Turbomolecular Pump Research Articles

A low noise cryogen-free scanning tunneling microscope-superconducting magnet system with vacuum sample transfer.

Imaging atomically resolved surfaces and performing spectroscopy of exotic surfaces at cryogenic temperature in the presence of the magnetic field is an engineering challenge. Additionally, performing these measurements in an all-cryogen-free environment compounds the above complexity due to the associated vibration and acoustic noise generated by the running of cryogenic cold heads. We here report successful integration of a cryogen-free scanning tunneling microscope (STM) with a cryogen-free superconducting vector-magnet, connected to an ultra-high vacuum cluster assembly for in situ sample transfer. We present details of the integration involving vibration and electrical noise isolation procedures allowing for operation of the STM at extremely low noise levels below 30 fA/Hz during normal operations of the complete vacuum-line assembly with multiple turbomolecular pumps. We demonstrate the above STM capability at cryogenic temperature and in the presence of the magnetic field through atomic resolution imaging of graphite and thin films of gold on the mica substrate transferred in situ to the STM chamber. We also demonstrate spectroscopy signatures of the superconducting gap in MgB2 thin films. The design of our in-house customized cluster-vacuum-line assembly provides unsought opportunities in continuous uninterrupted imaging of ultra-clean in-vacuum grown surfaces without the need for cryogenic refills in either the STM or the magnet.

Rotor Balancing for Magnetically Levitated TMPs Integrated With Vibration Self-Sensing of Magnetic Bearings

Due to the rotor unbalance of the magnetically levitated turbo molecular pump (TMP), this article presents a novel high-precision field balancing method based on regular control mode without trial weight. First, the static/dynamic unbalance vector expressions of the magnetically levitated rotor are analyzed and derived in polar coordinates frame. Second, according to the synchronous currents and displacement responses of the rotor at a fixed speed, the correction weight can be solved by the double-plane correction method based on equivalence principle of the magnetic forces. Then, in order to reduce the deviation between theoretical and actual value of the magnetic bearing parameters, this article proposes a second correction method by correcting the conversion coefficient matrix from online identification procedures. The proposed method, which can eliminate the errors introduced by the oversimplification of dynamic model in regular control, is especially suitable for the magnetically levitated rotor system with strong gyroscopic effects and asymmetric structure. Finally, the experimental results on a magnetically levitated TMP prototype validate the effectiveness of the proposed method. Compared with the original unbalance of rotor, the synchronous current amplitude declined by 99.0%, and the synchronous displacement amplitude also declined by 96.1% with the proposed method. A high-precision field balancing has been achieved.

A New Modeling Method to Reveal Pumping Mechanism of Turbomolecular Pump

In order to meet the calculating requirements of high speed and miniaturized turbomolecular pump (TMP), a new modeling method is proposed for a rotor-stator row. In the same Cartesian coordinate system, the analytical equations of blade row are derived according to the real three-dimensional geometric model. A self-defining procedure is written to simulate the flow of gas molecules in TMP based on test particle Monte Carlo method. The procedure not only can calculate transmission probability of rotor row, stator row and a rotor-stator row but also evaluate the pumping performance of different blade parameters. The simulation results and known experimental data have a good agreement to confirm the feasibility of presented modeling method. The flow analysis shows that molecules at outlet of rotor row tend to accumulate in large radius and this phenomenon is obvious for high rotational speed. The differences were found between a single-stage row and a rotor-stator row. In rotor row, the molecular density at the rear blades is the highest. This is beneficial for pumping speed of TMP because 57% of molecules at the rear blades are likely to reach outlet. This will provide a direction for the structural optimization design of the blades in the future. In stator row, the molecular density reaching outlet does not significantly increase with the increase of blade velocity ratio, which indicates that the stator row is mainly used to increase the pressure ratio of TMP. The analysis of molecular density in each region reveals the pumping mechanism of TMP.

