Turbomolecular Pump Research Articles

CALCULATION OF THE MAIN CHARACTERISTICS OF A HYBRID VACUUM PUMP

Data are presented for calculating the main characteristics of a hybrid turbomolecular vacuum pump operating in the molecular gas flow mode. The pump contains a block of turbomolecular stages, an intermediate stage and a molecular stage with screw channels made on a cylindrical rotor. To determine the probabilities of gas molecules passing through the entire flow part of the pump in the forward and reverse directions, the Monte Carlo method in a three-dimensional formulation was used. The program allows you to evaluate the influence of the dynamic and geometric parameters of the flow path on the main characteristics of the pump in order to optimize them.

Structural optimization and flow field analysis of turbomolecular pump based on a new performance prediction algorithm

In the present study, a new turbomolecular pump (TMP) performance prediction algorithm is proposed according to the variable surface combined blade row (VSCBR) geometric model. The simulation calculation program is designed to perform structural optimization and flow field analysis. Research on the pumping performance of the traditional straight blade row (TSBR) indicates that when the blade velocity ratio is greater than 1, the increase in the pumping speed and compression ratio of the TMP gradually tends to stabilize. Response surface methodology is used to optimize the structural parameters of the first four stages of the combined blade row. The optimized VSCBR increases the pumping speed by 18.2% compared to that of the TSBR. The flow field analysis based on the optimized VSCBR shows that gas molecules reaching the rear blades are likely to approach the outlet, and the proportion of gas molecules in this region exceeds 50%. Therefore, the blades we designed should be conducive to additional gas molecules reaching the outlet.

Numerical simulation of neutral gas dynamics in the W7-X sub-divertor

The present work presents a 2D and 3D modeling of the neutral gas flow in the sub-divertor region of the W7-X. The investigations have been done using the DIVGAS code. The complex 2D and 3D geometries of the divertor components in the sub-divertor region have been considered and the Standard and High-Iota magnetic configurations have been numerically simulated. The main objective of this study is to investigate the dynamics of neutral particles in the sub-divertor region including the effects due to geometry and toroidal and poloidal leakages located at the divertor targets and baffles on the achieved pumping efficiency. A sensitivity analysis has been performed for the effect of various geometrical and flow parameters on the pumping performance, under different plasma scenarios. The considered incoming fluxes in the sub-divertor range between 1020 to 1022 (H2 s−1). The main conclusions, which can be extracted from the present numerical analysis could be summarized as follows; a large fraction of incoming neutral particle flux i.e. >70% on the low iota side and >40% for the high iota side is leaked back to the main divertor region, while higher incoming neutral fluxes facilitate the increase of the pumped flux as well as the decrease of the outflux. It has been estimated that a small fraction ∼3%–4% of the incoming neutral flux is being pumped via the turbo-molecular pumps. The closure of the toroidal leakages as well as the inclination of the pumping gap panel by 9o facilitate the increase of the pumped flux, but considering the all the engineering constraints, the latter option seems to be more easy to be implemented. For low incoming neutral fluxes (∼1020 H2 s−1) and for the case of AEH section, free molecular flow conditions are estimated and therefore neutral-neutral collisions could be neglected. For higher incoming neutral fluxes and for both AEH and AEP sections neutral-neutral collisions play a significant role in the flow establishment. A comparison with available experimental measurements of the neutral pressure in the sub-divertor has been performed for Standard and High-Iota plasma discharges. The 3D DIVGAS simulations predict qualitatively the experimental data with relative deviation between 25 and 63%. All the above numerical findings will actively support the optimization of the W7-X particle exhaust, in view of the experimental campaign OP2.

