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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Eliminating Signal Bias Caused by Vacuum System Backstreaming in the Diagnostic Residual Gas Analyzer of ITER

In fusion neutral gas analysis, such as with the Diagnostic Residual Gas Analyzer (DRGA) for ITER, the primary measurement range of interest comprises the low-amu species (1 to 6), especially deuterium and helium. The challenge in successfully obtaining accurate measurements is two-fold. First, the sensitivity of the method must be sufficient to resolve trace amounts accurately; typically, one percent or less. Second, the gas signal from the fusion processes must be free of bias caused by the latent presence (from system outgassing and/or vacuum backstreaming) of these gases to enable accurate interpretation of the measured signal. This latter criterion can be problematic for the lightest gases since there is a propensity for some fraction of the pumped gas load to undergo a phenomenon known as backstreaming. This behavior is manifested in pumping systems for gas properties related to relative atomic weight (lightest) and size (smallest). Backstreaming results in a significant amount of the pumped gas undertaking a reverse flow and re-entering the measurement region; thus, contaminating the forward, real-time measurement. To fully eliminate this adverse effect, a conductance-limiting device – or orifice – has been installed in the high-vacuum pumping system of the present ITER DRGA prototype. The system was already equipped with a secondary turbomolecular pump (TMP), but with limited effectiveness against backstreaming in the inter-pump volume (IPV). This orifice is placed within the suction inlet coupling of the secondary TMP, which is downstream of the IPV. Its objective is to eliminate the backstreaming phenomenon by increasing the back pressure in the IPV. However, the orifice sizing must take into consideration other factors, such as the diagnostic measurement objectives. For example, in the ITER DRGA, one of the measurement requirements is a dynamic response time of ~1s. Fortunately, an added benefit of the pumping restriction created by the orifice is that the upstream pressure increase is beneficial for the DRGA’s optical gas analysis (OGA) sensors. These sensors are attached to the IPV in the present design. The glow discharges, when used as an OGA light source, will typically have a brighter light emission with increasing plasma cell pressure. In addition to the fusion machine research sector, there are other potential applications of this pumping technique where the monitoring of lighter gas concentrations is essential, such as the photolithography process for the semiconductor fabrication of integrated circuits. This presentation will describe the vacuum system used to demonstrate a process to eliminate backstreaming as well as show test results to verify the accomplishment of this critical objective.

Marcus, Chris↗
NASA NTRS1966

Special treatment reduces helium permeation of glass in vacuum systems

Internal surfaces of the glass component of a vacuum system are exposed to cesium in gaseous form to reduce helium permeation. The cesium gas is derived from decomposition of cesium nitrate through heating. Several minutes of exposure of the internal surfaces of the glass vessel are sufficient to complete the treatment.

Bryant, P. J.↗
NASA NTRS1993

Caps Seal Boltholes On Vacuum-System Flanges

Sealing caps devised for boltholes on vacuum-system flanges. Used in place of leak-prone gaskets, and provide solid metal-to-metal interfaces. Each sealing cap contains square-cut circular groove in which O-ring placed. Mounted on studs protruding into access ports, providing positive seal around each bolthole. Each cap mates directly with surface of flange, in solid metal-to-metal fit, with O-ring completely captured in groove. Assembly immune to misalignment, leakage caused by vibration, and creeping distortion caused by weight of port. O-ring material chosen for resistance to high temperature; with appropriate choice of material, temperature raised to as much as 315 degrees C.

Roman, Robert F.↗
NASA NTRS1993

Analysis of high vacuum systems using SINDA'85

The theory, algorithms, and test data correlation analysis of a math model developed to predict performance of the Space Station Freedom Vacuum Exhaust System are presented. The theory used to predict the flow characteristics of viscous, transition, and molecular flow is presented in detail. Development of user subroutines which predict the flow characteristics in conjunction with the SINDA'85/FLUINT analysis software are discussed. The resistance-capacitance network approach with application to vacuum system analysis is demonstrated and results from the model are correlated with test data. The model was developed to predict the performance of the Space Station Freedom Vacuum Exhaust System. However, the unique use of the user subroutines developed in this model and written into the SINDA'85/FLUINT thermal analysis model provides a powerful tool that can be used to predict the transient performance of vacuum systems and gas flow in tubes of virtually any geometry. This can be accomplished using a resistance-capacitance (R-C) method very similar to the methods used to perform thermal analyses.

