[en] Inelastic collisions with CO2 buffer gas cool a pure electron gas in a Penning-Malmberg trap at low magnetic fields. 0.6 eV electrons are cooled by down to 30% of their original temperature

[en] For the first time, high amplitude (Δn/n ≅ 40%), high Q (up to 100,000) BGK modes have been controllably excited in a plasma. The modes are created by sweeping an excitation voltage downwards in frequency, thereby dragging a phase space 'bucket' of low density into the bulk of the plasma velocity distribution. The modes have no linear limit, and differ markedly from plasma waves and Trivelpiece-Gould modes

[en] A Gabor lens, a type of plasma lens, utilizes the internal electric field of a trapped electron plasma to focus high energy positively charged particles, such as protons or ions [1]. This lens is formed within a non-neutral plasma confined by magnetic and electric fields in a Penning-Malmberg trap [2]. Compared to traditional magnetic lenses, Gabor lenses offer the potential for highly efficient and compact particle focusing. The focal length (f) of the Gabor lens depends on the strength of the radial field generated by the non-neutral plasma, which is determined by the plasma density (n_e), the kinetic energy of the positively charged particle (U), and the length of the plasma (l) via 1/f=e^2 n_e l/(4e₀ U) where e is the magnitude of the electric charge of the electron, and e₀ is the permittivity of free space [3]. In this study, our aim is to attain a plasma density on the order of 10^15 m^-3 to achieve a desired focal length of 1m for the Gabor lens. The practical implementation of an electron plasma faces challenges related to confinement, density, lifetime, and stability. We analyze these characteristics within our trapped electron plasma. Additionally, we present the results of applying a well-established manipulation technique—rotating electric fields—to control the plasma radius [4], aiming for longer plasma lifetimes and higher plasma densities. The attainment of prolonged plasma storage times and elevated plasma densities holds significant promise for advancing Gabor lens technology, crucial for a multitude of applications including particle accelerators and beam focusing systems. [1] Gabor, D. (1947). A space-charge lens for the focusing of ion beams. Nature, 160(4055), 89-90. [2] Fajans, J., & Surko, C. M. (2020). Plasma and trap-based techniques for science with antimatter. Physics of Plasmas, 27(3), 030601. [3] Pozimski, J., & Aslaninejad, M. (2013). Gabor lenses for capture and energy selection of laser driven ion beams in cancer treatment. Laser and Particle Beams, 31(4), 723-733. [4] Ahmadi, M., et al. (Alpha Collaboration). (2018). Enhanced control and reproducibility of non-neutral plasmas. Physical Review Letters, 120(2), 025001.

[en] For the first time, high amplitude (Δn/n≅40%), high Q (up to 100,000) Bernstein, Greene, and Kruskal modes have been controllably excited in a plasma. The modes are created by sweeping an excitation voltage downwards in frequency, thereby dragging a phase space 'bucket' of low density into the bulk of the plasma velocity distribution. The modes have no linear limit and differ markedly from plasma waves and Trivelpiece-Gould modes

[en] The excitation of synchronized Bernstein, Greene, and Kruskal (BGK) modes in a pure electron plasma confined in Malmberg-Penning trap is studied. The modes are excited by controlling the frequency of an oscillating external potential. Initially, the drive resonates with, and phase-locks to, a group of axially bouncing electrons in the trap. These initially phase-locked electrons remain phase-locked (in 'autoresonance') during a subsequent downward chirp of the external potential's oscillation frequency. Only a few new particles are added to the resonant group as the frequency, and, hence, the resonance, moves to lower velocities in phase space. Consequently, the downward chirp creates a charge density perturbation (a hole) in the electron phase space distribution. The hole oscillates in space, and its associated induced electric field constitutes a BGK mode synchronized with the drive. The size of the hole in phase space, and thus the amplitude of the mode, are largely controlled by only two external parameters: the driving frequency and amplitude. A simplified kinetic theory of this excitation process is developed. The dependence of the excited BGK mode amplitude on the driving frequency chirp rate and other plasma parameters is discussed and theoretical predictions are compared with recent experiments and computer simulations

