60 research outputs found
Fast Timing for High-Rate Environments with Micromegas
The current state of the art in fast timing resolution for existing
experiments is of the order of 100 ps on the time of arrival of both charged
particles and electromagnetic showers. Current R&D on charged particle timing
is approaching the level of 10 ps but is not primarily directed at sustained
performance at high rates and under high radiation (as would be needed for
HL-LHC pileup mitigation). We demonstrate a Micromegas based solution to reach
this level of performance. The Micromegas acts as a photomultiplier coupled to
a Cerenkov-radiator front window, which produces sufficient UV photons to
convert the ~100 ps single-photoelectron jitter into a timing response of the
order of 10-20 ps per incident charged particle. A prototype has been built in
order to demonstrate this performance. The first laboratory tests with a
pico-second laser have shown a time resolution of the order of 27 ps for ~50
primary photoelectrons, using a bulk Micromegas readout.Comment: MPGD2015 (4th Conference on Micro-Pattern Gaseous Detectors, Trieste,
Italy, 12 - 15 October, 2015). 5 pages, 8 figure
Impact of GEM foil hole geometry on GEM detector gain
Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.Peer reviewe
Results from the CERN pilot CLOUD experiment
During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm -3 s -1, and growth rates between 2 and 37 nm h -1. The corresponding H2O concentrations were typically around 106 cm -3 or less. The experimentally-measured formation rates and htwosofour concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 °C
Precise timing with the PICOSEC-Micromegas detector
This work presents the concept of the PICOSEC-Micromegas de-tector to achieve a time resolution below 30 ps. PICOSEC consists of a two-stageMicromegas detector coupled to a Cherenkov radiator and equipped with a photo-cathode. The results from single-channel prototypes as well as the understanding ofthe detector in terms of detailed simulations and preliminary results from a multi-channel prototype are presented.Peer reviewe
A large area 100 channel Picosec Micromegas detector with sub 20 ps time resolution
The PICOSEC Micromegas precise timing detector is based on a Cherenkov
radiator coupled to a semi-transparent photocathode and a Micromegas
amplification structure. The first proof of concept single-channel small area
prototype was able to achieve time resolution below 25 ps. One of the crucial
aspects in the development of the precise timing gaseous detectors applicable
in high-energy physics experiments is a modular design that enables large area
coverage. The first 19-channel multi-pad prototype with an active area of
approximately 10 cm suffered from degraded timing resolution due to the
non-uniformity of the preamplification gap. A new 100 cm detector module
with 100 channels based on a rigid hybrid ceramic/FR4 Micromegas board for
improved drift gap uniformity was developed. Initial measurements with 80 GeV/c
muons showed improvements in timing response over measured pads and a time
resolution below 25 ps. More recent measurements with a new thinner drift gap
detector module and newly developed RF pulse amplifiers show that the
resolution can be enhanced to a level of 17~ps. This work will present the
development of the detector from structural simulations, design, and beam test
commissioning with a focus on the timing performance of a thinner drift gap
detector module in combination with new electronics using an automated timing
scan method
Towards robust PICOSEC Micromegas precise timing detectors
The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector
consisting of a Cherenkov radiator combined with a photocathode and a MM
amplifying structure. A 100-channel non-resistive PICOSEC MM prototype with
10x10 cm^2 active area equipped with a Cesium Iodide (CsI) photocathode
demonstrated a time resolution below 18 ps. The objective of this work is to
improve the PICOSEC MM detector robustness aspects; i.e. integration of
resistive MM and carbon-based photocathodes; while maintaining good time
resolution. The PICOSEC MM prototypes have been tested in laboratory conditions
and successfully characterised with 150 GeV/c muon beams at the CERN SPS H4
beam line. The excellent timing performance below 20 ps for an individual pad
obtained with the 10x10 cm^2 area resistive PICOSEC MM of 20 MOhm/sq showed no
significant time resolution degradation as a result of adding a resistive
layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B4C)
photocathode presented a time resolution below 35 ps; opening up new
possibilities for detectors with robust photocathodes. The results made the
concept more suitable for the experiments in need of robust detectors with good
time resolution
Progress on the PICOSEC-Micromegas Detector Development : Towards a precise timing, radiation hard, large-scale particle detector with segmented readout
This contribution describes the PICOSEC-Micromegas detector which achieves a time resolution below 25 ps. In this device the passage of a charged particle produces Cherenkov photons in a radiator, which then generate electrons in a photocathode and these photoelectrons enter a two-stage Micromegas with a reduced drift region and a typical anode region. The results from single-channel prototypes (demonstrating a time resolution of 24 ps for minimum ionizing particles, and 76 ps for single photoelectrons), the understanding of the detector in terms of detailed simulations and a phenomenological model, the issues of robustness and how they are tackled, and preliminary results from a multi-channel prototype are presented (demonstrating that a timing resolution similar to that of the single-channel device is feasible for all points across the area covered by a multi-channel device).Peer reviewe
Therapeutic Validity and Effectiveness of Preoperative Exercise on Functional Recovery after Joint Replacement: A Systematic Review and Meta-Analysis
Background: Our aim was to develop a rating scale to assess the therapeutic validity of therapeutic exercise programmes. By use of this rating scale we investigated the therapeutic validity of therapeutic exercise in patients awaiting primary total joint replacement (TJR). Finally, we studied the association between therapeutic validity of preoperative therapeutic exercise and its effectiveness in terms of postoperative functional recovery. Methods: (Quasi) randomised clinical trials on preoperative therapeutic exercise in adults awaiting TJR on postoperative recovery of functioning within three months after surgery were identified through database and reference screening. Two reviewers extracted data and assessed the risk of bias and therapeutic validity. Therapeutic validity of the interventions was assessed with a nine-itemed, expert-based rating scale (scores range from 0 to 9; score ≥6 reflecting therapeutic validity), developed in a four-round Delphi study. Effects were pooled using a random-effects model and meta-regression was used to study the influence of therapeutic validity. Results: Of the 7,492 articles retrieved, 12 studies (737 patients) were included. None of the included studies demonstrated therapeutic validity and two demonstrated low risk of bias. Therapeutic exercise was not associated with 1) observed functional recovery during the hospital stay (Standardised Mean Difference [SMD]: −1.19; 95%-confidence interval [CI], −2.46 to 0.08); 2) observed recovery within three months of surgery (SMD: −0.15; 95%-CI, −0.42 to 0.12); and 3) self-reported recovery within three months of surgery (SMD −0.07; 95%-CI, −0.35 to 0.21) compared with control participants. Meta-regression showed no statistically significant relationship between therapeutic validity and pooled-effects. Conclusion: Preoperative therapeutic exercise for TJR did not demonstrate beneficial effects on postoperative functional recovery. However, poor therapeutic validity of the therapeutic exercise programmes may have hampered potentially beneficial effects, since none of the studies met the predetermined quality criteria. Future review studies on therapeutic exercise should address therapeutic validity. (aut.ref.
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