Vacuum Chamber Research Articles

Longitudinal phase space diagnostics with a nonmovable corrugated passive wakefield streaker

Time-resolved diagnostics at free-electron laser (FEL) facilities, in particular electron beam longitudinal phase space (LPS) and FEL power profile measurements, provide information highly valuable for users, machine development studies, and beam setup. We investigate the slice energy resolution of passive streaker setups, in particular the effect of an energy chirp on the measured slice energy spread. Downstream of the hard x-ray SASE2 beamline at the European XFEL, these measurements are enabled by a single-plate nonmovable passive wakefield streaker, essentially a rectangular corrugated plate placed inside a vacuum chamber. We show measurements with a time resolution down to a few femtoseconds and an energy resolution down to a few MeVs. Published by the American Physical Society 2024

In Situ Pulsed Hydrogen Implantation in Atom Probe Tomography.

The investigation of hydrogen in atom probe tomography appears as a relevant challenge due to its low mass, high diffusion coefficient, and presence as a residual gas in vacuum chambers, resulting in multiple complications for atom probe studies. Different solutions were proposed in the literature like ex situ charging coupled with cryotransfer or H charging at high temperature in a separate chamber. Nevertheless, these solutions often faced challenges due to the complex control of specimen temperature during hydrogen charging and subsequent analysis. In this paper, we propose an alternative route for in situ H charging in atom probe derived from a method developed in field ion microscopy. By applying negative voltage nanosecond pulse on the specimen in an atom probe chamber under a low pressure of H2, it is demonstrated that a high dose of H can be implanted in the range 2-20 nm beneath the specimen surface. An atom probe chamber was modified to enable direct negative pulse application with controlled gas pressure, pulse repetition rate, and pulse amplitude. Through electrodynamical simulations, we show that the implantation energy falls within the range 100-1,000 eV and a theoretical depth of implantation was predicted and compared to experiments.

Dam–calf contact rearing in Switzerland: Aspects of management and milking

Cow-calf contact (CCC) rearing is becoming an increasingly popular alternative to the common practice of early separation of cow and calf in dairy management. Milkability can be impaired in nursing cows, which contributes to the loss of machine milk yield caused by calf intake, especially in pure dam-calf contact (DCC) systems. The aims of this study were (1) to describe the current status quo of DCC rearing regarding management and milking and (2) to evaluate the effects of DCC (suckling and milking vs. milking alone) and the effects of different types of DCC on milkability parameters, teat condition, and behavior during milking on Swiss DCC farms. By means of 17 telephone interviews with DCC farmers, we collected data on DCC management, housing, separation and weaning processes, milking procedures and techniques, and perceived milkability problems. Subsequently, we collected data on 10 of the interviewed DCC farms (183 cows): 4 DCC farms with a whole-day contact (WDC) system, 3 farms with DCC before milking (CBM), and 3 farms with DCC after milking (CAM). Five farms on which calves had no contact with dams were chosen as reference farms (178 cows). Using a milk flow meter, the occurrence of ejection disorders, bimodality of the milk flow curve, machine milk yield, duration of the decline phase, and duration of prestimulation were measured. The average mouthpiece chamber vacuum during the main milking phase and hind leg activity during milking were measured using a pressure sensor and an accelerometer, respectively. After cluster removal, the teat condition was evaluated, and a stripping milk sample was taken for fat content analysis. The interview results revealed that 8 of the 17 farms surveyed had a WDC system, and 2 farms operated a daytime DCC system. Contact before milking was applied by 3 farms, and 3 farms allowed CAM. On one farm, calves had access to dams 3 times a day. A great diversity in cow-calf management was found. In the on-farm data collection, 20 milkings of a total of 701 milkings examined met the criteria for a clear ejection disorder, with 17 of these observations occurring on WDC farms and none on reference farms. The stripping milk fat content was lower in nursing cows, indicating a lower degree of udder emptying. Machine milk yield was higher in nursing CAM cows than in nursing WDC and CBM cows. Farm types did not differ regarding teat condition, hind leg activity, or the occurrence of bimodal milk flow curves. In conclusion, the large variation in individual management approaches to DCC rearing even within DCC types, such as calf housing or cow breeds, implies caution when interpreting results. Contact after milking may be the system most beneficial for some productivity parameters, but adequate calf supply must be ensured. Higher amounts of milk remaining in the udder after cluster removal indicate that nursing can affect milkability, but future research should consider the effects of udder filling before milking to better interpret the fat content of stripping milk.

