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Gibson Mines 0052N 11565.Pdf (7.904Mb) EXPLORATION OF COSMIC-RAY PROPAGATION AND THUNDERSTORM MODELS TO EXPLAIN UNUSUAL EVENTS MEASURED WITH THE SURFACE DETECTOR OF THE PIERRE AUGER OBSERVATORY by Joseph Gibson c Copyright by Joseph Gibson, 2018 All Rights Reserved A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Applied Physics). Golden, Colorado Date Signed: Joseph Gibson Signed: Dr. Frederic Sarazin Thesis Advisor Golden, Colorado Date Signed: Dr. Uwe Greife Professor and Head Department of Physics ii ABSTRACT The Surface Detector at the Pierre Auger Observatory has recorded events that have an unusually large footprint on the array and lasts 100 times longer than a typical cosmic ray signal. This thesis explores possible models to explain the source of these unusual signals. The proposed models show that the unusual signals are not a result of a cosmic ray shower but are instead likely a result of a lightning-related phenomenon. The attachment process and the return stroke can create E-fields strong enough to create runaway relativistic electron avalanches. This process creates a cascade of high energy electrons that can span over 100 meters and induces high energy photons that can travel a few kilometers. The Surface Detector would be able to measure the high energy particles resulting from this runaway process. The simulated model of the return stroke produced a signal on the ground that was able to match the long-time of the unusual events. This very preliminary model provides some insights for some of the unusual events, but a complete explanation for the events remains elusive. iii TABLE OF CONTENTS ABSTRACT ......................................... iii LISTOFFIGURESANDTABLES............................. vi LISTOFABBREVIATIONS ................................ ix ACKNOWLEDGMENTS ...................................x CHAPTER 1 UNUSUAL EVENTS OBSERVED WITH THE PIERRE AUGER COSMIC-RAYOBSERVATORY . .1 1.1 CosmicRayOverview ............................... 1 1.2 PierreAugerObservatory . ...4 1.3 ThePierreAugerSurfaceDetector . .....5 1.3.1 EventReconstruction. .8 1.4 Observation of unusual events with the SD Detector . ..........10 1.4.1 TimingandGeometryReconstruction . 11 CHAPTER 2 SIMPLE COSMIC RAY PROPAGATION MODELS . 17 2.1 PropagationModels............................... 18 2.1.1 SubluminalPropagationModel . 19 2.1.2 ShockWavePropagationModel . 21 2.2 Conclusions ..................................... 26 CHAPTER 3 PRODUCTION OF RELATIVISTIC RUNAWAY ELECTRON AVALANCHES IN LIGHTNING STRIKES? . 28 3.1 TheLightningDischargeProcess . ..... 28 3.1.1 Initiation of Lightning, and the Quasi-Static BackgroundField . 30 iv 3.1.2 LeaderSteppingProcess . 31 3.1.3 Attachmentprocess. 34 3.1.4 ReturnStroke................................ 34 3.1.5 OthertypesofCGLightning . 36 3.1.6 CharacteristicsofLightning . .... 36 3.2 Runaway Relativistic Electron Avalanche . ........36 CHAPTER4 LIGHTNINGMODELS . 43 4.1 ChargedChannelModel ............................. 45 4.2 AttachmentPointModel . 49 4.3 CurrentChannelModel ............................. 53 4.4 ReturnStrokeModel ............................... 55 4.5 Conclusions ..................................... 60 CHAPTER5 CONCLUSION................................ 61 5.1 FutureWork.....................................62 REFERENCESCITED ................................... 63 APPENDIX ADDITIONAL UNUSUAL EVENT IMAGES . 68 v LIST OF FIGURES AND TABLES Figure 1.1 Schematics for the development of a Extensive Air Shower..........3 Figure1.2 HillasDiagram............................... ...4 Figure 1.3 Map of Pierre Auger Observatory and Main Components of an SD Station . 6 Figure1.4 ExampleofanEASsignalintheSD. .....9 Figure1.5 ExampleofthesignalintensityofanEAS. .........9 Figure 1.6 Timing and Geometrical Characteristics of an UnusualEvent . 12 Figure 1.7 Footprint and Lateral Distribution Function of an UnusualEvent. 13 Figure1.8 IncompleteLongSignalMeasurement . ........15 Figure 2.1 Schematic of the Spherical Inflation Model . ..........18 Figure 2.2 Schematic and Simulated Results of a Propagation Model ......... 20 Figure 2.3 Lengthened Time Signature in the Propagation Model 4 km from the Source .....................................21 Figure 2.4 Schematic of the Subluminal Propagation Model . ...........22 Figure 2.5 Simulation Results of the Subluminal Model . ..........23 Figure2.6 SchematicoftheShockWaveModel . ...... 24 Figure 2.7 Simulation Results of the Shock Wave Model . .........25 Figure 3.1 Upper atmospheric lightning and electrical discharge phenomena associatedwiththunderstorms . 29 Figure 3.2 Processes in a typical negative downward lightning strike with a rough estimateofthetimingforeachprocess. 