Titanium Sublimation Research Articles

Long-pulse diagnostic calorimeter for the negative ion source testbed BATMAN upgrade.

The RF-driven negative ion source testbed BATMAN upgrade is being developed at IPP Garching in the framework of the ion source development for ITER and DEMO neutral beam injection systems. The testbed has recently been enhanced to allow for steady state operation with a focus on beam optics studies. The previous titanium sublimation pumps and inertial calorimeter limited the beam pulse length to about 6s every 3min. The upgrade comprises a long-pulse compatible, actively cooled diagnostic calorimeter. This has been designed and is currently being manufactured to substitute the inertially cooled calorimeter that has limited diagnostic capabilities. The new diagnostic calorimeter consists of a copper plate with dimensions of 910 × 660 × 25mm3 placed about 2m from the ion source extraction grids, and through a novel solution, it will provide a 2D profile of beam power density with a 20mm spatial resolution. Water flowing through cooling channels embedded in the copper plate will actively cool the calorimeter, which is loaded with about 160 kW beam power at ITER-relevant current density, but 45 kV acceleration. A fraction of the beam will pass through many small apertures (ø2mm) positioned in the calorimeter plate and will be collected by thin (0.2mm) copper foils attached to the calorimeter back side. Evaluation of power density will be performed by measuring the temperature of the heat flux foils with a high-resolution infrared camera observing the calorimeter from the back side and calibrated by thermocouples.

A Study of the Gettering Characteristics of Getter Pumps for Different Gases

The gettering characteristics of Ti–Zr–Al getter pumps with internal and external heaters have been measured for Н2 and CO. The results are compared to the measured similar characteristics of an NEX‑Torr D 100-05 combined pump from SAES Getters and a titanium sublimation film at temperatures of 300 and 77 K.

Vacuum System of the NICA Project

This paper presents the progress of development of the NICA project vacuum system. The main vacuum requirements in the chain of accelerators and the current status of work are described. Special attention is paid to the problems of achieving ultra-high vacuum in the booster. The test bench for the study of most efficient pumping tools for the beam chamber of the superconducting fast cycling synchrotron has been designed and built for this purpose in cooperation with the VakuumPraha Company (Prague, Czech Republic). The vacuum distribution in the superconducting accelerators with “warm” chamber parts at room temperature was simulated using specialized software. The simulation showed that it is necessary to install additional pumping equipment along the booster perimeter. To solve this problem, the original design of a titanium sublimation pump operating at cryogenic temperatures is under development in collaboration with the Budker Institute of Nuclear Physics (Novosibirsk, Russia).

Application of compact Non-Evaporable Getter and Sputter Ion Pump combination in UHV system of HIAF

HIAF-BRing, a new multi-purpose accelerator facility of the High Intensity Heavy-Ion Accelerator Facility project, requires an extremely high vacuum lower than 10−9 Pa to fulfill the requirements of radioactive beam physics and high energy density physics. Use of large speed Titanium sublimation pump (TSP) in combination with Sputter ion pumps (SIP) is not always feasible due to space limitations. A novel combination pump, based on Non Evaporable getter (NEG) and a 10 l/s SIP (NEXTorr® D 2000-10) has been evaluated as it provides large speed in a more compact design. The two combination pumps (TSP + SIP and NEXTorr D 2000-10) have been tested by dynamic flow method to measure the ultimate pressure, the pumping speed and the suitability for HIAF. Test results show that both combination pumps can be used in the pressure range of 10−10 Pa. The ultimate pressure of TSP + SIP combination pump is slightly lower than NEXTorr D 2000-10, but the latter one has much larger sorption capacities (H2: 210200 Pa l vs 265 Pa. l; CO: 430 Pa. l vs 24 Pa. l), which means it is applicable to a wider pressure range. At the same time, after twenty activation cycles, the initial pumping speed of NEXTorr D 2000-10 for H2 and CO decreased less than 10% as compared with the initial pumping speed of the first activation, which meets the actual vacuum system requirement of HIAF. A dedicated vacuum chamber with collimator and NEXTorr D 2000-10 has been designed and manufactured to stabilize the dynamic vacuum by decreasing the heavy ion induced gas desorption and increasing the gas pumping speed. The static and dynamic vacuum pressure evolution has been simulated to verify the feasibility of the NEXTorr D 2000-10 used in the HIAF-BRing.

