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High quality x-ray sources are required for fundamental research in atomic physics and material science. Third generation synchrotron light sources fulfil this need in most aspects, producing a high flux with x-ray energies up to 100's keV and a narrow bandwidth . However, the maximum photon energy produced by synchrotrons is limited by facility size, electron beam energy and magnet strength constraints. Hence, in this thesis an inverse Compton scattering (ICS) source has been designed for production of high energy X-rays (Eγ ≤ 402.5 keV) from the CBETA multi-turn energy recovery linac (ERL), with high flux (F = 3.22 x 10¹⁰ ph/s) and narrow bandwidth (ΔEγ/Eγ = 0.5% rms). Similarly, high quality γ-ray sources (Eγ > 1 MeV) are in demand for experimentation in nuclear photonics, photonuclear radioisotope production, nuclear forensics and proliferation. Whilst bremsstrahlung and radioisotope γ-ray sources could be used, they are not ideal as bremsstrahlung is inherently broadband and radioactive isotopes produce a low flux. Currently ICS sources, such as HIγS, produce γ-rays up to 100 MeV with high photon fluxes (F=5 x 10⁸ ph/s), however the bandwidth (ΔEγ/Eγ = 2.5% FWHM) is too large for some experiments. Hence, the DIANA ERL driven ICS source is designed to provide narrowband (ΔEγ/Eγ = 0.5% rms) γ-ray production (Eγ ≤ 20.11 MeV) at higher flux (F = 6.08 x 10¹⁰ ph/s). Various accelerators can provide electron beams to drive ICS sources, though large scattered photon fluxes require a high average electron beam current and small emittance, whilst narrow bandwidths require small emittance and small electron beam energy spreads. Therefore, this thesis develops optimisation methods for ICS production of narrow bandwidth photons at high flux. Currently, most ICS sources utilise storage rings, with high average beam current and moderate electron bunch energy spread, or linacs, with small emittance and energy spread. ERLs can provide electron beams with small emittance, energy spread and high average beam current simultaneously. Hence ERLs are ideal drivers of ICS sources. In this thesis two ICS sources are designed: the CBETA x-ray ICS source and the DIANA γ-ray ICS source. Methods for predicting the flux and the produced photon spectrum are developed and a series of optimisations toward maximal narrowband photon production are proposed. Applications of the produced narrow-band, high energy photons are then investigated for x-rays and γ-rays and photon production from ERL driven ICS sources is compared with other light sources.

Antihydrogen is now routinely formed in ALPHA by combination of antiproton and positron plasmas. Formed anti-atoms with energy less than around 0.5 K are trapped in an octupole-based Ioffe-Pritchard magnetic trap. Reducing trapped antihydrogen energy is expected to increase precision in experiments that measure fundamental antihydrogen properties for precise comparison to hydrogen. Cooling is expected to permit confinement in a shallower magnetic trap, hence reducing magnetic field errors in gravity experiments and increasing sensitivity in experiments that measure the hypothetical antihydrogen charge. In antihydrogen spectroscopy experiments, cooling is expected to increase laser interaction time, thus narrowing spectral linewidth. A technique to adiabatically cool antihydrogen is presented, which involves trapping in a short magnetic well, before slowly (compared to the antihydrogen speed) expanding the trap volume along the trap axis. During magnetic release, lower energy anti-atoms are expected to escape and annihilate when the trap depth is lower which happens later in time. Adiabatically cooled (Trial A) annihilation times are compared to control samples held in the small (Trial B) and large (Trial C) magnetic volumes, showing Trial A anti-atoms are lost on average when the trap depth is 0.081 +/-0.007 K, compared to 0.223 +/- 0.009 K and 0.173 +/- 0.011 K for Trials B and C respectively. Results of detailed Monte Carlo simulations are presented, which show that Trial A anti-atoms have average energies 1.616 +/- 0.002 and 1.558 +/- 0.002 times lower than Trials B and C respectively, corresponding to a 37.9 +/- 0.1 % energy decrease during expansion and achieving mean final energy 0.2226 +/- 0.0002 K. The magnetic trap expands predominantly in the axial direction, giving rise to a 68.1 +/- 0.2 % axial and 14.2 +/- 0.2 % transverse energy decrease resulting from non-trivial energy mixing dynamics. Two adiabatic models that make limiting assumptions about the energy mixing dynamics are shown to bound the simulation results, confirming the cooling is consistent with an adiabatic process. A possible factor of around 10 increase in precision of antihydrogen charge measurements is presented and a potential issue for the use of axial adiabatic cooling in ALPHA antihydrogen spectroscopy experiments is raised, that a significant fraction of adiabatically cooled anti-atoms tend not to occupy the spatial region of the 1S-2S spectroscopy laser beam.

