B. T. Huffman

The radiation tolerance of specific optical fibres exposed to 650 kGy(Si) of ionizing radiation

The LHC upgrade will extensively increase the area of silicon detectors used in the ATLAS experiment and require substantial changes to the readout system of both the ATLAS and CMS experiments. The two experiments are expected to use optical systems for part of the data and control paths which must withstand levels of radiation equivalent to a dose of approximately 400 kGy(Si) at 30 cm from the collision region (including a safety factor of 1.5). As part of the search for acceptably radiation hard optical fibres, four Graded Index multimode (GRIN) optical fibres and one single-mode (SM) fibre were tested to 650 kGy(Si) equivalent dose. One of the GRIN fibres was also tested at 5 different dose rates, in order to understand the dose rate effects. These tests have validated the radiation tolerance of a single-mode fibre and two multimode fibres for use at the SLHC for warm operation. Some interesting features of the time dependence of the fibre radiation damage and future plans are discussed.

The radiation hardness of specific multi-mode and single-mode optical fibres at -25°C beyond a full SLHC dose to a dose of 500 kGy(Si)

The optical fibres that will be used in SLHC detectors will be exposed to high doses and low temperatures in the inner detectors. A number of Single-Mode (SM) and Multi-Mode (MM) fibres have been tested for radiation hardness by exposure beyond a full SLHC dose to 500 kGy(Si) in the -25°C operating temperatures expected in the upgraded inner detectors. From these measurements conservative estimates of the level of Radiation Induced Absorption (RIA) have been calculated for these fibres in realistic paths through an upgraded inner detector. Two SM fibres have been found whose total calculated RIAs were much lower than the budgeted 1 dB, despite the high dose rates used in the experiment. The RIAs for the DrakaElite Super RadHard Single-Mode Fiber and Fibre X were calculated to be 0.142 and 0.064 dB respectively. Another SM and a MM fibre showed high levels of RIA during the experiment, however they cannot be ruled out as candidate fibres due the the high dose rate of 27 kGy(Si)/hr used.

A study of the effect of radiation on the mechanical strength of optical fibres

The fibres used for the readout of the upgraded LHC detectors for the High Luminosity Large Hadron Collider (HL-LHC) will be exposed to very high radiation doses of up to ~ 500 kGy(Si). This study has focused on the mechanical reliability of optical fibres after radiation to the levels expected at HL-LHC. Multimode and single-mode fibres from two manufacturers were tested.

A study of the effect of a 500 kGy(Si) radiation dose on the bandwidth of a radiation hard multi-mode fibre

The fibres used for the readout of the upgraded LHC detectors for the High Luminosity Large Hadron Collider (HL-LHC) will be exposed to very high radiation doses of up to ~ 500 kGy(Si). From DC measurements of the radiation induced absorption, several singlemode (SM) and multimode (MM) fibres have been qualified. The effect of radiation damage on fibres is also expected to have an adverse impact on the fibre bandwidth. This paper explains the theoretical reasons for this and presents results of extensive tests to determine the significance of this effect for one of the previously qualified radiation-hard multi-mode fibres.

Radiation hardness of two CMOS prototypes for the ATLAS HL-LHC upgrade project

The LHC luminosity upgrade, known as the High Luminosity LHC (HL-LHC), will require the replacement of the existing silicon strip tracker and the transistion radiation tracker. Although a baseline design for this tracker exists the ATLAS collaboration and other non-ATLAS groups are exploring the feasibility of using CMOS Monolithic Active Pixel Sensors (MAPS) which would be arranged in a strip-like fashion and would take advantage of the service and support structure already being developed for the upgrade. Two test devices made with the AMS H35 process (a High voltage or HV CMOS process) have been subjected to various radiation environments and have performed well. The results of these tests are presented in this paper.

Plans for the Phase II upgrade to the ATLAS detector

CERN has planned a series of upgrades for the Large Hadron Collider (LHC). The last in this current series of planned upgrades is designated the High Luminosity LHC (HL-LHC) and as the name suggests will bring the Luminosity up to 5 × 1034 cm−2s−1. The ATLAS detector will be extensively changed to meet the challenges of this upgrade (termed the Phase II upgrade). There are many systems that require modification in this regime, but this paper focuses on the subsystems requiring the most radical changes. The ATLAS inner tracker is being completely rebuilt for Phase II. The TRT is removed in favor of an all-new all-silicon tracker. The changes to the pixel system, barrel and end-cap strip detectors are explained. In addition, the muon detector will be modified and the muon and electron triggers will be modified to include tracking regions of interest and to improve muon resolution. In this way trigger rates can be brought under control while maintaining constant trigger thresholds.

The radiation tolerance of MTP and LC optical fibre connectors to 500 kGy(Si) of gamma radiation

The LHC luminosity upgrade, known as the High Luminosity LHC (HL-LHC), will require high-speed optical links to read out data from the detectors. The optical fibre connectors contained within such a link must have a small form factor and be capable of operating in the harsh radiation environment at the HL-LHC. MTP ribbon fibre connectors and LC single fibre connectors were exposed to 500 kGy(Si) of gamma radiation and their radiation hardness was investigated. Neither type of connector exhibited evidence for any significant radiation damage and both connectors could be qualified for use at HL-LHC detectors.

Radiation hardness studies of AMS HV-CMOS 350 nm prototype chip HVStripV1

CMOS active pixel sensors are being investigated for their potential use in the ATLAS inner tracker upgrade at the HL-LHC. The new inner tracker will have to handle a significant increase in luminosity while maintaining a sufficient signal-to-noise ratio and pulse shaping times. This paper focuses on the prototype chip HVStripV1 (manufactured in the AMS HV-CMOS 350nm process) characterization before and after irradiation up to fluence levels expected for the strip region in the HL-LHC environment. The results indicate an increase of depletion region after irradiation for the same bias voltage by a factor of ≈2.4 and ≈2.8 for two active pixels on the test chip. There was also a notable increase in noise levels from 85 e− to 386 e− and from 75 e− to 277 e− for the corresponding pixels.

Further studies of the effect of radiation on the mechanical strength of optical fibres

Studies were performed of the mechanical reliability of optical fibre, before and after radiation, to a dose expected for tracking detectors at HL-LHC of 500 kGy(Si). The studies used a 2-point bend test system and were able to determine the fibre stress corrosion susceptibility parameter, n. The comparison of the radiation-induced changes in the n-value allowed us to determine if there was any deterioration in mechanical reliability of the two fibre types tested. The measured n-values for two multi-mode fibres showed some evidence for an increase after radiation which implies that the mechanical reliability of these fibres will not be compromised by radiation to the expected doses at the HL-LHC.

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.