Ultrahigh sensitivity SIMS analysis of oxygen in silicon

We report on the detection of very low oxygen concentration in silicon by a secondary‐ion mass spectrometry (SIMS) method. Using a magnetic IMS 6F Cameca SIMS spectrometer and applying a very high primary Cs+ ion flux, prolonged presputtering, extensive vacuum chamber baking, titanium sublimation pump, and an LN trap, we have reached a detection limit of ~2 × 1015 O atoms/cm3 in chemical vapor deposition epitaxial Si films. This value appears to be at least 10 times lower than in any published or unpublished source known to the authors, including the reference sensitivities listed by the instrument manufacturer. Most likely, the key improvement that has allowed us to drive the detection limit to 1015 at/cm3 is the use of an ion pump in the analysis chamber. The working pressure in our analysis chamber is ~10−10 Thorr, ie, 1 decade lower than that the commercially equipped with a turbo pump. This paper demonstrates optimized analytical conditions for the oxygen measurements in Si, as a function of depth: (i) Very shallow profiles are practically impossible to measure accurately because of native oxide at the surface. (ii) Shallow‐to‐medium range profiles, up to ~20 μm, are the most amenable to SIMS measurements. (iii) Medium‐to‐deep (~20‐50 μm) range is required to follow interdiffusion and segregation in epitaxial layers when the oxygen‐free layer is grown on a CZ Si substrate. (iv) Extremely deep profiles, up to full thickness of the wafer, definitely necessitate beveling.

Effect of the allotropic transition in titanium on its interatomic interaction energy

The variation of interatomic interaction energy during allotropic transition in titanium is established by analyzing the stress and temperature dependences of durability. This energy is ≈458 kJ/mol in bodycentered β-Ti at a temperature of T > 1155 K, which agrees well with the titanium sublimation heat, and ≈305 kJ/mol in hexagonal close-packed α-Ti at T < 1155 K. Literature data confirming the conclusions drawn are discussed.

Characterization and performance improvement of the large titanium sublimation pumps in the AUG and W7‐X neutral beam injectors

The experimental devices ASDEX Upgrade (AUG) and Wendelstein 7‐X (W7‐X) are equipped with two neutral beam injectors each for plasma heating with up to 20MW. Four large titanium sublimation pumps (TSPs) (4×1.5×0.2m3) in each injector provide proper vacuum conditions (below 10−2Pa) during the 10s beam pulse with a gas feed of up to 30 Pa×m3/s. A maximum pumping speed of up to 3000m3/s for H2 is obtained by frequent renewal of the Ti coating at the pump surfaces. Ti is sublimed from 4m long ohmically heated hanging pairs of Ti sublimation wires. So far, all pairs of wires were operated with constant current during 120s, despite of the large spread of the resistance of the wires. Tests have been performed in a dedicated test facility in order to characterize the pumping performance for H2 with different parameters for sublimation power and time. The data gathered can be used to simulate fully operative TSP systems for real NBI operation scenarios in AUG and W7‐X, so as to find an optimal sublimation strategy for the TSPs.

A compact atomic beam based system for Doppler-free laser spectroscopy of strontium atoms.

We report the construction of a simple, light weight, and compact atomic beam spectroscopy cell for strontium atoms. The cell is built using glass blowing technique and includes a simple titanium sublimation pump for the active pumping of residual and background gases to maintain ultra-high vacuum. A commercially available and electrically heated dispenser source is used to generate the beam of Sr atoms. We perform spectroscopy on the 5s2S01→5s 5pP11 transition to obtain a well resolved Doppler free spectroscopic signal for frequency stabilization of the laser source. This design can be easily extended to other alkali and alkaline earth metals.

