Pulsed-Power Approach to Pair Production in Magnetic Fields below the Schwinger Limit

Magnetic pair production has never been observed due to the strength of the Schwinger field. We show that relativistic lepton pairs can be created by bombarding the magnetic fields of pulsed-power driven loads with laser-driven electron beams. In one setup, a metal rod z-pinch is compressed to <100 µm by Sandia’s Z Machine (< 30 MA); in a second configuration, x-pinches with currents as low as 1 MA are utilized. Electrons with energies ~10 GeV [1] bend in these fields (10⁴ T to several 10⁵ T) and generate pairs via the Breit-Wheeler and trident processes. We report analytical calculations and EPOCH simulations that extract the dependencies of the pair yield on parameters characterizing the loads and electron beams [2]. This work is also of astrophysical significance, as magnetic pair production is thought to be fundamental to pulsar magnetosphere dynamics and connected to the mystery of Fast Radio Bursts (FRBs). Thus, developing an experimental testbed that mimics these conditions could provide valuable data for validating models that seek to describe FRBs. Experimentally, the exponential suppression of the pair process is anticipated to be a source of shot-to-shot variability, as the mean-free-path varies quickly; for example, it is ~1 parsec at 42 kT for a 3 GeV photon, but drops to 1 mm at 200 kT for a 6 GeV photon.

[1] Picksley, A., et al. Physical Review Letters 133, 255001 (2025).

[2] Williams, C. & Younis, D. "Pulsed-Power Approach to Pair Production in Magnetic Fields below the Schwinger Limit", in preparation.