Measurements of extended magnetic fields in laser-solid interaction

Magnetic fields generated from a laser-foil interaction are measured with high fidelity using a proton radiography scheme with x-ray fiducials. In contrast to prior findings under similar experimental conditions, this technique reveals the self-generated, Biermann-battery fields extend beyond the edge of the expanding plasma plume to a radius of over 3.5 mm by <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>t</a:mi></a:math>=<b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mo>+</b:mo><b:mn>1.4</b:mn></b:math> ns. An analysis of two monoenergetic proton populations confirms that proton deflection is dominated by magnetic fields far from the interaction (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mo>></c:mo><c:mn>2</c:mn></c:mrow></c:math> mm) and electric fields are insignificant. The results are not captured in state-of-the-art magnetohydrodynamics simulations and suggest the need to consider additional physics mechanisms for the magnetic field generation and transport in laser-solid interactions. Published by the American Physical Society 2024