High Luminosity LHC Upgrade Research Articles

A Nb-Ti 90 mm Double-Aperture Quadrupole for the High Luminosity LHC Upgrade

The luminosity upgrade of the LHC requires replacing the magnets around the ATLAS and CMS experiments with larger aperture dipoles, quadrupoles and correctors. The goal is to have a magnetic lattice that can allow to halve the beam size in the collision points with respect to present baseline. Within the framework of HiLumi LHC, CEA-Saclay studied the replacement of the 70-mm double aperture quadrupole Q4, with a 90-mm magnet based on Nb-Ti technology. The main challenges are due to the distance between the beams of 194 mm, giving a non-negligible magnetic coupling between the two apertures. The coil chosen to be the baseline is a single layer with 15-mm-width cable of the LHC MQ quadrupole. The mechanical structure is based on stainless steel collars to withstand the Lorentz forces. The iron yoke has a magnetic function, and guarantees the alignment of the two apertures. Electromagnetic and mechanical aspects and effects of unbalanced regimes on the field quality have been analyzed. A 3-D design of the coil ends is obtained by minimizing both the integrated multipoles and the peak field.

Nb3Sn High Field Magnets for the High Luminosity LHC Upgrade Project

The high luminosity upgrade of the Large Hadron Collider at CERN requires a new generation of high field superconducting magnets. High field large aperture quadrupoles (MQXF) are needed for the low-beta triplets close to the ATLAS and CMS detectors, and high field two-in-one dipoles (11-T dipoles) are needed to make room for additional collimation. The MQXF quadrupoles, with a field gradient of 140 T/m in 150 mm aperture, have a peak coil field of 12.1 T at nominal current. The 11-T dipoles, with an aperture of 60 mm, have a peak coil field of 11.6 T at nominal current. Both magnets require Nb 3 Sn conductor and are the first applications of this superconductor to actual accelerator magnets. Collaboration between the US LARP (LHC Accelerator Research Program) and CERN is developing the MQXF magnets, whereas the 11-T dipole magnets are being developed by CERN and Fermilab. This paper reviews the status of Nb 3 Sn technology for accelerator magnets, discusses its main challenges, and discusses how the MQXF and 11-T designs are addressing them.

A fourfold segmented silicon strip sensor with read-out at the edges

The High-Luminosity LHC upgrade (HL-LHC) is expected to increase the present luminosity by an order of magnitude in the years after 2022. This will necessitate the construction of silicon tracking detectors with a significantly higher radiation hardness and a higher channel granularity to cope with the higher track occupancy. In addition, a contribution from the tracking system to the first trigger stage and a reduction of the material budget would be desirable. The current concept for an upgraded CMS Tracker is based on silicon sensor modules formed of a sandwich of two strip sensors with front-end electronics at the sensor edge. This arrangement allows us to use the displacement of coincident hits in the two stacked sensor planes as a measure of particle momentum. As a consequence it is possible to identify locally particles with low transverse momentum which are not relevant for the Level-1 trigger decision. By applying a momentum cut of 1–2GeV, the data rate can be reduced by an order of magnitude. This paper introduces a new strip sensor design with a fourfold segmentation along the strips. The inner strips have an offset of half a pitch with respect to the outer strips and are connected to the pre-amplifiers at the edge via routing lines in between the outer strips. The challenge lies in minimizing the induced signals on the routing lines. Several prototypes have been tested and the results are reported. The possible application for the CMS Tracker upgrade is discussed.

Suppression of Higher Order Modes in an Array of Cavities Using Waveguides

An application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400MHz is currently under discussionin the framework of the High Luminosity LHC upgrade program [1,2]. A structure consisting of two 800MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between “warm” and “cold” parts of the collider vacuum chamber. Unfortunately, it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. We describe the results obtained for arrays of 2, 4 and 8 cavitiesin this paper.

Charge collection efficiency simulations of irradiated silicon strip detectors

During the scheduled high luminosity upgrade of LHC, the world's largest particle physics accelerator at CERN, the position sensitive silicon detectors installed in the vertex and tracking part of the CMS experiment will face a more intense radiation environment than the present system was designed for. Thus, to upgrade the tracker to the required performance level, comprehensive measurements and simulation studies have already been carried out.Essential information of the performance of an irradiated silicon detector is obtained by monitoring its charge collection efficiency (CCE). From the evolution of CCE with fluence, it is possible to directly observe the effect of the radiation induced defects on the ability of thedetector to collect charge carriers generated by traversing minimum ionizing particles (MIPs).In this paper the numerically simulated CCE and CCE loss between the strips of irradiated silicon strip detectors are presented. The simulations based on the Synopsys Sentaurus TCAD framework were performed before and after irradiation for fluences up to 1.5 × 1015 neqcm−2 for n-on-p sensors. A two level defect model and non-uniform three level defect model were applied for the proton irradiation simulations, and a two levelmodel for neutrons. The results are presented together with the measurements of strip detectorsirradiated by different particles and fluences and show considerable agreement for both CCE and its position dependency.

