Self-Organized Kilotesla Magnetic-Tube Array in an Expanding Spherical Plasma Irradiated by kHz Femtosecond Laser Pulses

By using a millijoule kHz femtosecond laser pulse to irradiate a preformed expanding spherical plasma, which is driven by a prepulse with intensity of $1\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, we observe fast-electron-mediated filamentary structures and an accompanying self-organized magnetic-tube array with 2000 T via time-resolved magneto-optical polarization rotation measurements. We reveal that these periodical filamentary structures predominantly originate from ejected energetic electron flows from the inner denser region of the spherical plasma, which will induce the electron Weibel instability and magnetic field organization and amplification in the expanding plasma in 2 ps. These results open new paths to investigate amplification of intense magnetic fields and the radiation signature from gamma-ray bursts just by means of a much smaller and robust experimental platform.

Figure 1

Schematic of the experimental setup.

Figure 2

(a)–(d) Experimental images of the expanding spherical plasma and electron-mediated filaments at 200 and 1 ps before the main pulse and 1 and 2 ps after the main pulse, respectively.

Figure 3

Recorded images and retrieved radiographs of self-organized magnetic field structures. (a)–(d) Intensity distribution of the probe beam due to the Faraday effect on CCD camera 1 [(a),(b)] and camera 2 [(c),(d)] [(a) and (c) captured at 1.3 ps and (b) and (d) captured at 3.9 ps after the main laser]. (e) Intensity curves of the probe beam along the $y$ axis in the arrows’ position of (a) (green) and (c) (orange). (f) Magnetic field distribution calculated by the intensity difference of (a) and (c).

Figure 4

Summarized results of PIC simulations. (a) Simulation results of the electron momentum at 216 fs (80 laser periods) after the start of driving laser pulse from the left side; initial plasma density (purple line). Insert: Reflux electron (shown in green) energy spectrum. (b) Magnetic field intensity (red line) and magnetic energy (green line) after laser leaves by simulations and linear theory of Weibel instability (blue dash-dotted line) as a function of the time. (c),(d) The electron density and quasistatic magnetic fields at 1.35 ps. (e)–(g) The contour plots of magnetic field strength $B=\sqrt{B_x^2+B_y^2}$ lies in the ($x$, $y$) plane corresponding to the time points with stars marked in (b), respectively.