Record accumulation of antiprotons in a Penning-Malmberg Trap and their preparation for improved production of antihydrogen beams

Abstract

CERN's AD/ELENA ``antimatter factory'' - unique worldwide - serves several experiments, all of which use electromagnetic traps to accumulate antiprotons for fundamental science. The GBAR experiment employs a charge-exchange reaction between an antiproton beam and a positronium cloud to produce antihydrogen for gravitational studies. GBAR has also pioneered an electrostatic scheme using a pulsed drift tube to decelerate the 100 keV antiproton beam, rather than slowing the antiprotons in a foil, as is commonly done in other experiments. Following first results producing a 6 keV antihydrogen beam directly after the decelerator, a trap has now been installed to increase the production rate. The emittance growth resulting from the deceleration is reduced in the trap by Coulomb interaction with a cold electron cloud. The antiproton cloud is further compressed using rotating wall cooling and can be re-accelerated up to energies of 10 keV, including a time focus. Here we describe the commissioning results, trapping 56(3)\% of the ELENA beam, delivering $6.4(0.4)~\times~10^{6}$ antiprotons per shot for improved production of antihydrogen, and a record accumulation of over $6.4(0.4)~\times~10^{7}$ antiprotons in under 35 minutes.

Figures (10)

• Figure 1: Schematic layout of the GBAR antiproton beamline. The antiproton beam ($\mathrm{\overline{p}}$) from ELENA enters from the left, is slowed through the GBAR decelerator and transported to the antiproton trap ($\bar{p}$ trap, PT) for cooling, before extraction and transport to the reaction chamber. The assembly incorporates an electron gun (e-gun), magnetic guiding coils and various electrostatic beam optics, including Einzel lenses (EL), steerers, and a quadrupole triplet (QT). Microchannel-plate (MCP) detectors, flux monitors, and a pair of scintillation counters are also installed for diagnostics.
• Figure 2: Detailed drawing of the electrode array within the antiproton trap, with dimensions in mm. The Multi-Ring Electrode (MRE) assembly consists of a central RE section for the confinement of antiprotons and electrons, and high-voltage electrodes (HV1-3) dedicated to antiproton capture and acceleration. To ensure efficient beam transport, a series of four Einzel lenses (PT-EL1-4) are positioned downstream to focus and deliver the beam toward the reaction chamber.
• Figure 3: Voltages along the trapping axis illustrating the operational sequence: (a) electron pre-loading, (b) antiproton capture, switching the HV1 electrode, (c) sympathetic cooling of antiprotons with cold electrons, (d) rotating wall compression, (e) extraction, and (f) acceleration to 1-10 keV.
• Figure 4: (a) Electric signal recorded by the flux monitor when a 100 keV antiproton beam is dumped onto MCP2, without using the GBAR decelerator. No upstream annihilation signal is observed prior to the beam arrival at MCP2. (b) Correlation between the number of antiprotons and the integrated flux-monitor signal. The black dots represent the experimental data, and the red line indicates a linear fit. The data demonstrate a linear correlation with a deviation of approximately 3%.
• Figure 5: (a) Spatial profile and (b) electric signal for the 3 keV decelerated antiproton beam at MCP2. The circle in (a) indicates the active area of the MCP2. The bunch length in (b), defined as the full width at half maximum (FWHM) of the signal waveform, is 140 ns.