Turbomolecular Pump Research Articles

DUV cleaning of aluminium optics left at the atmosphere

The DISCO beamline at SOLEIL synchrotron radiation facility [1] is a low energy beamline (1-20 eV) with three end-stations. The imaging branch is the lowest energy of the three, ranging between 1 and 5 eV [2], for which ultra high vacuum is not mandatory. Therefore, the branch is separated from the beamline vacuum by a DN63CF suprasyl window protected for colour centre formation by suprasyl plate moveable under vacuum. In order to maximise the reflectivity in the photon energy domain of interest, all the mirrors specific to the branch have been coated with Al-MgF2. Commissioning and first year of exploitation were performed under primary vacuum conditions in the imaging branch line. During that period, the optics got heavily polluted, which induced a strong loss of photon flux. Al-MgF2 optics cannot be cleaned using oxygen plasma without heavy damages and loss of reflectivity. Therefore, the mirrors had to be removed and cleaned ex situ. Following this maintenance, the branch had been re-exploited under high vacuum conditions assured by a turbomolecular pumping to provide what we expected to be better protection of the optical elements. Although the very first photometric measurements showed a gain in flux, very soon the photon flux starts decreasing.

The thermal behaviour of the tritium source in KATRIN

The tritium source in the Karlsruhe Tritium Neutrino Experiment (KATRIN) will deliver 1011 β decay electrons per second, in order to determine the mass of the electron antineutrino through analysing the tritium β spectrum. The source is built of a 10m long beam tube of 90mm inner diameter, which is operated at 30K. Gaseous tritium is injected through a central injection chamber and diffuses towards the tube ends, where it is pumped by large turbomolecular pumps and further processed in a closed tritium loop. In order to achieve the KATRIN sensitivity of 0.2eV/c2, the decay rate in the source (and hence the tritium density profile) must be stable to a level of ±0.1%. As the density profile is influenced by the beam tube conductance, both the temperature stability and the temperature homogeneity must be within a range of ±0.03K at 30K. A thermosiphon with saturated neon was developed for this purpose, with horizontal evaporator tubes connected all along the 10m beam tube. The system behaviour was tested in a 12m long test cryostat, containing the original beam tube with the adjacent pumping chambers, as well as the cooling circuits and the thermal shields. The so-called “Demonstrator” was operated in the Tritium Laboratory Karlsruhe (TLK) being connected to the cryogenic infrastructure of KATRIN. The temperature stability was found a factor 20 better than specified, achieving a standard deviation of only 1.5mK/h, which corresponds to ΔT/T=5×10−5h−1 relative stability at 30K. The ±0.03K temperature homogeneity along the 10m beam tube was not yet reached, because of an increased heat load through the pump ports. The repeatability of the temperature measurement with vapour pressure sensors was within ±0.004K.

In situ measurements of krypton in xenon gas with a quadrupole mass spectrometer following a cold-trap at a temporarily reduced pumping speed

A new method for measuring trace amounts of krypton in xenon using a cold trap with a residual gas analyzer has been developed, which achieves an increased sensitivity by temporarily reducing the pumping speed while expending a minimal amount of xenon. By partially closing a custom built butterfly valve between the measurement chamber and the turbomolecular pump, a sensitivity of 40 ppt has been reached. This method has been tested on an ultra-pure gas sample from Air Liquide with an unknown intrinsic krypton concentration, yielding a krypton concentration of 330±200 ppt.