Влияние межступенчатого канала на эффективность молекулярной ступени комбинированного турбомолекулярного насоса

The interstage channel is one of the factors affecting the efficiency of the molecular drag stage in a hybrid turbomolecular pump (TMP). The influence of parameters of the channel on the pumping performance of the molecular drag stage is investigated. The offered approach allows calculating the pumping performance of a molecular drag stage taking into account the effect of the interstage connecting channel on the pumping process. The comparison of the pumping characteristics of a molecular drag stage obtained in calculation taking into account the effect of the channel and excluding it is given. This article assesses the efficiency of the molecular drag stage in a hybrid TMP depending on geometric and dynamic parameters of the channel. The outcomes and recommendations allow to expand the range of working pressures of a hybrid TMP exclusively by means of parameters of the connecting channel.

Исследование межступенчатого канала комбинированного турбомолекулярного насоса

The calculation is based on the use of Monte Carlo method (method of test particle), which consists in the statistical modeling of processes. The article describes an algorithm to construct a mathematical model step by step. The article defines both a probability for gas molecules to pass through the interstage channel of a hybrid turbomolecular pump in forward and backward direction. The effect of the movable walls limiting the channel is taken into account. Results and, accordingly, recommendations, given in the article, can be used in designing a flow passage of the hybrid turbomolecular pumps. The dependencies of a probability for gas molecules to pass through the interstage canal on the relative parameters determining the geometry and dynamics of the channel walls are given

Driver Circuit Improvement of Eddy Current Sensor in Displacement Measurement of High-Speed Rotor

Displacement sensor is the key component of the magnetic levitation system. Reducing complexity and improving reliability of the sensor circuits are very important to mass production of magnetic levitation devices. In this article, an improved driver circuit of eddy current sensor is proposed. In order to generate a stable oscillating source with high stability and good precision of frequency, a crystal oscillator circuit with power boost is used to replace the traditional Colpitts oscillator circuit. The improved modulation circuit is composed of passive components with a simple structure for improving reliability. The parameters design method of the modulation circuit is analyzed in detail, which greatly affects the sensitivity and linearity of the sensor. The experimental results show that the designed eddy current sensor has good linearity (1.12%) and sensitivity (2.14 V/mm), and it can ensure the stable operation of the magnetic levitated turbomolecular pump at the rated speed.

Nutation Mode Suppression of Magnetically Levitated Turbo-Rotor via Damping Optimization

The significant nutation will degrade the stability of high-speed magnetically levitated turbo-rotor system. This article presents a damping optimization method to suppress the nutation mode. The proposed method consists of two parts: nutation compensation and damping optimization. The nutation compensation with the cross-channel displacement signal is designed in detail to increase the damping force of nutation mode in the first part. The root locus of the closed-loop rotor system is used to analyze the effect of damping compensation. The control parameters are iterated to configure the pole of the nutation mode with the goal of making the rotor system have the optimal damping ratio at the nutation mode. Finally, simulation results show that the nutation damping ratio of the rotor system with the proposed method is greater than 0.658, and the experiment results on a magnetically levitated turbomolecular pump prototype validate that the proposed damping optimization method can effectively suppress the nutation mode and its power spectrum level is below $-$60 dB over the entire speed range.

Water pumping performance of a Cryo–TMP combination pump

There is an increasing need to systematically investigate the performance of commercial Cryo–TMP [in-line Cryogenic Water Pump (CWP) + Turbo Molecular Pump (TMP)] combination pumps. In this study, the factors affecting the pumping speed of water in a Cryo–TMP, such as the number of cold rings, dimensions, shape, etc., are systematically analyzed by Monte Carlo simulation. We constructed a test dome and a Cryo–TMP500 based on the simulation results to measure the strict effective pumping performance of the Cryo–TMP. In addition, we established a systematic measurement method for pumping performance using the Cryo–TMP500 in three experimental modes: TMP-only mode, CWP-off mode, and CWP-on mode. The results show that the water pumping speed of the Cryo–TMP500 with only one cold ring is ∼76% of that of a standalone cryopump (∼30 000 L/s) with the same opening inlet diameter; this speed is 22 550 L/s, which is in good agreement with the simulation result of 23 276 L/s. The pumping speeds for non-condensable gases (H2, N2) are 8%–19% higher than expected.

