from a container with different liquid precursor levels (2, 4, and 6 cm). The accuracy and consistency of the measurements were within an acceptable tolerance range for the three liquid levels (Actual fill level : 2, 4, and 6 cm/Estimated fill level : 2.1, 3.8, and 5.9 cm) In summary, a sensor based on an ultrasonic technique has been developed for monitoring precursor consumption in an CVD system. The prototype sensors developed in this study are expected to be used successfully in semiconductor fabrication.
VT-TuP-7 A Comparative Analysis of Four Stanford Research Systems Quadrupole Residual Gas Analyzers Through Quantitative Helium Leak Detection Measurements P.A. Adderley, M. Poelker, M.L. Stutzman, G.R. Myneni (Thomas Jefferson National Accelerator Facility) Over the past 10 years, quadrupole residual gas analyzers (RGAs) have become common vacuum diagnostic instruments. Much of the proliferation of this technology throughout the scientific community is due to the high reliability and relatively low cost of the modern RGAs. Jefferson Lab uses over 70 of these devices to diagnose vacuum limitations of the Ultra High Vacuum photoemission guns, monitor hydrocarbon contamination during production of superconducting radio frequency (SRF) accelerator cavities, and monitor helium processing in the SRF cavities. By far, the dominant use of the RGAs at Jefferson Lab is for leak detection. In this paper, we compare the performance of four RGAs from Stanford Research Systems and present detailed procedures that should be used in order to routinely obtain reliable and quantitative measurements of helium partial pressure.
VT-TuP-8 Secondary Electron Yield Measurements of TiN Coating and TiZrV Getter Film F. Le Pimpec, R. Kirby, F. King, M. Pivi (SLAC) In the beam pipe of the positron Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gases and secondary electron emission give rise to an electron cloud which can cause the loss of the circulating beam. One path to avoid the electron cloud is to ensure that the vacuum wall has low secondary emission yield and, therefore, we need to know the secondary emission yield (SEY) for candidate wall coatings. We report on SEY measurements at SLAC on titanium nitride (TiN) and titanium-zirconium-vanadium (TiZrV) thin sputter-deposited films, as well as describe our experimental setup.
VT-TuP-9 Photon Stimulated Desorption of the Low Temperature Aluminum Chambers for the Superconducting Wiggler G.Y. Hsiung, J.Y. Yang, C.C. Chang, S.N. Hsu (NSRRC, Taiwan); J.R. Chen (NSRRC, NTHU, Taiwan) A Superconducting Wiggler, SW6, has been installed in the 1.5 GeV electron storage ring of Taiwan Light Source (TLS) to obtain higher brilliance hard X-ray synchrotron light. The beam duct for the SW6, made of A6061 aluminum alloy, is operated at a temperature of ~ 100 K. It was concerned the gas molecules desorbed from exposure to the scattered light will be reabsorbed and piled up on the surface oxide layers that is difficult to be removed. To evaluate the photon stimulated desorption (PSD) from the low temperature beam duct, a test chamber has been installed in the 19B1(PSD) beam line of TLS for synchrotron light exposure at a critical photon energy of 2.14 keV. The yield of PSD is measured by a throughput method. The chamber was cooled by liquid nitrogen from outside. The residual gas analyzers measure the gas species that reflects the PSD behavior. The result for the beam test at the beam line will be described and the commissioning for the SW6 in the storage ring will also be addressed.
VT-TuP-10 Characteristics of the Axial-symmetric Transmission Gauge on the Pressure Measurement in the Vacuum Environment including Ions and Electrons N. Takahashi, Y. Tuzi (ULVAC Inc., Japan); I. Arakawa (Gakushuin Univ., Japan) The pressure reading of an ordinary ionization gauge is disturbed by the detection of electrons and ions generated outside of the gauge. The elimination efficiency of the axial-symmetric transmission gauge (AT gauge) for the disturbances was examined by the external sources of electrons and ions designed for this purpose. The electron source was composed of a tungsten filament and an electron collector. The ion source was made from a BA gauge from which the top electrode of the grid was removed so that ions escaped out of the ionizer. For comparison, a BA gauge and an extractor gauge were examined under the similar condition of the AT gauge. The pressure readings of BA gauge and extractor gauge showed very low pressure when the external electron source was running. In contrast, the readings of the AT gauge was not affected by the external electron source, because the ion collector is shielded by cover electrode and the retarding field for the electron is created by the end plate of the Bessel-box type energy analyzer in the AT gauge. The gas phase ions generated in the ion source of the AT gauge and ions from the external source was clearly separated in the energy spectra of AT gauge. The spectra were obtained by scanning the path energy of the analyzer of the AT gauge. The pressure measurement without the effect of ions from the outside of the gauge is made by the proper adjustment of the path energy of the analyzer. The energy analyzer in the AT gauge works as a cut off filter for the charged particles coming from the outside of the gauge as well as the original role for the rejection of the soft x-rays and ESD ions generated in the ionizer.
