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The pBR322 plasmid DNA was irradiated with 35 MeV electrons, 228 MeV protons and 300 kVp X-rays to quantify DNA damage and make comparisons of DNA damage between radiation modalities. Plasmid was irradiated in a medium containing hydroxyl radical scavengers in varying concentrations. This altered the amount of indirect hydroxyl-mediated DNA damage, to create an environment that is more closely associated with a biological cell. We show that increasing hydroxyl scavenger concentration significantly reduced post-irradiation DNA damage to pBR322 plasmid DNA consistently and equally with three radiation modalities. At low scavenging capacities, irradiation with both 35 MeV electrons and 228 MeV protons resulted in increased DNA damage per dose compared with 300 kVp X-rays. We quantify both single-strand break (SSB) and double-strand break (DSB) induction between the modalities as a ratio of yields relative to X-rays, referred to as relative biological effectiveness (RBE). RBESSB values of 1.16 ± 0.15 and 1.18 ± 0.08 were calculated for protons and electrons, respectively, in a low hydroxyl scavenging environment containing 1 mM Tris–HCl for SSB induction. In higher hydroxyl scavenging capacity environments (above 1.1 × 106 s−1), no significant differences in DNA damage induction were found between radiation modalities when using SSB induction as a measure of RBE. Considering DSB induction, significant differences were only found between X-rays and 35 MeV electrons, with an RBEDSB of 1.72 ± 0.91 for 35 MeV electrons, indicating that electrons result in significantly more SSBs and DSBs per unit of dose than 300 kVp X-rays.

Although accelerator technology has matured sufficiently, state-of-the-art x-ray linacs for radiotherapy and cargo-scanning capture merely 30%–50% of the electrons from a thermionic cathode, requiring a higher cathode current and leaving uncaptured electrons to cause problems such as back bombardment on the cathode leading to a shortening of cathode life. Any solution to increase capture should be effective, simple, reliable, compact, and low cost in order to be adopted by the industry. To address this, we present the design of a 6 MeV high capture efficiency S-band electron linac that captures 90% of the initial dc beam. This linac does not require any extra parts that would increase the cost as the high efficiency is achieved via a low-field amplitude in the first bunching cell to decrease the number of back-streaming electrons, to velocity bunch the electron beam, and recapture back-streaming electrons. Under the low field amplitude, any electrons launched at decelerating phases travel backward with low speeds, thus most of them can catch the next rf cycle, and get reaccelerated/recaptured. As the electron speed is low, the cell length is also shorter than existing linacs. Such a short field is achieved by the use of asymmetric cells with differential coupling to the side-coupled cells. Our novel design has implications for all commercial high current thermionic gun linacs for increasing beam current and increasing cathode lifetime.

This paper describes the design of a recirculating linac as a driver for the suite of seeded free-electron lasers (FELs) proposed in the UK New Light Source (NLS) project. The choice of superconducting technology for NLS is required in order to deliver bunches at high repetition rates up to 1 MHz. This raises the question of whether a shorter linac in recirculating mode can deliver the beam quality required for seeded FELs. To design such a facility, careful layout choices and optimizations must be made to ensure emittance growth is minimized. Effects leading to emittance dilution include chromatic transport terms, incoherent and coherent synchrotron radiation. The design outlined here is based on a modular philosophy to separate beam injection and extraction from a three stage compression scheme. The design uses many novel design concepts and optimizations to deliver the necessary high peak currents while preserving beam quality for seeded FELs. Start-to-end simulations including the FELs show that the necessary pulse coherence and output power can be provided from the beam thus generated.

This thesis describes various design options for beam spreaders to allow the inclusion of multiple beam lines as an integral part of X-ray Free Electron Laser (FEL) facilities. The accelerator configuration driving an X-ray FEL follows a linear geometry so as to maintain the ultra-bright properties of the electron beam generated at the injector. Bending the beam is typically restricted only to the bunch compressor chicane in order to avoid an increase in transverse emittance due to the emission of coherent synchrotron radiation. Unlike storage ring based light sources, X-ray FELs serve either one experiment at a time or a number of experiments (quasi-simultaneously) by splitting the radiation from a single FEL line; the radiation pulse repetition rate is set by the injector and the technology used for acceleration. Multiple beam lines provide flexibility in experiments and provide access for a greater number of users. However, in providing multiple beam lines, bending the electron beam is unavoidable and its high quality (i.e. low emittance, low energy spread and high peak current) must be ensured by very careful design of the beam spreader. Two main aspects of the beam spreader design (namely, the options for switching and the lattice design) have been studied and are presented here in detail. Two lattice design concepts, one based on a Triple Bend Achromat magnetic lattice and the other based on a Double Bend Achromat magnetic lattice, are discussed. The relative merits, advantages and disadvantages of these design options are detailed, including mitigation of the effects from coherent synchrotron radiation which include increases in both the beam emittance and energy spread. Experimental studies related to the Triple Bend Achromat arc on the ALICE facility are used to recommend beam diagnostics and instrumentation in different spreader design concepts. The results presented in this thesis will be central to the design of an optimised beam spreader for any future UK X-FEL facility.