Optimization of Large Titanium Sublimation Pumps for the Neutral Beam Injection System on AUG and W7-X

The neutral beam injection (NBI) system for the magnetic confinement experiments ASDEX Upgrade (AUG) and Wendelstein 7-X (W7-X) require a vacuum system with a high pumping speed of up to 3000 $\text{m}^{3}$ /s for $H_{2}$ and a large capacity with a gas feed of up to 30 Pa $\text{m}^{3}$ /s and 10 s. It must ensure a maximum vacuum level of $10^{-2}$ Pa in any section of the neutral beam line in order to avoid reionization losses. The large titanium sublimation pumps (TSPs) of the NBI system at AUG have been proved suitable for operation within the permanent stray magnetic field of W7-X (up to 30 mT) if they are operated with 200–500-Hz sine ac instead of dc for the ohmic heating of the 4-m long hanging pairs of titanium sublimators. During each heating cycle, the pair of sublimators experiences a reversible thermal expansion of around 50 mm and, in addition, the tantalum core of the sublimators is subject to material creep, leading to residual lengthening. When this lengthening reaches 70 mm after 80–100 thermal cycles (3.5–4.5 h operation time), the wires contact the bottom of the NBI vessel causing a short circuit. In order to extend the availability and operation time of the TSP, a modification of the sublimator with a tantalum–tungsten core with 2.5% W is tested, for which less creep is expected. The first results confirm a reduction in the creep rate by a factor of $\sim 20$ . This allows sublimation of the whole Ti inventory without intermediate maintenance of the TSP. Furthermore, possible short-circuit mitigation strategies are discussed.

Design of the torus interface for the neutral beam injectors of Wendelstein 7-X

A neutral beam injection (NBI) heating system for the stellarator project Wendelstein 7-X (W7-X) is currently under construction at the Max Planck Institute for Plasma Physics (IPP) Greifswald, Germany. The NBI at W7-X is based on the similar system in operation on the tokamak ASDEX Upgrade at IPP in Garching, Germany, and makes use of radio-frequency-driven positive ion sources. Two NBI injectors are going to be installed in W7-X, each being capable of hosting four ion sources. Initially each injector is being equipped with two ion sources of 1.8 (2.5)MW beam power each in H (D). Accelerated positive ions are going to be neutralized and transported inside an NBI-box, which also hosts a residual ion dump, titanium sublimation pumps and a calorimeter. The beams are focused at a point 6.5m downstream of the ion sources and are injected into the plasma vessel of W7-X through two ports. The NBI boxes and their NBI ports are connected by NBI–torus interfaces, which are made of several components that minimize beam losses while protecting the port walls and bellows from energetic re-ionized particles and beam intersection. This paper describes the design of the NBI–torus interface, including the shape optimization of a beam scraper and the integration of beam diagnostics.

Control and calculation of the titanium sublimation pumping speed and re-ionisation in the MAST neutral beam injectors

A high pumping speed is required in neutral beam injectors to minimise re-ionisation of the neutral beams. The neutral beam injectors on MAST use titanium sublimation pumps. These pumps do not have a constant pumping speed; their pumping speed depends on the gettering surface history and on both the integrated and applied gas load. In this paper we describe a method of maintaining a constant pumping speed, through different evaporation schemes, specifically suitable for operations of the MAST neutral beam injector beamlines for both short and relatively long beam pulses by measurement of the pressure in the beamline. In addition the MCNP code is then used to calculate the pumping speed and gas profile in the beamline by adjusting the input pumping speed to match the measured pressure. This allows the resulting gas profile to be used for calculation of the re-ionisation levels and an example is given.

AC operation of large titanium sublimation pumps in a magnetic field: Results of the test stand for the W7-X neutral beam injectors

A neutral beam injection (NBI) system is being built for the Stellarator experiment Wendelstein 7-X (W7-X) currently under construction at IPP Greifswald. The NBI system consists of two injectors which are essentially a replica of the system present in the Tokamak experiment ASDEX-Upgrade at IPP Garching. A vacuum system with high pumping speed and large capacity is required to ensure proper vacuum conditions in the neutral beam line. For this purpose, large titanium sublimation pumps (TSP) are installed inside the NBI boxes, consisting of 4m long hanging wires containing Ti and the surrounding condensation walls. The wires are DC ohmically heated up with 142A to Ti sublimation temperature. A TSP system has been operated since many years in the AUG-NBI system, sublimating Ti in the pauses between the plasma discharges, when no magnetic field is present. However, at W7-X the superconducting coils generate a magnetic field permanently during experimental campaigns, whose stray B field with a maximum of 30mT, affects the TSPs. Operated with DC, the wires would be deflected against the surrounding panels due to the Lorentz force. A simple possible solution is heating with AC, which reduces the wire deflection amplitude, inducing a risky wire oscillation. The feasibility of the AC operation in an equivalently strong B field such as the stray B field around W7-X has been demonstrated in a test stand for different AC waveforms and frequencies. Several test campaigns have shown no qualitative difference in the pumping properties between AC and DC operation of the TSP and no critical dynamic behaviour of the wires.

