Vacuum Feedthrough Research Articles

Comparative Analysis of Vacuum Feedthroughs for the DTT ICRH System

Comparative Analysis of Vacuum Feedthroughs for the DTT ICRH System

SLIM Tricks: Tools, Concepts, and Strategies for the Development of Planar Ion Guides.

Traveling wave ion mobility experiments using planar electrode structures (e.g., structures for lossless ion manipulation, TW-SLIM) leverage the mature manufacturing capabilities of printed circuit boards (PCBs). With routine levels of mechanical precision below 150 μm, the conceptual flexibility afforded by PCBs for use as planar ion guides is expansive. To date, the design and construction of TW-SLIM platforms require considerable legacy expertise, especially with respect to simulation and circuit layout strategies. To lower the barrier of TW-SLIM implementation, we introduce Python-based interactive tools that assist in graphical layout of the core electrode footprints for planar ion guides with minimal user inputs. These scripts also export the exact component locations and assignments for direct integration into KiCad and SIMION for PCB finalization and ion flight simulations. The design concepts embodied in the set of scripts comprising SLIM Pickins (PCB CAD generation) and pigsim (SIMION workspace generation) build upon the lessons learned in the independent development of the research-grade TW-SLIM platforms in operation at WSU. Due to the inherent flexibility of the PCB manufacturing process and the time devoted to board layouts prior to manufacturing, both scripts serve to enable rapid, iterative design considerations. Because only a few predefined parameters are necessary (i.e., the TW-SLIM monomer width, x position following a TW Turn, and y position following a TW Turn) it is possible to design the exact component layouts and accompanying simulation space in a manner of minutes. There is no known limitation to the board layout capacities of the scripts, and the size of a designed layout is ultimately constrained by the abilities of the final PCB design and simulation tools, KiCad and SIMION, to accommodate the thousands of electrodes comprising the final design (i.e., RAM and software overhead). Toward removing the barriers to exploring new SLIM tracks and the likelihood of layout errors that require considerable revision and engineering time, the SLIM Pickins and pigsim tools (included as Supporting Information) allow the user to quickly design a length of planar ion guide, simulate its abilities to confine and transmit ions, compare hypothetical board outlines to given vacuum chamber dimensions, and generate a near-production ready PCB CAD file. In addition to these tools, this report outlines a series of cost-saving strategies with respect to vacuum feedthroughs and vacuum chamber design for TW ion mobility experiments using planar ion guides.

RF conditioning to suppress multipactor discharge for helicon wave current drive in KSTAR

The efficient off-axis non-inductive current drive using auxiliary power is essential for the steady state operation of tokamaks. In previous studies, a helicon wave current drive has been proposed for high beta plasma in several fusion devices, and the 476-MHz radio-frequency (RF) system for the proposed helicon wave has been installed in KSTAR. However, multipactor discharge occurred inside the waveguide system, including the vacuum feedthrough (VFT), and it interrupted the normal RF propagation to plasma. Thus, for successful helicon wave current drive, suppressing the multipactor discharge in the waveguide system, including the 6–1/8″ coaxial type VFT and the newly manufactured helical type traveling wave antenna (TWA) is essential before installation in KSTAR. RF conditioning utilizing a short pulse modulation during a long period helps suppress the multipactor discharge, enabling the 1-MW 476-MHz RF to pass through the entire waveguide system despite the existence of multipactor discharge. Following RF conditioning in VFT with a short pulse modulation, the newly manufactured helical type TWA and VFT for helicon wave current drive have been successfully installed in KSTAR.