This thesis describes various design options for beam spreaders to allow the inclusion of multiple beam lines as an integral part of X-ray Free Electron Laser (FEL) facilities. The accelerator configuration driving an X-ray FEL follows a linear geometry so as to maintain the ultra-bright properties of the electron beam generated at the injector. Bending the beam is typically restricted only to the bunch compressor chicane in order to avoid an increase in transverse emittance due to the emission of coherent synchrotron radiation. Unlike storage ring based light sources, X-ray FELs serve either one experiment at a time or a number of experiments (quasi-simultaneously) by splitting the radiation from a single FEL line; the radiation pulse repetition rate is set by the injector and the technology used for acceleration. Multiple beam lines provide flexibility in experiments and provide access for a greater number of users. However, in providing multiple beam lines, bending the electron beam is unavoidable and its high quality (i.e. low emittance, low energy spread and high peak current) must be ensured by very careful design of the beam spreader. Two main aspects of the beam spreader design (namely, the options for switching and the lattice design) have been studied and are presented here in detail. Two lattice design concepts, one based on a Triple Bend Achromat magnetic lattice and the other based on a Double Bend Achromat magnetic lattice, are discussed. The relative merits, advantages and disadvantages of these design options are detailed, including mitigation of the effects from coherent synchrotron radiation which include increases in both the beam emittance and energy spread. Experimental studies related to the Triple Bend Achromat arc on the ALICE facility are used to recommend beam diagnostics and instrumentation in different spreader design concepts. The results presented in this thesis will be central to the design of an optimised beam spreader for any future UK X-FEL facility.

Although accelerator technology has matured sufficiently, state-of-the-art X-ray linacs for radiotherapy and cargo-scanning capture merely 30-50% of the electrons from a thermionic cathode, requiring a higher cathode current and leaving uncaptured electrons to cause problems due to back bombardment, shortening of cathode life, etc. Any solution to increase capture should be effective, simple, reliable, compact, and low cost in order to be adopted by industry. To address this, we present the design of a 6 MeV high capture efficiency S-band electron linac that captures 90% of the initial DC beam. This linac does not require any extra parts that would increase the cost as the high efficiency is achieved via a low-field-amplitude in the first bunching cell to decrease the number of backstreaming electrons, to velocity bunch the electron beam, and recapture backstreaming electrons. Under the low field amplitude, any electrons launched at decelerating phases travel backward with low speeds, thus most of them can catch the next RF cycle, and get re-accelerated/recaptured. As the electron speed is low, the cell length is also shorter than existing linacs. Such a short field is achieved by the use of asymmetric cells with differential coupling to the side-coupled cells. Our novel design has implications for all commercial high current thermionic gun linacs for increasing beam current and increasing cathode lifetime.

Energy-recovery linacs (ERLs) have been emphasised by the recent (2020) update of the European Strategy for Particle Physics as one of the most promising technologies for the accelerator base of future high-energy physics. The current paper has been written as a base document to support and specify details of the recently published European roadmap for the development of energy-recovery linacs. The paper summarises the previous achievements on ERLs and the status of the field and its basic technology items. The main possible future contributions and applications of ERLs to particle and nuclear physics as well as industrial developments are presented. The paper includes a vision for the further future, beyond 2030, as well as a comparative data base for the main existing and forthcoming ERL facilities. A series of continuous innovations, such as on intense electron sources or high-quality superconducting cavity technology, will massively contribute to the development of accelerator physics at large. Industrial applications are potentially revolutionary and may carry the development of ERLs much further, establishing another shining example of the impact of particle physics on society and its technical foundation with a special view on sustaining nature.

In this brief overview we will reflect on the process of the design of the linear collider (LC) final focus (FF) optics, and will also describe the theoretical and experimental efforts on design and practical realisation of a prototype of the LC FF optics implemented in the ATF2 facility at KEK, Japan, presently being commissioned and operated.

The Energy Recovery Linac (ERL) paradigm offers the promise to generate intense electron beams of superior quality with extremely small six-dimensional phase space for many applications in the physical sciences, materials science, chemistry, health, information technology and security. Helmholtz-Zentrum Berlin started in 2010 an intensive R\\&D programme to address the challenges related to the ERL as driver for future light sources by setting up the bERLinPro (Berlin ERL Project) ERL with 50 MeV beam energy and high average current. The project is close to reach its major milestone in 2020, acceleration and recovery of a high brightness electron beam. The goal of bERLinProCamp 2019 was to discuss scientific opportunities for bERLinPro 2020+. bERLinProCamp 2019 was held on Tue, 17.09.2019 at Helmholtz-Zentrum Berlin, Berlin, Germany. This paper summarizes the main themes and output of the workshop.