The acceleration of charged particles with ultrafast terahertz electromagnetic radiation could enable new, and improve many of aspects of, accelerator applications. These include providing shorter electron bunches for ultrafast time-resolved pump-probe spectroscopy, enabling complex longitudinal profiles to be imparted onto charged particle bunches and significantly improving the ability to synchronise an accelerator to an external laser. In this thesis I present investigations into terahertz radiation sources that enabled the generation of terahertz radiation with attractive properties for accelerator based applications. Specific attention has been paid to temporally tunable sources that generate strong longitudinally polarised electric field components as these enable a free-space co-linear interaction geometry to be implemented. A simulation describing the propagation of radiation from such sources has been developed. Terahertz sources have been designed and the radiation generated characterised via electro optic detection. These include a radially biased photoconductive antenna (PCA) based source of which the longitudinally polarised terahertz electric field component was found to have an amplitude of 2.22 kVcm-1 as well as a near-single cycle temporal profile. This radially biased PCA was used in conjunction with the Accelerators and Lasers in Combined Experiments (ALICE) energy recovery linear accelerator at the Daresbury Laboratory in an electron acceleration experiment. To enable higher longitudinally polarised terahertz electric field strengths to be obtained, as well as the ability to temporally tune the terahertz radiation, generation within non-linear optical crystals was investigated. Magnesium-oxide doped stoichiometric lithium niobate (MgO:SLN) was investigated as a possible candidate due to its high non-linear susceptibility tensor and reported ability to impose temporal tuning directly from the pump laser beam. A scheme consisting of two MgO:SLN crystals each generating a separate linear polarised terahertz pulse which were then combined via a lens was designed and built. Electro optic detection techniques were used to characterise the radiation generated from this source. Peak terahertz electric fields amplitudes of 11.6 kVcm-1 and 47 kVcm-1 were measured for both the longitudinally and transversely polarised field components respectively. Temporal profiles measured from both the longitudinally and transversely polarised electric field components showed electric field periods of approximately 300 fs. This method of generating terahertz radiation employed a pulse-front tilt technique. Allowing for the same scaling as recently reported in the literature for MgO:SLN generation techniques, which will in principle allow this method to scale to longitudinally polarised terahertz electric field profiles in excess of 1 MVcm-1.

The cross sections for neutral current (NC) deep inelastic scattering (DIS) in e+p collisions with a longitudinally polarised positron beam are measured at high momentum transfer squared (Q2 > 185 GeV2) at the ZEUS detector at HERA. The HERA accelerator provides e+-p collisions at a centre-of-mass energy of 318 GeV, which allows the weak contribution to the NC process to be studied at high Q2. The measurements are based on a data sample with an integrated luminosity of 135.5 pb-1 collected with the ZEUS detector in 2006 and 2007. The single differential NC cross sections dsigma/dQ2, dsigma/dx and dsigma/dy and the reduced cross section are measured. The structure function xF3 is determined by combining the e+p NC reduced cross sections with the previously measured e-p measurements. The interference structure function xF 3^gamma,Z is extracted at Q2 = 1500 GeV2. The cross-section asymmetry between the positive and negative polarisation of the positron beam is measured and the parity violation effects of the electroweak interaction are observed. The predictions of the Standard Model of particle physics agree well with the measurements.

The cross sections for neutral current (NC) deep inelastic scattering (DIS) in e+p collisions with a longitudinally polarised positron beam are measured at high momentum transfer squared (Q2 > 185 GeV2) at the ZEUS detector at HERA. The HERA accelerator provides e+-p collisions at a centre-of-mass energy of 318 GeV, which allows the weak contribution to the NC process to be studied at high Q2. The measurements are based on a data sample with an integrated luminosity of 135.5 pb-1 collected with the ZEUS detector in 2006 and 2007. The single differential NC cross sections dsigma/dQ2, dsigma/dx and dsigma/dy and the reduced cross section are measured. The structure function xF3 is determined by combining the e+p NC reduced cross sections with the previously measured e-p measurements. The interference structure function xF 3^gamma,Z is extracted at Q2 = 1500 GeV2. The cross-section asymmetry between the positive and negative polarisation of the positron beam is measured and the parity violation effects of the electroweak interaction are observed. The predictions of the Standard Model of particle physics agree well with the measurements.

Cette thèse présente un travail relatif à l'étude de la structure en spin longitudinal du nucléon. Le but est de déterminer la contribution des constituants du proton, quarks et gluons, à la formation de son spin 1/2. L'analyse s'appuie sur les données de l'expérience COMPASS qui bénéficie d'un faisceau de muons polarisés à 200 GeV diffusé sur les protons polarisés d'une cible d'ammoniac (NH₃) de 1,2 m de long. On mesure l'asymétrie de spin longitudinal des sections efficaces de diffusion profondément inélastique. On extrait la fonction de structure en spin du proton, g₁p, étendant la couverture cinématique mondiale à des régions inexplorées jusqu'à maintenant (0,0036 < x < 0,57; 1,03 < Q² (GeV/c)² < 96 et 23 < W² (GeV/c)² < 320). Les résultats, d'une grande précision statistique, sont inclus dans une analyse des données mondiales de g₁p, g₁d et g₁n (proton, deutéron et neutron) au 2ème ordre de QCD afin de paramétrer les distributions de quarks et de gluons polarisés. L'étendue de la couverture cinématique en x et Q² des données mondiales de g₁, un élément déterminant pour la sensibilité à la polarisation des gluons ΔG, s'avère trop limitée pour constituer une extraction précise de celle-Ci. Néanmoins, l'analyse QCD permet de déterminer la contribution du spin des quarks au spin du proton à 0.26<ΔΣ<0.33 à Q² = 3 (GeV/c)² dans le schéma MSbar. L'étude montre que l'incertitude principale sur ΔΣ est liée au choix des formes fonctionnelles utilisées dans la régression des données. Enfin, la règle de somme de Bjorken, qui constitue un test de QCD, est vérifiée avec une précision de 9% en utilisant les données de COMPASS uniquement. / The work presented in this thesis is related to the study of the longitudinal spin structure of the nucleon. The aim is to determine the contribution to the spin 1/2 of the proton in terms of its constituents, quarks and gluons. The analysis is performed on the data taken with the COMPASS experiment, which benefits from a polarised muon beam at 200 GeV scattered off polarised protons from an ammonia target of 1.2 m long. The double longitudinal spin asymmetry of deep inelastic scattering cross-Section. The spin-Dependent structure function of the proton g₁p is derived from these measurements, which extend the kinematic world coverage to unexplored region so far (0,0036 < x< 0,57; 1,03 < Q² (GeV/c)² < 96 and 23 < W² (GeV/c)² < 320).The results obtained with a high statistical precision are included in a Next-To-Leading order QCD analysis of world g₁p, g₁d and g₁n (proton, deuteron and neutron) data to parametrise the polarised quark and gluon distributions. The g₁ world coverage of the x and Q² kinematic domain, which is a key point in the sensitivity to the gluon polarisation ΔG, turns out to be too limited for an accurate ΔG determination. Nevertheless, the QCD analysis allows to determine the quark spin contributions to the proton spin to 0.26<ΔΣ<0.33 at Q² = 3 (GeV/c)² in the MSbar scheme. The dominant uncertainty on ΔΣ is related to the choice of functional forms assumed in the fit. Finally, the Bjorken sum rule, which constitutes a fundamental test of QCD, is verified on the COMPASS data alone with a precision of 9%.