PRIMER PROTOTIPO DE TRAMPA FRÍA CON PASANTE ELÉCTRICO PARA VACÍODE BAJO COSTO

n a previous work, Conde Garrido and Silveyra proposed a novel cold trap (baffle) technology capable of trapping contaminants in vacuum systems. The baffle was designed to be applied in systems to synthesize chalcogenide glass thin films by pulsed laser deposition. While traditional baffles are cooled down with compression cooling systems or cooling solutions such as liquid nitrogen, the reported baffle is cooled down by the thermoelectric effect, which allows for reducing the capital investment, operating costs, as well as start-up and maintenance times. This paper presents the construction, tuning, and characterization of the first physical prototype of the baffle. The characterization included, first, the control of the final pressure reached by the device. To characterize the thermal performance of the baffle, a temperature measurement system was designed and manufactured. Within this measurement system, we highlight a low-cost electric vacuum feedthrough. The results indicate that the constructed baffle can reach pressures lower than 2×10−5mbar, while the cold surfaces reach temperatures of approximately−12◦C. The vacuum and cold temperature levels meet the required conditions for the pulsed laser deposition of chalcogenide glass thin films. However, temperatures are not as low as those estimatedfor the virtual prototype (down to−50◦C). Thermal bridges and resistances present in the fabricated device, neglected in the model, were then identified, pointing out opportunities for improvement. Finally, revisions to the current design are proposed that simplify its manufacturing process, improve its robustness and efficiency, and facilitate its operation and maintenance.

New ASDEX Upgrade ICRF antenna vacuum feedthrough: Optimization status

A new design concept aims to improve the voltage stand-off by using two repositioned 9-inch Al2O3 windows, to avoid/reduce the neutron impact on the ceramic by moving the window far from antenna, and to reduce the nearby E-fields by optimizing the shape of the conducting structures. New RF windows position is found to be close to the voltage node and determined from the standing wave patterns at the most used frequency of 36.5 MHz. The return loss coefficient S11 is between -30 and -55 dB for the whole operating frequency range. The calculated power losses for the new RF window structures are less than 0.13 kW each at 1 MW of incident power. Modelling shows maximum E-field less than 1.9 kV/mm in a torus and private vacuum of the feedthrough. The dimensions, E-fields and transmission make this design relevant to a possible DEMO ICRF system.

Development of a soft x-ray (SXR) array diagnostic system on versatile experiment spherical torus (VEST).

A new soft x-ray (SXR) array diagnostic system has been developed on versatile experiment spherical torus (VEST) for measurements of 2D SXR emissivity profile and identification of poloidal mode structure. Through tomographic inversion techniques, 2D SXR emissivity profile can be acquired from the line-integrated SXR data, which enables the visualization of mode structure of plasma instability, such as the magnetohydrodynamics mode. The SXR array diagnostic system consists of two 20-channel arrays positioned at the middle and the top on the same poloidal plane for horizontal and vertical lines of sight, respectively. Each array of the diagnostic system uses absolute extreme ultraviolet photodiode array as the detector. To apply appropriate filters (up to four) for different energy regimes without breaking the vacuum, a filter wheel and its rotatable vacuum feed-through are installed behind the pinhole. SXR data are acquired with a digitizer at the sampling rate of up to 125MHz. Finally, we discuss initial measurement data obtained from Ohmic plasma in VEST.

Development of a space irradiance simulator for advanced studies and materials research

A lab-scale experimental apparatus that mimics the solar-thermal environment of space has recently been developed and tested at NASA Kennedy Space Center in support of novel materials research for future space science and exploration applications. The Space Irradiance Simulator (SIRS) apparatus exposes specimens up to roughly 61 mm in diameter to a similar thermal environment that exists at distances as close as 0.4 AU from the Sun. This includes a high vacuum environment, access to a deep cryogenic background temperature with optical properties that closely imitate a blackbody, and irradiance from a broadband solar “point” source at fluxes as high as 9300 W/m2. Cooling is provided by a Gifford-McMahon cryocooler capable of 25 W of cooling power at 20 K, with a base temperature of 14 K. A commercially available Xenon lamp acts as the solar source, creating broadband electromagnetic radiation with a spectrum similar to that of the Sun. Light is beamed through the vacuum chamber and onto a sample suspended within the cold-mass via a flexible quartz fiber bundle in conjunction with a custom vacuum feedthrough. The system design, fabrication, and operation are discussed; and results from the initial checkout testing of the system are presented.

