Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Geomagnetic storms are primarily driven by the rapid transfer of energy from the solar wind to the magnetosphere. The mechanism of energy transfer involves the merging of the interplanetary magnetic field to the geomagnetic field in a process known as magnetic reconnection. This leads to an influx of energetic, charged particles into the magnetosphere so that current systems are enhanced. Specifically, an increase in the equatorial ring current leads to a decrease in the surface field. Geomagnetic storms are thus characterized by a strong decline in the horizontal components of the geomagnetic field, lasting from several hours to days. The intensity of a storm is described by the disturbed storm-time index, which is essentially a measure of the deviation from the typical quiet day variation along the equator. Severe storms can lead to the disruption of high frequency (HF) communications as a consequence of a strongly perturbed ionosphere. By the same token, the global positioning system (GPS) can become highly unreliable during magnetically disturbed conditions, yielding distance errors as large as 50 meters. The impact of geomagnetic activity and other solar-driven processes on technology systems are collectively known as space weather. Magnetic field sensing thus forms an important part of space weather forecasting and is vital to space science research as a means of improving our understanding of solar wind-magnetosphere interactions. This study examines the use of magnetometers built as SQUIDs (Superconducting Quantum Interference Devices) for monitoring the geomagnetic field for space weather forecasting purposes. A basic theory of superconductivity is presented and subsequently the key aspects governing the operation of SQUIDs are discussed. Space weather is also introduced with respect to the various processes on the sun that perturb the magnetosphere and hence the geomagnetic field. The method of analysis was basically to Fourier-transform the data using the Wiener-Khintchine theorem. A systematic approach to Fourier analysis is thus presented, demonstrating the superiority of the Wiener-Khintchine theorem in noise reduction. The suitability of SQUID magnetometers for space science research is demonstrated by a comparative study between SQUID and fluxgate datasets for magnetic storms during 2011. Strong correlation was observed between the frequency content of the SQUID and fluxgate signals. This result supports South Africa’s SQUID project, currently undertaken as a collaborative effort between SANSA Space Science and the Department of Electrical and Electronic Engineering at Stellenbosch University. This thesis thus lays a foundation for future research involving advanced magnetometry using SQUIDs. / AFRIKAANSE OPSOMMING: Geomagnetiese storms word hoofsaaklik gedryf deur die vinnige oordrag van energie van die sonwind na die magnetosfeer. Die meganisme van energie oordrag behels die samesmelting van die interplanetêre magneetveld met die geomagneetveld, in 'n proses wat bekend staan as magnetiese heraansluiting. Dit lei tot 'n instroming van energieke elektries-gelaaide deeltjies, tot in die magnetosfeer, met die gevolg dat magnetosferiese elektriese stroomstelsels versterk word. 'n Toename in die ekwatoriale ringstrome lei spesifiek tot 'n afname in die horisontale komponent van die geomagnetiese veld. Geomagnetiese storms word dus gekenmerk deur 'n sterk afname in die horisontale komponent van die geomagnetiese veld, ‘n afname wat etlike ure tot dae kan duur. Die intensiteit van 'n storm word beskryf deur die storm-tyd versteurings indeks , 'n maatstaf van die afwyking van die tipiese stil dag magnetiese variasie langs die ewenaar. Ernstige storms kan lei tot die ontwrigting van hoë frekwensie (HF) kommunikasie as 'n gevolg van 'n erg versteurde ionosfeer. Soortgelyk kan die Globale Posisionering Stelsel (GPS) hoogs onbetroubaar word tydens magneties versteurde toestande, en posisiefoute so groot as 50 meter veroorsaak. Die impak van geomagnetiese aktiwiteit en ander sonkrag gedrewe prosesse op tegnologie is gesamentlik bekend as ruimteweer. Magneetveldmetinge vorm dus 'n belangrike deel van ruimteweervoorspelling en is noodsaaklik vir ruimtewetenskaplike navorsing as 'n middel om die sonwind-magnetosfeer interaksies beter te verstaan. Hierdie studie ondersoek die gebruik van SQUID (Engels: Superconducting Quantum Interference Device) magnetometers vir die monitering van die geomagnetiese veld vir ruimteweervoorspellingsdoeleindes. ’n Basiese teorie van supergeleiding word aangebied, waarvolgens die sleutelaspekte van SQUIDs bespreek word. Ruimteweer word ook voorgestel in terme van die verskillende prosesse op die son wat die aarde se magnetosfeer en dus die geomagnetiese veld versteur. Die analisemetode wat hier gebruik word, is om die Fourier-transform van data met die Wiener-Khintchine theorema te bereken. A sistematiese metode vir Fourier-analise word aangebied, wat die superiorireit van die Wiener-Khintchine teorema vir ruisvermindering demonstreer. Die geskiktheid van SQUID magnetometers vir ruimtewetenskaplike navorsing word gedemonstreer deur ’n vergelykende studie tussen SQUID- en vloedhek-datastelle vir magnetiese storms gedurende 2011. Sterk korrelasie is waargeneem tussen die frekwensie-inhoud van die SQUID- en vloedhekseine. Hierdie resultate ondersteun Suid-Afrika se SQUID-projek, wat tans as ’n samewerkingspoging tussen SANSA Space Science en die Departement Elektriese en Elektroniese Ingenieurswese aan die Universiteit van Stellenbosch bedryf word. Hierdie tesis lê ’n fondasie vir toekomstige navorsing oor gevorderde magnetometrie met SQUIDs.

