Understanding how low energy electrons control the variability of the Earth's electron radiation belts

The electron radiation belts are regions of geomagnetically trapped electrons, surrounding the Earth, presenting hazards to operational satellites. On the timeframe of hours, both the energy and particle flux of the radiation belts can change by orders of magnitude. Variations in the high energy relativistic electron flux depend on transport, acceleration, loss processes, and importantly, on the lower energy seed (10s – 100s keV) population. Seed population electrons are supplied to the radiation belt region during geomagnetically active periods and can be accelerated to higher energies via a range of processes. Unlike the higher energy, $>$1 MeV electrons, the azimuthal drift of the seed population is strongly affected by the convection electric field. Using fourteen years of electron flux data from low Earth orbit (LEO) satellites, a statistical study was performed on the magnetic local time distribution of three seed population energies, across a range of activity levels, defined by the geomagnetic indices AE, AE*, Kp, the solar wind velocity, and V$_sw$B$_z$. During periods of high activity, dawn-dusk flux asymmetries of over an order of magnitude were observed for $>$30 and $>$100 keV electrons, due to increased flux in the dawn sector. For $>$300 keV electrons, magnetic local time asymmetries were also present, but arose primarily due to a decrease in the average dusk-side flux beyond L* $\sim$4.5. A novel method was developed that utilizes measurements from low altitude, polar orbiting POES and MetOp satellites to retrieve the seed population at a pitch angle of 90$^o$. The resulting dataset offers a high time resolution, across multiple magnetic local time planes, and was used to formulate event-specific low energy boundary conditions for the British Antarctic Survey Radiation Belt Model (BAS-RBM). This new low energy boundary condition from LEO data has a higher spatial and temporal resolution, and a broader L* coverage, than previous work. The impact of variations in the seed population on the 1 MeV flux level was explored using the 3-D BAS-RBM to solve a diffusion equation for the electron phase space density. For some periods, an enhancement in the seed population was vital to recreate observed 1 MeV flux enhancements. A series of idealised experiments with the 2-D BAS-RBM were performed which highlight a careful balance between losses and acceleration from chorus waves. Our results show that seed population enhancements alter this balance by increasing the phase space density gradient, and consequently, the rate of energy diffusion, allowing acceleration to surpass loss. Additionally, pre-existing energy gradients in the phase space density and the duration of chorus wave activity determine whether $>$500 keV electrons were enhanced due to local acceleration.Cambridge University Earth System Science Doctoral Training Partnership (ESS DTP), grant number NE/L002507/

A5_4 Water Under the Bridge

 This paper looks into Michael Faraday’s attempted experiment in 1832 to determine whether he could detect a current from the interaction of the water in the River Thames with the Earth’s magnetic field. The possibility of using such a current to power a 60W light bulb is then investigated. The paper finds that the current measured in the experiment is minimal to the degree that it would not have been detected and it would be implausible to power a light bulb from the effect

A5_7 Neutron activation of the Unity Node of the ISS

The paper describes the calculation of the annual radiation dose of an astronaut on the ISS from gamma rays created by solar neutron activation of the aluminium structure of the Unity Node. It is calculated that the annual dose is 2.32 x 10-5 mSv, and the solar neutron flux required to reach the maximum legal annual dose is 828 neutrons cm-3 s-1. The results show that the annual neutron activation gamma ray dose is very small compared to the legal limit (some six orders of magnitude smaller)

A5_8 A Great Punch Line

Leicester University has a prodigious history with its Karate Club and this paper investigates the total force transferred in a Karate punch and the mass limit needed for a person to be able to break wood with such a technique. The results show that the mass needed to overcome the Ultimate Tensile strength of wood is 104 kg

A5_1 Power of a Star in an Unreasonably Priced Car

The inaugural Formula E motor-racing championship features electric cars whose batteries are not currently capable of lasting an entire race, meaning drivers must change cars halfway through. This paper investigates the possibility of using solar panels to recharge the battery during the race; thereby ensuring only 1 car per driver is required. Whilst it is established that the car could support a sufficiently large solar array, the required area of 1920m2 is clearly too large to be of practical use

A5_5 Don’t go to the Dark Side!

This paper investigates the assumptions made in “A5_2 Living in the Dark” as to whether a satellite at the second Lagrangian point will be completely in the shadow of its host planet. The paper finds that while this assumption holds to some degree for satellites in orbit about Mercury and a hot Jupiter at Mercury’s orbital distance, a satellite at Earth’s L2 point would still receive a portion of its flux directly from the Sun

A5_6 Pyramid of Geezers

 An investigation is conducted into the maximum size of the popular challenge, the ‘human pyramid’. Under the assumption that the formation consists of people with perfect balance, the limitations upon the size therefore arise from the strength of the individuals. It is found that for a pyramid consisting of males of uniform mass, the maximum height is four tiers, potentially five if the individuals were marginally stronger than average. For a pyramid of men, women, and children, assembled with the highest mass on the base, the maximum achievable height was six tiers

A5_10 An Interstellar Mess Up?

The paper investigates the physical implications behind the recent film Interstellar, surrounding the tidal forces acting on the planets orbiting the Supermassive Black Hole. The paper determines the minimum radii for each system to approach the structure, and finds that Earth-like planets could exist within the system, with a planet of Earth density corresponding to a Black Hole mass of 8x107 M☉. It is also found that the crew would be able to traverse the event horizon without damage to the spacecraft

A5_2 Living in the Dark

A body placed at the second Lagrangian point of many host planets would not experience directly incident solar radiation; however, re-emissions from the host planet would impact the satellite. This paper looks into the time taken for the satellite to reach the temperature required for liquid water. Various host planets are considered and the radius of the satellite varied to examine the effect on the heating time. The paper finds that while a satellite around Earth would provide the longest habitable period, the time frame to reach a suitable temperature is the greatest. A satellite placed around a hot Jupiter would reach habitability the fastest

A5_3 Are the Boots a Lie?

An investigation is described regarding the spring constant of the material used to create the boots worn by the leading character in the game ‘Portal’. Within the game, the boots allow the character to fall from any height without injury. It is found that this is a possible feat using a spring constant of approximately 1 Nm-1 but the design must differ considerably from that depicted in the game