Time: 9:00 a.m., June 15,2017(Thursday)

Venue: Meeting Room at the 3rd Floor, Building No.7

Biograpgy: 

　　Thomas Claysonis a researcher at the Plasma Physics group at Imperial College London UK, currently in the final year of his PhD under the supervision of Dr. Francisco Suzuki-Vidal and Prof. Sergey Lebedev. His research is within the field of High-Energy Density Physics (HEDP) and his currently studying radiative effects on strong shocks in plasmas. As part of his research he has: 

　　² Played a pivotal role in experiments on counter-propagating radiative shocks on the Orion Laser Facility, UK. 

　　² Worked as part of an international team performing experiments on the Prague Asterix Laser System, Czech Republic. 

　　² Run experiments to study radiative shocks in gases on the MAGPIE facility (Mega Ampere Generatorfor Plasma Implosion Experiments) at Imperial College London. 

　　² Published several papers in HEDP (as 1st author) and PRL journal. 

　　² Presented research at several conferences including HEDLA 2016 and APS 2016 in the USA, MEC2017 in France and ICHED 2017 in Japan. 

Abstract: 

　　We present results from experiments to produce collisional counter-propagating radiative shocks, allowing for the study of reverse shocks and radiative effects. The Orion high-power laser facility (8 beams delivering a total of 3.2 kJ in 1 ns, achieving intensities of ~6x10¹⁴ W/cm²), at AWE Aldermaston in the UK, was used to ablate two solid plastic piston on the sides of a gas cell, filled with noble gases between 0.1 and 1.0 bar. This drove two counter-propagating radiative shocks, at velocities of 80±10 km/s, into the gas cell which collided and formed a reverse shock. Before colliding, these shocks experienced strong radiative effects resulting in the formation of a steady radiative precursor and significant radiative cooling allowing for post-shock compressions estimated to be of the order of×25±2.  

　　The interaction of two identical radiative shocks, as presented in these experiments, is a model for the reflection of both hydrodynamics and radiation off a perfectly reflective surface, providing a unique platform for numerical validation and laboratory astrophysical models. While the collision of two independent shocks is a rare astrophysical event, the formation of reverse shocks, which bare many similarities with these experiments, are common place. These can occur, for instance, when supernovae remnants interact with dense molecular clouds, within the bow shock of jets launched from young stars, in stellar accretion columns on young stars or in cataclysmic variable systems.  

　　 X-ray backlighting and optical self-emission streak imaging were used to image the shock front and collision dynamics. Meanwhile multi-frame and streaked interferometry were used to simultaneously study the radiative precursor. Results show good agreement with both 1D and 2D numerical simulations. These experiments compared the shock and collision dynamics in different gases (Ne, Ar, Kr, Xe), while maintaining a constant mass density to ensure similar shock hydrodynamics. Shocks in high atomic number gases exhibited enhanced radiative effects, such as a larger radiative precursor, while shocks in lighter gases exhibited features suggesting the formation of hydrodynamic instabilities.