Angle-resolved X-ray photoelectron spectroscopy intensity modeling of SiNx ultrathin layer grown on Si (100) and Si (111) substrates by N2 plasma treatment

In this work, we investigate the silicon nitridation process using a N2 plasma Glow Discharge Source (GDS) in an ultra-high vacuum chamber. In situ Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) measurements were performed to determine various chemical environments of the surface species. The main goals of this study are determination of the film chemical composition, to estimate its thickness and identify various phenomena taking place during the nitridation process under different experimental conditions. To achieve these objectives, we developed an ARXPS intensity model for an ultrathin SiNx overlayer. Based on the ARXPS results, which indicate that the silicon nitride film is not homogenous, we adopted a bi-layer model composed of two SixNyOz layers with varying thickness and chemical composition. The model is built from analysis of photoelectron intensities, considering a comparison between experimental and theoretical data. This bi-layer model revealed that the silicon nitride layer consists of a surface layer composed of approximately equal amounts of silicon and nitrogen (50% each), and an interfacial layer containing varying amounts of oxygen depending on experimental parameters. The presence of oxygen is due to residual air contamination in the vacuum chamber and/or to Si native oxide. The estimated thickness of silicon nitride film is less than 9 nm, depending on the nitridation time and temperature.The model developed in this work enabled us to study the effects of initial surface state (as received or chemically cleaned), Si substrate crystallographic orientation (such as (100) and (111)), and the nitridation temperature (room temperature and 500°C). The diffusing species (N+, N2+, O+), which play a crucial role during nitridation, were found to be influenced by temperature, treatment time, and substrate orientation. The diffusion phenomenon competed with other processes such as NO desorption, leading to a significant impact on formation of the SiNx film. Furthermore, we compared the thickness obtained from the ARXPS model using cross-sectional High-Resolution Transmission Electron Microscopy (HR-TEM) images. Additional Low-Energy Electron Diffraction (LEED) measurements indicated that the SiNx film was amorphous.

Resonant cavity method based on RF measurement and simulation for measuring complex permittivity or permeability of RF absorbing materials

Accurate measurement of complex permittivity and/or permeability of radio-frequency (RF) absorbing materials is essential to predict the performances of higher-order-mode damping in damped accelerating cavities or in vacuum chambers. We propose an improved resonant cavity method that can be used as a complement to the widely used Nicolson–Ross–Weir method for measuring the RF characteristics of materials. The conventional resonant cavity method is based on the cavity perturbation theory. However, the measurements are inaccurate when losses in the materials are large. The improved method we propose determines the complex permittivity or permeability of materials from the measured resonant frequencies and Q factors based on eigenmode simulations. Because the reliability on the eigenmode calculation for RF cavities with lossy materials has become sufficiently reliable, determination of complex permittivity and permeability can be achieved using such a simulation software. We demonstrate this method using ferrite HF70 (TDK Corp.), which is useful for RF absorbers in damped accelerating cavities or in vacuum chambers.

Influence of the Experimental Setup on Electromagnetic Pulses in the VHF Band at Relativistic High-Power Laser Facilities

We present experimental results for the controlled mitigation of the electromagnetic pulses (EMPs) produced in the interactions of a 1 PW high-power 30 fs Ti:Sa laser VEGA-3 with solid-density targets transparent to laser-forward-accelerated relativistic electrons. This study aims at the band of very high frequencies (VHFs), i.e., those in the hundreds of MHz, which comprise the fundamental cavity modes of the rectangular VEGA-3 vacuum chamber. We demonstrate mode suppression by a tailoring of the laser-produced space charge distribution.

Influence of Nb substrate morphology and atomic structure on Sn nucleation and early Nb3Sn growth

The enhanced accelerating performance of Nb3Sn-coated Nb superconducting radio frequency (SRF) cavities is severely limited by quenching sites at material defects formed during the Nb3Sn film growth procedure. In this work, we aimed to understand the complex surface-mediated interactions that drive initial Nb3Sn formation during the Sn vapor deposition procedure used to fabricate Nb3Sn coated SRF cavities. Nb substrates were modified, coated with Sn, and then characterized using an ultra-high vacuum (UHV) chamber equipped with metal deposition and in situ surface analysis capabilities. The atomic structure of the Nb oxide surface was modified to assess how the Nb surface defect density and crystallographic orientation impact the size of nucleated Sn islands and relative Nb3Sn growth rates. Formed Nb3Sn/Nb surfaces were visualized using ex situ scanning electron microscopy (SEM) and post-deposition annealing revealed Sn desorption and Nb3Sn degradation pathways. Finally, we showed that the Sn deposition conditions can be modified to overcome the growth barriers that are imposed by the Nb morphology. This study provides a unique bridge between fundamental growth studies in pristine conditions with observed phenomena of Nb3Sn grown on realistic cavity surfaces.

