Antiproton Confinement in a Penning-Ioffe Trap for Antihydrogen

Antiprotons ($\overline{p}$) remain confined in a Penning trap, in sufficient numbers to form antihydrogen ($\overline{\mathrm{H}}$) atoms via charge exchange, when the radial field of a quadrupole Ioffe trap is added. This first demonstration with $\overline{p}$ suggests that quadrupole Ioffe traps can be superimposed upon $\overline{p}$ and $e^{+}$ traps to attempt the capture of $\overline{\mathrm{H}}$ atoms as they form, contrary to conclusions of previous analyses.

Figure 1

(a) Outside and (b) cutaway views of a Penning-Ioffe apparatus. Many cylindrical ring electrodes can be biased to form Penning traps for antiprotons, positrons, and electrons. An external 1 Tesla bias field, directed along the central symmetry axis of these electrodes, is produced by a large external solenoid (not shown). Two pinch coils add a gradient to the axial field. The radial quadrupole Ioffe field is produced by four racetrack coils.

Figure 2

Current bars of simple (a) quadrupole and (b) octupole Ioffe traps are parallel to an externally produced bias magnetic field. Currents in pinch coils add an axial gradient.

Figure 3

Cross section of cylindrical ring electrodes (black) in which $\overline{p}$ are stored, with superimposed magnetic field lines (blue) and electrostatic equipotentials in 5 V intervals (red). Magnetic field lines, (a) without and (c) with current in the pinch coils, diverge so as to intersect electrodes, even as they make a magnetic field whose magnitude increases with distance from the trap axis and center. The corresponding electrostatic well depths for a $\overline{p}$ moving along a field line are represented in (b) and (d).

Figure 4

Fraction of about 90 000 (circles) and 280 000 (triangle) trapped $\overline{p}$ that survive a radial Ioffe quadrupole field that is ramped up to a given current, held 300 s, and ramped back down.

Figure 5

Fraction of electrons that survive a radial Ioffe quadrupole field that is ramped up to a given current, held 0, 300, or 600 s, and ramped back down.