First Attempts at Antihydrogen Trapping in ALPHA

Abstract

The ALPHA apparatus is designed to produce and trap antihydrogen atoms. The device comprises a multifunction Penning trap and a superconducting, neutral atom trap having a minimum-B configuration. The atom trap features an octupole magnet for transverse confinement and solenoidal mirror coils for longitudinal confinement. The magnetic trap employs a fast shutdown system to maximize the probability of detecting the annihilation of released antihydrogen. In this article we describe the first attempts to observe antihydrogen trapping.

Aspects of neutral atom traps for antihydrogen spectroscopy

“…Acknowledging the advantage of trapped atoms over the other options, both ALPHA [26] and ATRAP [4] have deployed magnetic traps for their created antihydrogen atoms. The challenge of simultaneously confining neutral atoms and their charged particle constituents, positrons and antiprotons, in addition to electrons for cooling the antiprotons, led the ALPHA Collaboration to opt for a modified Ioffe-Pritchard trap using an octupolar racetrack coil instead of the usual quadrupole which has been ATRAP's option.…”

Magnetic multipole induced zero-rotation frequency bounce-resonant loss in a Penning–Malmberg trap used for antihydrogen trapping

“…This operation is common in mixing procedures used to synthesize H. This mechanism can cause p's to be lost over a wide range of parameters, including p's that are well within the radii previously identified as safe. 12,13 Loss only occurs when the p's pass through the ⍀ r = 0 resonance slowly, but such changes are now common in these mixing cycles, 10,11 as slow changes are believed to decrease the energy and increase the trapping probability of the resulting H.…”

“…The bounce-resonant loss may seriously complicate efforts to trap H. The most efficient H formation schemes now known 3,4,9 are all potentially subject to this loss. Indeed, in the most recent experiments, 10,11 which have attempted to make relatively cold H by slowing the movement of the electrostatic potentials, the likelihood of this loss is enhanced. A large fraction ͑over 20%͒ of the p's were lost in the experiments described here ͑see Fig.…”