Temporally Controlled Modulation of Antihydrogen Production and the Temperature Scaling of Antiproton-Positron Recombination

We demonstrate temporally controlled modulation of cold antihydrogen production by periodic RF heating of a positron plasma during antiproton-positron mixing in a Penning trap. Our observations have established a pulsed source of atomic antimatter, with a rise time of about 1 s, and a pulse length ranging from 3 to 100 s. Time-sensitive antihydrogen detection and positron plasma diagnostics, both capabilities of the ATHENA apparatus, allowed detailed studies of the pulsing behavior, which in turn gave information on the dependence of the antihydrogen production process on the positron temperature $T$. Our data are consistent with power law scaling $T^{-1.1\pm 0.5}$ for the production rate in the high temperature regime from $\sim 100\mathrm{meV}$ up to 1.5 eV. This is not in accord with the behavior accepted for conventional three-body recombination.

Figure 1

Spatial and temporal distributions of $\overline{p}$ annihilations during the modulated RF heating of the $e^{+}$ plasma, illustrating modulated $\overline{\mathrm{H}}$ production. (a) Heat on-off, and (b) off-on cycles. In the upper panels the heat off period is shaded.

Figure 2

Measurements of $e^{+}$ plasma cooling time. Plotted are $f(t{)}^2-f_0^2$ (proportional to $\Delta T$) versus time after RF removal. RF amplitudes of 25 mV (red), 13 mV (green), and 5 mV (black) were applied.

Figure 3

Onset of $\overline{\mathrm{H}}$ production upon heat off at $t=0$. (a) The data with $\Delta T=870\mathrm{meV}$ (error bars). Green curve: the $e^{+}$ temperature evolution with ${\tau }_e=0.48\mathrm{s}$. Red curve: a representative fit to Eq. (1), giving $R_{\overline{\mathrm{H}}}\propto T^{-1.2}$. Dashed red curve: exponential fit. Blue: the case with $R_{\overline{\mathrm{H}}}\propto T^{-4.5}$. (b) The data and representative fits for different $\Delta T$. Fit time windows (indicated by solid curves) were set with $T_{\mathrm{low}}=1\mathrm{meV}$ (see text). The data sets (which are vertically displaced for clarity) were taken with between $0.7–1.6\times {10}^5$ $\overline{p}$.

Figure 4

Dependence of $P$ on (a) $\Delta T$ and on (b) the time after start of the mixing for the $\Delta T=870\mathrm{meV}$ data set. Open squares and circles are with the standard fits to Eq. (1), while filled ones are with the exponential fits. For the standard fits in (b), $T_0$ was fixed (to 150 K here) to achieve convergence. The plotted errors are statistical only.