Compression of Antiproton Clouds for Antihydrogen Trapping

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.

Figure 1

Schematic diagram of the ALPHA apparatus. A moveable probe on the right alternately inserts an electron gun and a MCP/phosphor assembly. The graph below the schematic plots the axial magnetic field in the trap.

Figure 2

$\overline{p}$ and $e^{-}$ images showing the effects of compression, and the resulting radial profiles. The solid (red) lines are Gaussian-like [i.e., $\exp (-|r/r_0{|}^k)$, where $k\approx 2$] fits to the radial profiles.

Figure 3

(a) The cooled $\overline{p}$ cloud radius as a function of the radius of the $e^{-}$ plasma used to cool the $\overline{p}$s. The various symbols correspond to trials with differing total electron numbers (100–165 M). The $e^{-}$ plasma radii for the open symbols were measured directly from the images; the radii for the solid symbols were calculated from the central intensity as described in the text. The inset figure shows the measured and inferred values for the points in the circle data set where both methods could be employed. (b) The cooling efficiency (see text) as a function of the $e^{-}$ plasma radius.

Figure 4

The (a) $e^{-}$ radius and (b) $\overline{p}$ density as a function of time, for fast and slow compression. Note that the $\overline{p}$ density does not track the $e^{-}$ compression if the latter is fast.

Figure 5

The $\overline{p}$ cloud radius as a function of the $e^{-}$ plasma radius for the slow compression data shown in Fig. 4.