Vacuum Compatibility Research Articles

Measurement of carbon condensates using small-angle x-ray scattering during detonation of the high explosive hexanitrostilbene

The dynamics of carbon condensation in detonating high explosives remains controversial. Detonation model validation requires data for processes occurring at nanometer length scales on time scales ranging from nanoseconds to microseconds. A new detonation endstation has been commissioned to acquire and provide time-resolved small-angle x-ray scattering (SAXS) from detonating explosives. Hexanitrostilbene (HNS) was selected as the first to investigate due to its ease of initiation using exploding foils and flyers, vacuum compatibility, high thermal stability, and stoichiometric carbon abundance that produces high carbon condensate yields. The SAXS data during detonation, collected with 300 ns time resolution, provide unprecedented signal fidelity over a broad q-range. This fidelity permits the first analysis of both the Guinier and Porod/power-law regions of the scattering profile during detonation, which contains information about the size and morphology of the resultant carbon condensate nanoparticles. To bolster confidence in these data, the scattering angle and intensity were additionally cross-referenced with a separate, highly calibrated SAXS beamline. The data show that HNS produces carbon particles with a radius of gyration of 2.7 nm in less than 400 ns after the detonation front has passed, and this size and morphology are constant over the next several microseconds. These data directly contradict previous pioneering work on RDX/TNT mixtures and TATB, where observations indicate significant particle growth (50% or more) continues over several microseconds. The power-law slope is about −3, which is consistent with a complex disordered, irregular, or folded sp2 sub-arrangement within a relatively monodisperse structure possessing radius of gyration of 2.7 nm after the detonation of HNS.

The suitability of 3D printed plastic parts for laboratory use

3D printing has become popular for a variety of users, from home hobbyists to scientists and engineers interested in producing their own laboratory equipment. In order to determine the suitability of 3D printed parts for our plasma physics laboratory, we measured the accuracy, strength, vacuum compatibility, and electrical properties of pieces printed in plastic. The flexibility of rapidly creating custom parts has led to the 3D printer becoming an invaluable resource in our laboratory. The 3D printer is also suitable for producing equipment for advanced undergraduate laboratories.

PCTFE as a solution to birefringence in atom trap viewports.

We have developed and characterized optical viewports with the glass-to-metal seal made by the plastic PCTFE (polychlorotrifluoroethylene). The goal is to reduce stress-induced birefringence while maintaining ultra-high vacuum compatibility. We have maintained a Stokes parameter S3 of 0.9986, and achieved <5 × 10(-11) Torr partial pressure of air. We have also measured the diffusion and permeation of helium through PCTFE and placed upper limits on nitrogen, oxygen, and argon permeation, as PCTFE has been suggested as an o-ring for transport of environmental noble gas samples, though we know of no other noble gas measurements.

DLC 코팅된 가이드레일을 이용한 볼베어링 직선 이송 스테이지의 진공환경 제어 특성 분석

Recently, there is an increase in the need for precision linear stages with vacuum compatibility in such areas as lithograph y equipment for wafer or mask manufac- turing, mask mastering equipment for optical data storage and electron beam equipment. A simple design, high stiffness and low cost can be achieved by using ball bearings. However, a ball bearing have friction and wear problems just as in ambient air. In order to decrease the friction, a special finish, a diamond-like carbon (DLC) film coating, is applied to the surface of a guide rail by sputtering deposition. This paper presents the result of an experimental investigation on the control performance of a ball bearing ‐guided linear motion stage under two environmental conditions: in air and vacuum. A comparison between the results with and without the DLC coating was also considered in the experimental investigation.Received 21 July 2014Revised 28 July 2014Accepted 29 July 2014

Vacuum compatibility of 3D-printed materials

The fabrication fidelity and vacuum properties are tested for currently available 3D-printed materials including polyamide, glass, acrylic, and sterling silver. The silver was the only material found to be suitable to ultrahigh vacuum environments due to outgassing and sublimation observed in other materials.

Design and R&amp;D of Thermal Sensors for ITER Neutral Beam Injectors

In-vessel components of Megavolt ITER Injector and Concept Advancement, the ITER neutral beam injector prototype, will be instrumented with different sensor technologies mainly for protection and thermal control: thermocouples (TCs) will be used as thermal sensors distributed on all the in-vessel components, accelerometers as boiling detectors mounted on tubes of cooling channels subjected to high heat fluxes, fiber Bragg gratings as thermal sensors on high-voltage panels, strain gauges (SGs) as strain sensors on panels subjected to out-of-plane deformations. ITER in-vacuum cabling requires to use mineral insulated (MI) cables that exhibit radiation hardness and Ultra High Vacuum (UHV) compatibility. A common issue related to sensors cabled with MI (TCs, accelerometers, and SGs) involves the realization of UHV compatible terminations needed with provide vacuum tightness and mechanical robustness. Prototypes of MI TCs with 0.5-, 0.8-, and 1.0-mm cable diameter and with metallic/ceramic brazed terminations have been procured and tested; all sensors passed electrical and leak tests, including electrical insulation, continuity, dielectric, helium bombing, and thermal cyclic tests, so demonstrating the measuring capability and UHV compatibility. Custom sensor fastenings, custom remote handling compatible connectors, and safety important signal feedthroughs have been designed considering all the boundary conditions and the required number of sensors as obtained from the analyses.

