Damage mechanisms in superconductors due to the impact of high energy proton beams and radiation tolerance of cryogenic diodes used in particle accelerator magnet systems

High energy hadron accelerators such as the Large Hadron Collider (LHC) at CERN and its planned upgrade to achieve higher luminosity, the High Luminosity Large Hadron Collider (HL-LHC), require superconducting magnets to provide strong magnetic fields, needed to steer and focus the particle beams at these high energies. During operation the superconducting magnets and their components are exposed to radiation resulting from primary and secondary particles from two main sources of beam losses. During normal operation, steady state losses resulting from interaction of the particle beams with residual gas molecules or from particle debris in interaction points affect the accelerator magnets and their components along the machine. In case of failures, significant parts of the beam can be lost in a short time, resulting in localized damage due to heating from energy deposition, which in turn causes thermo-mechanical stresses and strains. In the HL-LHC, novel focusing superconducting quadrupole magnets will be installed, based on Nb$_3$Sn and located close to the interaction points. Furthermore, the beam intensity will be doubled. Both, steady state losses and the severity of losses due to fast failures scale with the beam intensity. In this thesis, effects of beam losses on accelerator magnet components were studied. Firstly, the effects of high intensity and high energy proton beam impact on the low temperature superconductors (LTS) Nb-Ti, Nb$_3$Sn and tapes based on the high temperature superconductor (HTS) YBCO were studied. An experiment was performed where beam was directed on superconductors in a cryogenic environment in CERN’s HiRadMat facility. The performance of the superconductors was afterwards analyzed for their critical transport current, critical field and temperature, as well as inspected with optical and electron microscopic methods. The experimental setup, the observed damage mechanisms and the subsequent analysis are discussed. Secondly, the powering layout of the magnet circuits foresees the use of cryogenic power diodes, connected in parallel to each magnet, serving as passive protection in case of a quench. The diodes are located in close proximity to the beam axis and are affected by the enhanced radiation levels close to the interaction points. To identify a diode type that can be safely operated during the lifetime of HL-LHC, the radiation hardness of existing LHC-type diodes and prototype diodes, that are expected to be more radiation tolerant were tested. An experiment was set up, which allowed the irradiation and in situ measurements of three different types of diodes at cryogenic temperatures. All prototypes were analyzed for forward and reverse bias voltage characteristics and the temperature dependence while warming up. Their thermal annealing potential could also be evaluated. The experimental setup, the in situ measurements and the subsequent analysis are discussed

Characterization of the ALPIDE chip with Helium-4 ions for Proton Computed Tomography

Particle therapy has become an appealing therapeutic option for patients with various tumor types. The physical properties of charged particles allow for an improved dose distribution conformality compared to conventional photon-based radiotherapy. This advantage translates into a reduction of unwanted side effects from radiation treatment and in the long run will improve the patient’s quality of life. A team at the University of Bergen is developing a proton Computed Tomography (pCT) scanner prototype. This technology will primarily work as a supplement to particle therapy as it aims to enhance the accuracy of the pre-calculated dose plans applied during treatment. The pCT system is a Digital Tracking Calorimeter (DTC) consisting of multiple layers of the ALPIDE CMOS Monolithic Active Pixel Sensor with the aim of tracking protons and measure its energy. This thesis studies the ALPIDE chip towards its medical applications in the future DTC. It will describe the clusters created on the chip by helium ions and alpha particles with a focus on the parameters that affect the pixel size of the clusters. Results from an analysis of a helium microbeam indicate that the size of a cluster correlates with the position of the incoming particle on the pixel and hence, the interior location of the energy deposition. These clusters varied in size from 5 to 35 pixels when the beam scanned the chip in µm steps. Moreover, an experiment conducted during this project shows that the size of the clusters is dependent on the temperature of the chip and that the average size of the cluster gets larger with increasing temperature. In the end, the results obtained from an ALPIDE telescope irradiated with high energetic helium beams is described. This experiment shows that the clusters used in tracking increases in size at higher Linear Energy Transfer (LET) of the particles.Masteroppgave i fysikkMAMN-PHYSPHYS39

