I. Tsurin

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 High Luminosity 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 spatial resolution, 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 and for p-type silicon sensors with various layouts from different vendors. All tested sensors were 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 charge even after the lifetime fluence expected at the HL-LHC.

Proton tracking for medical imaging and dosimetry

For many years, silicon micro-strip detectors have been successfully used as tracking detectors for particle and nuclear physics experiments. A new application of this technology is to the field of particle therapy, where radiotherapy is carried out by use of charged particles such as protons or carbon ions. Such a treatment has been shown to have advantages over standard x-ray radiotherapy and as a result of this, many new centres offering particle therapy are currently under construction - including two in the U.K.. The characteristics of a new silicon micro-strip detector based system for this application will be presented. The array uses specifically designed large area sensors in several stations in an x-u-v co-ordinate configuration suitable for very fast proton tracking with minimal ambiguities. The sensors will form a tracker capable of giving information on the path of high energy protons entering and exiting a patient. This will allow proton computed tomography (pCT) to aid the accurate delivery of treatment dose with tuned beam profile and energy. The tracker will also be capable of proton counting and position measurement at the higher fluences and full range of energies used during treatment allowing monitoring of the beam profile and total dose. Results and initial characterisation of sensors will be presented along with details of the proposed readout electronics. Radiation tests and studies with different electronics at the Clatterbridge Cancer Centre and the higher energy proton therapy facility of iThemba LABS in South Africa will also be shown.

A double-sided, shield-less stave prototype for the ATLAS Upgrade strip tracker for the High Luminosity LHC

A detailed description of the integration structures for the barrel region of the silicon strips tracker of the ATLAS Phase-II upgrade for the upgrade of the Large Hadron Collider, the so-called High Luminosity LHC (HL-LHC), is presented. This paper focuses on one of the latest demonstrator prototypes recently assembled, with numerous unique features. It consists of a shortened, shield-less, and double sided stave, with two candidate power distributions implemented. Thermal and electrical performances of the prototype are presented, as well as a description of the assembly procedures and tools.

Thin silicon detectors for tracking in high radiation environments

The upgrade of the present Large Hadron Collider to high luminosity will impose the use of a factor of ten more radiation tolerant silicon sensors (microstrip and pixel) for the vertex and tracker system upgrades. The requirement for extreme radiation tolerance to hadron radiation is certainly the most stringent requirement for the HL-LHC sensors, but other parameters are also desirable, in particular a reduced mass of the whole systems. The use of thinner sensors than the standard 300 J.1m thick presently adopted could contribute to the reduction of the material in the acceptance volume of the experiments. It is now known that the thickness has also effects on the radiation tolerance of the sensors. The comparison of the signal generated by minimum ionising particles in 100, 140 and 300 J.1m thick sensors irradiated with reactor neutrons to various tluences up to the highest expected for the innermost pixel layers of the upgraded ATLAS experiment (2×1016 neq cm-2) are presented. Conclusions about the fluences where a given thickness gives the best signal are drawn from the experimental results to provide guidance for the optimal choice of thickness for segmented silicon sensors to be deployed in harsh hadron radiation environments.

A new silicon tracker for proton imaging and dosimetry.

For many years, silicon micro-strip detectors have been successfully used as tracking detectors for particle and nuclear physics experiments. A new application of this technology is to the field of particle therapy where radiotherapy is carried out by use of charged particles such as protons or carbon ions. Such a treatment has been shown to have advantages over standard x-ray radiotherapy and as a result of this, many new centres offering particle therapy are currently under construction around the world today. The Proton Radiotherapy, Verification and Dosimetry Applications (PRaVDA) consortium are developing instrumentation for particle therapy based upon technology from high-energy physics. The characteristics of a new silicon micro-strip tracker for particle therapy will be presented. The array uses specifically designed, large area sensors with technology choices that follow closely those taken for the ATLAS experiment at the HL-LHC. These detectors will be arranged into four units each with three layers in an x–u–v configuration to be suitable for fast proton tracking with minimal ambiguities. The sensors will form a tracker capable of tracing the path of ~200 MeV protons entering and exiting a patient allowing a new mode of imaging known as proton computed tomography (pCT). This will aid the accurate delivery of treatment doses and in addition, the tracker will also be used to monitor the beam profile and total dose delivered during the high fluences used for treatment. We present here details of the design, construction and assembly of one of the four units that will make up the complete tracker along with its characterisation using radiation tests carried out using a 90Sr source in the laboratory and a 60 MeV proton beam at the Clatterbridge Cancer Centre.