A design method of a mode control and an unbalance vibration control for five-axes active magnetic bearing systems

Mass unbalance of magnetically levitated rotors causes deteriorations of dynamic and static characteristics. To avoid this problem, it is necessary that mode matrices (i.e., a mode selection/distribution matrices) are adjusted appropriately. This is because these matrices are set based on the rotor’s centre of gravity and magnetic force coefficients of electromagnets. It takes long time to adjust the parameters of the mode matrices by trial and error. To design these parameters efficiently, we propose an adjustment method based on experimental analysis. Experimental results of step response show effectiveness of the proposed method. On the other hand, the eccentricity of the rotor causes unbalanced vibration, which is a common problem in rotating machinery. To suppress the vibration, automatic balancing system (ABS) and peak-of-gain control (PGC) are utilised. By using the ABS (the PGC), the bearing stiffness at rotational frequency is decreased (increased). In previous works, implementation methods for these have not been presented fully. Thus, in this paper, we considered the implementation of the ABS and the PGC. Moreover, practical advantages of the PGC/ABS are demonstrated by rotational tests of a turbo molecular pump.

Метод расчета оптимальной откачной характеристики турбомолекулярного вакуумного насоса

Метод расчета оптимальной откачной характеристики турбомолекулярного вакуумного насоса

Vacuum System of the Large Cyclotrons at VECC

Variable Energy Cyclotron Centre (VECC) has two large cyclotrons, K-130 cyclotron and K-500 cyclotron. The first beam in the room temperature K-130 cyclotron (RTC) was accelerated in June 1977. The cyclotron accelerated and delivered alpha and proton beams consistently to the cyclotron users for several years. Heavy ion beams were available in this cyclotron from 1997 to 2007. Presently, the cyclotron is working as a primary source for RIB production. The cyclotron has an acceleration chamber volume of about 28 m3. The total length of beam line is about 65 m. Vacuum of the order of 1 x 10−6 mbar is presently maintained in the cyclotron and beam line using diffusion pumps. It is one of the largest vacuum systems operating in India. It is consistently being operated 24 x 7 round the year giving beam to the cyclotron users. A K-500 superconducting cyclotron (SCC) with K=520 has been constructed at Kolkata. SCC will be used to accelerate beams to 80 MeV/A for light heavy ions and about 10 MeV/A for medium mass heavy ions. Three turbo molecular pumps are connected to the acceleration chamber. Three cryopanels placed inside the lower dees in the valley gap of the superconducting magnet are available in the accelerating chamber for achieving high vacuum. The acceleration chamber having a volume of about 1.0 m3 was operated using turbomolecular pumps, liquid nitrogen cooled panels and liquid helium cooled cryopanels at different stages during beam commissioning. Differential pumping is provided across the RF liner to avoid distortion. The first beam line of about 21 m has been installed in the cyclotron. The outer vacuum chamber of the cyclotron magnet cryostat has active pumping. The vacuum system of the superconducting cyclotron is also operating reliably round the clock throughout the year. The paper describes the details of the vacuum systems of the large cyclotrons at VEC Centre Kolkata India, its commissioning and operating experience.

Design and construction of a target chamber and associated equipments for the BARC Charged Particle Detector Array

A 60 cm diameter spherical high-vacuum target-chamber with side-opening hemispherical-lids, two ancillary-chambers, beam-line-tubes, tees and other high-vacuum components, and chamber-lid handling systems have been designed, constructed and installed for the Charged Particle Detector Array in BARC-TIFR Pelletron-LINAC Facility, Mumbai. This array of several tens of Si-CsI detector modules and other ancillary-detectors will be used for investigations in fusion-fission dynamics, nuclear structure at elevated temperatures and angular momenta, exotic nuclear clusters and related fields. This paper describes the unique features of the system that aid different coincidence experiments, the chamber fabrication experience and the pump-down characteristics with a turbo molecular pump. Unlike many other target chambers in use, this chamber allows multiple overall geometrical configurations to be set to reach experimental goals. For instance, by replacing a hemispherical-lid from one side with a flat-lid, the overall configuration becomes hemispherical. This way, high geometrical efficiency can be provided to an ancillary gamma detector array by allowing it to move close to target from the flat-lid side, although with some sacrifice of geometrical efficiency for charged particles. In experiments where a further improvement of geometrical efficiency for a gamma array is desired, a third compact-cylinder configuration can also be arrived at. Thinned portion of the lids of the chamber also allow neutron coincidence measurements with charged particles and gamma rays.