Development of a Fast Cluster Finding self-seeded trigger demonstrator

The ABC 130 chip developed for the high luminosity LHC(HL-LHC) upgrade of the ATLAS silicon strip tracker implements a Fast Cluster Finder (FCF). The FCF is capable of reading out certain track cluster information serially with a clock rate up to 640 MHz, sufficient to output the location within the 40 MHz collision frequency. An external correlator circuit can be used to find the position coincidence of clusters at two adjacent layers of silicon sensor. The coincidence offset is related to the transverse momentum of the track, and therefore it provides information which may contribute to a Level-1 trigger decision. These circuit elements have been implemented in a sensor doublet configuration coupled to an FPGA which executes the correlator algorithm. Design and test results of this system are presented.

Design Optimization of the New D1 Dipole for HL-LHC Upgrade

The High-Luminosity Large Hadron Collider upgrade (LHC) project aims to increase the peak luminosity of the LHC to 5 ×1034 cm - 2s - 1, and a total integrated luminosity of 3000 fb - 1 from 2020 to 2030 by upgrading the low-beta insertion system for the ATLAS and CMS experiments. The aperture of the insertion magnets including the focusing/defocusing quadrupoles and separation dipoles will be doubled to achieve a smaller β*. This paper presents the latest design updates of the separation dipole D1 magnet, including the study of the different cable types to vary the main field; the modifications of the iron shape for the new design options to minimize the iron saturation effect on field quality; and the optimization of the coil ends to reduce the peak field and higher order harmonic field integrals in the ends.

3D sensors and micro-fabricated detector systems

Micro-systems based on the Micro Electro Mechanical Systems (MEMS) technology have been used in miniaturized low power and low mass smart structures in medicine, biology and space applications. Recently similar features found their way inside high energy physics with applications in vertex detectors for high-luminosity LHC Upgrades, with 3D sensors, 3D integration and efficient power management using silicon micro-channel cooling. This paper reports on the state of this development.

Upgrading the ATLAS silicon tracking for the HL-LHC

After successful operation of the LHC at a centre-of-mass energy of 8TeV in 2012, the energy is expected to go up to 14TeV in the next few years. A total integrated luminosity of up to 300fb−1 is foreseen to be reached by 2022. At that time, the LHC will undergo a major upgrade to the High Luminosity LHC (HL-LHC), which is designed to deliver of order five times the LHC nominal instantaneous luminosity along with luminosity leveling. The final goal is to extend the data set to 3000fb−1 by around 2030. Current planning in ATLAS involves significant upgrades to the detector during the consolidation of the LHC to reach full energy and further upgrades to accommodate running already beyond nominal luminosity this decade. The challenge of coping with HL-LHC instantaneous and integrated luminosity, along with the associated radiation levels, requires further major changes to the ATLAS detector. The designs are developing rapidly for an all-new inner-tracker, significant upgrades in the calorimeter and muon systems, as well as improved triggers and data acquisition. These proceedings concentrate on the HL-LHC upgrade of the ATLAS Inner Tracker (ITK), which consist of replacing the entire current Inner Detector (silicon pixels, silicon strips and transition radiation tracker) with a completely new silicon-only system. This new ITK will be made from several pixel and strip layers, and is designed to withstand the extreme radiation environment in close proximity to the HL-LHC interaction point which broadly speaking means an order of magnitude higher radiation hardness than the existing ID. At the same time, the radiation length should be kept to the level of the present system or below. In the current planning, the pixel system involves 4 barrel layers and 6 disks on each side for a total pixel area of 7m2 and 400 million channels. The strip system will contain 5 barrel layers and 7 end-cap disks, covering 200m2 of silicon and 45 million channels.

