High Luminosity Upgrade Of The Large Hadron Collider Research Articles

Lorentz angle measurements as part of the sensor R&D for the CMS Tracker upgrade

The CMS detector is one of the main experiments at the LHC accelerator at CERN. Its 200 M2 silicon strip tracker was designed to withstand the radiation of 10 years of LHC operation. The foreseen high luminosity upgrade of the LHC imposes even higher demands on the radiation tolerance and thus requires the construction of a new tracking detector. To determine the properties of different silicon materials and production processes, a campaign has been started by the CMS Tracker Collaboration to identify the most promising candidate material for the new CMS tracker.The silicon sensors of the CMS tracker are operated in a 3.8 T magnetic field. Charges created by traversing ionizing particles inside the active sensor volume are deflected by the Lorentz force. The Lorentz angle, under which the charge drifts through the sensor, is strongly dependent on the mobility, which in turn depends on the electric field and may depend on the radiation damage created by the particles produced by the LHC. Studying this is part of the campaign mentioned above.This contribution summarizes the Lorentz angle measurements at magnetic fields of up to 8 T performed on small strip sensors after mixed irradiation with protons and neutrons to fluences of up to 5.8 × 1015 neq/cm2 and gives a comparison to a simple simulation model.

Evaluation of slim-edge, multi-guard, and punch-through-protection structures before and after proton irradiation

Planar geometry silicon pixel and strip sensors for the high luminosity upgrade of the LHC (HL-LHC) require a high bias voltage of 1000V in order to withstand a radiation damage caused by particle fluences of 1×1016 1MeVneq/cm2 and 1×1015 1MeVneq/cm2 for pixel and strip detectors, respectively. In order to minimize the inactive edge space that can withstand a bias voltage of 1000V, edge regions susceptible to microdischarge (MD) should be carefully optimized. We fabricated diodes with various edge distances (slim-edge diodes) and with 1–3 multiple guard rings (multi-guard diodes). AC coupling insulators of strip sensors are vulnerable to sudden heavy charge deposition, such as an accidental beam splash, which may destroy the readout AC capacitors. Thus various types of punch-through-protection (PTP) structures were implemented in order to find the most effective structure to protect against heavy charge deposition. These samples were irradiated with 70MeV protons at fluences of 5×1012 1MeVneq/cm2–1×1016 1MeVneq/cm2. Their performances were evaluated before and after irradiation in terms of an onset voltage of the MD, a turn-on voltage of the PTP, and PTP saturation resistance.

A visualization of the damage in Lead Tungstate calorimeter crystals after exposure to high-energy hadrons

The anticipated performance of calorimeter crystals in the environment expected after the planned High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN has to be well understood, before informed decisions can be made on the need for detector upgrades. Throughout the years of running at the HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons that have been shown to cause cumulative transparency losses in Lead Tungstate scintillating crystals. In this study, we present direct evidence of the main underlying damage mechanism. Results are shown from a test that yields a direct insight into the nature of the hadron-specific damage in Lead Tungstate calorimeter crystals exposed to 24GeV/c protons.

Development of Precision Muon Drift Tube Detectors for the High-Luminosity Upgrade of the LHC

For use at the future Super-LHC a new type of muon detector has been developed. It is based on the proven MDT drift tube design, but with tubes of half the diameter, leading to higher rate capabilities by an order of magnitude. We present test results on efficiency and position resolution at high background rates and describe the practical implementation in a real-size prototype.

Limits on upgrade tracker layout from particle fluxes, signal-to-noise, and occupancy

Abstract We have investigated the layout for the inner tracking detector for ATLAS at the high luminosity upgrade of the LHC with respect to radiation damage and occupancy. Using simulated particle fluxes, we evaluate the signal-to-noise ratio based on measured radiation damage data, and estimate the expected occupancy. Tracking performance simulations yield alternative occupancy numbers and we find satisfactory agreement between the both. The dependence of occupancy and signal-to-noise on the location are used to evaluate the layout of the upgraded ATLAS inner detector.

Radiation hard diamond pixel detectors

Even though the LHC has not yet begun, already a high luminosity upgrade of the LHC is being planned. The sensors at radii of about 3 cm will have to withstand an expected fluence exceeding 10 16 particles/cm 2 in 5 years. At this fluence current silicon sensors cease to function. Due to its large bandgap and high displacement energy, diamond is an intrinsically very radiation hard material. Combined with its fast charge collection, its low dielectric constant and the absence of thermally generated leakage current, diamond is a very interesting detector material for the sensors close to the beam. A full size, 61×16.5 mm 2, ATLAS pixel module using chemical-vapor deposition (CVD) diamond was built and characterized in a beam test. The measured position resolution is consistent with the expected binary resolution. The efficiency was larger than 97%. Nowadays also large size single-crystal CVD diamonds are available. A single-crystal diamond was used to produce a 2880 channel pixel detector. This detector showed an 99.992±0.002% efficiency at an electric field as low as 0.25 V/μm.

Development of large area integrated silicon tracking elements for the LHC luminosity upgrade

For tracking at a high luminosity upgrade of the LHC, detector granularity, scale, and radiation resistance must increase. Material burden, cost, and construction must be kept manageable. One configuration which may facilitate these requirements is to build large multi-module units referred to here as “staves”. Design issues and prototyping results for staves are discussed.