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No description available.

A coherent Diffraction Radiation (CDR) originating from a dual-target system was investigated theoretically and experimentally. Diffraction Radiation is emitted when a bunch of charged particles moves in the vicinity of an optical obstacle. The coherency of the effect is achieved when electrons in the bunch radiate in phase, i.e. the wavelength of the radiation is comparable to or larger than the bunch length. An experimental setup at the CLIC Test Facility 3 (CTF3) at CERN was modified by installation of a second target. In the experiment two targets are positioned to one side of the beam and the radiation originating from them is translated towards a Michelson interferometer. The ultimate goal of the experiment is to reconstruct the longitudinal parameters of the beam from the CDR spectrum. A precise knowledge of the bunch time profile is particularly important in the context of a luminosity challenge in the future linear colliders and therefore the development of a non-invasive and robust longitudinal beam diagnostic technique is very important. A theoretical model based on the classical Diffraction Radiation theory was devel- oped to calculate the spatial distributions of the CDR from the dual-target system and based on this knowledge to calculate a single electron spectrum which is used in a bunch shape reconstruction. The Kramers-Kronig analysis as a tool for the bunch profile reconstruction was studied theoretically. The CDR spatial distributions were measured at the experimental setup and compared with the theory. The ability of the two-target system to cut-off the backgrounds originating upstream of the experimental setup was tested.

The interaction of a laser pulse of relativistic intensity (≥1×1018 Wcm−2) with a solid target results in the creation of a quasi-electrostatic field at the rear surface of the target. This field is strong enough (TVm−1) to ionise and accelerate ions from the target surface via the Target Normal Sheath Acceleration (TNSA) mechanism. The resulting beam has many desirable properties for a large range of potential applications. The work presented in this thesis aims at optimising and controlling the ion beam properties. Firstly, an investigation of laser driven ion acceleration using ultrahigh contrast (1010), ultrashort (50 fs) laser pulses focused to intensities up to 1021 Wcm−2 on thin foil targets is presented. It is found that irradiation at normal (0◦) incidence produces higher energy ions than oblique incidence (35◦), contrasting sharply with previous work at lower intensities. These findings are confirmed by 1D boosted PIC simulations and can be explained by the acceleration of fast electrons being dominated by a new absorption process. The effects of target composition and thickness on the acceleration of carbon ions are also discussed and compared to calculations using analytical models of ion acceleration. Next, an investigation of the transverse refluxing of fast electrons in targets of limited lateral size is reported. The targets were irradiated by high intensity (∼1×1019 Wcm−2), picosecond laser pulses. The maximum energy of the resulting TNSA proton beams is found to increase with decreasing target surface area. This is explained by the presence of a laterally spreading electron population that reflects off the target edges and enhances the TNSA accelerating field. In addition it is demonstrated that this laterally refluxing electron population can be used to control the spatial intensity distribution of the TNSA proton beam, by changing the geometry of the target. This technique offers encouraging prospects for many applications of laser accelerated ions. Finally, a characterisation study of debris emission generated by the interaction of high power laser pulses with solid targets is presented. Targets of thickness ranging from 1 mm to 5 nm were irradiated by high intensity (∼1×1020 Wcm−2), picosecond laser pulses. The resulting debris emission is found to be directed along the target normal axis at both the rear and front of the target. The front emission profile is found to be similar to a plasma expansion profile. Hollow debris depositions of radius increasing with target thickness are measured from the target rear surface. This emission profile is explained by the propagation and breakout of a laser driven shock at the rear of the target.

This thesis presents experimental measurements, supported by particle-in-cell simulations, of ion beams accelerated by high intensity laser plasma interactions, spanning both the sheath acceleration and radiation pressure dominated regimes. For interactions of laser intensities rv 1020 W I cm? with micron thick gold targets rear surface sheath acceleration w~ seen to dominate. Proton beam spatial profiles revealed multiple concentric rings for target thicknesses ~ 20 tun. The number of rings increased with decreasing target thickness with no rings for thicknesses > 50 uu: It is postulated that these concentric rings stem from a larger number of recirculations of laser accelerated electrons through thinner targets. In following investigations structured proton beam profiles were observed from the interaction of nanometer scale targets at intensities of rv 1021 W Icm2. The most striking bubble-like structure, observed for the thinnest (5 nm) targets, closely resembles a Rayleigh- Taylor-like instability, a clear indication of radiation pressure driven acceleration. Both the experimental results and simulations also exhibit narrow energy spread features in the carbon ion spectra. Finally, a rv 5 ps, CO2 laser (A = 10.6 p,m) with intensity rv 1015 W Icm2 was focused onto an overdense hydrogen gas target. Transverse probing revealed a hole boring shock front associated with the first phase of radiation pressure acceleration. The accelerated proton beams contained up to 3 X 1012 protons/MeV [et, with energy spreads as low as r-;» 4 %. The ion energies scaled linearly with increasing integrated laser energy as expected from acceleration by hole boring.

The ATLAS experiment is being assembeled as a general purpose particle detector to exploit the physics discovery potential of the Large Hadron Collider. The SemiConductor Tracker (SeT), one of the central subsystems of ATLAS, requires alignment of O(lDJ.Lm) for good performance. The alignment program consists of a set of proceedures to establish the location of detector elements. This includes optimised design and construction prior to operation. This thesis describes Electronic Speclde Pattern Interferometry (ESPI), a technique used to measure deformation at the micron level which has been applied to SCT components during design and prototype development. ESPI creates contour maps of objects under study, helping a qualitative understanding of object behaviour as well as providing measurements. ESPI measurements of the thermal deformation of SCT detector modules are presented. A modified ESPI interferometer was developed to create contours of vibration amplitude. Tests were performed on well-understood objects to ensure consistency between the interpretation of Vibration ESPI results and known object behaviour. The technique was then used to measure the behaviour under acoustic driving of prototype SCT support structures made of Carbon-Fibre Reinforced Plastic (CFRP) materials. Several low modes of oscillation were found, as well as the oscillator quality factor, for each of the CFRP structures studied. These results provide design input for SCT construction by specifying resonant frequencies to avoid) and corroborate the validity of Finte Element Analysis studies on these inhomogeneous materials used in the ATLAS SCT. High event statistics will permit ATLAS perform precision Electroweak measurements. This thesis presents a study of the statistical resolution with which the decay width of the W boson, rw will be measured.

The TOTEM experiment at the LHC will measure the total proton-proton cross-section with precision of 1%, elastic proton scattering over a wide range in momentum transfer and diffractive dissociation, including single, double and central diffraction topologies. This dissertation reports on the tracking performance of the Roman Pots in view of the physics programme of TOTEM.

This thesis is an investigation using the finite volume method to examine the flow of carrier gas and nanoparticles through a particle beam cluster machine. Nanoparticle clusters are a relatively new material, which often have novel properties due to the ratio of the number of atoms at their surface compared to number of atoms within their volume. Although two dimensional, it offers an insight into the characteristic sonic/supersonic expansion of a free gas jet into a partial vacuum. Tests were performed with different geometry and pressure, to view changes of the nanoparticle trajectory through the cluster machine. The aim is to use this greater understanding, to examine how the efficiency of a particle beam cluster machine can be improved.