SIMULATION OF GAS RELEASE FLOWS FROM THE FLOW SURFACES OF TURBOMOLECULAR VACUUM PUMPS

An algorithm for modeling and an example of calculating gas release flows from the surfaces of the flow part of a turbomolecular pump by the Monte Carlo method in a three-dimensional setting low-density gas flow is considered.

Cavity Ring-Down Spectroscopy for Molecular Trace Gas Detection Using A Pulsed DFB QCL Emitting at 6.8 µm

A trace gas sensor based on pulsed cavity ring-down spectroscopy (CRDS) was developed for measurement of the ν4 fundamental vibrational band of ammonia (NH3) centered at 1468.898 cm−1. A pulsed distributed feedback quantum cascade laser (DFB-QCL) operating at 6.8 µm (1470.58 cm−1) quite well covered the absorption band of the ammonia and strong fundamental vibrational absorption bands of different molecular gases in this unexplored region. The cavity was partially evacuated down to 0.4 Atm by a turbo-molecular pump to reduce the partial interference between the NH3 spectra and water near the absorption peak of ammonia. A sensitivity of nine parts per billion was reached for a measurement time of 120 s as well as an optical path length of 226 m. The device demonstrated high spectral performance and versatility due to its wide tuning range, narrow linewidth, and comparatively high-energy mid-IR radiation in the relatively unexplored 6.8 µm region, which is very important for high-resolution spectroscopy of a variety of gases.

Improvement of deuterium emission by St 172 NEG pump in a sealed off vacuum device

Zirconium based alloys are proved to be a good material for hydrogen storage as well as a vacuum pump. A non evaporable getter pump based on St 172 was tested for deuterium storage capacity in a sealed off vacuum device. The vacuum in the range of ultra high vacuum was maintained by the getter pump by gettering. Initial vacuum was created by a turbo molecular pumping system. After activation of the getter, test chamber was charged at 1 bar and 3 bar deuterium pressure for 24 h in two different experimental campaigns. After charging with deuterium, the chamber was pumped to ultimate vacuum and isolated from the TMP. The partial pressure of deuterium for different temperature of the getter was measured in sealed condition. Higher charging pressure improves the partial pressure of deuterium during desorption cycle. The experimental details and the results are presented in this article.

High-Precision Position Error Correction Method for the PMSM Based on Low-Order Harmonic Suppression

Accurate rotor position is necessary for high-performance control of a permanent-magnet synchronous motor. Compared with the methods using position sensors to detect rotor position, the sensorless methods can simplify the motor structure and enhance the reliability. To improve the estimation accuracy of sensorless methods, the position error correction method based on the low-order harmonic suppression is proposed in this article. The low-order harmonics generated by the position error are analyzed in detail, which will cause extra motor losses. The position error signal can be reconstructed by low-order harmonics that are extracted by rotating the frame transformation and low-pass filter. And the estimated position can be corrected using the reconstructed signal. The proposed method can not only improve the position estimation accuracy, but also suppress the low-order harmonics, which can reduce motor losses and enhance the motor performance. Based on space vector pulsewidth modulation, the proposed method is independent of motor parameters. It can be applied to the sensorless methods that can obtain voltages. The position error correction method has well dynamic performance and great robustness. The effectiveness is verified by the experiments on the turbo molecular pump.