[en] We present a method for generating cold neutral atoms via charge exchange reactions between trapped ions and Rydberg positronium. The high charge exchange reaction cross section leads to efficient neutralisation of the ions and since the positronium-ion mass ratio is small, the neutrals do not gain appreciable kinetic energy in the process. When the original ions are cold the reaction produces neutrals that can be trapped or further manipulated with electromagnetic fields. Because a wide range of species can be targeted we envisage that our scheme may enable experiments at low temperature that have been hitherto intractable due to a lack of cooling methods. We present an estimate for achievable temperatures, neutral number and density in an experiment where the neutrals are formed at a milli-Kelvin temperature from either directly or sympathetically cooled ions confined on an ion chip. The neutrals may then be confined by their magnetic moment in a co-located magnetic minimum well also formed on the chip. We discuss general experimental requirements. (paper)

[en] Recent experiments showed the possibility of creating long-lived, nonlinear kinetic structures in a pure-electron plasma. These structures, responsible for large-amplitude periodic density fluctuations, were induced by driving the plasma with a weak oscillating drive, whose frequency was adiabatically decreased in time [W. Bertsche, J. Fajans, and L. Friedland, Phys. Rev. Lett. 91, 265003 (2003)]. A one-dimensional analytical model of the system was developed [L. Friedland, F. Peinetti, W. Bertsche, J. Fajans, and J. Wurtele, Phys. Plasmas 11, 4305 (2004)], which pointed out the phenomenon responsible for the modifications induced by the weak drive in the phase-space distribution of the plasma (initially Maxwellian). In order to validate the theory and to perform quantitative comparisons with the experiments, a more accurate description of the system is developed and presented here. The new detailed analysis of the geometry under consideration allows for more precise simulations of the excitation process, in which important physical and geometrical parameters (such as the length of the plasma column) are evaluated accurately. The numerical investigations probe properties and features of the modes not accessible to direct measurement. Due to the presence of two distinct time scales (because of the adiabatic chirp of the drive frequency), a fully two-dimensional numerical study of the system is expected to be rather time consuming. This becomes particularly important when, as here, a large number of comparisons (covering a wide range of drive parameters) are performed. For this reason, a coupled one-dimensional, radially averaged model is derived and implemented in a particle-in-cell code

[en] Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen

[en] We have demonstrated production of antihydrogen in a 1 T solenoidal magnetic field. This field strength is significantly smaller than that used in the first generation experiments ATHENA (3 T) and ATRAP (5 T). The motivation for using a smaller magnetic field is to facilitate trapping of antihydrogen atoms in a neutral atom trap surrounding the production region. We report the results of measurements with the Antihydrogen Laser PHysics Apparatus (ALPHA) device, which can capture and cool antiprotons at 3 T, and then mix the antiprotons with positrons at 1 T. We infer antihydrogen production from the time structure of antiproton annihilations during mixing, using mixing with heated positrons as the null experiment, as demonstrated in ATHENA. Implications for antihydrogen trapping are discussed. (fast track communication)

[en] Ultracold atom-based electron sources have recently been proposed as an alternative to the conventional photo-injectors or thermionic electron guns widely used in modern particle accelerators. The advantages of ultracold atom-based electron sources lie in the fact that the electrons extracted from the plasma (created from near threshold photo-ionization of ultracold atoms) have a very low temperature, i.e. down to tens of Kelvin. Extraction of these electrons has the potential for producing very low emittance electron bunches. These features are crucial for the next generation of particle accelerators, including free electron lasers, plasma-based accelerators and future linear colliders. The source also has many potential direct applications, including ultrafast electron diffraction (UED) and electron microscopy, due to its intrinsically high coherence. In this paper, the basic mechanism of ultracold electron beam production is discussed and our new research facility for an ultracold, low emittance electron source is introduced. This source is based on a novel alternating current Magneto-Optical Trap (the AC-MOT). Detailed simulations for a proposed extraction system have shown that for a 1 pC bunch charge, a beam emittance of 0.35 mm mrad is obtainable, with a bunch length of 3 mm and energy spread 1%