Operation Of Chamber Research Articles

Fabrication Processes for Iridium/Rheiiium Combustion Chambers

Chemical vapor deposition (CVD) has been used to fabricate rhenium liquid rocket combustion chambers since 1979. CVD iridium was first applied to rhenium chambers for high temperature oxidation protection in 1986. The addition of iridium permits chamber operation for long durations at temperatures around 2200°C and provides a specific impulse increase on the order of 3 to 5%. Since 1986, CVD iridium/rhenium (Ir/Re) chambers have been successfully hot-fire tested at various facilities in both nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) and oxygen/hydrogen (02/H2) bipropellants, the latter at mixture ratios ranging from 4 to 17, for a total of nearly 200 hours. An alternate processing method being investigated is to form the rhenium by powder metallurgy (PM) and apply the iridium by electrodeposition (ED). To date, hot-fire testing of chambers produced by this ED/PM method includes 43 seconds in NTO/MMH and approximately 11 hours in 02/H2 at mixture ratios of 3 to 4, a range having an oxidizing potential that may actually be benign to unprotected rhenium. These processing methods and their relationship to fabricating Ir/Re combustion chambers, as well as test methods for evaluating their efficacy, have been evaluated and a means of comparing the severity of different tests has been developed.

Diffusion cloud chamber operation and the background gas effect

Key design and operational aspects for thermal diffusion cloud chamber (TDCC) applications are discussed in the context of a two-dimensional solution to the mass and energy balances describing diffusion through a stagnant background gas. The important issue of buoyancy-driven convective disturbances and their impact upon nucleation measurements made using a diffusion cloud chamber are discussed. A new derivation of the relation that predicts the upper limit of total pressure allowed for stable (the absence of buoyancy-driven convective disturbances) operation of the diffusion cloud chamber is presented. For the first time, this limit of stable operation can be predicted prior to making experimental measurements. Nucleation data obtained in our laboratory are examined in the context of this predicted limit of stable operation. New nucleation data are presented for 1-pentanol using helium as a background gas. Only data corresponding to stable operation in the cloud chamber is used in the analysis. The effect of background gas on nucleation we have reported previously is confirmed for 1-pentanol, as well as for all the other alcohols that have been investigated in our laboratory.

Study of ageing and gain limits of microstrip gas chambers at high rates

The CMS experiment comprises MSGCs as one of the key detection elements for high luminosity tracking at LHC. In _addition to the high dose rate of 10 mC/year per cm of strip, these detectors have to survive the hostile presence of highly ionizing particles, neutrons low energy gammas and hadrons. In this report we present the results of systematic tests on maximum safe operational gain limits in MSGCs before the discharge. Long term ageing tests performed on prototype open ‘banana’ modules envisaged to be arranged around the interaction region in the forward part of the CMS tracker show no evidence of gain drop up to equivalent ∼ 10 years of LHC operation. A comparison is made between argon and neon gas mixtures with DME in equal proportions by investigating long term irradiation effocts on chamber operation by introducing controlled and reproducible pollution in the gas lines.

Operation of high rate microstrip gas chambers

We describe recent measurements carried out in well controlled and reproducible conditions to help understanding the factors affecting the short- and long-term behaviour of Microstrip Gas Chambers. Special care has been taken concerning the gas purity and choice of materials used in the system and for the detectors construction. Detectors built on glasses with surface resistivity in the range 10 13 –10 15 Ω/□ have shown satisfactory performance as they do not show charging-up process at high rate and stand the large doses required for the future high luminosity experiments (∼10 mC-cm −1 .yr −1 ). Concerning the lifetime measurements, it has been observed that chambers manufactured on high-resistivity glass are far more susceptible of suffering ageing than detectors made on low resistivity, electron-conducting supports, independently of the metal used for the artwork (chromium or gold) at least in clean gas conditions. The successfully operation in the laboratory of detectors manufactured on diamond-coated glass with a surface resistivity around 10 15 Ω/□ confirms the last statement. Results from a long-term, high rate beam test are also reported.

The full-length prototype of the KLOE drift chamber

The main goal of the KLOE experiment is the study of CP violation in the K mesons system, with an accuracy of 10 −4 in the measurement of Re( ε′ ε ) . This task imposes strong constraints on the design and operation of the drift chamber, which must reconstruct the charged decays of low momentum K L's and K S's with high efficiency and high resolution. A full-length prototype of the chamber has been built and tested on a 50 GeV/ c beam. The analysis of the large sample of data has allowed a detailed study of the time to distance relations as a function of the track parameters and of the peculiar geometry of the drift cell. The detector performance, in terms of efficiency, spatial resolutions and dE dχ resolution, is illustrated and discussed.

