Laboratory Astrophysics

Astrophysicists and plasma physicists are using different approaches to understanding some of the mysterious behaviour of the Universe. Astronomers use Earth- and space- bound observatories to study spectacular phenomena from the solar wind to supernovae, remnants, radiative jets, and gamma-ray bursts, whilst theorists use computers to make sense of the observations. The concepts used to understand laser- plasmas such as hydrodynamics, relativistic plasmas, radiation flow, atomic physics, opacity, and equation of state are also applied to improve our understanding of stars and nebulae.

Powerful lasers can produce high energy density plasmas and drive strong, radiative, or collisionless shocks. With careful design, and the application of appropriate theory, these laboratory plasmas can be linked to astronomical plasma such as shocks and jets associated with supernova remnants and protostellar stars. The advantage of an experiment is that it can be repeated and the plasma probed until the physics and interactions are well understood. Will laser-plasma experiments open up a new way to explore our galaxy in the laboratory on Earth? Current experiments will help us find out.

Illustration of the plasma jet created by the Vulcan laser.

In a recent experiment using the Vulcan laser, plasma jets were created through the collision of two laser-produced plasmas. The targets were simple; two thin foils are placed at an angle of 140° to each other to form a v-shaped foil. Vulcan deposits energy in the foil sufficient for them to explode, and plasmas from the rear face of these foils collide. Conservation of momentum drives plasma jets at speeds of ~ 300 km/s. By carefully choosing the foil thickness and material to suit the laser conditions, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with protostellar stars. Results from these experiments allow the study the effect of an ambient gas on jet propagation. Nominally identical experiments were conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow.