Ultra low-emittance electron beams are required for the next generation of electron-positron colliders (eg. CLIC) and X-ray light sources (eg. NLS). The tolerances on the beam size, orbit and stability are two to three orders of magnitude greater than at current facilities. For example, at CLIC the beams will be roughly 1 nanometre high and they must be stabilised at the sub nanometre level at the interaction point in order to achieve the high luminosity required for Higgs boson and supersymmetry physics. Similar demands must be met to achieve peak brilliance at X-ray free electron laser (XFEL) light sources. Because of the bunch structure of such accelerators a feedback system for beam orbit stabilisation must operate on the 1-100 nanosecond timescale, which is extremely challenging. The Feedback on Nanosecond Timescales (FONT) project has been supported (by PPARC and STFC) to develop low-latency feedback prototypes for this purpose. The prototypes have been tested in beamlines at SLAC and KEK and feedback latencies as low as 23ns and 132ns have been demonstrated with all-analogue, and digital, systems respectively. We now propose to extend this technology to the development of a feed-forward system for correction of longitudinal phase instabilities in the CLIC drive beam. Such instabilities present a potential 'show-stopper' for the CLIC approach of decelerating a low-energy, high-current drive beam to provide high-gradient acceleration to a high-energy, low-current main beam. Therefore, development of an appropriate correction system has been assigned a high priority in the CLIC R&D programme for the next 5 years, leading towards a technical design report in 2016. CERN is explicitly supporting the FONT group at the John Adams Institute (JAI)/ Oxford to work on this system as a key part of the UK/CERN R&D programme on CLIC. Conceptually many of the CLIC feed-forward system demands are similar to those of the FONT feedback prototypes: low latency, high bandwidth and high drive power over short timescales (hundreds of ns). However, the design parameters call for a dynamic range of +-375 urad kick to the 2.5 GeV drive beam, with 10ns bandwidth, and a pulse length of 240ns. This presents a major challenge for the drive amplifier system. The current CLIC drive beam feed-forward system outline design (subject to revision) will require around 800 amplifiers, with a total peak power of 200 MW, and an estimated system cost of around £60M. This presents a considerable opportunity for an industrial company to participate in the advanced engineering required for design for manufacture, and the resulting business. The student will work with the JAI/Oxford FONT group to develop radio frequency (RF) components for the feed-forward system. We propose to design and fabricate prototype amplifier components. Initial component design will be done in JAI/Oxford. Production design and fabrication will be done by TMD. Prototypes will be bench tested in Oxford, and shipped to CERN for installation in the CTF3 beamline for subsequent operations with the electron beam. The student will work with groups that have international profiles in this area. The JAI/Oxford group has developed RF devices for the FONT system tests at SLAC and KEK. These are world-leading low-latency beam feedback systems. TMD has world-class manufacturing capability in high-power RF devices and considerable experience with particle physics accelerator projects. The project team has a demonstrated track record in this area: JAI/Oxford and TMD collaborated between 2004 and 2008 (via a CASE studentship project) on the high-power drive amplifier for the FONT4 feedback system at KEK. The team will provide many opportunities, options and flexibility to pursue development of the hardware and general training in RF design. This is an extremely exciting and challenging project that is vital for the future development of high-current drive-beam accelerators.

The 'trapped ion clock with enhanced reliability' project (TICKER) brings together world leading expertise in metrological-grade ion trap development, ultrastable room-temperature cavity-stabilised lasers, and laser source development to deliver unprecedented performance in a field-deployed state-of-the-art optical clock. Optical atomic clocks (OACs) have made extraordinary improvements over the last few decades and represent the pinnacle of precision measurement technology. The extreme accuracy of OACs enables exciting new opportunities for both fundamental physics and technology from detecting dark matter, relativistic geodesy, and improving satellite navigation accuracy. However, the science and technology impact from the current generation optical atomic clocks has been limited for the wider technology and industry base as they are fragile and complex laboratory-sized systems operated in well-controlled environments by skilled scientists. These limitations mean that only a handful of operational examples exist worldwide, restricted to National Metrology Institutes (NMIs) such as NPL. To unlock the transformative potential from OACs they must become simpler and more robust. This cannot be achieved by simply shrinking a laboratory clock; new approaches and technologies are called for. We will develop the technologies that bypass these constraints and allow the creation of practical optical clocks, focusing on the singly ionised strontium-88 (Sr+) system as the most viable candidate. Within this project we will develop metrological-grade ion traps that are manufacturable and robust enough to operate in less-well-controlled remote locations and mobile platforms, a transportable environmentally insensitive optical reference cavity, and a 422-nm DFB laser as a low-power and robust source for laser-cooling the ion. Atomic clocks based on trapped ions are inherently simpler and require lower power to operate than the other major class of high-performance clocks - neutral atom lattice clocks. Ion clocks also have relaxed requirements of the clock-laser, making them more suitable for noisy environments. Trapping and laser cooling a single ion requires less than a watt of RF power and less than a milliwatt of optical power; the electrode structure and vacuum system can be miniaturised and ruggedised using established techniques aided by finite element analysis. The Sr+ system is particularly attractive because the clock transition can be measured in a way that provides low sensitivity of the centre frequency to the environment. Additionally, the transitions in its simple energy level structure can mostly be addressed with commodity lasers. One exception is the 422-nm laser-cooling transition. Currently this light must be produced from either a vibration sensitive ECDL laser or inefficient frequency doubling from an infrared DFB laser. A 422-nm DFB laser would enable a great improvement in the SWAP and robustness. NPL's patented cubic cavity design is the leading transportable and force insensitive design and will be adapted to suit the requirements of field-deployable atomic clocks. Reducing the volume of the cubic cavity spacer from 125 cc to 27 cc still provides good frequency stability while greatly reducing the required environmental shielding. Moreover, we have invented a novel technique that exploits material anisotropy to further reduce environmental impact, which will extend the temperature-insensitivity alongside the force- and vibration-insensitive design. Together, with the addition of an optical frequency comb (being developed at pace under many other programs, to the requirements of optical clocks) we address the major challenges that are preventing optical clocks from field deployed applications.

A waveguide can be used to compress frequency-modulated pulses. Consider compression of a quasi-monochromatic pulse with frequency monatonically varying in time from one frequency (w1) to another frequency (w2). This pulse is then propagated down a dispersive medium in which the group velocity of the wave is a function of frequency only. If the wave group velocity in the dispersive medium is an increasing function of frequency, vgr(w2) > vgr(w1), then the tail of the pulse will overtake its leading edge, resulting in pulse shortening and a corresponding growth in the amplitude if the losses are sufficiently low. Compression experiments were first carried out using a smooth metal waveguide and were found attractive because of its capability of handling high power. However a serious drawback of a smooth waveguide as a powerful compressor is its operation very close to the cut-off. In optimum cases, the frequency at the beginning of an input pulse should be only 0.5-1% above the cut-off frequency. If one uses such a compressor at the output of a powerful amplifier, then the low-frequency part of the amplification band will be reflected back to the amplifier resulting in its possible parasitic self-oscillation (RF isolation using unidirectional elements is impossible at very high power). We propose to design and construct a waveguide with a helical corrugation of its inner surface as the frequency dispersive medium, to couple a pair of circularly polarized partial modes of the smooth waveguide having significantly different group velocities. Pulse compression using a 3-fold helically corrugated waveguide using an optimised frequency swept pulse generated by a state-of-the-art programmable Arbitary waveform generator and microwave sweeper will be studied, with the predictions of theory compared to experiment. We propose also to design, build and investigate the use of a larger diameter 5-fold helically corrugated waveguide as the frequency dispersive medium to compress MW frequency swept pulses generated by a gyrotron travelling wave amplifier. The advantage of using a 5-fold helical structure as compared to a 3-fold helical waveguide is that it requires the use of a higher order mode and hence the diameter of the compressor is increased which means that higher peak power radiation can be propagated down the compressor before the electric fields becomes excessively large resulting in RF breakdown. A favourable wave dispersion can be synthesized for the higher-order modes (near cut-off TE2,2 mode which couples to a counter-rotating TE3,1 mode) excited in a 5-fold helical compressor resulting in an increase of the helical waveguide diameter by a factor of 1.5-2 (without significant overlapping of the coupling bands) and correspondingly in an enhancement of its RF breakdown strength. Unique high power (multi-MW), short pulse (~1ns) radiation required in a number of applications will be generated.

This proposal will transfer knowledge, expertise and experience gained under PPA/F/S/2001/00656, 'Gyro-Amplifiers for high-field-gradient accelerators and industrial applications' to industry. This activity will build upon existing skills in industry which are currently underutilised due to a lack of the necessary expertise and experience. A relatively small investment of time and assistance is required to allow industry personnel to full exploit their capabilities. Strathclyde University is uniquely placed to provide this assistance as a leading research team in the field with an excellent track record both in research and teaching. Our experience in teaching postgraduate candidates from industry as well as academic backgrounds will greatly facilitate the knowledge transfer activities, while our research background provides us with a pre-existing code suite read for industry use. We also have well developed remote teaching experience using video conferencing. This allows us to efficiently update industry expertise and modelling capability to full exploit the most recent advances in simulation code development. We will verify the transfer of design capability to industry with the co-design of a Gyro-TWA interaction region for operation in the Ka-band frequency range. This design will then be validated by the construction and test of a Ka-band Gyro-TWA helically corrugated interaction region. The aim is to demonstrate world leading UK capability in a new atmospheric window. This capability is of interest for several defence applications as well as for use in high resolution RaDAR and space RaDAR. The new capability can also be applied in the areas of future high gradient particle accelerator structures and plasma diagnostics. We will build increased information transfer capability and develop computer simulation model transfer paths between research providers and industrial partners facilitating future co-operative ventures and reducing the time and costs associated with future knowledge transfer activities.

The principle aim is the investigation of the pseudospark discharge resulting in the generation of electron beam pulses with the highest simultaneous current density and brightness of any known type of electron beam source. Having constructed and operated the first coherent radiation source based on a pseudospark discharge, we have recently measured a high current density (1.5kAcm [-2]) electron beam of brightness 10[11] to 10[12] Am[-2]rad[-2], the proposed programme aims to enhance our understanding of the physics the pseudospark discharge as the size of this plasma cathode is reduced and to produce and transport for the first time small (mm and sub-mm) diameter electron pulses of exceptionally current density and beam quality. The power that can be generated from free electron radiation sources in the hundreds of GHz to THz frequency range has been limited by the fact that as the frequency is increased, the diameter of the interaction has to be reduced in order to prevent the maser becoming overmoded resulting in a loss of the temporal and spatial coherence of the output radiation. The reduction in the size of the interaction region makes it increasingly difficult (if not impossible) using conventional cathodes to focus and form high current density, high quality electron beams through the small size interaction region of a high frequency maser. It is our intention to combine the collective knowledge and expertise of three leading university research groups in the fields of 1) pseudospark physics, 2) computational modelling of millimetre wave sources and design of THz components and 3) advanced millimetre wave manufacturing technologies, to investigate the use of pseudospark sourced electron beam pulses to generate high power, high frequency coherent electromagnetic radiation via the klystron (200GHz) and backward wave (390GHz up to 1THz) instability.