Three-dimensional annihilation imaging of trapped antiprotons

Real-time imaging for dose evaluation during antiproton irradiation

Online monitoring of the stopping distribution of particle beams used for radiotherapy provides the possibility of detecting possible errors in dose deposition early during a given treatment session, and may therefore help to improve the quality of the therapy. Antiproton annihilation events produce several long-range secondary particles which can be detected in real time by standard high energy particle physics detector systems. In this note, Monte Carlo calculations are performed in order to study the feasibility of real-time imaging by detecting charged pions produced during antiproton irradiation of typical biological targets. A simple treatment plan in a water phantom is simulated and the results show that by detecting pi+/- the position and the size of the planned target volume can be located with precision in the order of 1 mm.

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+/-0.5) for the production rate in the high temperature regime from approximately 100 meV up to 1.5 eV. This is not in accord with the behavior accepted for conventional three-body recombination.

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.

Search for laser-induced formation of antihydrogen atoms

Antihydrogen can be synthesized by mixing antiprotons and positrons in a Penning trap environment. Here an experiment to stimulate the formation of antihydrogen in the n = 11 quantum state by the introduction of light from a CO2 continuous wave laser is described. An overall upper limit of 0.8% with 90% C.L. on the laser-induced enhancement of the recombination has been found. This result strongly suggests that radiative recombination contributes negligibly to the antihydrogen formed in the experimental conditions used by the ATHENA Collaboration.

Evidence for the production of slow antiprotonic hydrogen in vacuum

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton (p)-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H2+ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.

Effects of extreme magnetic quadrupole fields on penning traps and the consequences for antihydrogen trapping

Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen.

Spatial distribution of cold antihydrogen formation

Antihydrogen is formed when antiprotons are mixed with cold positrons in a nested Penning trap. We present experimental evidence, obtained using our antihydrogen annihilation detector, that the spatial distribution of the emerging antihydrogen atoms is independent of the positron temperature and axially enhanced. This indicates that antihydrogen is formed before the antiprotons are in thermal equilibrium with the positron plasma. This result has important implications for the trapping and spectroscopy of antihydrogen.