Vacuum chambers for Swiss Light Source arcs

The vacuum chambers for diffraction limited storage ring differ from the previous storage rings generation in three main aspects: the cross-section dimension, which is divided by a factor of 2 or more to fit smaller magnet apertures; the material, which includes much more copper for heat dissipation and to limit resistive wakefields; the coating of the inner surface with a nonevaporable getter (NEG) to ensure good pumping level despite low conductance. This paper gives a detailed description of the vacuum chambers’ design used in the arc section of SLS 2.0, starting with conceptual design choices based among others on synchrotron radiation heat and wakefield considerations. The particular case of the main bending magnet vacuum chamber is explained in detail from design to manufacturing, including the development of an appropriate NEG coating procedure. Finally, the overall assembly of a 17 m long arc, its activation to reach pressure in the 10−11 mbar range followed by transport and installation into the magnets is presented. This validates the choice of activation for an arc vessel made out of copper, with wall thicknesses as small as 1 mm and with less than 0.5 mm clearance to magnet poles. Published by the American Physical Society 2024

Research on the drone endoscopic system for fusion reactors

This paper proposes an air-ground separation drone endoscopic system (DES) design scheme for the fusion reactor internal inspection task. A foldable rotor drone with vertical takeoff and landing capability is used as the main body of DES. The nest platform is designed separately from the drone to reduce the weight. Meanwhile, the nest platform can be installed with a safety cable and 2D code to realize emergency rescue and precise take-off and landing. DES adds 3D lidar sensors for 360° stereo sensing, realizing real-time positioning in dark or even lightless environments in vacuum chambers. The first-generation DES prototype is developed, and the flight test is performed inside the PF6 superconducting coil shell by fusing 3D lidar point cloud data with visual camera image data. The results show that the position error of DES is stabilized within ±0.05 m during the hovering phase. The error is mainly due to the narrow space inside the PF6 coil shell, which produces a perturbed flow field on the DES. In general, the DES accomplished circumferential autonomous flight control and 3D point cloud data acquisition in a confined space, proving the feasibility of drone inspection in vacuum chambers.

Frequency selective asymmetric coupled-fed (ACS) antenna using additive manufacturing

In this study, the development of diverse antenna designs using additive manufacturing processes, specifically spanning from L-band to K-band is proposed. All designs are implemented on a flexible FR4 substrate to make them suitable for wearable sensors and biomedical applications. The fabrication process involves the utilization of aerosol jet printing with nanoparticle silver ink, followed by curing in a vacuum chamber. Additionally, screen printing with copper paste is employed as another method, with subsequent curing in a laminator. The reflection coefficient (S11) and radiation patterns for the simulated design and fabricated samples were found to align closely. The achieved return loss consistently reaching −10 dB across fairly large operating frequency range underscores the efficacy of the proposed antennas and their associated additive manufacturing mechanisms. The design and simulation were performed using Ansys high frequency structural simulator (HFSS), and the parameters under test for the fabricated antennas were validated using a vector network analyzer (VNA) to assess overall performance.

Research on welding simulation for vacuum chamber test specimens

The vacuum chamber is an important component of nuclear fusion devices, and the deformation control of the welding process is relatively strict. In this paper, the isothermal multi-level cyclic loading tests have been conducted to explore a nonlinear mixed hardening mode, which can be used as the material input for the welding simulation. Then, welding simulation has been performed for test specimens of the vacuum chamber, and the deformation of test specimens has been obtained under different welding paths. After the first welding simulation is completed, the clamp and limiting plates have been designed based on the deformation of the test specimens. The welding simulation has been performed again with the clamp and limiting plates, in order to evaluate the rationality of the welding process and the design for the clamp and limiting plates. Finally, according to the determined welding process and design for the clamp and limiting plates, welding tests have been conducted, and the welding deformation has been measured. It is found that the difference between the measurement values of the tests and the simulation results is small, which implies that the welding simulation is reasonable.

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.

