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Summary form only given. A range of pulsed microwave sources, under investigation at the University of Strathclyde, require the generation of multi-kilo-ampere, relativistic, electron beams1,2. These may be mono-energetic or varying in energy throughout the duration of the pulse (dependant on the source in question), however all require a driving supply capable of dealing with potentially rapid changes in the accelerating diode impedance.

Summary form only given. The auroral density cavity (a region of partial plasma depletion situated at an altitude of around 3200km at the Earth's pole) has been studied to have a background plasma density ∼106m−3, and plasma frequency ∼9kHz. Auroral Kilometric Radiation (AKR) is produced when particles descend through this region and are magnetically compressed as they approach the Earth's magnetosphere and through conservation of the magnetic moment, a horseshoe shaped velocity distribution with a large spread in pitch factor is formed as the particles sacrifice axial for rotational momentum. Satellites have observed that the AKR is emitted and extends down to the local electron cyclotron frequency with peaks in frequency at ∼300kHz, powers ∼109W and with emission efficiency ∼1% of the total precipitated electron kinetic energy. Theory has shown this type of distribution to be unstable to cyclotron emissions in the X-mode [1].

Summary form only given. Microwave pulse compression has applications in radar technology and plasma diagnostics. The pulse compressor requires a dispersion curve with a monotonic group velocity and low losses in a reasonable wide frequency band. It can be achieved by the helically corrugated waveguide (HCW) [1–3] with both axial and azimuthal periodicity that couples modes in the circular waveguide to generate new operating eigen waves. The HCW has successfully been used in the gyro-TWA [4,5], gyro-BWO [6,7] and pulse compressor[8–10]. Following the success of a pulse compressor using a 3-fold HCW, the dispersion characteristic of the 5-fold HCW has been analytically, numericall y studied and measured. The compression factor of the compressor was also measured.

Summary form only given. During the transit of an electron beam through a background plasma, instabilities can occur that may result in highly dynamic behaviour. This behaviour may be important in fast-ignition inertial confinement fusion. In one method of this type of fusion, a deuterium-tritium pellet is compressed by lasers to very high densities. An ignition laser pulse then interacts with a directional gold cone to produce a highly relativistic electron beam that streams into the compressed pellet. This beam-plasma interaction can result in the two-stream instability. The dynamics associated with this instability is investigated in this work. It has been proposed that this instability can resonantly decay into ion-acoustic waves which can then be damped by the ion collisions to dissipate the beam energy, heating the fusion fuel1,2. To investigate this behaviour, computational simulations have been undertaken in the two-dimensional particle-in-cell (PiC) code XOOPIC. These simulations have investigated a lower energy, low density regime where a 50kV, 24A, rectilinear electron beam is injected into a waveguide bounded, magnetically confined, cylindrical plasma column of a density of 1.8×1016m−3. Using the parameters from this simulation, a low temperature, low density laboratory experiment is currently being designed to provide an experimental benchmark for the results predicted by the code. This will provide an enhanced confidence in the use of PiC and other numerical methods to predict the dynamics of fusion relevant conditions.

Summary form only given. One of the on-going research programs, at the University of Strathclyde, involves the development of high-power, pulsed, Free-Electron Masers (FEMs) with the lasing cavity defined using periodic corrugations on the drift-tube walls1–4. These corrugations form 1D and 2D Bragg resonators, whose reflection bands determine the dominant resonance of the maser5. Proper selection of the FEM undulator magnetic field strength, allows for efficient extraction of energy from a mildly relativistic (400 – 500 keV) electron beam at the resonant frequency of the lasing cavity, leading to monochromatic output at power levels of several tens of megawatts and pulse durations of ∼150ns (determined primarily by the pulse duration of the driving power supply of ∼250ns).

Summary form only given. A key design process in the construction of a waveguide component is the cold-test stage, involving measuring the response of the component to radiation, propagating with a specific electromagnetic mode and a certain frequency, or range of frequencies. However, for components that require high order modes, such as resonant cavities used in high-power1, or high-harmonic gyrotrons, it can be challenging to generate the necessary mode. A scheme for co-harmonic generation of radiation through the cyclotron resonance maser instability has been proposed2,3, involving the generation of two harmonics of the cyclotron frequency, with the electromagnetic modes stimulated being the TE 2,2 and TE 4,3 .

Summary form only given. Electron cyclotron radio emissions, known as Auroral Kilometric Radiation (AKR) originate in the X-mode from regions of locally depleted plasma in the terrestrial polar magnetosphere. A laboratory experiment was constructed to study the emission mechanism of AKR scaled to microwave frequencies [1-2]. 3D PiC simulations of the experiment were conducted to study resonant energy transfer with nonazimuthally symmetric modes of the bounding radiation structure. These 3D simulations show the backward-wave resonance to be resilient to Doppler broadening of the beamwave coupling [3]. It would suggest that the auroral process may emit with backward-wave coupling giving a spectral downshift and thus avoiding the upper hybrid stopband [4].