RF-driven electron plasma generation for Gabor lens applications

A Gabor lens, a type of plasma lens, utilizes the internal electric field of a confined electron plasma to focus high-energy positively charged particles such as protons and ions [1]. The lens is formed within a non-neutral plasma confined by static electric and magnetic fields in a Penning-Malmberg trap [2]. Compared to traditional magnetic lenses, Gabor lenses offer the potential for compact, high-efficiency particle focusing. The focal length f depends on the plasma density n_e, the kinetic energy U of the focused particles, and the plasma length l, as given by 1/f = e^₂n_el / (4ε₀U) where e is the elementary charge and ε₀ is the vacuum permittivity [3]. In this work, our aim is to attain a plasma density on the order of 10¹⁵ m^-3 to achieve a desired focal length of 1 m for the Gabor lens.

The practical implementation of an electron plasma for Gabor lens applications faces challenges related to confinement, density, lifetime, and stability. We investigate these key characteristics within our trapped electron plasma. Additionally, we demonstrate a radio-frequency (RF) excitation method that generates a dense plasma from a small initial population of trapped electrons. The applied RF signal energizes these seed electrons, causing ionization of the background gas. This process increases the total number of trapped electrons by more than an order of magnitude and significantly increases the plasma density. Furthermore, this technique enables stable confinement over an extended period, as long as the RF excitation is maintained. The ability to sustain a high-density plasma with a long lifetime represents a significant step toward the practical realization of Gabor lenses for applications in particle accelerators and beam-focusing systems.

[1] D. Gabor, Nature 160, 89 (1947).

[2] J. Fajans & C.M. Surko, Phys. Plasmas 27, 030601 (2020).

[3] J. Pozimski & M. Aslaninejad, Laser Part. Beams 31, 723 (2013).