Modeling the performance of a single rotor row in a turbomolecular pump using the TPMC method: effects of operational and geometric variables

Modeling the performance of a single rotor row in a turbomolecular pump using the TPMC method: effects of operational and geometric variables

Development of a research cryostat for direct thermoacoustic cooling and conversion of hydrogen

Hydrogen thermoacoustics is a relatively unexplored but promising topic for development of new cryocoolers and hydrogen liquefaction. This paper describes a new research cryostat designed to investigate hydrogen as a working fluid in thermoacoustic systems. The cryostat is a modular, turbo-molecular pump driven, vacuum chamber with a 4.2 K pulse-tube cryocooler capable of 45 W of cooling at 50 K. Using this cryostat, a feasibility study of direct thermoacoustic cooling with ortho-parahydrogen conversion is initiated. An acoustic resonator system is designed to have the fundamental acoustic mode excited via imposed temperature gradient in a porous stack between the ambient environment and cold bar connected to the cryocooler. The generated acoustic waves transfer heat inside another porous stack to produce a refrigeration effect at cryogenic temperatures. In addition, the regenerator solid matrix will be catalyzed for ortho-parahydrogen conversion to demonstrate a novel combination of cooling and conversion of cryogenic hydrogen in a single device. Design, construction, and performance of the cryostat and modelling results for one thermoacoustic system are reported.

Non-invasive rotor temperature detection of magnetically levitated turbo molecular pump based on high-frequency inductance

The rotor temperature has a significant effect on the reliable operation of the magnetically levitated turbo molecular pump (MLTMP). Therefore, it is crucial to monitor the rotor temperature during the operation of the MLTMP to prevent irreversible demagnetization of the permanent magnet and improve production efficiency. However, direct measurement of rotor temperature is a challenge due to the complexity of installing a temperature sensor on the high speed spindle. This paper presents a non-intrusive method for detecting rotor temperature based on high-frequency(HF) inductance estimation. On this basis, a novel method is proposed that injects a HF rotating voltage into the stationary coordinate frame and introduces synchronous demodulation to achieve accurate estimation of the HF inductance. Finally, the experimental results conducted on the MLTMP test bench indicate that the proposed method can effectively detect the rotor temperature, and the temperature error is within 3 ∘C.

Closed-cycle noble gas recycling system for high-repetition rate high-harmonic generation.

We present a compact closed-loop recycling system for noble and inert gases. It has been developed for an extreme-ultraviolet (XUV) frequency comb based on high-harmonic generation at 100 MHz repetition rate. The system collects gas injected at several bars of backing pressure through a micrometer-sized nozzle into the laser-interaction region with a differential pumping system comprising turbomolecular pumps, and subsequently compresses the gas to a pressure of up to 200bar. By drastically reducing the waste of expensive gases such as xenon and krypton, it enables the long operation times needed for spectroscopic measurements, as well as for continuous operation of the XUV frequency comb.

A novel twisted rotor blade suitable for high-speed turbomolecular pumps: Numerical modelling and structural optimisation

To meet the urgent need for a new design concept and solve the inaccuracy of existing performance prediction algorithms for high-speed turbomolecular pumps (TMPs), a new algorithm based on a novel twisted rotor blade is proposed. In this algorithm, the blade angle of the turbine rotor row progressively decreases from the root to the tip of the blade tooth. The feasibility and accuracy of the simulation algorithm were verified through experiments. The dependence of the simulation results on the number of simulated molecules was discussed. Both theoretical analysis and simulations confirmed the necessity of setting a twisted rotor blade in the turbine combined blade row. A comparative analysis on the performance of conventional straight-blade and twisted-blade structures based on the first-four stages of turbine combined blade rows of the F-63/55 TMP was conducted. The results indicated that the maximum pumping speed coefficient and maximum compression ratio of the optimised twisted-blade structure increased by 4.59% and 22.26%, respectively. This novel blade structure overcomes the limitations of the conventional straight-blade structure. Progressively decreasing the rotor blade angle from the root to the tip of the blade tooth is beneficial for improving the performance of TMPs. This study provides a new design concept and performance prediction algorithm for the structural optimisation of high-speed TMPs.