A double-sided silicon micro-strip Super-Module for the ATLAS Inner Detector upgrade in the High-Luminosity LHC

The ATLAS experiment is a general purpose detector aiming to fully exploit the discovery potential of the Large Hadron Collider (LHC) at CERN. It is foreseen that after several years of successful data-taking, the LHC physics programme will be extended in the so-called High-Luminosity LHC, where the instantaneous luminosity will be increased up to 5 × 1034 cm−2 s−1. For ATLAS, an upgrade scenario will imply the complete replacement of its internal tracker, as the existing detector will not provide the required performance due to the cumulated radiation damage and the increase in the detector occupancy. The current baseline layout for the new ATLAS tracker is an all-silicon-based detector, with pixel sensors in the inner layers and silicon micro-strip detectors at intermediate and outer radii. The super-module is an integration concept proposed for the strip region of the future ATLAS tracker, where double-sided stereo silicon micro-strip modules are assembled into a low-mass local support structure. An electrical super-module prototype for eight double-sided strip modules has been constructed. The aim is to exercise the multi-module readout chain and to investigate the noise performance of such a system. In this paper, the main components of the current super-module prototype are described and its electrical performance is presented in detail.

Characterisation of micro-strip and pixel silicon detectors before and after hadron irradiation.

The use of segmented silicon detectors for tracking and vertexing in particle physics has grown substantially since their introduction in 1980. It is now anticipated that roughly 50,000 six inch wafers of high resistivity silicon will need to be processed into sensors to be deployed in the upgraded experiments in the future high luminosity LHC (HL-LHC) at CERN. These detectors will also face an extremely severe radiation environment, varying with distance from the interaction point. The volume of required sensors is large and their delivery is required during a relatively short time, demanding a high throughput from the chosen suppliers. The current situation internationally, in this highly specialist market, means that security of supply for large orders can therefore be an issue and bringing additional potential vendors into the field can only be an advantage. Semiconductor companies that could include planar sensors suitable for particle physics in their product lines will, however, need to prove their products meet all the stringent technical requirements. A semiconductor company with very widespread experience of producing science grade CCDs (including deep depletion devices) has adapted their CCD process to fabricate for the first time several wafers of pixel and micro-strip radiation hard sensors, suitable for future high energy physics experiments. The results of the pre-irradiation characterization of devices fabricated with different processing parameters and the measurements of charge collection properties after different hadron irradiation doses up to those anticipated for the (larger area) outer pixel layers at the high-luminosity LHC (HL-LHC) are presented and compared with results from more established particle physics suppliers.

Annealing at Different Temperatures of Silicon Microstrip Detectors After Severe Hadron Irradiation

Two rather recent results from studies performed for preparing high resolution sensors for the future supercolliders (HL-LHC at CERN) have proven that silicon detectors read out with low noise electronics can be used for tracking minimum ionizing particles (mip) after doses up to if high bias voltage and adequate cooling can be routed to the sensors. These are the discovery of the charge multiplication mechanism taking place in irradiated n-in-p silicon detectors and the suppression of the reverse annealing. A discussion of this last feature and the influence of the annealing temperature is presented here.

Changes of the particle detection properties of irradiated silicon microstrip sensors after room temperature annealing

The electrical properties of hadron irradiated silicon detectors change over several years after irradiation. This annealing process has a strong dependence on temperature and it can be accelerated or decelerated by lowering or elevating the temperature at which the sensors are kept. This is exploited to investigate the long term behaviours of irradiated silicon detectors that are, or will be, installed in the experiment at the current and upgraded LHC at CERN. Elevated temperatures (up to 80°C) are used to accelerate the effect of annealing to study the expected changes of the sensor performances over several years of room temperature equivalent time. Low temperatures are applied to the sensors also when not operated to suppress undesired effects of annealing. The acceleration factors with respect to nominal room temperature (RT = 20°C) have been established monitoring the changes of the capacitance-voltage characteristics (CV) with time at various temperatures. In the experiments, the maximum high temperature envisaged out of operation cannot exceed much 20°C. It is important to measure the changes of the relevant parameters (charge collection reverse current, noise) at this temperature to verify the annealing behaviours in realistic conditions for planning the operation scenario (i.e. bias voltage and temperature during and outside operation) of the silicon sensors. We show here the study of room temperature annealing of the charge collection, reverse current and noise of silicon microstrip detectors after two doses of hadron irradiation (2 and 10 × 1015 neq cm−2) . These doses are chosen to represent the expected levels in the future upgrade of the LHC at CERN (High Luminosity LHC, HL-LHC) for the microstrip and pixel layers. The measurements show that a suitable choice of annealing time at 20°C can partially recover the degraded charge collection and reduce the reverse current after a given dose of hadron irradiation.

Recent results and experience with the Birmingham MC40 irradiation facility

Operational experience with the recently upgraded irradiation facility at the University of Birmingham is presented. This is based around the high intensity area of the MC40 medical cyclotron providing proton energies between 3 and 38 MeV and currents ranging from tens of fA to μA. Accurate dosimetry for displacement damage and total ionizing dose, using a combination of techniques, is offered. Irradiations are carried out in a temperature controlled chamber that can be scanned through the beam, with the possibility for the devices to be biased, clocked, and read-out. Fluence up to several 1016 1 MeV neq/cm2 and GRad ionizing dose can be delivered within a day.