First Light Fusion (FLF) are attempting to harness fusion energy through hypersonic impact
of targets containing voids fi lled with fusion fuel. They wish to diagnose the conditions within
these voids. Development of novel methods to achieve this goal was the motivation for this
PhD project. Possible probes identifi ed were particle beams and X-rays generated by high
power lasers such as the Cerberus laser at Imperial College and X-pinch produced X-rays.
To predict the time of impact and synchronise a diagnostic probe by creating and sending
a trigger in advance, a sensor known as a Faraday gate was used, which detects projectiles
using electromagnetic induction. Experimental work on Faraday gates showed a linear relation
between projectile velocity and output voltage and that gates were sensitive to projectiles with
velocities ranging between a few ms^-1 and several kms^-1. Preliminary work commenced on
a theoretical model to predict projectile velocity from the voltage induced within a Faraday
gate. Tests on the validity of the model initially showed good agreement.
Source sizes from Cerberus-generated X-rays were measured to be between 10 and 100 um
for foil targets. Source sizes from 5 um diameter carbon fibre were found to be <5 um but
results were limited by low flux. X-pinch source sizes were found to be between 10 and 50 um
and by manipulating the detector, smaller sources <10 um were measured. The average lower
sizes and variability found for X-pinch sources means they are the preferable X-ray source for
imaging FLF experiments. Source sizes for Cerberus-generated proton beams were measured
to be between 5 and 40 um and varied over the beam profi le. The peak beam energy of 10 MeV
limits penetration beyond a mm of FLF target, sufficient penetration would require protons
with energy >40 MeV and a PW laser system, compared with Cerberus which is currently
TW.
An experiment was devised to laser launch a foil flyer, to emulate an FLF projectile, which
was then probed using Cerberus. A Q-switched Nd:YAG laser system was installed to launch flyers. Initial results showed that the drive laser caused flyers to respond in a time similar to
the YAG laser pulse duration of 20 ns. Optical imaging with light from Cerberus showed flyer
velocities up to 1.2 kms^-1 and laser energy conversion efficiencies up to ~30%. Results for
varying probe times showed an almost linear relationship between flyer displacement and time,
concurring with previous experiments. A Cerberus-generated proton beam was used to image
a flyer and investigate any electromagnetic fields. A shot taken with the proton beam arriving
1.6 us after flyer launch showed no observable deflection behind the flyer. An upper limit on
the fields was determined to be an electric fi eld of ~9x10^5 Vm^-1 or a magnetic field of 38 mT.