CHRONIC INHALATION TOXICITY AND CARCINOGENICITY STUDIES ON-CHLOROPRENE IN RATS AND HAMSTERS

Three groups of 100 Wistar rats and Syrian golden hamsters of each sex were exposed by inhalation to 0, 10, or 50 ppm (v/ v)-chloroprene for 6 h/day, 5 days a week for up to 24 and 18 mo, respectively. To maintain the chemical Integrity of this highly reactive material in the exposure chambers,-chloroprene vapor was generated from freshly distilled chloroprene (99.6% -chloroprene; 0.3% -chloroprene and <50 ppm chloroprene dimers) by passing nitrogen through liquid-chloroprene at 0 C. This mixture was then conducted through Teflon and stainless steel transport tubes into the main airflow for the chambers. After 72 wk on test a technical fault in chamber operation procedures resulted in the accidental death of 87 male and 73 female rats at 10 ppm unrelated tochloroprene. Otherwise, survival of the remaining 10 ppm rats and the rats exposed at 50 ppm was unaffected by exposure. Survival among both groups of hamsters exposed to-chloroprene was higher than the controls. All treated rats exhibited slight restlessness during exposure, but only during the first few weeks on test. At 50 ppm, rats also showed an increased incidence of alopecia, slight growth retardation, and an increased incidence of foci of altered liver cells, a change frequently seen in aged rats. Hamsters showed only a slight growth retardation and a slight reduction in amyloidosis at 50 ppm. No serious adverse effects were seen in either species at 10 ppm. Overall, there was no evidence of carcinogenicity related to-chloroprene exposure in either rats or hamsters at vapor concentrations as high as 50 ppm.

Operation of microstrip gas chambers manufactured on glass coated with high-resistivity diamond-like layers

We describe recent observations and measurements realized with microstrip gas chambers (MSGCs) manufactured on borosilicate glass coated with a thin layer of diamond-like carbon (DLC) having a surface resistivity around 4 × 10 16 Ω/▭ . The role of the back-plane electrode configuration and potential in the detector performance has been studied. Even for this very high resistivity of the coatings, MSGCs operate differently from those manufactured on bare boro-silicate glass; the charge gain increases with the radiation flux for counting rates above 10 3 Hz/mm 2, reaching a value 60% higher for 10 5 Hz/mm 2. This behavior does not depend on the presence and potential of the back-plane electrode; however, both maximum gain and rate capability are influenced by the drift field. From this study, compared with measurements realized previously with other detectors, we deduce that for stable high rate operation of MSGCs the resistivity of the coating should not exceed ∼10 15 Ω/▭.

Properties of C 2H 2F 4-based gas mixture for avalanche mode operation of resistive plate chambers

Some properties of a 90% C 2H 2F 4 gas mixture, used to operate resistive plate chambers in the avalanche mode, are determined by comparing the experimental results with the prediction of simple analytical calculations. The fast charge distribution of the signal induced on pick-up electrodes is reproduced by means of a Monte Carlo simulation of the avalanche development. In addition, predictions for a gas mixture with poor content of C 2H 2F 4 are given for comparison.

On the high gain operation of low-pressure microdot gas avalanche chambers

Microdot avalanche chambers (MDOT) equipped with thin semitransparent Cr photocathodes, were characterized with UV photons at low gas pressure. Gains superior to 10 4 were reached with gas multiplication at the dots. In a mode where preamplification in the gas volume precedes the additional dot multiplication, gains superior to 10 6 were measured at 30–60 torr of propane. The fast amplification mechanism results in narrow high amplitude pulses with 2–3 ns rise time, visible with no further electronic amplification means. We present here our preliminary results and briefly discuss potential applications.

METIER (modular ecotoxicity tests incorporating ecological relevance) for difficult substances. 4. Test chamber for cladocerans in flow-through conditions

Continuous-flow systems in toxicity testing are advantageous because they introduce constant toxicant concentrations and constant food to the test organisms and continuously purge wastes. Therefore, continuous-flow systems are particularly useful in hazard assessment of substances that may readily be lost from test chambers (i.e., poorly water soluble, volatile, readily biodegradable or photodegradable, hydrolitically unstable compounds). Within METIER (Modular ecotoxicity tests incorporating ecological relevance), a European Union-funded project, a basic design for a standard flow-through exposure system was developed. This paper addresses the adaptation of the flow-through system for use with cladocerans, which involved designing a suitable test chamber and appropriate operation procedures. The sublethal toxicity of a reference compound (3,4-dichloroaniline) to Daphnia magna Straus was evaluated under both flow-through and semi-static conditions. Tests conducted under flow-through conditions provided a less sensitive measure of toxicity than under semi-static conditions. This result is probably a function of the higher food availability within the flow-through system. The no-observed-effect concentration for reproduction was the most sensitive endpoint and was 5 μg/L in the flow-through system and 2.5 μg/L in semi-static conditions.