Time-resolved observation of 150 kHz high-power pulse burst high-frequency discharge using a high-speed video camera and an intensified charge coupled device camera

The discharge phase and time evolution of a 150 kHz high-power pulse burst discharge were observed. A vacuum chamber was constructed by connecting glass tubes on which a solenoid coil was wound. Burst pulses with a width of 1000 μs and a repetition rate of 10 Hz were applied to the solenoid coil. A high-speed video camera and an intensified CCD camera were used to record photographs of the discharges. Observation of the discharge phase using a high-speed camera showed that the discharge occurs at the time of 40 μs and propagates from the wall of the cylindrical reactor. Over time, the discharge pattern evolves, and a branched pattern appears. The number of the branches changes with time. The discharge blinks synchronize with the instantaneous power, which suggests that the discharge is generated and maintained by the electrostatic field generated by the sides of the coil. The propagation velocity calculated from downstream decreases with increasing pressure and increases with increasing power.

Thermal Engineering of the Cryogenic Beam Position Monitors for the EIC Hadron Storage Ring

The Electron Ion Collider (EIC) Hadron Storage Ring (HSR) will reuse most of the existing superconducting magnets from the RHIC storage ring. However, the existing stripline beam position monitors (BPM) used for RHIC will not be compatible with the planned EIC hadron beam parameters that include higher intensity, shorter bunches, and some operational scenarios with large radial offsets of the beam in the vacuum chamber. To address these challenges, the existing RHIC stripline BPMs will be decommissioned, and a new BPM design using button pick-ups integrated in a new vacuum interconnect/bellows assembly will be installed adjacent to the decommissioned BPMs.A dedicated analysis of the new BPM housing and button pick-up design has been conducted to assess the thermal effects caused by heat conduction, beam induced resistive wall heating and the RF heating from the BPM signal propagation through the cryogenic cables. This paper reports on the thermal design and analysis results to quantify the heat transfer and temperature distribution that can be expected on the new HSR cryogenic BPM.

Using mylar-insulated cryopumping panels to improve vacuum level during warm temperature testing at JSC’s large thermal vacuum facilities

Johnson Space Center’s Space Environment Simulation Lab (SESL) has both Chamber A, the world’s largest purpose-built thermal vacuum chamber capable of creating deep space conditions, and Chamber B, the largest human rated thermal vacuum chamber. A unique design feature of these chambers is the gaseous helium cryopumping panels within the liquid nitrogen shroud. This shroud is used to bring the chamber to cryogenic temperatures while the cryopumping panels trap gasses on its surface area to create a high vacuum environment of 5*10−6 Torr. In preparation for the James Webb Space Telescope (JWST) flight test, a series of functionals required the chamber to run at higher temperatures, and therefore did not need active cooling from the liquid nitrogen shroud. During testing, cryopumping panels were used to mitigate contamination during this main shroud warm-up. One of the cryopumping panels in Chamber A was covered with several layers of aluminized mylar to thermally protect the zone from the warmed shroud. This strategy was effective and became part of operations during JWST testing. Currently, Chamber B has requests for both commercial and NASA space suit tests at both high and low temperatures to validate thermal models. High temperature tests could benefit from reduced heater demand with an insulated shroud while still sustaining the high vacuum environment provided by the cryopumping panels. This paper will quantitatively define the thermal loads on the panels used in previous Chamber A warm up sequences. Additionally, this report will perform thermal analyses to assess the feasibility of adding layers of aluminized mylar to the cryopumping panels of Chamber B.

Cryogenic vacuum chamber testing of a conductively-cooled, high temperature superconducting rotor for a 1.4 MW electric machine for aeronautics applications

This paper presents the second ever demonstration of a superconducting rotor cooled only via conductive connection to a cryocooler, i.e., without pumped or solid cryogens. The full-scale rotor was operated statically in its intended environment – about 1e-3 torr vacuum with only conductive cooling through mechanical connections to a cryocooler contained on the rotor. Stable operation of the rotor in a representative magnetic environment was demonstrated up to its rated direct current (57.2 A) and the designed temperature limit for the superconductor (62 K). Additional electrical measurements increased confidence that the superconducting coils functioned as intended. A collection of steady state temperature distributions was measured at operating and non-operating conditions. In all but one case, the observed temperature gradient between the cold tip and superconducting coils satisfies the design but with little margin. Opportunities to reduce the gradient are identified.