Conceptual design of the MGI system for JT-60SA

Disruption mitigation is of high priority for future tokamaks like ITER and DEMO. Massive gas injection (MGI) has proven to be an effective method in medium size machines and will likely be part of future disruption mitigation systems. For further research, the large superconducting tokamak JT-60SA will be equipped with a MGI system as an experimental equipment. This system will consist of two in-vessel MGI valves, which are mounted in opposite segments of the machine, vacuum feed throughs, a gas preparation system and an industrial PLC for control. The MGI valves are a scaled version of the spring-driven valve used in ADSEX Upgrade with an internal gas reservoir of 815 cm³, a maximum mitigation gas pressure of 6.5 MPa, a closing pressure of about 2 MPa, a nozzle diameter of 28 mm and an opening time below 2 ms. CFD simulations with common gas mixtures indicate a peak flow rate of 3.8 kg/s after 1.6 ms. The valve has a size of 140 mm x 110 mm x 292 mm. The gas preparation system allows easy and reproducible mixing of two gases by using an electronic pressure controller.

Gigabit Ethernet Daisy Chain on FPGA for COMET Readout Electronics

The COMET experiment at J-PARC aims to search for the neutrinoless transition of a muon to an electron. We have developed the readout electronics board called ROESTI for the COMET straw tube tracker. We plan to install the ROESTI in the gas manifold of the detector. The number of vacuum feedthroughs needs to be reduced due to space constraints and cost limitations. In order to decrease the number of vacuum feedthroughs drastically, we developed a network processor with a daisy-chain function of Gigabit Ethernet for the FPGA on the ROESTI. We implemented two SiTCPs, which are hardware-based TCP processors for Gigabit Ethernet, in the network processor. We also added the data path controllers which handle the Ethernet frames and the event data. The network processor enables ROESTI to process the slow control over UDP/IP and to transfer event data over TCP/IP. By using the network processor, we measured the throughput, the stability, and the data loss rate for two to six ROESTIs. In any number of boards, the throughput of the event data transfer achieved the theoretical limit of TCP over the Gigabit Ethernet stably and ROESTI stably sent 100% of the data.

RF discharge mirror cleaning for ITER optical diagnostics using 60 MHz very high frequency

• First mirror cleaning using 60 MHz very high frequency was optimized. • The pre-matching element is reducing the power consumption. • Cleaning homogeneity on a curved and large size mirror was measured. • End-of-Cleaning Indicator using Optical Emission Spectroscopy was demonstrated. For the fusion reactor ITER, a mandatory monitor of the fusion device and plasma will be performed with optical diagnostic systems. For the metallic first mirrors, the recovery of the reflectivity losses due to dust deposition is proposed to be carried out for 14 different optical diagnostic systems by the plasma cleaning technique. In this work, we studied the influence of the electrode area on the electrode potential as a function of the applied power with a 60 MHz radio very high frequency source. Unshielded copper disks with different diameters were constructed to study the impact of the electrode area in the range of 90 cm 2 to 1200 cm 2 , which corresponds to an Edge Thomson Scattering area ratio of 0.15 to 2. It was observed that the absolute value of the resulting bias decreased from 280 V to 15 V with the increase of the area for a given RF power. Moreover, the power consumption was reduced by 43 % using a pre-matching element close to the vacuum feedthrough. The cleaning homogeneity on a curved and a large size mirror was studied, and the difference between the center and edge maximum/minimum was around 20 % and 40 % for the curved and large size mirror, respectively. For ITER, it is required to have an End-of-Cleaning Indicator (ECI), which shows when the cleaning process would be stopped. In this work, we studied the feasibility of Optical Emission Spectroscopy (OES) as a real-time control tool for the RF cleaning process. With 13.56 or 60 MHz, it was possible to use OES as ECI by following the molybdenum (Mo), rhodium (Rh), and aluminum (Al) emission lines. The decrease of Al I line and increase of the Mo I and Rh I line were recorded as a function of the cleaning time.