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteria

In this paper we present results of a two-dimensional (z,r) treatment of the mass and energy transfer processes that occur during the operation of a thermal diffusion cloud chamber. The location of the wall is considered in solving the mass and energy transport equations, in addition to the vertical distance, z, between the upper and lower plate surfaces. We examine the effect of aspect (diameter to height) ratio on chamber operation; the effects of operation with either a dry or a wet interior chamber wall on temperature, supersaturation, nucleation rate, and total density profiles in the chamber; the effect of overheating the interior of the chamber wall on these conditions within the cloud chamber; and the effects associated with using different density background gases on the operation of the chamber. In a second paper, immediately following, we apply the formalism and the solutions developed in this paper to address the important problem of buoyancy-driven convection that can accompany (seemingly normal) operation of thermal diffusion cloud chambers in nearly all ranges of total pressure and temperature.

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. II. Stability of operation

In this paper, the second of a series of two presenting a detailed description of thermal diffusion cloud chamber operation, we address the operational stability of the vapor–gas mixture in a diffusion cloud chamber with respect to density profile extrema and the accompanying possibility of buoyancy-driven convective flow disturbances. We examine conditions for stable operation (no convective flow disturbances) in the central portion of the cloud chamber, as well as conditions necessary for stable operation in the vicinity of the cloud chamber wall. We find that the total density profile in the central portion of the cloud chamber can pass through a density minimum even though the density at the upper plate surface is less than the density at the lower plate surface. This local density profile inversion can result in unstable (convective) behavior that propagates through the cloud chamber. Furthermore, we find that local extrema in the total density profile near the chamber wall can lead to subtle, convective flows that are difficult to detect yet can exert a profound influence on nucleation in the central portion of the cloud chamber. We have developed a simple method to estimate the limiting total pressure in a cloud chamber that will support stable operation. From results of our investigations based upon this method, it appears that the thermal diffusion cloud chamber is best suited for experiments at higher temperatures where the accessible total pressure range is largest. Finally, we find that results of our investigation into the effects of total pressure and kind of background gas on nucleation in diffusion cloud chambers involving the low molecular weight alcohols and hydrogen and helium background gases cannot be explained on the basis of these kind of density disturbances occurring within the diffusion cloud chamber. Also, for (relatively) low vapor pressure materials, such as 1-pentanol or other high molecular weight alcohols and alkanes stability limitations may preclude nucleation measurements at low temperatures using a diffusion cloud chamber altogether.

Avalanche and streamer mode operation of resistive plate chambers

A resistive plate chamber was operated at voltages increasing in steps of 200 V over a 3 kV interval and the transition between the avalanche and streamer modes was studied. The avalanche amplitude was observed to be exponentially dependent on the operating voltage up to a value, characteristic of the gas, where the avalanche saturation occurs and delayed streamer signals start to appear. Signal waveforms, charge and timing distributions are reported.

Calibration of CMD-2 drift chamber

The experience gained during four years of operation of the CMD-2 drift chamber is reported. Offline calibration of the DC parameters using a sample of Bhabha scattering events is described. Fine corrections to the Lorentz angle allow one to improve the momentum resolution. The systematic error in the determination of the polar angle was substantially decreased when information from the Z-chamber cathode was used for calibration.

High rate operation of micro-strip gas chambers

We describe the development of micro-strip gas chambers (MSGC) able to withstand the very high rates met in detectors for high luminosity experiments. A light and cheap mechanical assembly suited for mass-production of modules has been implemented. To prevent charging-up processes, affecting gain at high rates, we have tested substrates with surface resistivity in the range 10/sup 14/-10/sup 15/ /spl Omega///spl square/: stable gains at rates above 10/sup 6/ mm/sup -2/ s/sup -1/ have been achieved at avalanche sizes of 10/sup 5/ using electron-conducting and diamond-coated glass. A systematic search has been undertaken to define the purity levels of gas and materials necessary for long-term operation, with the goal of reaching a collected charge above 100 mC cm/sup -1/ without degradation. This has been achieved operating in very clean conditions with argon-dimethylether. A dose-rate dependence of the ageing behaviour has been found alerting on the relevance of measurements realized at too high currents.