The effects of wakefields are a universally challenging topic in accelerator physics and are critically important due to their impact on beam quality. Wakefields can dilute the beam emittance and in the worst case can cause a beam break up (BBU) instability. Several types of wakefields exist, each with their own separate sources and influences on the beam. The wakefields considered in this Thesis are geometric, where the electric fields excited by the charged particles diffract off the accelerator walls at a transition in the beam pipe and travel back to the beam. These can be further split into longitudinal wakefields which alter the energy spread and length of the bunch, and transverse wakefields which transversely kick the beam and increase the transverse emittance, reducing the beam quality. Long-range wakefields span from one particle bunch to a trailing bunch, whereas short-range wakes effect the bunch that excites the wakefield. This Thesis presents a framework which includes the cell and structure design of a linac and calculation of the wakefields excited in disc-loaded linac structures. In this framework, I have produced analytical expressions of the long-range wakefields, and a method to fit numerical short-range wakefields to analytical formula. These procedures would be advantageous to the accelerator community for use in general linac design. This framework has been used to calculate the wakefields of the Compact Linear Accelerator for Research and Applications (CLARA) S-band linac structure as well as the X-band Accelerator for Research and Applications (XARA) structure, a linac designed to fulfil the aims of the CLARA project to be a Free Electron Laser (FEL) test facility to study novel acceleration techniques. The XARA project serves as an alternative or an upgrade to the CLARA phase 2 system, upgrading the beam energy from 250 MeV to ~ 1 GeV. This will reduce the achievable wavelength of the FEL setup by a factor of ~ 16, allowing many biological and ultra-fast dynamics processes to be studied, which is particularly attractive to the accelerator community. This thesis introduces a design of an X-band linac for the XARA project capable of an average gradient of = 80 MeV/m, much higher than the CLARA S-band linac gradient of = 25 MeV/m (operated at 17.5 MeV/m). This gradient was chosen to ensure a beam momentum of greater than 70 MeV/m could be reached with only three RF modules due to spatial constraints. I have created a numerical tool which optimises the structural parameters and iris tapering to increase its efficiency while avoiding breakdown. This is combined with a study of the long-range and short-range wakefields to decide the parameters of the initial design. The calculations of the wakefields agree well with results from established wakefield codes ABCI and ECHO2D, while reducing the required CPU time by a factor of ~ 20-30. This allows the short-range wakefields to be calculated rapidly if design changes need to be made. The short-range wakefields, which I have calculated, are used in the beam dynamics code ELEGANT to study the electron beam in the XARA structure. The variation of the initial offset and charge of the bunch gives a preliminary indication of how sensitive the beam quality is to misalignments and how much charge can be placed in a bunch. The normalised emittance growth for a bunch charge of Q_b = 250 pC for a transverse offset of C_x = 0.253 mm was found to be Δ∈Nx/∈Nx = 270.8%. These simulations were carried out without a focusing magnetic lattice which would recenter the beam and alleviate the wakefields, however this could be done in a future study which will include a full design of a FODO lattice. These calculations are then validated by an analytical formulation where the emittance growth at the end of the linac agrees within ~ 12% between the two methods. There are a suite of misalignment studies needed to fully quantify systematic and random errors likely to be present in the XARA/UK-XFEL machine. My work serves as an important initial study on the linac design towards a fully realised XFEL facility at Daresbury Labs. This facility would be available to the accelerator community to perform a wide range of studies as well as test novel FEL schemes.