VT-TuP-11 Novel Modular Controller for Quadrupole Mass Spectrometers N. Mueller, S. Foster, G. Peter (Pfeiffer Vacuum) High performance single quadrupole mass spectrometers nowadays are used in a very wide range of applications. Some examples are accurate residual gas analysis down to the XHV range, vapor beam analysis and control in UHV-MBE tools, isotope ratio measurements, quantitative gas analysis in e.g. catalytic research, and process control in the chemical, pharmaceutical, and metallurgical industry. The very different demands of these applications can be fulfilled by very flexible and modular mass spectrometer controllers only. A novel system contained in a only 3u high 19 inch rack system has been developed that shows the following key features: Intel X-scale processor based controller with Windows CE.net operation system; high speed digital signal processor for mass spectrometer control and data acquisition to allow for scan rates down to 125 microsec / amu; communication to host computer via USB or Ethernet for network operation using OPC standards; fieldbus module to communicate with standardized industrial input / output modules; webserver for control of the system without the need for specific software; modular ion source supply with digital emission current controller for easy adaptation to different filament types, and individually exchangeable voltage supplies for ion lenses; voltages can be biased up to +/-1000V and polarity can be changed to detect positive as well as negative ions; ion counter for count rates up to 130MHz; high voltage supplies for operation various SEMs; autorange control for electrometer amplifiers; analog and digital input / output module for easy connection to external measurement and control devices. In combination with a wide selection of quadrupole rod systems, RF stages, ion sources and ion optics, this system allows for numerous applications from basic research to industry. Detailed functional description as well as data from selected applications will be presented.
VT-TuP-12 The Development of a New Vacuum System for the Injection Section of the TLS C.K. Chan, G.Y. Hsiung, K.Y. Kao, S.N. Hsu, J.Y. Yang, J.R. Chen (NSRRC, Taiwan) A new vacuum system for the injection section of the Taiwan Light Source (TLS) has been developed for improving the vacuum condition and the injection condition. The major problems to be solved include a higher heat load and a higher pressure rise from a superconducting wavelength shifter (SWLS), in-sufficient linear pumping speed near the ceramic chambers for the kickers and the injection chambers, et al. The new vacuum chambers to be replaced include (a) new kicker chambers, with thinner and wider aperture, with interior uniform Ti-coating for better injection efficiency and for preventing from SWLS irradiations; (b) new aluminum alloys vacuum chambers with interior NEG-coating for higher linear pumping speed; and (c) new beam duct for SWLS with lower outgassing rate. The pressure profile calculated by a computer program shows that the average vacuum pressure can be improved about 5 times lower based on this design. The results of the simulation and the vacuum test for the new chambers will be described.
VT-TuP-13 A Compact UHV-compatible Microprober with a Variable-Temperature Sample Stage H. Bando, Y. Aiura (National Institute of Advanced Industrial Science and Technology, Japan); A. Urata (International Servo Data Corp., Japan); I. Konishi (Ibaraki University, Japan); Y. Nishihara (Iaraki University, Japan) A compact ultra-high-vacuum-compatible microprober with a variable-temperature sample stage, which is suitable for in situ surface conductivity measurements, is presented. The equipment fits in a space of 300 mm x 300 mm x 100 mm. The vacuum chamber consists of a CF114 nipple with four CF70 and four CF34 ports. Each of four microprobes is position-controlled by a 3D stage made of stainless steel placed outside of the chamber through a CF34-based wobble stick. The bellows of the wobble sticks are of small diameter, allowing use of less-robust 3D stages. A variable-temperature sample stage is fixed symmetrically at the center of the chamber to minimize the thermal drift.