Technical Design Report for PANDA Electromagnetic Calorimeter (EMC)

This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface

Radiation effects on lasers Technical report, Jul. 1, 1965 - May 31, 1966

Effects of space radiation on laser

Irradiation of silicon particle detectors with MeV-protons

Silicon particle detectors are used in several applications and will clearly require better hardness against particle radiation in the future large scale experiments than can be provided today. To achieve this goal, more irradiation studies with defect generating bombarding particles are needed. Protons can be considered as important bombarding species, although neutrons and electrons are perhaps the most widely used particles in such irradiation studies. Protons provide unique possibilities, as their defect production rates are clearly higher than those of neutrons and electrons, and, their damage creation in silicon is most similar to the that of pions. This thesis explores the development and testing of an irradiation facility that provides the cooling of the detector and on-line electrical characterisation, such as current-voltage (IV) and capacitance-voltage (CV) measurements. This irradiation facility, which employs a 5-MV tandem accelerator, appears to function well, but some disadvantageous limitations are related to MeV-proton irradiation of silicon particle detectors. Typically, detectors are in non-operational mode during irradiation (i.e., without the applied bias voltage). However, in real experiments the detectors are biased; the ionising proton generates electron-hole pairs, and a rise in rate of proton flux may cause the detector to breakdown. This limits the proton flux for the irradiation of biased detectors. In this work, it is shown that, if detectors are irradiated and kept operational, the electric field decreases the introduction rate of negative space-charges and current-related damage. The effects of various particles with different energies are scaled to each others by the non-ionising energy loss (NIEL) hypothesis. The type of defects induced by irradiation depends on the energy used, and this thesis also discusses the minimum proton energy required at which the NIEL-scaling is valid.Piipohjaisia hiukkasilmaisimia käytetään laajalti niin ilmailussa, avaruustekniikassa kuin suurenergiafysiikan kokeissa. Piipohjainen hiukkasilmaisin on toiminnaltaan estosuuntaan kytketty diodi ja säteilyn, joka voi olla joko hiukkas- tai sähkömagneettista säteilyä, aiheuttamat vauriot vaikuttavat ilmaisimen sähköisiin ominaisuuksiin (virta-jännite, kapasitanssi-jännite) heikentäen sen toimintakykyä. Tulevaisuudessa ilmaisimilta tullaankin vaatimaan nykyistä suurempaa säteilynkestoa. Säteilynkestotutkimuksissa säteilyttävänä hiukkasena on usein neutroni, protoni tai elektroni. Suurenergiafysiikan kannalta protonisäteilytykset ovat erityisen tärkeitä, sillä niiden aiheuttamat vauriot ilmaisimessa ovat samankaltaisia kuin pionien aiheuttamat. Lisäksi MeV-protonien aiheuttama vauriomäärä on selvästi suurempi kuin neutroneilla ja elektroneilla lyhentäen näin säteilytysaikoja. Ilmaisimen toimintakykyä voidaan parantaa jäähdytyksellä. Tavallisesti säteilytykset tehdään kuitenkin huoneenlämmössä ja ilmaisin ei ole toiminnassa säteilytyksen aikana. Tämä väitöstutkimus keskittyy matalan lämpötilan säteilytyslaitteiston, jossa ilmaisimin pidetään toiminnassa ja sen sähköisiä ominaisuuksia mitataan myös säteilytyksen aikana, kehitykseen ja testaukseen. Laitteisto, joka on toteutettu Helsingin yliopiston 5 MV tandemkiihdyttimen yhteyteen, on testattu ja todettu toimivaksi tietyin rajoituksin, jotka liittyvät MeV-protonisäteilytyksiin