The ALPHA (Antihydrogen Laser PHysics Apparatus) collaboration at CERN is testing Charge-Parity-Time (CPT) symmetry through precise measurements with antihydrogen atoms and in the future will measure antihydrogen's free fall acceleration in Earth's gravitational field. The antihydrogen atoms are created by slowly merging cold plasmas of antiprotons and positrons. The production rate is highly sensitive to the parameters of these plasmas and typically only a few atoms have been available at a time for measurements. A limit is placed early on in the achievable number of trapped antihydrogen by the inefficiency when capturing antiprotons from the Antiproton Decelerator (AD). Historically, over 99 % of antiprotons are lost during the capture process as a result of the 5.3 MeV initial kinetic energy of the delivered beam. ELENA is a new storage ring coming online in 2021 which will lower this initial kinetic energy of the beam to 100 keV, improving the capture efficiency of antiprotons for ALPHA and other experiments. To accommodate for ELENA, it will be essential to upgrade the ALPHA antiproton Catching Trap (CT) and in particular the antiproton degrading apparatus which is responsible for slowing down the incoming beam to trappable energies. Following these upgrades, we expect the antiproton capture efficiency to increase from less than 1% to upwards of 50%. To effectively utilize the anticipated larger number of trapped antiprotons and translate this to a gain in antihydrogen production, new plasma manipulation and delivery techniques need to be developed. This thesis describes those upgrades and associated techniques which optimize the capture of antiprotons from ELENA, as well as the preparation and delivery of the antiprotons for antihydrogen creation. In this thesis, we first present the development of the new antiproton degrading apparatus to slow antiprotons delivered by ELENA. A combination of semi-analytic models and Monte Carlo particle tracking simulation techniques are used to design the new degrading apparatus. Next, we describe numerical simulations of a technique for non-destructively characterizing the parameters of the antiproton plasmas, and compare these against theory. Finally, a method for extracting controlled, reproducible beams of antiprotons from the CT is discussed. A combination of theoretical models and numerical simulations are assembled into a framework for understanding and modelling the extraction of these beams.

Beam profile and emittance monitoring is essential to understand the dynamic behaviour of the ensemble of particles in an accelerator beam. A non-invasive measurement of the beam profile ensures reliable measurements. One such device is the beam gas Ionisation Profile Monitor (IPM), which relies on detecting the ionisation products from the interaction between residual gas molecules in the vacuum of the accelerator and the beam particles. Traditional detectors in IPMs have limited the instruments reliability and performance. A novel approach using Timepix3 pixel detectors is explored in this thesis project which enables direct detection of ionisation electrons with a precise time resolution. A radiation hard readout system was developed to allow the maximum detection performance of the pixel detectors and beam measurements were recorded during 2018. A beam profile reconstruction method was developed that takes advantage of the information recorded by the Timepix3 detectors to identify and only select events that are associated with ionisation electrons. From these events, a beam profile was reconstructed and the beam size calculated by fitting a Gaussian model to the beam profile data or by calculating the RMS beam size directly. During 2018 a prototype IPM with pixel detectors was installed in the Proton Synchrotron at CERN. Beam profile measurements recorded with this instrument demonstrated the ability to measure the beam profile continuously throughout the beam cycle in the accelerator. Expected beam dynamics effects such as adiabatic damping and oscillations during transition crossing were observed with the instrument. The time resolution of the pixel detectors enabled bunch-by-bunch measurements of the beam profile by integrating the recorded events separately for each bunch over multiple turns.

Trapping mass spectrometers, such as Fourier transform ion cyclotron resonance and Orbitrap instruments, can obtain very high resolutions (~10^6 [1]), at the expense of having to trap ions for extended periods of time. This reduces cross-compatibility with chromatographic techniques such as ion mobility spectrometry, in which ion signal varies over milliseconds. Time-of-flight instruments operate on timescales in the order of 10 Âμs, however typically offer lower ultimate resolution due to constraints on ion path length in commercially viable devices. Furthermore, ToF devices use destructive detection methods, which can operate at single ion sensitivity - significantly more sensitive than ion trap mass analysers, which measure the (very small) image current induced in the device by ion motion. A device comprising segmented electrodes is proposed, which supports an Orbitrap-like electrostatic potential field spanning ~1.5 m axially to be used for mass-to-charge analysis of ions, using thin detector electrodes at the centre of ion oscillations to generate a strong, pulse-like induced signal, which can be used to elucidate the m/z of trapped ions. The proposed device is simulated in its entirety, using SIMION [2], to create the device and calculate the electrostatic potential, integrate ion trajectories, and measure induced signal; LTSPICE [3] to simulate transmission and amplification of the signal; and a proprietary program developed in C++ to process the signal. It is shown that the proposed device can reach resolutions of up to 250 000 in 5500 Âμs, and can reach resolutions of 15 000, with as few as 50 ions, in 3500 Âμs.