A forward silicon strip system for the ATLAS HL-LHC upgrade

In the year 2022 an upgrade of the Large Hadron Collider (LHC) is planned to increase the luminosity such that an integrated luminosity of Lint∼3000fb−1 can be accumulated by 2030 [1]. The radiation damage of the present inner tracker at this date and the high track density of the High Luminosity LHC (HL-LHC) require an upgrade of the inner tracker of the ATLAS (A Toroidal LHC ApparatuS) experiment. A new integration concept will be used: the readout electronics is directly glued on the strip surface of the silicon sensors and the sensors are glued to a support structure. For the barrel region this structure is referred to as a Stave and for the end-cap region it is referred to as a Petal. For tests a smaller version, the Petalet, will be build with two design concepts. In this article the construction method is explained and first hybrid test results for one Petalet sensor are presented.

Radioactivity of $\hbox{Nb}_{3}\hbox{Sn/Cu}$ Wires After Proton Irradiation

Superconducting magnets based on Nb3Sn technology are being developed for the LHC high luminosity upgrade. In this context, irradiation induced changes of the superconducting properties of state-of-the-art Ti and Ta doped Nb3 Sn wires are presently studied. During irradiation tests with protons of 65 MeV at the cyclotron of Universite Catholique de Louvain (UCL), 1.4 GeV at the CERN ISOLDE facility, and 24 GeV at the CERN IRRAD1 facility, the superconductor samples become radioactive and their handling must follow the legal specifications for radioactive materials. We have estimated the activation and the resulting ambient dose equivalent rate up to a fluence of 1017 p/cm2 with the Monte-Carlo Code FLUKA. The estimates were verified with experimental activation spectra. Samples for magnetization measurements with a mass of approximately 20 mg have to be considered as radioactive, but they do not have the potential to harm the operators handling them at radiation levels below 1 μSv/h. Larger samples (longer wires and sample holder materials like Cu and TiAl6V4) show correspondingly higher ambient dose equivalent rates and activation levels and they must be handled by radiation workers in designated areas, taking into account the standard precautions for work with radioactive materials. The use of radiation shielding during handling is recommended.

Planar pixel sensors for the ATLAS upgrade: beam tests results

The performance of planar silicon pixel sensors, in development for the ATLAS Insertable B-Layer and HighLuminosity LHC (HL-LHC) upgrades, has been examined in a series of beam tests at the CERN SPS facilities since 2009. Salient results are reported on the key parameters, including the spatialresolution, the charge collection and the charge sharing between adjacent cells, for different bulk materials and sensor geometries.Measurements are presented for n+-in-n pixel sensors irradiated with a range of fluences andfor p-type silicon sensors with various layouts from different vendors. All tested sensorswere connected via bump-bonding to the ATLAS Pixel read-out chip. The tests reveal that both n-type and p-type planar sensors are able to collect significant chargeeven after the lifetime fluence expected at the HL-LHC.

Heat transfer through cable insulation of Nb–Ti superconducting magnets operating in He II

The operation of Nb–Ti superconducting magnets in He II relies on superfluidity to overcome the severe thermal barrier represented by the cable electrical insulation. In wrapped cable insulations, like those used for the main magnets of the Large Hadron Collider (LHC) particle accelerator, the micro-channels network created by the insulation wrappings allows to efficiently transfer the heat deposited or generated in the cable to the He bath.In this paper, available experimental data of heat transfer through polyimide electrical insulation schemes are analyzed. A steady-state thermal model is developed to describe the insulation of the LHC main dipole magnets and the Enhanced Insulation proposed for the High Luminosity LHC upgrade (HL-LHC), according to the relevant geometric parameters. The model is based on the coupled mechanisms of heat transfer through the bulk of the dielectric insulation and through micro-channels between the insulation tapes.A good agreement is found between calculations and tests performed at different applied pressures and heating configurations. The model allows identifying the heat fluxes in the cable cross-section as well as the dimensions of the micro-channels. These dimensions are confirmed by microscope images of the two insulations schemes.

Conceptual Design of a Large-Aperture Dipole Magnet for HL-LHC Upgrade

The development of a large-aperture (120–180 mm) dipole magnet is proposed in the framework of the CERN-KEK cooperation program. The application target is the D1 magnet (separation dipoles) replacement for the HL-LHC (High Luminosity—Large Hadron Collider) upgrade. The Cos-theta type coil cross section and the shell-based structure are adopted in the conceptual design of this magnet. The nominal field is estimated to be 6–10 T at 1.9 K with a 30-mm-width coil arranged in two layers. The candidates of superconductor are <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Nb}_{3}\hbox{Al}$</tex> </formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex> </formula> and Nb-Ti. We present the analytical estimation of the key parameters of this magnet and the simulation of the actual design which includes the field quality, the stray field, and the stress distribution in the coil.

