7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Efficient generation of axial magnetic field by multiple laser beams with twistedpointing directions
Yin Shi 1, Alexey Arefiev 2, Jue Xuan Hao1 and Jian Zheng1,31
Department of Plasma Physics and Fusion Engineering, University of Science and Technology ofChina, Hefei 230026, China,
2
Department of Mechanical and Aerospace Engineering,
University of California at San Diego, La Jolla, CA 92093, USA ,3
Collaborative Innovation Center of IFSA,Shanghai Jiao Tong University, Shanghai 200240, Peoples Republic of Chinae-mail (speaker): shiyin@ustc.edu.cn
Strong laser-driven magnetic fields are crucial forhigh-energy-density and laboratory astrophysics research,but generation of axial multi-kT fields remains achallenge. The difficulty comes from the inability of aconventional linearly polarized laser beam to induce therequired azimuthal current or, equivalently, angularmomentum (AM). We show that several laser beams canovercome this difficulty.

intensities and pulse durations. Our scheme is well-suitedfor implementation using multi-kJ PW-class lasers,because, by design, they have multiple beamlets andbecause the scheme requires only linear-polarization.
References[1] Yin Shi et al, Phys. Rev. Lett. 130, 155101(2023)

The approach, illustrated in Figure 1 for four beams, ismotivated by the development of PW-class laser systems
like SG-II UP that will have multiple kilojoule-classpicosecond laser beams. Even though each laser beamalone carries no intrinsic OAM, we show that they canbe assembled to efficiently generate OAM in the plasmathat they irradiate. Multi-kJ PW-class laser systems like
LFEX, NIF ARC, and Petal offer the highest energy thatcan be delivered on a ps time scale. These lasers are allcomposed of multiple LP beamlets. The multi-beamlet
configuration is not just an essential feature of the laser
system design, but also the key to advanced laser-plasmainteraction regimes. The number of multi-beamlet
facilities will increase, as SG-II UP is due to be upgradedto have multiple kJ-class ps laser beams.
Our three-dimensional kinetic simulations demonstratethat a twist in their pointing direction enables them tocarry orbital AM and transfer it to the plasma, thus
generating a hot electron population carrying AM needed
to sustain the magnetic field. The resulting multi-kT fieldoccupies a volume that is tens of thousands of cubic
microns and it persists on a ps time scale. The twist in
the pointing direction of the pulses is the key to driving
an azimuthal plasma current that sustains the magneticfield. The twist angle is a convenient control knob for
adjusting the direction and magnitude of the axial
magnetic field.
The mechanism can be realized for a wide range of laser

Figure 1. (a) Setup for axial magnetic field generation
using four linearly-polarized Gaussian laser beams with
twisted pointing directions, shown with solid lines, and astructured target. The size of each beam is shown with acolor-coded ellipse in the emitter plane left side of thesimulation box and in the focus plane. (b) Projections of
the two planes on to the (y, z)-plane. The parameters
setting up the beam orientation are defined in the text. (c)Surface plots of the axial magnetic field B_x after thelasers have left the simulation box (t = 20 fs). The green,blue, and red surfaces represent B_x/B_0 = -0.1, -0.2,
and -0.8, where B_0 = 13.4~kT.