Submitted by Viviane Lima da Cunha (viviane@biblioteca.ufpb.br) on 2016-05-02T10:49:21Z No. of bitstreams: 1 arquivototal.pdf: 1791577 bytes, checksum: ecd7a6eb8a18230d0145c24932d9e248 (MD5) / Made available in DSpace on 2016-05-02T10:49:22Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1791577 bytes, checksum: ecd7a6eb8a18230d0145c24932d9e248 (MD5) Previous issue date: 2015-08-03 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The Hanbury Brown-Twiss experiment is very well established in quantum optics literature, so we devoted this dissertation in order to embed the parity and temporal reversal symmetry in the former experiment. Therefore, we developed the scattering matrix formalism which allow us use some techniques such as the scattering matrices' concatenation of di erent sections in terms of one matrix and the scattering problem of a parity and temporal reverse symmetric system. In this manner, we could derive the scattering matrix of a parity and temporal reverse symmetric Hanbury Brown- Twiss experiment(HBT-PT). With the possession of this matrix, we proposed a theoretical model which provides how to measure the symmetry of this system, which we called correlation functions formalism. In order to stablish the former formalism, we studied B uttiker formalism, which we veri ed how the correlation between 2 incident particles in a system relates to the noise due transport of this particles and what kind of noise we are treating in a given regime which the system is operating. Then, we found the input states in terms of the output states of two particles inciding in a multiterminal system, which we used it's scattering matrix to stablish the relation between the states. Thereat, we derived all the possibles correlations(therefore, the noise) of two incident particles in the former system. Thereby, we analysed the extreme cases of a barrier coupled to the HBT-PT experiment for the purpose of stablish which regime the experiment is symmetric adjusted, so, demonstrating the Hanbury Brown-Twiss E ect with parity and temporal reverse symmetries. / Sendo o experimento Hanbury Brown-Twiss bem estabelecido na literatura da otica quântica, dedicamos esta dissertação a embutir no mesmo experimento a questão da simetria por paridade e reversão temporal. Para tanto, abrimos mão do formalismo da matriz de espalhamento que permitiu nos utilizar tecnicas como a concatenação de matrizes de espalhamento de sec ções diferentes em termos de apenas uma matriz e o problema do espalhamento em um sistema simétrico por paridade e reversão temporal. Dessa forma, pudemos derivar a matriz de espalhamento para o experimento Hanbury Brown-Twiss com simetria de paridade e revers~ao temporal(HBT-PT). De posse dessa matriz, propusemos um modelo teórico que propicia a medição experimental a simetria desse sistema, o qual chamamos de formalismo das fun c~oes de correla c~ao. Para estabelecermos o formalismo supracitado, estudamos o formalismo de Buttiker, onde veri case como a correlaçãao entre 2 partículas incidentes em um sistema relaciona-se com o ru do devido ao transporte dessas part culas e que tipo de ru do estamos tratando, dado o regime em que o sistema está operando. Em seguida, encontramos os estados de entrada em termos dos estados de saída de 2 partículas incidindo em um sistema multiterminal, onde utilizamos a sua matriz de espalhamento para estabelecer a rela c~ao entre os estados. Com isso, derivamos todas as possíveis correlações (e, por conseguinte, o ruído) de 2 partículas incidentes nesse sistema. Assim, analisamos os casos extremos de uma barreira acoplada ao experimento HBT-PT, a m de estabelecer o regime em que o experimento está simetricamente ajustado e demonstramos o Efeito Hanbury Brown-Twiss por paridade e reversão temporal.