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Electron Beam Welding (EBW)
Published in Gary F. Benedict, Nontraditional Manufacturing Processes, 2017
The second category of pump, known as a diffusion pump, is used to create the high level of vacuum required in a EBW-HV chamber or in the electron gun. To generate this high level of vacuum as fast as possible, a roughing pump is first used to rapidly reach a partial vacuum level, then a diffusion pump is used to remove the remaining air molecules, thus producing the high vacuum.
Fundamentals of Vacuum and Plasma Technology
Published in Andrew Sarangan, Nanofabrication, 2016
The layout of a typical vacuum system is shown in Figure 2.8. Initially, roughing pumps are used to reach from atmosphere down to about 10 mT, and then a high-vacuum pump is initiated to reach lower pressures while the roughing pump continues to pump the exhaust port (foreline) of the high-vacuum pump. A high-vacuum pump cannot be used to pump down directly from atmosphere. Since turbo molecular pumps are constructed from lightweight aluminum to allow high rotation speeds, they are not strong enough to withstand the forces that will occur at higher pressures. In fact, sudden venting of the pump that is running at full speed can cause catastrophic damage to the vanes. On the other hand, if a pump is started at rest from atmosphere, it will never reach full rotation speed due to the excessive drag forces. Additionally, due to the open construction of the pump, at higher pressures and short mean free paths, the compression ratio will also be extremely poor.
Confirmation and Quantification of Gas Flow into Capsules
Published in Fusion Science and Technology, 2023
M. Aggleton, S. Bhandarkar, A. Nikroo
Our main purposes here are to weed out plugged CFTAs significantly farther upstream than previously done and to provide a clear understanding of the CFTA fill rate that can inform the NIF of the target performance for the shot. This is accomplished by monitoring the rate of Xe gas filling the CFTA capsule using a XRF technique.2 A careful balance needs to be struck when filling with xenon. A minimum level of gas is required to observe a reliable signal on the XRF; however, too much pressure can exceed the target specifications and expose the CFTA to unnecessary risk. The standard fill pressure for an ignition target is approximately 300 Torr above ambient. To avoid exceeding this pressure, the capsule is first pumped out for 5 min using a roughing pump, then filled to 1000 Torr with xenon in an ambient environment.
Final Design of Vacuum Pumping Systems for the Material Plasma Exposure eXperiment
Published in Fusion Science and Technology, 2023
Jonathan Perry, Adam Aaron, Chris Stone, Arnold Lumsdaine
The pressure during plasma operations is analyzed using the Monte Carlo simulator Molflow+ to generate a 3D pressure profile. It is assumed that plasma pumping occurs during plasma operations. This assumption means that 99% of the gas load is at the PMI chamber. Therefore, only the PMI chamber was analyzed. A geometric model as shown in Fig. 8 is generated in Molflow+ based on the dimensions of the PMI chamber and roughing pump train vacuum port. Given that the expected pressure range of the PMI chamber is 1 to 10 Pa, the turbo pump train is not incorporated into the simulation. The turbo pump train pumping speed contributes very little in this pressure range. In Molflow+, the walls of the system are divided into planar facets. Figure 8 identifies the facet that is assigned as the roughing pump train (specifically 7600 L/s), as well as the plasma gas source. Two scenarios are tested to measure the pressure profile with the minimum gas supplied (4.5 sLm) and the maximum gas supplied (10 sLm). All remaining walls are given a conservative baked stainless steel outgassing rate of 1 × 10−9 Pa‧L‧s−1‧cm−2. Results of the steady-state simulation shown in Fig. 9 demonstrate that a roughing pump train sized to 7600 L/s is sufficient in maintaining the PMI pressure between 1 to 10 Pa.
PHENIX U.S.-Japan Collaboration Investigation of Thermal and Mechanical Properties of Thermal Neutron–Shielded Irradiated Tungsten
Published in Fusion Science and Technology, 2019
Lauren M. Garrison, Yutai Katoh, Josina W. Geringer, Masafumi Akiyoshi, Xiang Chen, Makoto Fukuda, Akira Hasegawa, Tatsuya Hinoki, Xunxiang Hu, Takaaki Koyanagi, Eric Lang, Michael McAlister, Joel McDuffee, Takeshi Miyazawa, Chad Parish, Emily Proehl, Nathan Reid, Janet Robertson, Hsin Wang
Previous tests in the Low Activation Materials Development and Analysis Laboratory for thermal diffusivity used a Netzsch LFA-457 MicroFlash instrument, which has a three-sample carousel and uses a laser pulse to heat the front surface of a thin sample and an infrared detector to record backside temperature rise. The LFA-457 has a roughing pump and argon fill gas for measurements and can reach to vacuum levels of 10–3 Torr. For very thin materials with higher thermal diffusivity, including tungsten, the laser pulse width (>0.6 ms) is not short enough compared with the time to reach half maximum (half-time t1/2) of the recorded transient. A standard size sample is typically 12.7 or 10 mm in diameter and 2 mm thick. For irradiation, these standard size samples are too large because of activation concerns. Additionally, for measurement temperatures above ~500°C in the Netzsch LFA-457, oxidation can occur on tungsten because of the low vacuum conditions and tungsten’s sensitivity.