T. R. Weber

Plasma manipulation techniques for positron storage in a multicell trap

New plasma manipulation techniques are described that are central to the development of a multicell Penning trap designed to increase positron storage by orders of magnitude (e.g., to particle numbers N⩾1012). The experiments are done using test electron plasmas. A technique is described to move plasmas across the confining magnetic field and to deposit them at specific radial and azimuthal positions. Techniques to fill and operate two in-line plasma cells simultaneously, and the use of 1kV confinement potentials are demonstrated. These experiments establish the capabilities to create, confine, and manipulate plasmas with the parameters required for a multicell trap; namely, particle numbers >1010 in a single cell with plasma temperature ⩽0.2eV for plasma lengths ∼10cm and radii ⩽0.2cm. The updated design of a multicell positron trap for 1012 particles is described.

Extraction of small-diameter beams from single-component plasmas

A nondestructive technique is described to extract small-diameter beams from single-component plasmas confined in a Penning-Malmberg trap following radial compression using a rotating electric field. Pulsed beams with Gaussian radial profiles and diameters as small as 50μm are extracted from electron plasmas initially 2mm in diameter. A simple theory for the beam diameter predicts 4λD (full width to 1∕e), where λD is the Debye length, in good agreement with experimental measurements on electron plasmas. Applications and extensions of this technique to create bright, finely focused beams of positrons and other scarce particles are discussed.

Electrostatic beams from tailored plasmas in a Penning-Malmberg trap

In recent work, a technique was developed to extract high quality beams from single-component plasmas confined in a Penning-Malmberg trap in a 4.8 T magnetic field. In this paper, a procedure is developed to extract these beams from the confining magnetic field and then focus them to create especially tailored electrostatic beams. Electron beams are extracted from the field in two stages: they are first transported to a region of reduced field (1 mT), and then taken to zero field with a nonadiabatic, fast extraction. Once in the field-free region, the beams are focused using an Einzel lens. Experimental results and numerical simulations are presented to illustrate the extraction and focusing process. Theoretical expressions are developed to describe the modifications to the relevant beam energy and spatial distributions. Where possible, analytic expressions are presented for the case relevant here of beams with Gaussian radial profiles. Beam emittance considerations are discussed as well as prospects for further development of these techniques. Application of these techniques to provide high-quality positron beams is also discussed.

Creation of finely focused particle beams from single-component plasmas

In a recent communication [Danielson et al., Appl. Phys. Lett. 90, 081503 (2007)], a nondestructive technique was described to create finely focused beams of electron-mass, charged particles (i.e., electrons or positrons) from single-component plasmas confined in a Penning–Malmberg trap. This paper amplifies and expands upon those results, providing a more complete study of this method of beam formation. A simple model for beam extraction is presented, and an expression for a Gaussian beam profile is derived when the number of extracted beam particles is small. This expression gives a minimum beam diameter of four Debye lengths (full width to 1/e) and is verified using electron plasmas over a broad range of plasma temperatures and densities. Numerical procedures are outlined to predict the profiles of beams with large numbers of extracted particles. Measured profiles of large beams are found in fair agreement with these predictions. The extraction of over 50% of a trapped plasma into a train of nearly ide...

Energy spectra of tailored particle beams from trapped single-component plasmas

A nondestructive technique was developed recently to create beams of electrons (or positrons) with small transverse spatial extent and high brightness from single-component plasmas confined in a Penning–Malmberg trap [T. R. Weber et al., Phys. Plasmas 90, 123502 (2008)]. A model for beam extraction was developed that successfully predicts the resulting beam profiles. This model is used here to predict the beam amplitudes and the energy distribution of the beams as a function of the exit-gate voltage. The resulting expressions, suitably scaled by the plasma parameters, depend only on the exit-gate voltage and the electrode radius. Predictions of the theory are confirmed using electron plasmas. This technique permits the formation of beams with both small transverse spatial extent and small energy spread. Applications involving antimatter beams (e.g., positrons) are discussed, including bright beams for improved spatial resolution, short pulses for time-resolved studies, and cold beams for improved energy r...

Note: Electrostatic beams from a 5 T Penning-Malmberg trap.

A procedure is described to extract beams from specially tailored electron plasmas in a Penning-Malmberg trap in a 4.8 T field. Transport to 1 mT is followed by extraction from the magnetic field and electrostatic focusing. Potential applications to positron beams are discussed.

New plasma tools for antimatter science

Much progress has been made recently to create cold antimatter plasmas and to exploit them for a variety of fundamental scientific studies and technological applications. In particular, single-component plasmas are a unique medium with which to manipulate antimatter without the usual deleterious effect of annihilation with matter. The work described here focuses on the development of new plasma tools for the trapping and manipulation of antimatter plasmas and beams, with immediate applications to positron science. Progress is described in three key areas: radial compression of single-component plasmas using rotating electric fields in a novel, strong-drive regime [1]; experiments and complementary theoretical modeling of the extraction of beams with small transverse spatial extent from single-component plasmas [2]; and work to develop a multicell trap to increase by orders of magnitude the capacity for antiparticle storage [3]. Potential applications of these tools and challenges for future research are discussed.

Tailored Particle Beams From Single‐Component Plasmas

Recently, we developed a non‐destructive technique to create narrow beams of electrons (or positrons) of adjustable width and brightness from single‐component plasmas confined in a Penning‐Malmberg trap [Weber et al., Phys. Plasmas 13, 123502 (2008)]. Here, we review highlights of that work and discuss the distributions in energy of the extracted beams. A simple model for beam extraction predicts Gaussian beam profiles, with transverse spatial widths dependent on the number of particles in the beam. A Maxwellian energy distribution is predicted for small beams. The predictions of the theory are confirmed using electron plasmas. Extraction of over 50% of a trapped plasma into a train of nearly identical beams is demonstrated. Finally, the possibility of creating high quality, electrostatic beams by extraction from the confining magnetic field is discussed.

Next Generation Trap for Positron Storage

Progress toward the development of a novel multicell Penning-Malmberg trap is described that will be capable of accumulating orders of magnitude more positrons than is possible presently. This design represents the next major step in antimatter storage technology. Experiments with test electron plasmas establishing techniques critical to the implementation of a practical multicell trap are presented. The latest design for a 21 cell trap capable of accumulating and storing more than 5 x 10^^ positrons is described. This trap could facilitate multiplexing the output of the new generation of positron sources either operating now or currently under development, as well as the potential to provide record-high bursts of positrons for a variety of applications.

New Plasma Tools for Antimatter Science

Much progress has been made recently to create cold antimatter plasmas and to exploit them for a variety of fundamental scientific studies and technological applications. In particular, single-component plasmas are a unique medium with which to manipulate antimatter without the usual deleterious effect of annihilation with matter. The work described here focuses on the development of new plasma tools for the trapping and manipulation of antimatter plasmas and beams, with immediate applications to positron science. Progress is described in three key areas: radial compression of single-component plasmas using rotating electric fields in a novel, strong-drive regime [1]; experiments and complementary theoretical modeling of the extraction of beams with small transverse spatial extent from single-component plasmas [2]; and work to develop a multicell trap to increase by orders of magnitude the capacity for antiparticle storage [3]. Potential applications of these tools and challenges for future research are discussed.