Noise and Cluster Size Studies of ALPIDE-CMOS Pixel Sensor for pCT

The use of proton beam has been introduced in medical physics for therapeutic purposes in cancer treatment and it has been proven much more efficient than conventional X-ray. Treatment planning in proton therapy is usually provided with information from X-ray CT where X-ray attenuation in tissue is needed to be converted to proton stopping power. This conversion leads to several uncertainties because proton interacts with matter in a different way than the photon. An intuitive way to mitigate this problem is using charged particles as the basis for the CT-scan and this is the time when the idea of “Proton CT” came up. There are nearly 10 pCT prototypes worldwide and all are designed with two separate devices for proton tracking and calorimetry. Few recent studies discovered the potential of merging these two separate systems into one uniquely featured Digital Tracking Calorimeter (DTC). The DTC is made of multiple layers of Monolithic Active Pixel Sensor (MAPS) chips. In this study, ALPIDE chip has been brought in as MAPS for DTC. The ALPIDE was developed for the heavy-ion experiment at CERN to detect high energy charged particles. For pCT, ALPIDE is conceptually an ideal sensor because of its low power consumption and chip area with more than half a million pixels with in-pixel readout scheme. This thesis is carried out in three main parts: • Characterization of ALPIDE chip focusing particularly on chip’s threshold and fake hit rate. • Measuring radiation-induced effects on the sensor performance. • Analysing sensor response for different types of radiation. In addition, I contributed to Proton Beam Test at OCL, Oslo and analyzed the data afterward. This thesis also includes the analysis performed on proton beam data and significant findings from the analysis. This study represents a key contribution to pCT in terms of defining the sensor behavior and interpreting sensor response.Master's Thesis in PhysicsMAMN-PHYSPHYS39

Characterization of the Optical and Electrical Properties of Proton-Irradiated 4H-Silicon Carbide

Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. Semiconductor materials with a high tolerance to radiation fields have applications in several aerospace power and satellite systems. SiC is under investigation due to its potential for such space material applications. The optical properties of the material are investigated using temperature-dependent photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated material is investigated over the temperature range of 900 – 1500 °C. Proton-induced irradiation damage is apparent in the 4H-SiC material, affecting both the optical and electrical characteristics of the devices. The radiative behavior of the nitrogen-related near band edge transitions is significantly reduced as a result of the irradiation with partial recovery observed after high-temperature thermal annealing at 1500 °C. A deeper trapping complex (EC-ET ≅ 380 meV) is detected as a result of irradiation and shows signs of activation due to thermal annealing. Initial indications taken from I-V measurements of the Schottky diodes reveal that proton irradiation followed by thermal annealing at 900 °C may, in fact, enhance the rectifying device characteristics. Increasing the anneal temperature (TA = 1300 °C) causes the device to fail entirely. Further annealing of the irradiated 4H-SiC at 1500 °C demonstrates recovery in the rectifying behavior of the material. Significant levels of deep level donor traps are observed, induced by irradiation in n-type material. Three detectable defect pairs emerge with energy levels ranging from 570 – 730 meV below the conduction band. The trap parameters were determined using curve-fitting algorithms. Upon high-temperature thermal annealing of the material, the trap center pairs showed little change in the energy levels and capture cross-sections while the density of traps decreased as temperatures increased. Full recovery of the material characteristics is not apparent after annealing at 1500 °C

Deep Level Defects in Electron-Irradiated Aluminum Gallium Nitride Grown by Molecular Beam Epitaxy

Aluminum gallium nitride (AlGaN)-based devices are attractive candidates for integration into future Air Force communication and sensor platforms, including those that must operate in harsh radiation environments. In this study, the electrical and optical properties of 1.0 MeV electron irradiated n-AlxGa1-xN are characterized for aluminum mole fraction x = 0.0 to 0.3 using deep level transient spectroscopy (DLTS), temperature-dependent Hall, and cathodoluminescence (CL) measurements. Following irradiation of the AlGaN, it is found that four different electron traps are created, having energy levels within 0.4 eV below the conduction band edge. Three of these traps correspond to radiation-induced traps previously reported in GaN, and they are found to deepen significantly in the energy band gap with increase in aluminum mole fraction. The room temperature carrier concentration decreases following irradiation, and the carrier removal rate is found to depend foremost on the initial carrier concentration, regardless of the aluminum mole fraction. Also, following 1.0 MeV electron irradiation at a fluence of 1x1017 cm-2, the peak CL intensities of the samples are reduced, on average, by 50%. In spite of these findings, it is concluded that n-AlxGa1-xN is intrinsically more tolerant to radiation than conventional semiconductor materials such as GaAs and Si