Validation of the diamond detectors for the Super Fragment Separator beam diagnostics

The Super-FRS at the FAIR accelerator complex will adopt Chemical Vapor Deposition diamond detectors as radiation-hard particle rate counters. Their role will be to monitor the beam transmission for beams with ions rates up to 107 ions/spill and to calibrate the other beam diagnostics devices that are in duty at higher beam intensities. The target vacuum chamber of the Super-FRS hosts a 7 × 7 mm2 single crystal diamond and a 25 × 25 mm2 polycrystalline diamond: they are required to detect crossing particles with high efficiency (> 98%) in the case of heavy ion species (Ar to U), and to stand for several years in an environment in which they can potentially accumulate a dose of a few MGy per year. Laboratory measurements and beam test campaigns were arranged in the past years for the validation of the proposed sensors, in particular for the case of the polycrystalline technology. Here we report the outcome of the irradiation of a sensor based on a 20 × 20 mm2 polycrystalline diamond produced by Element Six, with high intensity 1 GeV/nucleon Pb and U beams at GSI (Darmstadt). The detector signal shape characteristics and the ion counting efficiency have been monitored by interleaving periods of low ions rates, to evaluate possible damages or performance degradation during and after a total bombardment of about 6 × 1011 heavy ions.

In situ effective pumping speed measurements as a tool for non-evaporable getter activation and saturation monitoring

We have developed method of in situ effective pumping speed measurements based on injecting finite gas pulse into a vacuum volume and subsequent recording of pressure response using a Residual Gas Analyzer (RGA). The pressure burst caused by injected gas pulse falls exponentially in time and the exponential coefficient of such pressure decay is proportional to total effective pumping speed of all vacuum pumps acting on vacuum chamber volume. The effective pumping speed can be extracted from the dependence of injected gas species pressure vs time recorded by an RGA. Non-Evaporable Getters (NEGs) are widely used in multiple ultra and extremely high vacuum devices and applications during the last several decades. Areas of NEG applications were recently expanded into vacuum devices with relatively high-pressure levels (up to 10−7 Torr) by the invention of high capacity ZAO NEG which can be operated at elevated temperatures. The intrinsic property of all NEG-based vacuum pumps is the reduction of their pumping speed, called “NEG saturation”, after an extended period of operation. Typical time interval for such process can span from about a month and up to a few years depending on NEG type, vacuum level of NEG pump operation, and residual gas content. After that, the NEG pump will require a re-activation cycle to restore its pumping speed close to the initial value. For many applications it is difficult to realize what is the current pumping speed of NEG pump is and when the pump should be re-activated. A method for in situ effective pumping speed measurements developed in this study can be used as a tool for NEG-based pump activation and saturation monitoring. Application of such an approach to monitor pumping status of NEG pumps was utilized and will be continually used at Extended EBIS which was recently developed and commissioned for Relativistic Heavy Ion Collider (RHIC) and future Electron Ion Collider (EIC). The results obtained during commissioning are presented and discussed.

Synthesis of core–shell nanoparticles with liquid core using magnetron sputtering and capacitively coupled dusty plasmas

We succeeded in depositing amorphous carbon films around tin nanodroplets retained in a capacitively coupled plasma (CCP). High-pressure magnetron sputtering was used for synthesizing tin nanoparticles at the top of a vacuum chamber. Tin nanoparticles were transported to CCP at the bottom of the chamber, and they were trapped in the sheath above an rf electrode. Tin nanoparticles were heated above the mp by ion bombardment in CCP. We introduced methane into CCP to deposit amorphous carbon films around melted tin nanoparticles. The transmission electron microscope (TEM) images of core–shell nanoparticles showed completely spherical cores. We observed the melting of cores at the melting point of metal tin when we heated core–shell nanoparticles in TEM, suggesting that the amorphous carbon films protected cores from the oxidation. In addition, the amorphous carbon films were robust against the volume expansion of the cores due to melting.

Experimental investigation on initial arc formation in high-current drawn vacuum arc

Initial arc formation in high-current drawn vacuum arc was investigated experimentally and analyzed quantitatively in this paper. Experiments were conducted in a demountable vacuum chamber. Characteristics of molten metal bridges evolution and arc voltage indicated that initial arc formation could be divided into three stages. The correlation between the rupture of molten metal bridges and the fluctuation of arc voltage in stage 2 was analyzed. In addition, characteristics in stage 2 under different arc currents and opening speeds were analyzed quantitatively.