Versatile optical fiber feedthroughs for ultra-high vacuum applications

In this article we present an investigation of three different fiber optic vacuum feedthroughs. Using Swagelok-type tube fittings, metal tubings containing the optical fibers are sealed into a vacuum flange. This allows for easy replacement of the feedthrough without replacing the entire flange. Employing only epoxy resin for sealing the optical fiber into the feedthough we have measured a helium diffusion rate of 2.5⋅10−10 mbar ⋅ l/s, whereas with a combination of a solderglass and epoxy resin seal we have obtained a diffusion rate below 1⋅10−12 mbar ⋅ l/s. In a third approach, using small tolerance fiber optic ferrules in our feedthroughs, we have obtained helium diffusion rates of below 1⋅10−12 mbar ⋅ l/s, making these feedthroughs well suited for ultra-high vacuum applications.

Fabrication of non-magnetic multi-pin coaxial vacuum feedthrough system for cryogenic applications.

We have developed and tested a compact non-magnetic feedthrough made of epoxy resin and capable of maintaining vacuum leak tightness over a wide temperature range (300 K-4 K). It is equipped with 15 electrical pins and three 50 Ω coaxial lines. The feedthrough has been designed to apply a high voltage (up to 5 kV) and transmit radio-frequency signals for operating a Penning trap over a wide temperature range (300 K-4 K). The characteristic impedances of the coaxial lines have been measured at 300 K and 77 K and found to remain ∼50 Ω over the frequency range of our interest (10 MHz-80 MHz). The details of its fabrication and performance over a wide temperature range have been discussed.

Determination of Residual Stresses in Ceramic-Metal Brazed Joint using Finite Element Analysis (FEA) and Experimental Validation of the Results

Ceramic vacuum feedthroughs are an inevitable requirement for any vacuum system which requires electrical feedlines to be inserted into the vacuum environment. These feedthroughs consist of metal-ceramic-metal transition and, therefore, require the brazing process as a joining technique. This process allows joining two base materials, i.e., Alumina and Kovar, for this case, which manifests different thermo-mechanical response. The difference between the coefficient of thermal expansion (CTE) of these materials causes the development of residual stresses during the cooling phase of the brazing process. Such residual stresses, if not addressed properly, can lead to the failure in the brazed joint even before the design limits. The purpose of this study is to assess these stresses by performing the thermo-mechanical analysis of the brazing process of ceramic-metal assembly through finite element analysis (FEA) technique. This study includes the assessment of non-linear behavior (due to temperature-dependent material properties) of Alumina and Kovar assembly. Further, X-ray diffraction (XRD) based residual stress measurement technique has been utilized to validate the FEA results. The paper shall present the FEA methodology (model, boundary condition, and results) followed by the experimental results and their comparison.

Vacuum Feedthrough for a UV Region Cathodoluminescence Experiment with an Optical Fiber

Vacuum Feedthrough for a UV Region Cathodoluminescence Experiment with an Optical Fiber

A high-density customizable microwave vacuum feedthrough for cryogenic applications.

We have designed, constructed, and tested an electrical vacuum feedthrough that can carry a large number of microwave signal lines, has high vacuum compatibility, and is highly customizable. We found that it had a leak rate of approximately 10-7 Pa L/s (7.5 × 10-9 torr L/s), making it suitable for high-vacuum systems such as cryostats. The feedthrough is low-cost, and the printed circuit board-based design allows the choice of any surface-mountable microwave connector. We additionally verified operation through consistent use on a real cryogenic system and verified the mechanical robustness of the feedthrough.

Portable pulsed magnetic field generator for magnetized laser plasma experiments in low vacuum environments.

