Record Magnetic Field Generation by Short-Pulse Laser-Driven Capacitor-Coil Targets

Abstract

Magnetic fields generated by capacitor-coil targets driven by intense short-pulse lasers have been characterized using ultrafast proton radiography. A 1-kJ, 15-ps laser at a center wavelength of 1053 nm irradiated the back plate of the capacitor with an intensity of $\sim$8.3 $\times$ 10$^{18}$ W$/$cm$^{2}$, creating ultra large currents in the connecting coils. High-quality proton data obtained in the axial probing geometry show definitive signatures of magnetic field generation allowing precision measurement of the field distribution and strength. The data show a coil current of 120 $\pm$ 10 kA producing 200 $\pm$ 20 Tesla magnetic fields at the coil center at 1.127 ns afer the laser drive. This sets a record for magnetic field generation by the short-pulse-powered capacitor-coil targets.

Figures (3)

• Figure 1: (color online). Experimental setup illustrated with photographic images of the aligned targets (outlined in green), captured by the OMEGA EP target viewing system prior to the actual experiment. The capacitor-coil target consists of two parallel Cu foils connected by two parallel U-shaped Cu coils. The proton generation assembly is composed of a Cu foil mounted inside a plastic tube and a Ta foil attached to the tube end. An Au mesh is positioned 2.5 mm from the Cu foil and 4.5 mm from the center of the U-shaped coils. The Cu foil, Ta foil, and Au mesh are aligned parallel to each other.
• Figure 2: (color online). Proton radiograph obtained with 33 $\pm$ 0.5 MeV protons at $t=t_{0}+1.127$ ns, calibrated to the target plane by accounting for the system magnification. Darker areas correspond to higher detected proton fluxes. The blue dashed line outlines the contour of the coils showing a spatial scale consistent with the experimental setup, further confirming the image calibration. The black dashed line represents the reference mesh grid orientation without any rotation. The red solid line represents the rotated mesh grid orientation in strong magnetic fields. The rotation angle is determined by the tilt of the rotated red solid line relative to the reference black dashed line. Following the coil current from the right leg to the left leg, a distinct width variation is observed.
• Figure 3: (color online). (a) Synthetic proton radiograph on the target plane calculated with 120 kA current in each coil and no electric fields. Both mesh grid rotation inside the coils and the width variation from the right leg to the left are clearly seen. The white dashed line represents the reference mesh grid orientation without any rotation. The red solid line represents the rotated mesh grid orientation in strong magnetic fields. The rotation angle is determined by the tilt of the rotated red solid line relative to the reference white dashed line. (b) Synthetic proton radiograph calculated from the electric fields produced by a positive line charge within each coil, with a charge density of $+10\;\rm{nC}/\rm{mm}$. (c) The blue solid line represents the simulated rotation angle as a function of coil currents. The red dot indicates the experimentally measured rotation angle of 10.6$^{\circ}$$\pm$ 1$^{\circ}$ corresponding to a coil current of $120\pm 10$ kA. (d) The trace of the mesh grids and contour of the proton deflection around the coils in (a) is overlaid on top of the measured data as shown in Fig. \ref{['fig2']}.