Development of a high vacuum sample preparation system for helium mass spectrometer

A high vacuum sample preparation system for the 3He/4He ratio mass spectrometer (Helix SFT) has been developed to remove all the gaseous constituents excluding helium from the field gases. The sample preparation system comprises of turbo molecular pump, ion pump, zirconium getter, pipettes and vacuum gauges with controller. All these are fitted with cylindrical SS chamber using all metal valves. The field samples are initially treated with activated charcoal trap immersed in liquid nitrogen to cutoff major impurities and moisture present in the sample gas. A sample of 5 ml is collected out of this stage at a pressure of 10−2 mbar. This sample is subsequently purified at a reduced pressure of 10−7 mbar before it is injected into the ion source of the mass spectrometer. The sample pressure was maintained below 10−7 mbar with turbo molecular vacuum pumps and ion pumps. The sample gas passes through several getter elements and a cold finger with the help of manual high vacuum valves before it is fed to the mass spectrometer. Thus the high vacuum sample preparation system introduces completely clean, dry and refined helium sample to the mass spectrometer for best possible analysis of isotopic ratio of helium.

Preliminary Design of the Vacuum System for FAIR Super FRS Quadrupole Magnet Cryostat

The Super-Conducting Fragment Separator (Super FRS) of the Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt is a large-acceptance superonducting fragment separator. The separator consists of large dipole, quadrupole and hexapole superconducting magnets. The long quadrupole magnet cryostat houses the helium chamber, which has the magnet iron and NbTi superconducting coil. The magnet weighs about 30 tons. The helium chamber is enclosed in vacuum inside the magnet cryostat. Multilayer Insulation (MLI) will be wrapped around the thermal shield to reduce radiation loss. Polyster of MLI comprises the major component responsible for outgassing. In order to reduce outgassing, pumping at elevated temperatures has to be carried out. In view of the large size and weight of the magnet, a seal off approach might not be operationally feasible. Continuous pumping of the cryostat has also been examined. Pump has been kept at a distance from the magnet considering the effect of stray magnetic fields. Oil free turbo molecular pump and scroll pump combination will be used to pump down the cryostat. The ultimate heat load of the cryostat will be highly dependent on the pressure attained. Radiation and conduction plays an important role in the heat transfer at low temperatures. This paper presents the vacuum design of the long quadrupole magnet cryostat and estimates the heat load of the cryostat.

Three stage vacuum system for ultralow temperature installation

We use a three stage vacuum system for developing a dilution fridge at VECC, Kolkata. We aim at achieving a cooling power of 20μW at 100mK for various experiments especially in the field of condensed matter and nuclear physics. The system is essentially composed of four segments-bath cryostat, vacuum system, dilution insert and 3He circulation circuit. Requirement of vacuum system at different stages are different. The vacuum system for cryostat and for internal vacuum chamber located within the helium bath is a common turbo molecular pump backed by scroll pump as to maintain a vacuum ∼10−6mbar. For bringing down the temperature of the helium evaporator, we use a high throughput Roots pump backed by a dry pump. The pumping system for 3He distillation chamber (still) requires a high pumping speed, so a turbo drag pump backed by a scroll pump has been installed. As the fridge use precious 3He gas for operation, the entire system has been made to be absolutely leak proof with respect to the 3He gas.