Vacuum compatibility of silver and titanium parts made using three-dimensional printing

Three-dimensional (3D) printing has many advantages over conventional machining techniques, and it is particularly well suited for rapid production of prototypes. This Shop Note reports pump-down curves for a small ultrahigh-vacuum chamber loaded with 3D-printed silver and titanium parts. Neither material showed any measurable adverse affect on the ultimate base pressure achieved, which was approximately 5 × 10−10 Torr. 3D-printed metals can therefore be considered suitable for select ultrahigh-vacuum applications.

New Materials for Vacuum Chambers in High Energy Physics

Vacuum chambers must fulfil ultra-high vacuum requirements while withstanding thermo-mechanical loads. This is particularly true in high energy particle accelerator where interactions of particles with matter may induce thermal load, material activation, background… The choice of the material of the vacuum chamber is crucial for the final application. Metals such as stainless steel, copper and aluminium are usually used. Even with outstanding mechanical and physical properties, beryllium is used for very specific applications because of its cost and toxicity.Ceramics such as alumina are usually used for fast magnet vacuum chambers. With the next generation of high energy physics accelerator generation such as CLIC and TLEP, the problematic of high cyclic thermal load induced by synchrotron radiation is raised. This paper aims at defining some figures of merit of different materials with respect to several load scenarios and presents briefly their vacuum compatibility.

A Self-Alignment Sealing Hatch-Door System Updated for Airlock Chambers of KM6 Space Simulator

KM6 space simulator built in 1990s is currently the largest thermal vacuum test facility for spaceships and satellites in China. In order to meet new requirements of ground test for outer-cabin space walk of astronauts under China Manned Space Project II, a hatch-door system with ten rectangular doors in auxiliary horizontal chamber of KM6 space simulator has been updated since 2006. For the sake of pressure balance, every hatch-door is upgraded with a pressure regulator, which enables easy close and open of every hatch-door under no pressure difference. To improve vacuum compatibility of rotating hatch-doors, single axis hinge mechanism is renewed as biaxial hinge mechanism with more degrees of freedom for door spindle, which is combined with coordinated lock mechanism and O-ring sealing structure to realize the self-alignment sealing of hatch-door flange structure. Up until now, three manned spaceships of SZ-5, SZ-6 and SZ-7 have successfully finish thermal vacuum tests in auxiliary horizontal chamber with high performance of the updated hatch-door system as results.

Caesium oven design and R&D for the SPIDER beam source

In the ITER neutral beam injectors caesium will be used in the negative ion source to enhance the ion yield, by lowering the surface work function, and to reduce the co-extracted electrons. Fresh Cs has to be deposited almost continuously inside the plasma source and its injection is obtained by means of Cs ovens.Three independent Cs ovens have been integrated in the SPIDER (Source for Production of Ion of Deuterium Extracted from Rf plasma) beam source (BS). Since the entire BS is in-vacuum, a completely new design of the Cs ovens was required, assuring their vacuum and high temperature compatibility, and remote operation. They feature an ON–OFF valve and two independent heating systems to control the Cs evaporation and to avoid vapour condensing on the injection duct, by controlling the temperature. A Cs level indicator to measure the quantity of liquid caesium inside the reservoir, based on the electric resistance variation of an electrode, is proposed for the first time and a proof of concept is given.The oven design and the R&D activity on the level measurement system are presented.

Microwave stray radiation: Measures for steady state diagnostics at Wendelstein 7-X

The main heating system of W7-X will be a 10MW, 140GHz ECRH. It is expected that the non-absorbed ECRH power will be up to 1MW. Multiple reflections of the ECRH beam result in a nearly isotropic radiation background. The non-absorbed ECRH power has to be considered as an additional thermal load of microwave stray radiation for all W7-X in-vessel components.Several in-vessel diagnostics, especially magnetic diagnostics, partly consist of microwave absorbing materials. The microwave stray radiation could damage these components or, by evaporation due to overheating, perturb the operation of W7-X. Usually these diagnostics are protected against direct plasma radiation and are thermally connected to actively cooled structures. Nevertheless, ECRH stray radiation can cause a critical temperature increase.We present examples of ECRH stray radiation protection by metallic housing. The use of such housing may be in conflict with vacuum compatibility and in particular for magnetic diagnostics, with the requirement to avoid eddy currents limiting the time resolution of magnetic measurements.Details are given on the protection against ECRH stray radiation as well as on thermal connection concepts. Acceptance tests are presented on full-scale mockups.

