Streaming instabilities in converging geometry

We present an investigation into counter-streaming electron beams converging towards, and diverging from, a single point in two dimensions, leading to two-stream and current filamentation instabilities, which have radial and azimuthal density modulations, respectively. Using a semi-analytical approach and numerical simulations, we find no evidence for the two-stream instability in this geometry, but show that the system is unstable to the development of current filamentation

Controlled generation of ultra-short electron bunches using density modulation

Stimulated electron self-injection in the laser wakefield accelerator (LWFA) using density downramps is well known and regularly used to produce high energy electron bunches. The use of density gradients not only to stimulate injection but also control the properties of the injected electron bunch was recently presented by Tooley et al. [Phys. Rev. Lett. 119 , 044801 (2017)], in which the authors put forward a model for controlling the velocity of the back of the bubble and compared to 2D and 3D particle-in-cell (PIC) data. This model is discussed and used to identify suitable LWFA parameters for ultra-short injection and repeated injection of multiple bunches. Quasi-3D PIC data is used to demonstrate injection of multiple bunches well separated in energy

The effect of laser pulse evolution on down‑ramp injection in laser wakefield accelerators

Electron self-injection in laser wakefield accelerators (LWFAs) is an important determinator of electron beam parameters. Controllable and adjustable LWFA beams are essential for applications. Controlled injection by capturing sheath electrons can be achieved using plasma density down-ramps or bumps, which perturb the LWFA bubble phase velocity by varying the plasma frequency and by affecting relativistic self-focussing of the laser. We report on a comprehensive study, using particle-in-cell simulations, of the effect of laser pulse evolution on injection on density perturbations. We show how the LWFA can be optimised to make it suitable for use in a wide range of applications, in particular those requiring short duration, low slice-emittance and low energy spread, and high-charge electron bunches

Controlling the group velocity of an intense laser pulse using a pre-pulse

The accelerating structure of the laser wakefield accelerator (LWFA) is dynamic and highly sensitive to the local laser and plasma properties. It can expand and contract as it responds to the evolution of the laser and plasma fields. As a result, the position of, and environment within, the LWFA bubble are usually time dependent, which is not ideal for stable acceleration. Variations can have a negative impact on electron bunch properties, and are deleterious for ion channel lasers and plasma wigglers. We demonstrate how a laser pre-pulse improves the stability of the LWFA, and controls the evolution of the laser group and bubble velocity, which are important for determining LWFA dephasing and ultimately the electron bunch energy

Investigations into the volume plasma density grating waveplate

Volume density gratings produced by degenerate, counterpropagating laser pulses in plasma have several useful optical properties. Here we report on one of these in an investigation into creation of a transient plasma density grating that functions as a waveplate

Using a private 5G network to support the international broadcast of the coronation of HM King Charles III

Wireless cameras for news contribution feeds regularly use “bonded-cellular” devices, which connect to and split the encoded video across multiple public mobile network SIMs. However, in high demand density environments with large crowds, the public networks can quickly become saturated and unable to sustain the necessary bitrates to support high-definition video. To overcome this and provide uncontested wireless connectivity, the largest pop-up 5G standalone non-public (private) network of its type was deployed outside Buckingham Palace and along The Mall to Admiralty Arch to support news contributions for domestic and foreign broadcasters at the Coronation of HM King Charles III, without changing the contribution workflow. (This paper first appeared in the Proceedings of the 2024 NAB Broadcast Engineering and Information Technology Conference, and is reprinted with permission. https://nabpilot.org/beitc-proceedings/

Pop-up 5G standalone non-public networks (SNPNs) for live broadcast production

A portable, pop-up private standalone 5G network has been developed and deployed around the world in a series of successful proof-of-concepts for outside broadcast production in remote locations. The flexible software-defined radio (SDR) allows us to rapidly customise the network to the environment and requirements, with low-latency configurations and heavy uplink biasing in the bi-directional RF channel to support multiple wireless camera feeds. We used shared spectrum available in the n78 and upper n77 bands (3.3–4.2 GHz) in UK, Ireland, Kenya and New Zealand to deliver live-to-air footage. We explored the use of bonding multiple low Earth orbit (LEO) satellites and cellular backhaul, which allowed us to broadcast the Pitlochry Highland Games live from rural Scotland into the IBC 2022 show in Amsterdam. This paper will discuss the critical technical capabilities of the pop-up private 5G network and how broadcasters have rapidly deployed the technology to support historic and sporting events, including the final journey from Scotland of Queen Elizabeth II and the Danish parliamentary elections. We will also explore how to configure connectivity for optimum performance