Design and performance of the front-end electronics of the charged particle detectors of PADME experiment

The PADME experiment at LNF-INFN employs positron-on-target-annihilationto search for new light particles. Crucial parts of the experiment are the chargedparticle detectors, composed of plastic scintillator bars with light transmittedby wavelength shifting fibers to silicon photomultipliers (SiPMs). The location ofthe detector — close to a turbomolecular pump, inside a vacuum tank, and exposedto 0.5 T magnetic field — has driven the design of custom modular SiPM front-endand power supply electronics. The design of the system and its performance, confirmingthe desired sub-ns resolution on the reconstructed particle flying times, is shownand discussed.

Self-Identification and Balancing for AMB-Rotor System of Turbomolecular Pumps

Self-Identification and Balancing for AMB-Rotor System of Turbomolecular Pumps

Control of hydrogen concentration on InGaZnO thin film using cryopumping system

Amorphous InGaZnO thin film transistors (a-IGZO TFTs) have been extensively studied as driving transistors for large organic light emitting diode (OLED) displays due to its’ exceptional uniformity. However, the positive bias stability (PBS) of a-IGZO TFT is not sufficiently acceptable to endure the long on-stress time. Here, the effect of hydrogen impurities in a-IGZO channels on the stability and performance of TFTs used in OLED displays are investigated. The hydrogen content in the a-IGZO film is reduced to limit the formation of trapping sites for charge carriers and improve TFT stability. This study uses a cryogenic pumping system to reduce the hydrogen impurity density during the deposition process and examines the electrical characteristics of bottom-gate a-IGZO TFTs. The threshold voltage shift (ΔVth) of the a-IGZO TFT fabricated using the cryogenic pumping system was found to be reduced by 3.4–6.9 V, compared to the TFT fabricated using the turbo molecular pump system. The hydrogen and oxygen concentrations in the oxide thin films are quantitatively analyzed, and the mechanism of OH bonding acting as an electron trap during positive bias stress is explained. Overall, this study provides insights into the impact of hydrogen impurities in a-IGZO TFT stability and performance, as well as proposes a method using cryopump for reducing hydrogen impurities to improve OLED display reliability.

Magnetically Levitated Turbomolecular Pump

Magnetically Levitated Turbomolecular Pump

The annealing setup and associated monitoring system of the ELIADE HPGe clover detectors at ELI-NP

We report a dedicated setup built in-house for the annealing of the HPGe clover detectors of the ELI-NP Array of DEtectors (ELIADE) γ-ray spectrometer, as well as the post-annealing testing of these detectors with the standard 60Co & 152Eu radioactive calibration sources employing conventional analog electronics. Both the design and assembly of the annealing setup were performed at the Extreme Light Infrastructure — Nuclear Physics (ELI-NP) facility, Măgurele, Romania. A `radiation damage annealing assembly kit' (NRK-200 unit) from the detector manufacturer Canberra is utilized in heating and controlling the temperature of the Ge crystals of the annealed detector. The vacuum inside the detector was maintained throughout the annealing process by constantly pumping the system using a turbo-molecular pumping station. The temperature of the germanium crystals, located inside a vacuum sealed chamber, of the detector and the vacuum level of this chamber were monitored throughout the annealing process, via both in-person observation and remote (online) monitoring. The Graphic User Interface (GUI) of an underlying LabVIEW script was utilized for running the monitoring process of the temperature and vacuum pressure values via a local network. To have the option of real-time online monitoring of the temperature, vacuum pressure, we coupled the web application Grafana with the Influx DB of the annealing data, as well as the backup time information of an Uninterruptible Power Supply (UPS) unit used in system.

Fabrication and characterization of CaF2 target for multi-nucleon transfer reaction studies

Thin CaF2 targets with carbon backing are fabricated for the first time using physical vapour deposition technique at the target laboratory of IUAC, New Delhi to perform a multi nucleon transfer reaction on 10,11B＋40Ca systems using General Purpose Scattering Chamber (GPSC) facility. Ca being an oxidizing material, we have used molecular CaF2 as the target material instead of Ca. Using turbo-molecular pump based coating unit (TMPU), carbon is deposited on cleaned glass slide and then CaF2 is deposited on diffusion pump based coating unit (DPU). We are successful in fabricating CaF2 targets of thickness ≈264.4μg/cm2 on carbon backing of thickness ≈21.5μg/cm2. The thickness and purity measured by the crystal thickness monitor equipped with the vacuum chamber is verified by different techniques like alpha energy loss, Rutherford Back Scattering (RBS), Electron Diffraction Spectroscopy (EDS) and X-ray Diffraction (XRD). Small impurity level were smeared during the observation and the target is successfully used for nuclear reaction experiment. The fabrication of molecular Ca target is found to be more conducive to experimentation since they exhibit less oxidation and herewith we discuss about fabrication technique, experimentation and characterization.