A portable pulsed magnetic field generator for magnetized laser plasma experiments in low vacuum environments is presented. It is based on a classical high-voltage discharge pulsed power system. A 95 kA peak current was delivered at a 65 kV discharge voltage, which generated a quasiuniform magnetic field of 12T in a Φ8 mm × 8 mm volume. A compact, sealed design was developed to avoid short-circuit breakdowns caused by an ambient low-pressure gas medium. Design improvements were made to the vacuum feedthrough, the transmission line, and the magnetic coil. The system worked well in a low vacuum environment for a laser plasma experiment using a gas target. But at intermediate ambient gas pressure, the ambient gas was ionized around the surface of the coil at first and then the ionized gas diffused inward and outward slowly, which affected the laser plasma image in the coil. Experiments and simulations indicated that the ambient gas was ionized by the induced electric field. We developed analytical models of the induced breakdown of the ambient gas to guide the experimental design of a gas target. The analysis can also be used in the experimental design of a solid target in an intense pulsed magnetic field of hundreds of tesla that the induced breakdown along solid's surface dominates the process.

Design and implementation of a non-magnetic cryogenic multi-conductor vacuum feedthrough

A common issue for experiments requiring very low magnetic fields on vacuum and cryogenic systems is how to deal with the control of magnetic properties of electrical contacts. We describe the design and implementation of a generic sixty-four pin non-magnetic cryogenic vacuum feedthrough capable of disconnecting contacts on both sides of the vacuum boundary.

15 kV class high-voltage electrical vacuum feedthrough

In the feeder system of the Experimental Advanced Superconducting Tokamak (EAST), the high-voltage (HV) electrical vacuum feedthrough plays an important role in transmitting the voltage signals from one vacuum environment to anther vacuum environment under cryogenic temperature. Due to no commercial solutions, the feedthroughs for EAST were developed in the Institute of Plasma Physics, Chinese Academy of Sciences. In this paper, the structural design, electrical analysis, structural analysis and experiments involving thermal cycle, helium gas tightness, HV-leakage current and Paschen discharge are presented. The experimental result indicates that the leak rate of the developed feedthroughs was less than 1 × 10−9 Pa·m3·s−1. After the 5 thermal cycles from room temperature (RT) to 77 K, the HV-leakage current experiment under 10−3 Pa vacuum environment and the Paschen discharge experiments of feedthroughs were performed, the leakage current under 15 kV DC is lower than the allowable value 5 µA, and the leakage currents in helium gas and nitrogen gas from 1 Pa to 50 kPa are lower than the allowable value 10 µA.

In vessel electrical integration in ITER—Requirements & solutions

The ITER in-vessel electrical integration has been divided between several engineering activities to complete the distribution of more than 4000 cables around the inner wall of the vacuum vessel and divertor, using the upper and lower ports to exit from the vessel. Having met difficult requirements, this integration enables the measurements of key parameters of the burning ITER plasma. Most of the cables are mineral insulated (MI) cables with different diameter and type (twisted pair, quad core, triaxial, coaxial), with complex routing from the sensor to vacuum feedthrough across an in-vessel loom using a connection box located in a marshaling area at the ports. These cables have the function to connect the diagnostic sensors, located into the machine, to the data acquisition hardware in the diagnostic hall for plasma diagnostics and blanket and vessel monitoring Martinez et al. [3]. The in-vessel looms and the cables have to achieve adequate thermal contact to the vessel for cooling, and adequate neutronic protection for suitable performance of their measurement functions. The integration constraints for routing the in-vessel looms and cable tails behind blankets, and also the assembly constraints for these components will be described in this manuscript.

Spatially translatable optical fiber-coupled heterodyne interferometer.

An interferometer is a useful diagnostic tool for measuring line-averaged electron density but is limited in its use because it generally measures at a fixed location. We report here a spatially translatable fiber-coupled interferometer that measures the density of a high-speed MHD-driven plasma jet colliding with a target cloud. The interferometer uses a He-Ne laser coupled to a polarization-maintaining single mode optical fiber having a vacuum feedthrough. The interferometer provides a measure of the spatial-temporal profile of the line-averaged electron density from which the change in jet velocity as a result of its collision with the target cloud can be deduced.