Spinning rotor gauge based vacuum gauge calibration system at the Institute for Plasma Research (IPR)

The Steady-state Superconducting Tokamak (SST-1) is an indigenously built medium sized fusion device at IPR designed for plasma duration of 1000 seconds. It consists of two large vacuum chambers – Vacuum Vessel (16 m3) and Cryostat (39 m3) which will be pumped to UHV and HV pressures respectively using a set of turbo molecular pumps, Cryo-pumps and Roots pumps. The total as well as the partial pressure measurement in these chambers will be carried out using a set of Pirani gauges, Bayard Alpert type gauges, Capacitance manometers and Residual Gas Analyzers (RGA). A reliable and accurate pressure measurement is essential for successful operation of SST-1 machine. For this purpose a gauge calibration system is set up in SST-1 Vacuum laboratory based on Spinning Rotor Gauge which can measure absolute pressure in the range 1.0 mbar to 1.0 × 10−7 mbar. This system is designed to calibrate up to five gauges simultaneously for different gases in different operating pressure ranges of the gauges. This paper discusses the experimental set-up and the procedure adopted for the calibration of such vacuum gauges.

Design, fabrication, and performance testing of a vacuum chamber for pulse compressor of a 150 TW Ti:sapphire laser

A vacuum chamber, to house the optical pulse compressor of a 150 TW Ti:sapphire laser system, has been designed, fabricated, and tested. As the intensity of the laser pulse becomes very high after pulse compression, there is phase distortion of the laser beam in air. Hence, the beam (after pulse compression) has to be transported in vacuum to avoid this distortion, which affects the laser beam focusability. A breadboard with optical gratings and reflective optics for compression of the optical pulse has to be kept inside the chamber. The chamber is made of SS 316L material in cuboidal shape with inside dimensions 1370×1030×650 mm3, with rectangular and circular demountable ports for entry and exit of the laser beam, evacuation, system cables, and ports to access optics mounted inside the chamber. The front and back sides of the chamber are kept demountable in order to insert the breadboard with optical components mounted on it. Leak tightness of 9×10−9 mbar-lit/sec in all the joints and ultimate vacuum of 6.5×10−6 mbar was achieved in the chamber using a turbo molecular pumping system. The paper describe details of the design/ features of the chamber, important procedure involved in machining, fabrication, processing and final testing.

Indigenous development of ultra high vacuum (UHV) magnetron sputtering system for the preparation of Permalloy magnetic thin films

We have designed and developed an indigenous ultra high vacuum (UHV) sputtering system which can deposit magnetic thin films with high purity and good uniformity. The equipment consists of state-of the-art technologies and sophistication. Turbo-molecular pump combined with sputter ion pump is used to pump down the vacuum chamber up to 10−10 to 10−11 mbar of pressure. With this system it is possible to deposit coatings of various materials on a sample size of diameter 3". The Ni81Fe19 ferromagnetic thin films, with Tantalum (Ta) as a buffer and cap layers have been deposited on silicon substrates using this ultra high vacuum (UHV) sputtering system. The magneto transport measurement study indicated a significant variation in the AMR values of the films for varying thicknesses of tantalum and NiFe layers.

Development of a turbo-molecular pump with a magnetic shield function

To safely use turbo-molecular pumps (TMPs) in a magnetic field, it is necessary to reduce the eddy current induced in a rotating rotor. Instead of adding a magnetic shield facility to the TMPs available in markets, we developed a TMP with a magnetic shield function by replacing the housing material of the TMP with a ferromagnetic substrate SUS430. Before and after machining, the SUS430 was vacuum-fired at 700 °C for 10 h in order to attain a good vacuum quality and recover its high magnetic permeability. The magnetic shield efficiency of the TMP with SUS430 housing was then examined. When a perpendicular magnetic field of 9 mT was applied, the field inside the TMP was reduced to less than 0.3 mT. Next, we confirmed that the developed TMP shows good performance in achieving an ultrahigh vacuum in magnetic fields of up to 9 mT. The limit of the magnetic shield efficiency for the developed TMP is also discussed.

Focus on vacuum and cryogenics

Focus on vacuum and cryogenics

TriToP – A compatibility experiment with turbomolecular pumps under tritium atmosphere

A turbo-molecular pump with magnetic bearing type Oerlikon Leybold MAG W 2800 has been tested under tritium atmosphere for one year with an overall throughput of about 1.3 kg of tritium (≈5 × 1018 Bq) in a closed loop. Evolution of gas composition has been regularly checked by in-line mass spectrometry. Experimental data of two long term tritium runs followed by a non-tritium run are shown. Results are discussed with regard to materials used inside the pump volume. Possible consequences for the use at the KATRIN experiment are given.

