Structured targets for detection of Megatesla-level magnetic fields through Faraday rotation of XFEL beams

Abstract

A solid density target irradiated by a high-intensity laser pulse can become relativistically transparent, which then allows it to sustain an extremely strong laser-driven longitudinal electron current. The current generates a filament with a slowly-varying MT-level azimuthal magnetic field that has been shown to prompt efficient emission of multi-MeV photons in the form of a collimated beam required for multiple applications. This work examines the feasibility of using an x-ray beam from the European XFEL for the detection of the magnetic field via the Faraday rotation. Post-processed 3D particle-in-cell simulations show that, even though the relativistic transparency dramatically reduces the rotation in a uniform target, the detrimental effect can be successfully reversed by employing a structured target containing a channel to achieve a rotation angle of 10 −4 rad. The channel must be relativistically transparent with an electron density that is lower than the near-solid density in the bulk. The detection setup has been optimized by varying the channel radius and the focusing of the laser pulse driving the magnetic field. We predict that the Faraday rotation can produce 10 3 photons with polarization orthogonal to the polarization of the incoming 100 fs long probe beam with 5 × 10 12 x-ray photons. Based on the calculated rotation angle, the polarization purity must be much better than 10 −8 in order to detect the signal above the noise level.

Generation of megatesla magnetic fields by intense-laser-driven microtube implosions

“…Detecting MT-order magnetic fields inside a plasma presents a challenge for conventional techniques that rely on charged particle sources. In anticipation of achieving ultrahigh magnetic fields, there have been efforts to develop other techniques to infer the existence of strong B-fields inside a dense plasma in use of, for example, an XFEL photon beam with Faraday rotation effect 17,20,24 and spin-polarized neutrons 53 .…”

“…Laboratory generation of strong magnetic fields have been intensively studied [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] , because such fields may realize new experimental tools for fundamental studies and support diverse applications. Examples include plasma and beam physics [19][20][21][22][23][24] , astro- 25,26 and solar-physics 27,28 , atomic and molecular physics 29 , and materials science 30,31 .…”

The High Energy Density Scientific Instrument at the European XFEL

“…Understanding these processes provides deeper insight into material processing via ablation and warm dense matter (WDM) -a dense plasma state between the ideal solid and an ideal plasma. At electron-relativistic laser intensity (!10 18 W cm À2 ), generation of the extremely high magnetic fields (Wang et al, 2019), growth rates of instabilities (Ruyer et al, 2020;Gö de et al, 2017) and collisionless shocks (Fiuza et al, 2020) can be investigated. Fundamental understanding of these transient phenomena also helps to optimize and control the generation of bright particles (Wilks et al, 2001), X-ray line emission (Zastrau et al, 2010) and coherent attosecond extreme ultraviolet pulses (Wheeler et al, 2012) as a secondary source for a probe or a driver.…”

“…The current generates a filament with a slowly varying Mega-Tesla level azimuthal magnetic field that has been shown to prompt efficient emission of multi-MeV photons in the form of a collimated beam required for multiple applications. At the HED instrument, these shortlived transient magnetic fields can be diagnosed via Faraday rotation (Wang et al, 2019). 7.5.…”

ReLaX: the Helmholtz International Beamline for Extreme Fields high-intensity short-pulse laser driver for relativistic laser–matter interaction and strong-field science using the high energy density instrument at the European X-ray free electron laser facility

“…However, the number of Free Electron Lasers in the hard X-Ray regime is limited [9] , which makes the combination of highpower lasers and FELs a unique platform of research. In combination with the EuXFEL beam, it will enable novel investigations in a wide array of areas: properties of highlyexcited solids, high energy density states of matter [10,11] , probing quantum electrodynamics effects [12][13][14] , ionization dynamics at high intensities [15] , relativistic laser plasma interaction [16] , energetic particle propagation in matter [17][18][19] , the production of secondary high-energy photon and particle radiation sources [20][21][22] for material and biological [23] and medical sciences [24] are some of the main topics.…”