Antimatter Plasmas in a Multipole Trap for Antihydrogen

We have demonstrated storage of plasmas of the charged constituents of the antihydrogen atom, antiprotons and positrons, in a Penning trap surrounded by a minimum-$B$ magnetic trap designed for holding neutral antiatoms. The neutral trap comprises a superconducting octupole and two superconducting, solenoidal mirror coils. We have measured the storage lifetimes of antiproton and positron plasmas in the combined Penning-neutral trap, and compared these to lifetimes without the neutral trap fields. The magnetic well depth was 0.6 T, deep enough to trap ground state antihydrogen atoms of up to about 0.4 K in temperature. We have demonstrated that both particle species can be stored for times long enough to permit antihydrogen production and trapping studies.

Figure 1

Schematic diagram of the ALPHA apparatus. The graph shows the on-axis longitudinal magnetic field due to the solenoids and mirror coils. The blue (red) curve is the field with (without) the inner solenoid. The positron accumulator (not pictured) is located to the right of the apparatus.

Figure 2

Magnetic field strength versus radius for an ideal quadrupole (dashed line) and an ideal octupole (solid line). $B_w$ is the field at the inner wall (radius $r_w$) of the Penning trap.

Figure 3

The ratio of the number of positrons stored in the octupole field to the number stored without the field is plotted versus holding time, as measured with a Faraday cup and with two CsI detectors. Error bars (typically $\pm 10\%$) omitted for clarity. See text for explanation of the measurement cycle.

Figure 4

The ratio of the number of antiprotons stored in the octupole field to the number stored without the field is plotted versus holding time. Error bars are standard deviations for one set of measurements. Repeated measurements illustrate run-to-run variations. See text for explanation of the measurement cycle.