Capacitance-based absolute pressure gauge for beamline vacuum measurement applications

For low-pressure measurements, capacitance diaphragm-based absolute pressure gauges are used owing to their high accuracy, media independence, and simplistic design. Catering to the general requirements of synchrotron beamline vacuum measurements, a capacitance diaphragm-based absolute pressure gauge is designed, developed, tested, and calibrated. The sensor is having electrode assembly which forms a dual capacitor with the gauge body. The two capacitances are used in post-processing to reduce the noise levels and to enhance the precision and accuracy of the measurements. The reference side is at high vacuum of the level 5 × 10-5 Pa. The vacuum of the reference side is generated using a Turbo Molecular Pump and is sustained by pinching-off the reference side at this vacuum. A getter pump is provided and energized for improving the vacuum which otherwise gets deteriorated due to outgassing in the reference region of the gauge. The fabrication methods adopted for fabricating the gauge are novel. The diaphragm is fabricated from bulk material using the electrical discharge method (EDM). This helped in achieving a perfect diaphragm with linear deflection with pressure variation and attained a 100% success rate. Unlike the fabrication by welding of plate, this method is robust, economical, and helped in achieving similar properties across the gauges. The second innovation is in the fabrication of electrode assembly. Unlike commonly used electrodeposited electrodes; the presented technique used copper plates which sandwich the Alumina dielectric. The plates are bolted/brazed/welded across the ceramic disc with the help of pins which also help in the parallel connection of the dual capacitors are described later. This made this method of fabrication largely rejection free with the potential of repairs and testing with different plate configurations. This paper is presenting the design, production, and calibration of the gauge using these fabrication techniques for 1 × 103 Pa to 1 × 105 Pa.

Handling of high-volume High Purity Germanium gamma ray detector and repair with minimum resources – A case study

A High Purity Germanium (HPGe) detector is a high-resolution detector, used for gamma-ray spectroscopy. One such HPGe detector of our laboratory was showing poor resolution either due to malfunctioning of components or vacuum. This detector being a sophisticated instrument need to be operated in an environment with adequate cooling and humidity control. The optimum conditions such as maintaining liquid Nitrogen filling in Dewar at proper time and holding capacity of Dewar and humidity control environment could not be maintained due to lockdown conditions during the pandemic. This disrupted the functioning of the detector resulting in poor performance and poor resolution. One reason for such a behaviour is attributed to the condensation of moisture at the feed through points of High Voltage and failures of components such as preamplifier and Field Effect Transistor (FET). Transportation of the detector for repairs to France involves lengthy procedures, additional expenditure, custom clearance and safe transit. The possibility of performing the detector repair with the available facility on premise was explored. The repair involved breaking of vacuum in Clean room Facility, availability of Variac, Vacuum gauge, Dry Nitrogen, Helium leak detector, Liquid nitrogen, Temperature sensor with controller, Turbomolecular pump, Vacuum plunger etc. The diagnosis of cascading failure of components in the germanium detector and their rectification to restore its functionality with desired performance has been discussed in the present paper.