A front-end chip development for the sLHC CMS Silicon Strip Tracker

The FEAFS chiphas been designed for the upgrades of the CMS Silicon Strip Tracker,which is planned in view of the LHC high luminosity upgrade. Itsprimary function is to provide a 40 MHz selective readout of particlehits that will be used for the generation of the 100 kHz hardwaretrigger of the experiment within a latency of 6.4 μs. To achievethis goal, the chip identifies clusters of limited number of activatedstrips and correlated in position, in a given window, in two closelysuperimposed sensors connected to the same chip. Finally, trigger andDAQ data are transmitted off detector via a common link. The FEAFS chiphas been developed in IBM 0.13 μm technology. This paperpresents the design of the chip and test results.

Charge Collection Studies and Electrical Measurements of Heavily Irradiated 3D Double-Sided Sensors and Comparison to Planar Strip Detectors

Three-dimensional (3D) silicon detectors offer advantages over standard planar devices as more radiation hard sensors. These detectors and their applications in the upgrades of the LHC experiments are discussed. 3D detectors with a double-sided geometry have been fabricated as very short strip detectors with similar inter-column spacing as proposed for the ATLAS pixel detector and LHCb vertex locator upgrades. The detectors have been irradiated up to a fluence of 2 × 1016 cm-2 1 MeV equivalent neutrons, which is twice the expected dose of the inner pixel layer of the ATLAS detector and of the upgraded LHCb vertex locator for LHC high luminosity upgrade (HL-LHC) operation. Electrical measurements show a lateral depletion voltage of only 4 V for the device before irradiation which increases to 200 V after an irradiation to a fluence of 1 × 1016 cm-2 1 MeV equivalent neutrons. The strip isolation of the p-type detectors was robust to the maximum fluence. Charge collection studies have been performed with analogue readout with 25 ns shaping time, as required for LHC experiments. The response of the detectors to high energy electrons from a 90Sr source and a collimated pulsed laser light source are shown and compared with planar devices. The 3D detector, operated at no more than 350 V, is shown to have superior charge collection characteristics to planar devices for all the fluence range expected at HL-LHC even when compared to planar devices operating at 1000 V. When operated at a bias voltage of 350 V the 3D detector collects 2.8 times more charge than a p-type planar device operated at 1000 V after a fluence of 1016 cm-2 1 MeV equivalent neutrons. Charge multiplication in 3D detectors is also reported, in both 90Sr and laser tests, which leads to further enhancement in the charge collection and signal-to-noise ratio of the detector. The effect is demonstrated, through laser tests, to occur close to the junction electrode.

The radiation hardness and temperature stability of Planar Light-wave Circuit splitters for the High Luminosity LHC

High Luminosity LHC (HL-LHC) Inner Tracker designs may include the sharing of Timing, Trigger and Control (TTC) signals between several tracker modules.This is possible because the highest frequency signals are common to all modules.Such designs are an attractive option because they reduce the number of optical links required and hence the cost.These designs will require optical signal splitters that are radiation hard up to high doses and capable of operating in cold temperatures.Optical splitters are available as either fused-fibre splitters or Planar Light-wave Circuit (PLC) splitters.PLC splitters are preferable because they are smaller than fused-fibre splitters. A selection of PLC splitters from different manufacturers and of two different technologies (silica and glass based) have been tested for radiation hardness up to a dose of 500 kGy(Si) and for temperature stability.All the tested splitters displayed small increases in insertion losses ( < 0.1 dB) in reducing the operating temperature from 25°C to −25°C.The silica based splitters from all manufacturers did not exhibit significant radiation induced insertion losses, despite the high dose they were exposed to.The glass based sample, however, had a per channel radiation induced insertion loss of up to 1.16 dB.Whilst the silica based splitters can be considered as qualified for HL-LHC use with regards to radiation hardness, the glass technology would require further testing at a lower, more realistic, dose to also be considered as a potential component for HL-LHC upgrade designs.

Test beam results of 3D silicon pixel sensors for the ATLAS upgrade

Results on beam tests of 3D silicon pixel sensors aimed at the ATLAS Insertable B-Layer and High Luminosity LHC (HL-LHC) upgrades are presented. Measurements include charge collection, tracking efficiency and charge sharing between pixel cells, as a function of track incident angle, and were performed with and without a 1.6 T magnetic field oriented as the ATLAS inner detector solenoid field. Sensors were bump-bonded to the front-end chip currently used in the ATLAS pixel detector. Full 3D sensors, with electrodes penetrating through the entire wafer thickness and active edge, and double-sided 3D sensors with partially overlapping bias and read-out electrodes were tested and showed comparable performance.