One of the greatest problems facing modern physics is the apparent asymmetry between matter and antimatter. While the standard model of particle physics predicts that equal amounts of matter and antimatter were produced following the Big Bang, astronomical observations have revealed that our universe contains little or no primordial antimatter. Precision measurements of cold, trapped antiparticles can be used to probe fundamental symmetries, and may shed light on why antimatter is so scarce in our universe. The ALPHA experiment at the CERN Antiproton Decelerator studies magnetically trapped antihydrogen atoms, produced by slowly merging cold plasmas of positrons and antiprotons. The precision spectroscopy of antihydrogen has already provided unique, high-resolution tests of CPT invariance and theories of new physics beyond the standard model. During 2018, the ALPHA experiment was expanded with the addition of ALPHA-g, a vertical atom trap that is intended to make the first direct measurements of antimatter gravitation. The efficient transport of positron and antiproton plasmas into the ALPHA-g experiment will be essential to trapping large numbers of antihydrogen atoms. However, the transfer of low energy (< 100 eV) charged particles between separate traps with strong magnetic fields is challenging for a variety of reasons. This thesis describes the design and commissioning of charged particle beamlines for the upgraded ALPHA experiment, and the methods that were used to overcome these challenges. In this thesis, we first describe the development of a novel magnetic beamline for the ALPHA experiment. Semi-analytical and numerical models are used to characterise the dynamics of positron and antiproton bunches within this beamline. Next, we describe the implementation of the ALPHA-g beamlines at CERN during 2018. We review the specifications of the beamline magnets, and describe the control system used to manage their operation. Finally, a range of diagnostic tools are developed to experimentally measure the properties of actual positron and antiproton bunches. We combine data from a range of sources to evaluate the performance of the beamline, and show that large numbers of positrons and antiprotons can already be delivered to the ALPHA-g experiment. In summary, the work presented in this thesis is critical to a future 1% measurement of antimatter gravitation, as well as continued precision measurements of antihydrogen atoms.

Instrumentation of higher order modes (HOMs) excited in accelerating cavities for beam phase and position inference provides a noninvasive and economical beam diagnostic. The principles and techniques for this purpose are investigated for TESLA (TeV Energy Superconducting Linear Accelerator) cavities at the injector part of the newly built European XFEL and at FLASH, two free electron laser facilities based on the TESLA technology. I have designed and instrumented unconventional beam phase monitors based on monopole modes in TESLA cavities and demonstrated a routine resolution of 0.1 degrees with a broadband setup. The best resolution achieved with this system is 0.03 degrees. The resolution is largely limited by the signal power. In order to aid the monitor design and study its performance, I have employed a coupled circuit model which indicates that the resolution can be further improved by optimizing the SNR (signal to noise ratio) and sampling frequency. This is the first type of monitor that is able to probe online the beam phase directly w.r.t. the accelerating field in individual accelerating cavities. The system can be used for long term RF drifts monitoring and also be used to decouple the phase jitter and drift sources in the injector part of a linac. Therefore the system can provide valuable information for the low level RF system. Beam position monitoring based on dipole modes in TESLA cavities at FLASH was demonstrated for the first time to work stably over several months with below 5 micrometers resolution. The improvement is attributed to a focused campaign on various signal and analysis techniques. These techniques can be transferred with little effort to the similar system, now under design for the European XFEL. As a preparation for the beam position monitor for the third harmonic cavities at the E-XFEL, I have measured and characterized the HOM spectra for single and coupled cavities. In particular there existed no such measurements for eight coupled cavities. These measurements pave the way for the instrumentation of 3.9 GHz cavities and show that the modes are well damped to the required limit.