VT-TuP-14 The Effect of Dissolved Nitrogen Gas on the Density of Octoil-S --Working Fluid of the NIST 140 Pa Oil Ultrasonic Interferometer Manometer (UIM) Pressure Standard J. Hendricks, A.P. Miiller (National Institute of Standards and Technology) The NIST Low Pressure Manometry Laboratory provides primary national pressure standards ranging from 0.01 Pa to 360 kPa. The topic of this presentation is the study of the density of octoil-s, the working fluid the NIST 140 Pa oil UIM which is the current NIST standard covering the pressure range from 100 Pa down to 0.01 Pa. The oil manometer was developed to avoid the ~ 0.2 Pa room temperature mercury vapor pressure that limits the lowest absolute pressure that can be measured with the NIST 360 kPa, and 160 kPa mercury UIMs. The NIST 140 Pa UIM is used to calibrate customer pressure transducers such as Capacitance Diaphragm Gauges (CDGs) of the appropriate Full Scale (FS) range, 0.1 torr, 1 torr, and the bottom ranges (0.01 FS and 0.1 FS) of 10 torr CDGs. The relative change in density of octoil-s as a function of nitrogen gas pressure was determined using a vibrating tube densimeter with a manufacturer's stated uncertainty of 5x10^-6 g/cm³ and a repeatability of 1x10^-6 g/cm³. Results will be presented showing that the effect of dissolved gas on the density of octoil-s does not contribute significantly to the uncertainty of the 140 Pa oil UIM. In addition, the results show that the performance of a planned 1,400 Pa oil UIM will not be adversely impacted by this effect. Finally, planned integration of the densimeter to the NIST oil UIM will allow periodic checks of the density of the manometer fluid should contamination be suspected.}
VT-TuP-15 Vacuum Conditions in the Vicinity of a Field Emitter M. Zumer, B. Zajec, V. Nemanic (Jozef Stefan Institute, Slovenia) A basic characterization of novel field emitters is usually realized in a standard UHV chamber equipped with appropriate pumps. Their high pumping speed and the remote location of the vacuum gauge prevents to monitor the pressure changes during operation of the field emitter (FE). In most of the potential applications the FE runs in a small sealed device where the local pressure is frequently unknown and its influence on the device lifetime is often underestimated. A small glass envelope equipped with a miniature ion getter pump (IG), spinning rotor gauge (SRG) and a cathodoluminescent screen, was prepared to monitor properly these phenomena. The IG discharge current was calibrated versus pressure by the means of the SRG. Single-crystalline nanoparticles deposited onto molybdenum needles were used as field emitters. The initial pressure in a well outgassed envelope was in the UHV range, but its increase for three orders of magnitude was detected when the field emission current reached one microampere range at 1kV. A good correlation between the FE current and electron stimulated desorbed gases was found.
VT-TuP-16 Vacuum Improvements in the ISAC Low Energy Beam Transport Line for Reducing Beam Loss D. Yosifov, I. Sekachev (TRIUMF, Canada) Abstract: The TRIUMF 500 MeV cyclotron delivers proton beam currents up to 100 Î¼A into a dedicated beam line and target system for the production of radioactive ion beams (ISAC). Various radioactive species are produced in the target, which are then ionized and extracted. The ions pass through a mass separator and are transported via a low energy beam transport line to experimental areas or injected into an RFQ accelerator. The existing 14m section of the transport line is pumped by two 500 l/sec, and one 1000 l/sec turbo pumps to achieve an average beam on operating pressure of better then 3.0E-7 Torr. The calculated vacuum required to reduce beam losses due to ion collisions with the residual gas to 0.1%/m for high charge state ions is 2.0E-8 Torr. The outgassing rates for some materials used in the beam lines have been measured at TRIUMF and compared with available tabulated data. In the order to improve the vacuum in the beam line section with the highest outgassing rate a cryopump was installed and vacuum change monitored. A bake out test of a beam line section is also scheduled. This paper reports on the results from the vacuum improvement tests and some related calculations.
VT-TuP-17 Study of the Pump Pumping Performance after Heat is inputted into the Refrigerating Head of Cryopump H.-P. Cheng, C.-W. Sun, Y.-C. Lu (National Taipei University of Technology, Taiwan) This study places the heater on the second refrigerating head of Cryopump of closed loop Gifford-McMahon (G-M) that uses helium for refrigerant, and applies different energy on the heater to investigate the pumping performance of Cryopump. The test system is constructed based on the test specification suggested by Welch, the Cryopump model is ULVAC-10PU. Pirani gauge and ion gauge are placed around the chamber to measure the chamber pressure. Before heat is transferred to the heater, the nitrogen and argon pumping speed of the pump is 919~2,170 liter/sec and 1,770~4,060 liter/sec, respectively. After heat is transferred to the heater, when the input watt increases, the temperature of cryopanel surface increases and pumping performance decreases. In the experiment of nitrogen gas, the heater is inputted with 2.5W, 5W, 7.5W, 10W, 12.5W, 15W, 17.5W, of which the decrease in pumping performance is the most apparent in 17.5 W; the pumping speed dropped to 230~625 liter/sec. The corresponding gas throughput is 0.2~63 SCCM. The tested chamber pressure is 1.6E-03~3.0E-01 Pa. In the experiment of argon gas, the heater is inputted with 2.5W, 5W, 7.5W, 10W, 12.5W, 15W, of which the decrease in pumping performance is the most apparent in 15 W; the pumping speed dropped to 507~1,350 liter/sec. The corresponding gas throughput is 0.28~63.45 SCCM. The tested chamber pressure is 1.0E-03~1.5E-01 Pa.

Time Period TuP Sessions | Topic VT Sessions | Time Periods | Topics | AVS2004 Schedule