Introduction of ITER CODAC relevant technologies on JET and MAST

Abstract The JET control and data acquisition system (CODAS) is an integrated system that provides all the pulse based and continuous data acquisition, real time and slow control and control room interfaces for JET. It has a long history, dating back to the beginning of JET in 1980. It utilises both commercially available hardware along with many in-house modules. The software has grown up and evolved largely independently of other developments in big science. Similarly, the data acquisition system on MAST has a long history of evolution from previous facilities at Culham (COMPASS). It utilises commercially available and in-house hardware (some shared with JET CODAS) and software that has developed largely independently of JET and other external developments. More recently, we have begun to adopt some ITER CODAC relevant technologies on both JET and MAST, in part, to also introduce some standardisation between the two facilities. This started with a pilot project to create a cubicle and environment monitoring system using commercial hardware and EPICS monitoring and HMI. We have since gone on to implement several camera and spectrometer filter controllers, several types of turbomolecular pump controller, and various radiation protection monitors in EPICS on JET. We are also implementing a central information display system for MAST that links the OPC interface on the machine control through to several display screens showing the machine state using EPICS. We have several MARTe based real time applications on JET and are now developing an application to provide real time processing of high-resolution Thomson scattering data using MARTe V2 (an ITER/F4E initiative to improve the robustness of this real-time framework). We are also considering upgrading the existing MARTe applications to this version. On JET we have also started to use another ITER CODAC technology – SDN to supplement the ATM based real time control network on JET. Initially, as a proof of principle, a real time plasma profile display was implemented. This system is now being extended to include several real time data sources which will feed their data back into the ATM network and on to the real time controllers. Looking forward, we anticipate extending the JET real time network with a purely ITER CODAC/SDN connected real time control system and provide a richer ITER CODAC interface to the JET CODAS to accommodate the possibility of ITER diagnostics testing and provide a real stress test for ITER archiving technologies.

Thermo-structural analysis of SST-1 cryopump

A liquid nitrogen-based cryopump for Steady State Superconducting Tokamak (SST-1) is designed for pumping of water vapour from vacuum vessel during baking and under heavy gas load conditions. During baking, the load of the water vapour molecules increases while the resultant speed of available Turbo-Molecular Pumps is less for water vapour which increases the pressure of the vacuum vessel. Cryopump with the same opening area as of TMPs has more pumping speed for water vapour molecules. Hence, the said cryopump will pump water vapour molecules with higher pumping speed. In principle, water vapour molecules get condensed at a surface temperature of <120 K which corresponds to the saturation pressure of <10−10 mbar. The pump is based on the cryosorption principle where nitrogen gas and water vapour get adsorbed on to the cryosufaces at a temperature of <80 K. The amount of gas pumped and accumulated on cryosurfaces depends on many factors such as the temperature of a gas, microscopic surface roughness of cryosurface, its temperature and thermal conductivity, etc. [1]. Various components of this cryopump are thermal shield, cryopanels coated with suitable sorbent, baffles and vacuum chamber. For reliable and long duration operation of this pump, detailed thermal analysis is done to study the temperature distribution and thermal stresses generated for the efficient operation of the pump. Thermo-structural analysis of the developed pump is carried out for failure protection. The design by analysis method is followed to realize the concept of cryopump for SST-1 and the same is described in this paper.

Gas Flow in a Multistage Turbomolecular Vacuum Pump

The gas flow in a multistage turbomolecular pump is simulated so as to optimize the design of the rotor and stator blades. Monte Carlo software reveals how pump performance is affected by the geometry of the individual stages.

Adoption of getter pump for HTS superconducting cable system

For the superconducting cable operation in the real grid for over decades, one of the important technical challenges is maintaining vacuum rate of the thermal insulation cryostat vessels for avoiding system heat loss increase. When the vacuum rate is getting worse, turbo-molecular pumps etc. are usually adopted for that system. However, these pumps need to have some installation space and some electricity for the operation and moreover, periodic troublesome maintenance is needed. For the countermeasure of such issues, getter pump is selected and tested because of its smaller size, less electricity consumption and easy maintenance features. After confirming its effectivity as the vacuum pump by several investigations, this pump was employed for the termination vacuum vessel of the superconducting cable system in Yokohama. From the results of 3 weeks operation, evacuating performance exceeds turbo molecular pump and keeps vacuum state less than 1e-3 Pa stably, are confirmed respectively. This paper describes test results of the getter pump and its operation results for the real in grid system.