Spivey, R. A.↗
NASA NTRS1980

Experiments on the effect of ultraviolet on contamination in vacuum systems

A series of experiments designed to investigate the effect of irradiating a portion of a vacuum system with ultraviolet (UV) light are discussed. Data obtained with the quartz crystal microbalance show that, under ultraviolet irradiation, clean and contaminated mean different things than in situations that do not involve irradiation. The history of the chamber appears to be of paramount importance, not the pumping mechanism. UV irradiation check for contamination is recommended in critical experiments.

Kruger, R.↗
NASA NTRS1974

Semipermanent sealing of leaks in high vacuum systems

Silicone-rubber adhesive is applied externally to seal hair-line cracks in sections of high vacuum system while system is partially evacuated. No pretreatment of surface is required since adhesive will be drawn into crack while diffusion or ion pump is off.

Christian, J. D.↗
NASA NTRSDate not supplied

On Predicting Transient Pressure in Vacuum Systems Featuring Getter Materials

Getter materials have been used to reduce pressure or partial pressures in a variety of vacuum applications ranging from vacuum tubes to space flight science instruments. Testing of getter materials has tended to emphasize the capacity of candidate materials to collect specific gas species in sufficient quantities to size them in these applications. When determining a getter material’s capacity, it is typically subjected to enough excess target gas to ensure it sorbs as quickly as possible. However, when both the gas source strength and the getter’s sorption rate exhibit transient decay behavior, such data is not sufficient to predict the targeted species’ partial pressure within a vacuum system as a function of time.

M. S. Woronowicz↗
NASA NTRSDate not supplied

On Predicting Transient Pressure in Vacuum Systems Featuring Getter Materials

Getter materials have been used to reduce pressure or partial pressures in a variety of vacuum applications ranging from vacuum tubes to space flight science instruments. Testing of getter materials has tended to emphasize the capacity of candidate materials to collect specific gas species in sufficient quantities to size them in these applications. When determining a getter material’s capacity, it is typically subjected to enough excess target gas to ensure it sorbs as quickly as possible. However, when both the gas source strength and the getter’s sorption rate exhibit transient decay behavior, such data is not sufficient to predict the targeted species’ partial pressure within a vacuum system as a function of time.

M. S. Woronowicz↗
NASA NTRSDate not supplied

On Predicting Transient Pressure in Vacuum Systems Featuring Getter Materials

Getter materials have been used to reduce pressure or partial pressures in a variety of vacuum applications ranging from vacuum tubes to space flight science instruments. Testing of getter materials has tended to emphasize the capacity of candidate materials to collect specific gas species in sufficient quantities to size them in these applications. When determining a getter material’s capacity, it is typically subjected to enough excess target gas to ensure it sorbs as quickly as possible. However, when both the gas source strength and the getter’s sorption rate exhibit transient decay behavior, such data is not sufficient to predict the targeted species’ partial pressure within a vacuum system as a function of time.

Michael Woronowicz↗
NASA NTRS1971

Improved molecular sorbent trap for high-vacuum systems

Closed cycle refrigeration loop in which trays holding molecular sorbent are made to serve as cooling baffles improves the performance of high vacuum systems. High performance is obtained with almost no decrease in pumping speed.

Knechtel, E. D.↗
NASA NTRS1988

LIGO vacuum system study

A laser interferometer gravitational wave observatory (LIGO) is being developed with sensitivities which will have a high probability of detecting gravitational waves from astrophysical sources. A major component of LIGO is a total of 16 km of 1.2 m (48 inch) diameter tube at a pressure of less than 10 to the minus 8th power torr. It will be of 304L stainless steel procured directly from the steel mills with the initial hydrogen content specially reduced. Projections of the outgassing rates of hydrogen and of water vapor as a function of time are given and the uncertainties discussed. Based on these, a preliminary analysis of the vacuum system is presented.

Livas, Jeffrey C.↗