Smoke detector | EPFL Graph Search

A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about in diameter and thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system. Household smoke detectors, also known as smoke alarms, generally issue an audible or visual alarm from the detector itself or several detectors if there are multiple devices interlinked. Household smoke detectors range from individual battery-powered units to several interlinked units with battery backup. With interlinked units, if any unit detects smoke, alarms will trigger at all of the units. This happens even if household power has gon

Extension of miniature neutron scintillators features in CROCUS: novel acquisition scheme and extended flux range

Colin Rochat

The goal of this work was the improvement of the capabilities of a miniature neutron detector, for easing its use, and extending its range of applicability. Firstly, the Red Pitaya STEMlab 125-14 was the object of an exploratory study in order to propose an alternative method to the two current acquisition electronics based on photon counting, using analog and digital means. The study allowed to establish a new methodology based on the direct use of the SiPM pre-amplifier output, requiring the hypothesis that neutron events can be discriminated directly by pulse amplitude. It was first tested in the low neutron flux of the CARROUSEL facility, and the results were compared to the analog electronics. The agreement in count rate, spectrum, and linearity demonstrates the validity of this new methodology. Moreover, its application in CROCUS allowed demonstrating that it is working in reactor condition up to a flux of 1.13∗108 s−1cm−2. Secondly, an array of six miniature neutron detectors with different sensitivities was designed and tested. The qualification study in CARROUSEL allowed to show that all detectors behave normally, and that the sensitivity of the detectors increases as a function of the scintillator’s volume at low neutron flux, as expected. The conclusion is limited by the knowledge in effective dimensions of each scintillator. In a first experiment in CROCUS using the same setup, including digital threshold (50), a loss of linearity was observed simultaneously for all detectors at a power ofabout 4W(i.e. 7∗107s−1cm−2). As the cause was expected to be a higher gamma background, the experiment was repeated with a higher threshold (120): consistently with the CARROUSEL test, count rate and loss of linearity depends on the scintillation’s volume. Further studies are needed to conclude on the phenomenon at hand, but since the main parameter for gamma discrimination proved efficient, the gamma contribution increased at higher powers seems a good candidate. In conclusion, the results are globally satisfying for the new methodology with Red Pitaya STEMlab 125-14. However, the experimental campaign of this work was only a feasibility study. The results have to be confirmed with further studies. Moreover, this system could be improved. In particular, it can be adapted firstly for both RF inputs of Red Pitaya and secondly for dynamical measurements. The results of the multi-sized array of miniature neutron detector were also encouraging. However, the behaviour of certain detectors prevent to deduce with certainty some expected trends. Further studies have to be carried out by multiplying the number of detectors of each dimension.

2021

Determination of the Fast-Ion Phase-Space Coverage for the FILD Spatial Array of the ASDEX Upgrade Tokamak

Lorenzo Stipani

The fast-ion phase-space coverage of the ASDEX Upgrade Fast-Ion Loss Detectors (FILD) has been estimated and the results are presented here. To that end, a numerical tool has been developed to determine particle orbits that can be accepted by each detector in the machine, depending on their radial position, without colliding to the first wall. Two different plasma shapes have been analyzed and results show excellent phase-space coverage for mostly all the detectors, especially for those located at the midplane and below it. The methodology developed provides an excellent way to estimate the signal of these detectors depending on the plasma scenario and can be easily extended to other machines. Also, this study can be complemented with thermal analysis to consider the structural integrity of the detectors, allowing determining optimal operation parameters both from the signal and safety standpoints.

2019

Electron Cloud and Synchrotron Radiation characterization of technical surfaces with the Large Hadron Collider Vacuum Pilot Sector

Elena Buratin

This PhD thesis presents the experimental study on electron cloud (EC) and synchrotron radiation (SR) phenomena affecting the LHC storage ring performance. These phenomena are one of the major issues of the LHC storage ring, generating beam instabilities, pressure rise and heat loads on the beam pipes. This experimental study is carried out with an innovative system installed in a room temperature and field free section of the Large Hadron Collider (LHC), the Vacuum Pilot Sector (VPS). ln this system, several surfaces are simultaneously tested, in particular standard copper, amorphous carbon coating, NEG. Thanks to a wide spectrum of detectors, the EC and SR signals were studied as a function of beam parameters and beam pipe properties. The EC behaviour increases linearly with the number of bunches and bunch population above the multipacting threshold. This phenomenon increases linearly also with the bunch length for the Long Straight Sections of LHC (LSS). As expected, the bunch spacing has a crucial importance on the formation of EC dynamic: the 50 ns filling scheme avoids the multipacting effect at 450 GeV. At 6.5 TeV the photoelectron contribution is visible, with no multipacting. This scheme is not sufficient for the LHC collision studies and cannot be used as standard filling scheme. Instead, the 25 ns bunch spacing scheme suffers of EC; in this case this phenomenon can be drastically reduced only by bombarding the surface with electrons during dedicated scrubbing runs, or thanks to the installation of beam pipe surface with a low SEY, such as the amorphous-carbon coating. The measurements performed with pick-ups show the evolution of the EC dynamics for the first time in the LHC. The energy spectrum detectors and the gas analysers were also installed for the first time in the LHC history: the electron cloud spectrum and the gas composition could be measured during the machine operation. The electron energy spectrum evidences a peak at around 100 eV, corresponding to the accelerated electrons responsible for multipacting. The gas analysers measured the main gasses present in the LHC ultra-high vacuum system, such as methane, carbon dioxide and monoxide, water, hydrogen and traces of 2-Propynenitrile 3-fluoro (C3FN), probably linked to the effect of radiation into the kapton cables. It has been possible to estimate the Electron Stimulated Desorption (ESD) parameter of a copper surface as a function of the accumulated electron dose. The heat loads due to impedance, EC and SR were measured and, finally, the operation of HL-LHC machine has been estimated in terms of electron current, pressure and power deposition thanks to the results of this study. Doubling of the bunch population will increase the electron current and the pressure of one order of magnitude, while the deposited power due to EC will be smaller than 1 W/mchamber for a beam pipe SEY lower than 1.8.

EPFL2020