Analysis and Modeling of Rotor Slot Enclosure Effects in High-Speed Induction Motors

In this paper, the effects due to the presence of closed or open rotor slots in high-speed induction motors are presented. In particular, the problem linked to electromagnetic effects on the motor current is analyzed in detail. Two 32 000-r/min induction motor prototypes, the former with open rotor slots and the latter with closed ones, have been built and tested in order to verify the theoretical analysis. A modified steady-state equivalent circuit to take into account the electromagnetic effects of rotor closed slots is proposed, and experimental tests have been performed to validate the proposed model. The presented study is focused on high-speed induction motors for turbomolecular vacuum pumps.

Formation and stability of bulk carbonic acid (H2CO3) by protonation of tropospheric calcite.

Organic acids play an important role in the acidification of our atmosphere. These weak acids can contribute up to 60 % of the free airborne acidity. By far the most abundant organic acids are the C1 and C2 monocarboxylic acids, formic acid (HCOOH) and acetic acid (CH3COOH), which show mixing ratios in the gas phase ranging up to 20 ppb over land1,2 and down to 0.2 ppb in the remote oceanic boundary layer or troposphere.3,4 These acids are partitioned between the gas phase and the particulate phase, where roughly one half to two thirds can be found in particulate matter (PM2.5).2 The most important removal mechanism is dry deposition, which accounts for more than 90 % of the total organic acid deposition budget. The remaining fraction is removed by rain as particulate-phase acids, whereas removal by chemical reactions is negligible.1,5 In addition to the two most important organic acids, C3–C10 aliphatic monocarboxylic acids1 and C2–C11 aliphatic dicarboxylic acids1,2,6–11 as well as aromatic carboxylic acids1 have also been observed in air. The water-soluble fraction of organic carbon can on average consist of 35 % mono- and dicarboxylic acids.12 While the C2-dicarboxylic acid, oxalic acid (COOH)2, is commonly observed in all field studies, the C1-dicarboxylic acid, carbonic acid (H2CO3), has barely received any attention, mainly because it is thought that it immediately decomposes to water and carbon dioxide. However, it has previously been shown that gaseous, water-free carbonic acid is surprisingly stable,13 that amorphous and crystalline solids of pure carbonic acid can be produced and stored without decomposition at temperatures up to 230 K even in the presence of water14 and that this solid can be sublimed at, for example, 220 K and recondensed in vacuo at surfaces of lower temperature.15

Note: Automatic mass-flow configuration method for evaluating turbomolecular pump performance

An automatic mass-flow configuration method is presented for the evaluation of turbomolecular pump performance. This configuration method is used to obtain an effective mass-flow rate. In addition, the throughput, inlet pressure, and compression ratio are evaluated. The throughput increases with the mass-flow rate. Moreover, the compression ratio increases almost linearly with the outlet pressure for mass-flow rates from 2.97 × 10(-9) to 3.96 × 10(-7) kg/s. Finally, empirical correlations are proposed for the throughput and inlet pressure.

Design modification in rotor blade of turbo molecular pump

Performance of a Turbo Molecular Pump (TMP) is strongly related to the frequency of the rotor. As rpm increases deflection in the rotor blades starts to occur. Therefore, quality of material and blade design has been modified in order to obtain stable performance at higher speed. To reduce the deformation, stiffer material and change in blade design have been calculated. Significant improvement has been achieved in modeling the blade design using CATIA software. The analysis has been performed by ANSYS workbench. It is shown that the modification in the blade design of TMP rotor has reduced the structural deformation up to 66 percent of the deformation produced in the original blade design under the same conditions. Modified design achieved additional 23 percent rpm which increased TMP's efficiency.