Design on Ultrahigh Vacuum System with Titanium Pump

In order to meet the further requirements that study diamond-like carbon (DLC) films as rigid protective coating, a three-stage ultrahigh vacuum system composed of rotary vane pump and diffusion pump in parallel with TSP ( titanium sublimation pump) was designed mainly for getting limiting vacuum of 1.0×10-6Pa within 30 minutes in the vacuum chamber of about 0.23m3. The chamber is a horizontal cylinder supported by a saddle-shaped bracket and it has been proved to satisfy the requirements of strength and stiffness, it can be easy to get ultrahigh vacuum by TSP. Initiation pressure of the TSP was set to 10-3Pa vacuum after optimization analysis and the diffusion pump simultaneously was closed for the proper use. The system can be used as deposition equipment with the assistance of high and low vacuum measuring instruments and other accessories.

Design on UHV System with TSP

A UHV(ultra-high vacuum) system, which used as deposition equipment with the assistance of high and low vacuum measuring instruments and other accessories, was designed in this paper. A CMP (composite molecular pump) in parallel with TSP (titanium sublimation pump) as the main pump and a rotary-vane pump as the backing pump were designed in this system. After a CMP with displacement 2300l/s was chosen as the one of the main pumps, the total flow conductance between the outlet of vacuum chamber and the CMP was 1344l/s. The rough pump-down time was approximate 5 min by using a rotary-vane pump with pumping speeds 15l/s. In order to ensure the normal operation of the main pumps, a water chilling unit was designed in the system, which can achieve limiting vacuum of 5×10-6Pa in the vacuum chamber of 0.2 m3.

Hypervelocity Impact Effect of Molecules from Enceladus’ Plume and Titan’s Upper Atmosphere on NASA’s Cassini Spectrometer from Reactive Dynamics Simulation

The NASA/ESA Cassini probe of Saturn analyzed the molecular composition of plumes emanating from one of its moons, Enceladus, and the upper atmosphere of another, Titan. However, interpretation of this data is complicated by the hypervelocity (HV) flybys of up to ~18 km/sec that cause substantial molecular fragmentation. To interpret this data we use quantum mechanical based reactive force fields to simulate the HV impact of various molecular species and ice clathrates on oxidized titanium surfaces mimicking those in Cassini's neutral and ion mass spectrometer (INMS). The predicted velocity dependent fragmentation patterns and composition mixing ratios agree with INMS data providing the means for identifying the molecules in the plume. We used our simulations to predict the surface damage from the HV impacts on the INMS interior walls, which we suggest acts as a titanium sublimation pump that could alter the instrument's readings. These results show how the theory can identify chemical events from hypervelocity impacts in space plumes and atmospheres, providing in turn clues to the internal structure of the corresponding sources (e.g., Enceladus). This may be valuable in steering modifications in future missions.

Development and UHV testing of LN2 cooled Titanium Sublimation Pump

Titanium sublimation pumps (TSP) provide inexpensive large pumping speeds for active gases especially in UHV environment where residual gases are mainly H2 and CO etc. The pumping speed of TSP is independent of pressure in this range. Sublimation of Ti on liquid nitrogen (LN2) cooled surfaces is expected to provide large porosity in deposited film and this may also result in further enhancement of its pumping speed. Accordingly a liquid nitrogen cooled TSP was developed to achieve clean vacuum in 10−11 mbar range in combination of sputter ion pump which is mainly used to take care of inert gas load. The LN2 shroud was designed to have 1.9 litre capacity and offered approximately 2000 cm2 cooled surface area with approximately 250cm2 area coated with titanium film. This paper describes the performance of the TSP at room temperature as well as after cooling with LN2. Quadrupole mass analyzer was utilized to analyze residual gases. Simultaneously for pumping speed measurements for different gasses, a setup with known conductance was also appended.