An extended radon chamber model

The radon chamber model developed at the Paul Scherrer Institut (PSI) is covering differences in size between the different short-lived radon daughters by taking into account nuclide specific deposition and attachment rates. The resulting set of differential equations was analytically solved and the solutions were installed into a computer code. Different modes of operation of a radon chamber (continuous flow, pulse, and feedback) were analysed with the model. The influence of aerosol sampling on the chamber atmosphere was studied. Increasing the diffusion constant of the radon daughter clusters increases both attachment and deposition rates. As a consequence, the unattached concentration of the radon daughter with the shortest half-life, 218Po, is reduced relative to the radon progeny 214Pb and 214 Bi 214 Po , compared with calculations with equal mobilities of the radon progeny. The amount of 218Po activity deposited on the chamber walls also is increased relative to the other radon progeny if the size of 218Po is considered to be smaller.

Combustion and Emissions of Low Heat Rejection Ceramic Methanol ATAC Engines.

When methanol is used as fuel for internal combustion engines, formaldehyde and unburned methanol emissions can be a problem. To overcome this shortcoming, an engine with the active thermo-atmosphere combustion (ATAC) system was proposed, along with improvements in heat-insulating performance and the realization of high-temperature combustion by using ceramics for the combustion chamber walls. The combustion and emissions characteristics of this ceramic low heat rejection (LHR) methanol ATAC engine were investigated. Combustion performance was compared between operation with methanol and gasoline. When methanol was used, it was seen that the ATAC operation region was widened considerably. Also, a reduction in aldehyde emissions was achieved, due to the high-temperature operation of the combustion chamber. However, efficiency deteriorated at times due to early self-ignition timing. This was overcome by the use of lean fuel-air ratios, which resulted in both a reduction of NOx and an improvement in fuel consumption. With a premixed fuel supply system, wall surface ignition was unavoidable for combustion chamber surface temperatures greater than 800 K (527°C). Wall surface temperature swing and instantaneous heat flux increased substantially with ATAC operation under these conditions.

A computer-controlled tension monitoring system for drift chamber wires

We describe a wire tension monitor used in the construction and operation of a large drift chamber. This system monitored the tensions of up to 64 wires by locating their resonant frequencies using a sinusoidal current in a weak magnetic field. Wires of 20 μm tungsten and 100 μm aluminum whose lengths varied from 7 to 70 cm were monitored, with resonant frequencies ranging from 160 to 1850 Hz. A multiplexing scheme was implemented which dwelled on each wire for about half a minute. This monitor combined custom electronics with a commercial I/O board and a PC/286 computer. The short-term reproducibility ( σ) of the measurements was ±0.05g (±0.1%) for tungsten wires and 1.1 g (±1.0%) for aluminum wires. Limitations of the method are discussed.

NASA's biomass production chamber: A testbed for bioregenerative life support studies

The Biomass Production Chamber (BPC) located at Kennedy Space Center, FL, USA provides a large (20 m 2 area, 113 m 3 vol.), closed environment for crop growth tests for NASA's Controlled Ecological Life Support System (CELSS) program. Since the summer of 1988, the chamber has operated on a near-continuous basis (over 1200 days) without any major failures (excluding temporary power losses). During this time, five crops of wheat (64–86 days each), three crops of soybean (90 to 97 days), five crops of lettuce (28–30 days), and four crops of potato (90 to 105 days) were grown, producing 481 kg of dry plant biomass, 196 kg edible biomass, 540 kg of oxygen, 94,700 kg of condensed water, and fixing 739 kg of carbon dioxide. Results indicate that total biomass yields were close to expected values for the given light input, but edible biomass yields and harvest indices were slightly lower than expected. Stand photosynthesis, respiration, transpiration, and nutrient uptake rates were monitored throughout growth and development of the different crops, along with the build-up of ethylene and other volatile organic compounds in the atmosphere. Data were also gathered on system hardware maintenance and repair, as well as person-hours required for chamber operation. Future tests will include long-term crop production studies, tests in which nutrients from waste treatment systems will be used to grow new crops, and multi-species tests.

Optimization of design and beam test of microstrip gas chambers

We describe recent experimental and theoretical work aimed at optimizing the geometry and the operation of micro-strip gas chambers in order to improve their performance and reliability. With the help of a simulation program, we have studied the mechanism of signal propagation and analyzed the effects on signal shape and size of resistivity of strips, grouping of biased strips and the presence of a back-plane. Several detectors manufactured according to the results of the study and equipped with fast amplifiers have been installed in a test beam to study general operating characteristics, efficiency and localization accuracy; preliminary results of the data analysis are discussed.