Design and Analysis of liquid nitrogen cooled sorption cryopump for SST-1 Tokamak

Abstract SST-1 is a Steady State Superconducting Tokamak for a proposed plasma discharge of long duration. This plasma device has two vacuum vessels, the cryostat and the vacuum vessel (VV). Cryostat houses the superconducting magnet systems (TF and PF coils), LN2 cooled thermal shields and hydraulics for these circuits and the plasma will be confined inside the VV [ 1 ]. To have plasma discharges, ultra-high vacuum (UHV) is required to be maintained in VV [ 2 ]. To attain a vacuum level of ∼1 × 10-8 mbar in VV, the plasma-facing components (PFCs) are baked to a temperature of 250 °C and the vacuum vessel is baked to a temperature of 150 °C to remove impurities from the bulk of materials which are adsorbed/absorbed. In baking, the gas load of mainly water vapour and hydrogen gas is increased. The pumping system for vacuum vessel consists of six sets of turbo-molecular pumps (each set consist of 3 TMP) and one cryopump which is sufficient to achieve a vacuum of

Loss estimation, thermal analysis, and measurement of a large‐scale turbomolecular pump with active magnetic bearings

Temperature rise subjected to the copper losses and iron losses is an important issue for a magnetically suspended turbomolecular pump (MSTMP). In this study, the loss estimation, thermal analysis, and temperature rise measurement of a large-scale MSTMP are investigated. The copper losses and the iron core losses of two radial magnetic bearings, a thrust magnetic bearing, and a brushless direct current motor (BLDCM) are predicted by the analytical models. Based on the predicted loss values, the heat generation rates in the different parts of the large-scale MSTMP are calculated, then the thermal field of the prototype is analysed by the 3D finite-element model. The maximum temperatures estimated for the rotor part and stator part are located at the rotor sleeve and the winding end of BLDCM, which are 68.5 and 55.2 °C, respectively. The loss calculation and thermal field prediction is validated by the temperature rise test in a prototype of large-scale MSTMP with pumping speed of 4100 L/s, ultimate vacuum of 1.8 × 10−7 Pa, and rated speed of 21,000 r/min. The maximum error between the estimated and the measured temperature rise values is <5%.

Stabilization of a Magnetically Levitated Rotor in the Case of a Defective Radial Actuator

This article describes an operation mode for the stabilization of a 5-DOF active magnetic bearing system in the case of a damaged radial actuator. The proposed method has the task to stabilize the underactuated rotor to ensure a safe deceleration. The resulting underactuated system is not reachable for the admissible angular velocity range. Thus, the rotor could be destabilized for some operating points. However, for a real system with a nonideal isotropic magnetic behavior, the system is reachable for all angular velocities. For the stabilization of the underactuated system, PID controllers are used. The parameters of the PID controllers are calculated using the linear quadratic regulator method. This simple realization of the controllers implies a short computing time. To show the stability and the robustness of the designed controllers, different root loci are visualized. The proposed operating mode is able to prevent the safety bearings from wear and damage in the case of a defective magnetic actuator. Finally, the underactuated operation mode is experimentally validated on a turbomolecular pump, where the center of gravity is not located between the magnetic actuators.

Numerical simulation of gas flow through the flow part of a multi-stage turbomolecular vacuum pump

The modeling of gas flow through a multi-stage flowing part of a turbomolecular vacuum pump to optimize the parameters of rotor and stator impeller wheels is considered. The developed program of statistical modeling by the Monte Carlo method allows us to determine the influence of the geometric parameters of the stages on the pump performance indicators. Keywords turbomolecular pump, impeller wheels, maximum action speed, maximum pressure ratio, Monte Carlo method. marc081939@gmail.com