Experience of pumping the vacuum vessel of SST-1 during the baking cycle with indigenously developed liquid nitrogen cooled sorption pump

To achieve ultra-high vacuum in the vacuum vessel of SST-1, the baking of vacuum vessel is done to remove impurities like water vapour, carbon-dioxide and hydrocarbons etc. The maximum baking temperature of the plasma-facing components (PFCs) are around 250 °C and the vacuum vessel is around 150 °C. The gas load of water vapour increases significantly during the baking operation. Therefore, to pump the water vapour during baking, a customized liquid nitrogen cooled sorption pump was designed, fabricated and installed on the radial port of the machine. It is the first time that liquid nitrogen cooled Cryopump was used on the SST-1 machine. The pumping of water vapour, nitrogen and impurity gases was observed during the 11 days of operation. Commercial Cryopumps are operating at ∼10 K temperature and can pump hydrogen gas however, the direct mounting of these pumps during baking results in early regeneration of the pump due to high heat load. Therefore, the experience of pumping the vacuum vessel of SST-1 with the indigenous developed sorption pump in association with the Turbo-Molecular Pump (TMP) sets is discussed systematically in the present report. The partial pressure of the water vapour using TMP sets was 1.0E-6 mbar and after incorporating the sorption cryopump with the existing vacuum system, the partial pressure reached to 1.3E-7 mbar in 48 h at 230 °C PFCs temperature. The pressure attained in the vacuum vessel was ∼1.0E-7 mbar and the partial pressure of water vapour was ∼1.1E-8 mbar after ramp-down the PFCs to 50 °C temperature.

A simplified analysis method and suppression of the modalities of a magnetic levitation turbo rotor system

The modal vibration of the rotor of the magnetic levitated turbomolecular pumps(MLTMP) is one of the key issues affecting the high-speed stable operation of the magnetic levitation turbo rotor-bearing system. Aiming at the problem of the modal self-excited oscillation of the magnetic levitation turbo rotor system, a rotor dynamics modeling method is proposed according to the structural characteristics of the rotor. The variation rules of the rotor mode is obtained by the numerical simulation method and the experiment. Then, based on the proposed model, the phase compensation method is adopted to effectively restrain the modal self-excited oscillation of the rotor. Finally, experiments were carried out on the MLTMP prototype, and the results showed the accuracy and effectiveness of the proposed scheme.

Stability control of high-speed magnetic levitation turbomolecular pumps with shock-excited disturbance

The disturbance suppression of magnetic levitation turbomolecular pumps is a critical problem in industrial applications. This work addresses the stability control of high-speed magnetic levitation turbomolecular pumps with shock-excited disturbance. A disturbance suppression method based on improved linear extended state observer is proposed to attenuate the impact of external low-frequency disturbing force on a magnetic levitation turbomolecular pump. Firstly, a linear extended state observer of an active magnetic bearing is obtained by analyzing the rotor dynamics model. Then, the detailed descriptions of external disturbance suppression method using linear extended state observers and adaptive notch filters are discussed for the system. The boundary condition of the parameters of the improved linear extended state observer is determined. The root loci of the closed-loop system with improved linear extended state observers is also investigated. Finally, simulation and experimental results on a magnetic levitation turbomolecular pump show the applicability of the proposed method. The results show that the proposed method can attenuate the rotor vibration displacement caused by impact by 46.9%.

Design of vacuum system for NCST spherical tokamak

The NanChang Spherical Tokamak (NCST) is a new compact tokamak with an aspect ratio of R/a = 1.67. The vacuum system is one of the most important sub-systems of the tokamak device and has been designed especially for the NCST device. It consists of three main parts: a pumping system, a gas puffing system, and a wall conditioning system. The pumping system includes two turbo-molecular pumps, a cryopump, and two rotary pumps. The gas puffing system consists of a gas supply, transfer lines, a gas reservoir, pressure gauges, and piezoelectric valves. The wall conditioning system includes baking and glow discharge cleaning functions. The vacuum system and related experimental results are described in detail in this paper. The test results indicate that the NCST vacuum system is reliable. Inside the vessel, the ultimate pressure reached 4.2 × 10−6 Pa after 307 h of pumping. The upgraded gas puffing system can accurately control the gas entering the vacuum vessel. The wall conditioning systems, such as those for baking and glow discharge cleaning, also play a very important role in plasma operation. The plasma discharge results show that the basic function of the vacuum system meets the essential requirements of the present experiments on the NCST tokamak.