First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

Abstract

Novel experiments to study the strongly-driven collision of parallel magnetic fields in β∼10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell (PIC) simulations predict a stronger flux compression and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.

Anomalous plasma acceleration in colliding high-power laser-produced plasmas

“…From Eq. ( 1), the increment in the velocity from 42 km/s (only the Biermann fields) to 57 km/s (now with the antiparallel external field) can be explained by a 57/42 ∼ 1.4 times stronger magnetic field, or increment in the field from 1.6 to 2.3 T. Even though the initial external field strength of 0.1 T is weak (M A > 52 at t < 40 ns) and does not affect the initial plasma streams, it can be piled up as the plasma expands because of high conductivity, which has already been seen in previous experimental studies 13,14,16,43,44 by a factor of four, meaning that both parallel and anti-parallel external fields become comparable to the Biermann fields in the interaction region. As investigated in Ref.…”

“…Local plasma parameters and magnetic fields have been precisely diagnosed in gas-discharged plasmas such as TS-3 5,6 , MRX 7,8 , and pulse-powered devices 9,10 , with relatively low-beta (β < 1). a) Electronic mail: morita@aees.kyushu-u.ac.jp.Recently, strongly-driven MR has been studied using laserproduced plasmas [11][12][13][14][15][16][17][18][19] under strong magnetic fields generated by the interaction of high-power lasers with solids via the Biermann battery effect (∂ B/∂t ∝ ∇T e × ∇n e ) 20 . In contrast to other laboratory experiments, laser-produced plasmas with high temperatures and densities enable us to investigate MR in high-beta conditions, similar to those in magnetosheath (β ∼ 0.1-10) 21 and in accretion disks (β > 10) 22 .…”

“…In contrast to other laboratory experiments, laser-produced plasmas with high temperatures and densities enable us to investigate MR in high-beta conditions, similar to those in magnetosheath (β ∼ 0.1-10) 21 and in accretion disks (β > 10) 22 . However, few diagnostics are available in such small-scale plasmas, and recent studies have focused on topological change in a field [13][14][15] , global plasma structure [17][18][19] , and numerical simulations 11,12 . Although spatially and temporally resolved measurements of flow velocities, plasma parameters, and magnetic fields are required to fully understand physical processes such as the MR rate, no direct measurement of plasma parameters in inflow or outflow and magnetic fields have been performed in laserplasma experiment.…”

Regimes of magnetic reconnection in colliding laser-produced magnetized plasma bubbles

“…These profiles were previously used for simulations of OMEGA experiments presented in Refs. [11,12].…”

Electron energization during merging of self-magnetized, high-beta, laser-produced plasmas

“…2015; Rosenberg et al. 2015 a , b ). The quantity that is directly inferred from these measurements is not the magnetic field per se , but its integral, , along the proton path.…”