30 Figure 3.3 A vertical tripole representing the charge structure inside a thundercloud ................................. 32 vi Figure 3.4 Stepping process of the Lightning Leader . ..........33 Figure3.5 LightningCurrentDistribution . .........37 Figure3.6 EffectiveFrictiononaFreeElectron . .........39 Figure3.7 MonteCarloSimulationofRREA . ..... 42 Figure 4.1 Cutoff Fields Imposed on Lightning Simulations . ..........45 Figure4.2 ChargeChannelSchematic . ..... 46 Figure 4.3 2D projection of the electric field near the charged channel. 46 Figure4.4 EffectsofacutoffonE-fieldMagnitude . ....... 47 Figure 4.5 Paths of 1 MeV electrons in the Charged Channel Model .........48 Figure 4.6 Simulation Results of the Charged Channel Model . ...........49 Figure4.7 AttachmentPointModelSchematic . ....... 50 Figure 4.8 2D projection of the electric field near the lightning attachment point. 50 Figure 4.9 Paths of particles in the Attachment Point Model . ...........52 Figure 4.10 Simulation Results of the Attachment Point Model .............53 Figure4.11 CurrentChannelModelSchematic . ........54 Figure 4.12 2D projection of the electric field near the currentchannel. 54 Figure 4.13 Paths of particles in the Current Channel Model . ............56 Figure 4.14 Simulation Results of the Current Channel Model . ............57 Figure4.15 ReturnStrokeModelSchematic . ....... 58 Figure 4.16 Simulation Results of the Return Stroke Model . ............59 Figure A.1 Unusual events without the annular geometry and smallfootprint. 68 Figure A.2 Lightning Correlation with Unusual Events . .........69 Figure A.3 Additional ring shape footprints of unusual events . ............69 vii Figure A.4 Lightning Correlation with Unusual Events . .........70 FigureA.5 SignalTimingFits............................. 71 Table 3.1 Parameters of downward negative lightning . ...........38 Table 3.2 Parameters of downward positive lightning . ...........38 viii LIST OF ABBREVIATIONS ExtensiveAirShower.................................. EAS SurfaceDetector .................................... .SD FluorescenceDetectors. FD PhotomultiplierTube. PMT WorldWideLightningLocationNetwork. WWLLN RunawayRelativisticElectronAvalanche. ........RREA Intra-Cloud ........................................ IC Cloud-to-Ground .................................... .. CG ElectromagneticPulse . .. EMP ix ACKNOWLEDGMENTS Firstly I would like to thank Dr. Fred Sarazin for his guidance and patience. I would also like to thank Dr. Kyle Leach and Dr. Lawrence Wiencke for serving on my committee. To everyone in the Mines Astroparticle group, Kevin Merenda, Johannes Eser, Jeff Johnsen, thank you for the helpful and continual advice. To my friends and family thank you for the support and occasional distractions. Thank you, Emily, for your support and grammatical knowledge. x CHAPTER 1 UNUSUAL EVENTS OBSERVED WITH THE PIERRE AUGER COSMIC-RAY OBSERVATORY 1.1 Cosmic Ray Overview Over 100 years ago, Victor Hess showed that the amount of ionizing radiation increases with altitude and concluded there is a source of radiation coming from outer space, this radiation would become known as cosmic rays. In 1939, Pierre Auger discovered time co- incidences of ionizing radiation over long distances, this observation yielded the discovery of Extensive Air Showers (EASs) [1]. An EAS forms when a high-energy primary cosmic ray enters Earth’s atmosphere and interacts with atmospheric molecules creating a large number of secondary particles, eventually creating an extensive cascade of particles [1]. At the highest energies, the properties of a cosmic ray can only be deduced from the measured properties of the EAS it induces in the atmosphere. The development of an EAS has three components, a muonic, a hadronic and an electro- magnetic component. The composition and decay paths of these components are shown in Figure 1.1(a). When a cosmic ray enters the atmosphere the first interaction that occurs high in the atmosphere is a hadronic interaction. The hadronic component contains kaons, pions, protons, and neutrons. These particles form the shower core, as they produce all the other components of a shower and stay close to the shower axis. 98% of the shower energy, however, is eventually contained in the electromagnetic component [2]. The electromagnetic compo- nent originates from neutral meson decays and contains electrons, positrons, and gamma rays. Electrons with energy greater than 85 MeV can produce secondary particle showers via scattering, pair production, and bremsstrahlung radiation [2]. The muonic component of showers comes from the decay of pions and kaons and consists of muon and neutrinos. 1 Muons travel all the way to Earth’s surface with little interaction, thus the muons provide insight
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