Prototyping and testing of the Continuous External Rogowski ITER magnetic sensor

The measurement of the plasma current in ITER plays an outstanding role as it is part of the machine protection and is a safety-relevant measurement: it will be used in relation with regulatory limits to show that the operation remains within the safe envelope defined in the ITER license. The Continuous External Rogowski (CER) is an inductive sensor designed for current measurements and located in the casing of 3 Toroidal Field Coils (TFCs). After the completion of the design of the CER, 4 prototypes of the sensor were manufactured and R&D activities were performed under a Grant with the European Domestic Agency (F4E-GRT-012). The work was carried out between 2010 and 2011 by the ITERMAG consortium comprising 3 laboratories: CRPP (Switzerland) as leader, CEA (France) and RFX (Italy). The R&D campaign on CER prototypes consisted in the measurement of about 100 parameters to characterize the CER in terms of electrical, thermal, mechanical and also of vacuum compatibility. From these results, electromagnetic modeling of the CER response was performed. It is demonstrated that the CER fulfills ITER requirements. However, the vacuum compatibility of the prototype has to be improved and solutions to cope with this issue are proposed.

Deformation measurement of internal components of ASDEX Upgrade using optical strain sensors

A fibre-optic measurement system to analyse the deformation of in-vessel components has successfully been developed, installed and commissioned at ASDEX Upgrade (AUG). This technology has thereby been qualified for in-vessel use at experimental fusion devices. AUG is equipped with an internal conductor for passive plasma stabilisation called the Passive Stabilisation Loop (PSL), on which the recently installed 16 internal coils (B-coils) are directly mounted. The PSL structure is highly prone to vibrations, and the risk of resonant oscillations in response to B-coil induced forces necessitated the development of the present diagnostic. The diagnostic system consists of 34 fibre-optic strain sensors incorporated in two glass fibres. It is completely insensitive to electromagnetic disturbances. The fibres are customised to avoid inconvenient excess fibre length in the vacuum vessel. They were tested for their neutron tolerance and vacuum compatibility prior to installation. The actual sensors are embedded in stainless steel carriers that were attached to the PSL, which is made of copper, by laser welding. Appropriate welding parameters were determined in view of the metallurgical dissimilarity. The weld quality was approved by tensile tests and microscopic investigations. Accurate in-vessel positioning of the sensors was assured using a 3D measurement system and coordinates from CAD. The data acquisition allows a sampling rate of 1kHz. It was shown that the temporal and spatial resolutions of the system are sufficient to resolve the potentially dangerous bending eigenmodes of the PSL rings.

Functionalization of nanomaterials by non-thermal large area atmospheric pressure plasmas: application to flexible dye-sensitized solar cells

A key challenge to the industrial application of nanotechnology is the development of fabrication processes for functional devices based on nanomaterials which can be scaled up for mass production. In this report, we disclose the results of non-thermal radio-frequency (rf) atmospheric pressure plasma (APP) based deposition of TiO2 nanoparticles on a flexible substrate for the fabrication of dye-sensitized solar cells (DSSCs). Operating at 190 °C without a vacuum enclosure, the APP method can avoid thermal damage and vacuum compatibility restrictions and utilize roll-to-roll processing over a large area. The various analyses of the TiO2 films demonstrate that superior film properties can be obtained by the non-thermal APP method when compared with the thermal sintering process operating at 450 °C. The crystallinity of the anatase TiO2 nanoparticles is significantly improved without thermal agglomeration, while the surface defects such as Ti(3+) ions are eliminated, thus providing efficient charge collecting properties for solar cells. Finally, we successfully fabricated a flexible DSSC with an energy conversion efficiency of 4.2% using a transparent plastic substrate. This work demonstrates the potential of non-thermal APP technology in the area of device-level, nano-enabled material manufacturing.