A resistive pyrolytic radical source for gas-surface reaction studies

We describe a thermal gas cracker designed to produce low fluxes of gas-phase radicals for use in radical-surface reaction studies. A resistively heated thin piece of highly oriented pyrolytic graphite is used as the pyrolysis filament, with the major advantage that this material remains inert at high temperatures. The instrument is built within an existing titanium sublimation pump, which simplifies construction and allows for self-pumping of the radical source. Thermal generation of Cl atoms from Cl(2) was chosen to test the effectiveness of the instrument. (35)Cl and (37)Cl were generated with a concomitant decrease in parent (70)Cl(2) and (72)Cl(2) species, as monitored by a residual gas analyzer. The cracking fraction of Cl(2) as a function of cell temperature is reported, with nearly full conversion achieved at high temperature.

Computer-control of surface science experiments with LabVIEW

LabVIEW TM 2009-based remote and process control program for an ultra-high vacuum system and a variety of surface science experiments is presented. The apparatus consists of five individual recipients for sample preparation, surface analysis, scanning tunneling microscopy and a central chamber connecting them by means of gate-valves. All processes like electron-beam heating, ion sputtering, gas exposure, thermal and electron-beam evaporation, analysis techniques, sample manipulation can run under full automatic control; transfers are supported. A variety of useful auxiliary functions are implemented to control bake-out processes, titanium sublimation pumps, pressure regulation of leak valves but also data acquiring, automatic reporting through ftp and emails, as well as external communication and control via a TCP/IP connection with a portable PC. Important features of the software include a time- control module to operate up to five channels (repetitive heating, sputtering, gas exposure, evaporation and manipulation to evaporation positions) as well as full process control. Such tools allows us to set up automatically processed experiments that include e.g. the preparation of single-crystal surfaces, their AES (Auger electron spectroscopy) and LEED (low energy electron diffraction) analysis as well as the evaporation and various treatments of thin films.

“50 Years of Varian sputter ion pumps and new technologies”

Varian was co-founded by Russel Varian, the inventor of the Klystron, and its original activity was in the field of microwave electron tubes. The Sputter Ion pump (SIP) was invented as the solution for clean pumping of electron tubes. Following the SIP, the Ultra High Vacuum (UHV) technology was developed, mainly driven by High Energy Physics and Surface Science. During the two following decades most of Research & Development activities were focused to improve the operation of SIP towards high pressure. Most of the achievements were then made obsolete by turbomolecular pumps, which became the ideal complement of SIP at relatively high pressure. The range of applications for ion pumps than became more clearly defined as UHV. Therefore R&D focus moved to low pressure performance of SIP (magnetic field, controller, anode structure). A combination of sputter ion pumps with evaporable getters in the Titanium sublimation pump has been implemented since early times. More recently, the combination with non-evaporable getters (NEG) has become very common especially in particle accelerators. Integration of NEG in SIP, by applying inside the pump a NEG film with the technology originally developed at the European Organization for Nuclear Research (CERN) in Geneva, is the most recent development.

Conceptual design of the vacuum system of the Spanish synchrotron light source (ALBA) storage ring

ALBA will be a third generation synchrotron light facility to be built near Barcelona (Spain). The design phase of ALBA is almost completed and the first components are ready to be ordered. Commissioning of the storage ring is foreseen to start at the end of 2008. The circumference of the storage ring of ALBA is 268.8 m and it will be divided into 16 vacuum sections by ultra high vacuum (UHV) gate valves. The vacuum chamber will be made of stainless steel with vertical aperture of 28 mm and 72 mm width. The vacuum chamber will be connected to an antechamber with a slot of 10 mm height. The antechamber will have the crotch absorbers which will absorb the unwanted synchrotron radiation. The pumping will be by sputter ion pumps (SIP), NEG pumps and titanium sublimation pumps (TSP), with an overall pumping speed from SIP of 57,400 l/s. This will maintain an average dynamic pressure of around 1 × 10 −9 mbar to achieve a beam lifetime >15 h at the designed current.