arXiv subjects

Philip Bradford

Publications and source records attributed to Philip Bradford.

5 recordsLinked to original sources

arXiv2024

Currents from relativistic laser-plasma interaction as novel metrology for system stability of high-repetition-rate laser secondary sources

This work shows for the first time experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser plasma interaction for laser driven secondary sources. Such currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons. Therefore, return currents can be used as a metrological online tool in the optimization of many laser-driven secondary sources and for diagnosing their stability. We demonstrate the destruction free measurement of return currents at the example of a tape target system irradiated by the 1 PW VEGA3 laser at CLPU at its maximum capabilities for laser-driven ion acceleration. Such endeavour paves the ground for feedback systems that operate at the high-repetition-rate of PW-class laser systems.

physics.plasm-ph↗

arXiv2023

High-repetition-rate source of nanosecond duration kA-current pulses driven by relativistic laser pulses

We report the first high-repetition rate generation and simultaneous characterization of nanosecond-scale return currents of kA-magnitude issued by the polarization of a target irradiated with a PW-class high-repetition-rate Ti:Sa laser system at relativistic intensities. We present experimental results obtained with the VEGA-3 laser at intensities from 5e18 - 1.3e20 W/cm2. A non-invasive inductive return-current monitor is adopted to measure the derivative of return-currents on the order of kA/ns and analysis methodology is developed to derive return-currents. We compare the current for copper, aluminium and Kapton targets at different laser energies. The data shows the stable production of current peaks and clear prospects for the tailoring of the pulse shape, promising for future applications in high energy density science, e.g. electromagnetic interference stress tests, high-voltage pulse response measurements, and charged particle beam lensing. We compare the target discharge of the order of hundreds of nC with theoretical predictions and a good agreement is found.

physics.plasm-ph↗

arXiv2023

Measurement of magnetic cavitation driven by heat flow in a plasma

We describe the direct measurement of the expulsion of a magnetic field from a plasma driven by heat flow. Using a laser to heat a column of gas within an applied magnetic field, we isolate Nernst advection and show how it changes the field over a nanosecond timescale. Reconstruction of the magnetic field map from proton radiographs demonstrates that the field is advected by heat flow in advance of the plasma expansion. This changes the dynamics of high energy density plasmas, in which heat flows and fields are strongly coupled, and may disrupt magnetised inertial confinement fusion schemes.

physics.plasm-ph↗

arXiv2020

Electromagnetic pulse emission from target holders during short-pulse laser interactions

For the first time, a global model of electromagnetic pulse (EMP) emission connects charge separation in the laser target to quantitative measurements of the electromagnetic field. We present a frequency-domain dipole antenna model which predicts the quantity of charge accumulated in a laser target as well as the EMP amplitude and frequency. The model is validated against measurements from several high-intensity laser facilities, providing insight into target physics and informing the design of next-generation ultra-intense laser facilities. EMP amplitude is proportional to the total charge accumulated on the target, but we demonstrate that it is not directly affected by target charging time (and therefore the laser pulse duration) provided the charging time is shorter than the antenna characteristic time. We propose two independent methods for estimating the charging time based on the laser pulse duration. We also investigate the impact of target holder geometry on EMPs using cylindrical, conical and helical holders.

physics.plasm-ph↗

arXiv2018

THz pulses over 50 millijoules generated from relativistic picosecond laser-plasma interactions

Ultrahigh-power terahertz (THz) radiation sources are essential for many applications, such as nonlinear THz physics, THz-wave based compact accelerators, etc. However, until now none of THz sources reported, whether based upon large-scale accelerators or high power lasers, have produced THz pulses with energies above the millijoule (mJ) barrier. Here we report on the efficient generation of low-frequency (<3 THz) THz pulses with unprecedentedly high energies over 50 mJ. The THz radiation is produced by coherent transition radiation of a picosecond laser-accelerated ultra-bright bunch of relativistic electrons from a solid target. Such high energy THz pulses can not only trigger various nonlinear dynamics in matter, but also open up a new research field of relativistic THz optics.

physics.plasm-ph↗