Beamline mirrors and monochromator for X-ray free electron laser of SACLA

Beamline mirrors and a monochromator were developed as key optical devices for the Japanese XFEL facility, SPring-8 Ångstrom Compact Free Electron Laser (SACLA). The optics were designed for transporting extremely intense, transversely coherent XFEL light to the experimental stations. The mirror system delivers a pink beam with high intensity and an energy range below 15keV, while the monochromator with Si (111) covers wider energy range of 4–30keV with 0.01% bandwidth. For realizing high stability and contamination-free environment, the mechanics of these optical components were designed to have high stiffness with ultra-high vacuum (UHV) compatibility. After 100 days of operation, no radiation damage was observed on the mirror surfaces.

Brazing of photocathode RF gun structures in Hydrogen atmosphere: Process qualification, effect of brazing on RF properties and vacuum compatibility

In this paper, we report on the development of a brazing process for an ultra-high vacuum (UHV) compatible photocathode RF gun structure developed at our Centre. The choice of brazing alloy and its form, brazing clearance between parts to be joined and the brazing cycle adopted have been qualified through metallographic examination of identical joints on an OFE copper prototype that was cut open after brazing. The quality of brazed joint not only affects the UHV compatibility of the gun, but also influences the RF parameters finally achieved. A 2-D electromagnetic code, SUPERFISH, was used to predict the variation in RF parameters before and after brazing considering actual brazing clearances provided between the parts to be joined. Results obtained from low power RF measurements on the brazed gun structure confirm the integrity of the brazed joints and show good agreement with those predicted by electromagnetic simulations. The brazed gun structure has been leak-tested and pumped down to a vacuum level limited by the vacuum compatibility of the flange-fittings employed in the setup.

Design and development of collector for C-band 250 kW CW Klystron

The paper presents the design and development of collector for C-band 250 kW high power klystron. The design criteria for the collector assembly is selection of material, vacuum and high temperature compatibility, proper electron beam dispersion, minimum back scattering of electrons and thermal design for proper cooling at high power dissipation. All these aspects have been discussed for collector development in details. The collector has been designed in TRAK and then beam propagation has been analyzed in MAGIC 2D software. The thermal simulation has been done using ANSYS 11.0 (multi-physics). The outer surface of the collector has been grooved to facilitate its proper cooling. Design results are presented for water cooling with different flow rates and channel dimensions. OFHC copper material is chosen for collector which is suitable for vacuum and hydrogen brazing operations and good thermal properties for efficient cooling.

Performance validation tests on 80 K bubble type of shields for SST-1

The 80K thermal shields of Steady State Superconducting Tokamak (SST-1) minimize the steady state heat loads on the superconducting magnet system at 4.5K from ambient. Uniform temperature, vacuum and cryo compatibility is desired for the 80K shields. In order to meet these requirements, the bubble/embossed type of design concept is adopted. This design ensures lower pressure drop and better temperature uniformity within ±5K. Special attention has been given for preventing direct radiation on the magnet system. As part of performance validation tests, a group of 80K thermal shields have undergone rigorous testing protocols and procedures. The temperature distribution, helium leak tightness and insulation resistance tests have been carried out for SST-1 thermal shields before final assembly of the machine. The test design, procedures and results of the 80K thermal shields will be discussed in this paper.

Making a hybrid microfluidic platform compatible for in situ imaging by vacuum-based techniques

A self-contained microfluidic-based device was designed and fabricated for in situ imaging of aqueous surfaces using vacuum techniques. The device is a hybrid between a microfluidic poly(dimethyl siloxane) block and external accessories, all portable on a small platform (10 × 8 cm2). The key feature is that a small aperture with a diameter of 2-3 μm is opened to the vacuum, which serves as a detection window for in situ imaging of aqueous surfaces. Vacuum compatibility and temperature drop due to water vaporization are the two most important challenges in this invention. Theoretical calculations and fabrication strategies are presented from multiple design aspects. In addition, results from the time-of-flight secondary ion mass spectrometry and scanning electron microscopy of aqueous surfaces are presented.

Design optimization of the 100 kV HV bushing for ITER-DNB

The 100 kV bushing of the Diagnostic Neutral Beam (DNB) injector is a cylindrical feedthrough which forms the interface between the gas insulated transmission line and the torus primary vacuum and provides all necessary services to the beam source. All conventions for safety, voltage holding requirement, vacuum compatibility and the choice of materials have been addressed in the design. Finite Element Analyses (FEAs) for the electrostatic and the structural configuration is carried out to validate the design of the High Voltage Bushing (HVB). Several iterations and optimizations of the stress shields are carried out to meet electrostatic criteria, especially at the triple point (the ceramic, metal and vacuum joint), which is critical for good voltage holding. Structural analyses is carried out to assess the stress distribution in the fiber reinforced plastic insulator, the alumina insulator and the integrated HVB for different load cases like operational orientation (horizontal), normal operation and accidental case. Design is further validated for seismic conditions for Seismic Loading-2 (SL-2).