O-rings made from foam rubber are often used in sealing applications. Foam rubber have low (macroscopic) elastic modulus
E
0
resulting in a low nominal contact pressure when squeezed against a ...countersurface. In most cases the foam rubber is covered by a thin surface film with the effective elastic modulus
E
1
>
E
0
. We show that the nominal contact pressure may not be high enough for the contact area to percolate and the O-ring seal will leak. For the leakage calculations we use the Persson multiscale contact mechanics theory, and the (modified) Bruggeman effective medium theory for the fluid flow conductivity. The experimental input for the theory are surface roughness power spectrum, which was obtained from stylus topography measurements, and the elastic properties (
E
0
and
E
1
) of the rubber O-ring. As an application of this calculation method, we have used the preliminary as well as the final results of the laboratory gas tightness tests of the 136 New Small Wheel Micromegas Quadruplets performed at CERN, from February 2019 to May 2021, in the framework of the ATLAS Experiment upgrade. In the integration quality control, a novel method for gas tightness measurement, that we have called “Flow Rate Loss”, has been used as a baseline method.
Graphical Abstract
Arc suppression Snubbers offer safety in high energy superconducting magnet systems. Large superconducting magnets may have arcing across their breakers at the moment of slow dump initiation ...resulting from a sudden current redistribution in the powering circuit. The ATLAS Experiment at CERN experiences such arcing with its 7.3 H Toroidal magnet powering circuit. To discharge the magnets, the current is redistributed to a parallel branch called the Run Down Unit (RDU) by means of a breaker. Due to the physical layout and other metallic components in the vicinity, the power supply and RDU branches have undesirable and unavoidable parasitic inductance, causing a voltage spike over the main breakers at the moment of opening. The resulting arcing deteriorates the breaker contacts, resulting in increased operating temperatures and a more frequent need for maintenance. The arc suppression system developed takes the form of an RC Snubber (Resistor-Capacitor). The Snubber offers the current a low-impedance path, thus smoothing out the current redistribution and suppressing the voltage spike. This initial charging period of the capacitors gives the current enough time to overcome the parasitic inductance, therefore allowing the RDU to smoothly ramp up without a sudden voltage spike. To test the concept, a 1/50th scale demonstrator was developed and showed successful results. After the demonstrator, endurance testing of the electrolytic capacitors was performed to ensure no degradation of the charging characteristics for an equivalent of 20 years of operation. The Snubber was manufactured and implemented with successful results on the ATLAS Toroidal powering circuit.
In order to fully exploit the physics potential of the ATLAS experiment at the HL-LHC, the trigger rate of and maximum latency of the first-level trigger system will be increased to 1 MHz and 10μs, ...respectively. In addition, a new first-level muon track trigger with high momentum resolution based on the ATLAS precision Muon Drift-Tube (MDT) chambers will be employed which requires triggerless readout. The TDC ASICs of the current front-end electronics of the MDT chambers are incompatible with these requirements. The front-end boards, each with a TDC chip and three 8-channel amplifier–shaper–discriminator (ASD) chips have to be replaced. Therefore, a new octal ASD2 ASIC has been developed in modern 130 nm IBM/Global Foundries CMOS technology. The chip also contains a Wilkinson ADC to perform both time-over-threshold and signal charge measurement. The ASD design has been fully qualified for the serial production of 80000 chips for ATLAS. The performance in terms of signal rise time and channel uniformity significantly surpasses the one of the previous chip while keeping the power consumption constant. In addition to the characterization with test pulses, several chips have been mounted on the front-end boards and tested in a muon beam at the Gamma Irradiation Facility GIF++ at CERN up to high counting rates where the superior drift time and spatial resolution becomes evident.
•New Amplifier–Shaper–Discriminator chips for the readout of ATLAS (s)MDT chambers at HLLHC.•Design of new ASD chip in 130 nm CMOS IBM/Global Foundries technology completed.•Improved signal rise time and channel uniformity.•Radiation hardness far better than needed in the ATLAS muon spectrometer at HLLHC.•Successful full performance test in a muon beam at CERN under intense gamma irradiation.
This report provides an overview of the new results obtained by the ATLAS Collaboration at the LHC, which were presented at the Quark Matter 2018 conference. Furthermore these measurements were ...covered in 12 parallel talks, one flash talk and 11 posters. In this document, a discussion of results is grouped into four areas: electromagnetic interactions, jet quenching, quarkonia and heavy-flavour production, and collectivity in small and larger systems. Measurements from the xenon-xenon collisions based on a short run collected in October 2017 are reported for the first time.
Measurements of the Higgs boson properties at the Large Hadron Collider experiments require a thorough understanding and control of the detector performance. These proceedings describe the ...reconstruction, identification and calibration of photons at the ATLAS experiment, which are of particular importance for the measurements in the diphoton decay channel. The impact on the property measurements is shown, along with the results of the H→γγ measurements.
The ATLAS experiment will undergo a full replacement of its inner detector to face the challenges posed by the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). The new Inner Tracker ...(ITk) will have to deal with extreme particle fluences. Due to its superior radiation hardness the 3D silicon sensor technology has been chosen to instrument the innermost pixel layer of ITk, which is the most exposed to radiation damage. Three foundries (CNM, FBK, and SINTEF), have developed and fabricated novel 3D pixel sensors to meet the specifications of the new ITk pixel detector. These are produced in a single-side technology on either Silicon On Insulator (SOI) or Silicon on Silicon (Si-on-Si) bonded wafers by etching both
n
- and
p
-type columns from the same side. With respect to previous generations of 3D sensors they feature thinner active substrates and smaller pixel cells of 50 × 50 and 25 × 100 µm
2
. This paper reviews the main design and technological issues of these novel 3D sensors, and presents their characterization before and after exposure to large radiation doses close to the one expected for the innermost layer of ITk. The performance of pixel modules, where the sensors are interconnected to the recently developed RD53A chip prototype for HL-LHC, has been investigated in the laboratory and at beam tests. The results of these measurements demonstrate the excellent radiation hardness of this new generation of 3D pixel sensors that enabled the project to proceed with the pre-production for the ITk tracker.
The top quark is the heaviest known fundamental particle. As it is the only quark that decays before it hadronizes, this gives a unique opportunity to probe the properties of pseudo-bare quarks. This ...proceeding focuses on a few recent precision measurements of top-quark properties in top-quark pair events by the ATLAS Collaboration using LHC proton-proton collision data. Among these is the measurement of color flow and measurement of spin correlations in tt‾ pair production. Measurements of the top-quark mass and searches for rare top-quark decays are also presented.
Highlights from the ATLAS experiment Grabowska-Bold, Iwona; Jensen, Bengt; Ohm, Christian ...
Nuclear physics. A,
02/2019, Volume:
982, Issue:
C
Journal Article
Peer reviewed
Open access
This report provides an overview of the new results obtained by the ATLAS Collaboration at the LHC, which were presented at the Quark Matter 2018 conference. These measurements were covered in 12 ...parallel talks, one flash talk and 11 posters. In this document, a discussion of results is grouped into four areas: electromagnetic interactions, jet quenching, quarkonia and heavy-flavour production, and collectivity in small and larger systems. Measurements from the xenon-xenon collisions based on a short run collected in October 2017 are reported for the first time.
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