Positronium in the AEgIS experiment: study on its emission from nanochanneled samples and design of a new apparatus for Rydberg excitations

This experimental thesis has been done in the framework of AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy), an experiment installed at CERN, whose primary goal is the measurement of the Earth's gravitational acceleration on anti-hydrogen. The antiatoms will be produced by the charge exchange reaction, where a cloud of Ps in Rydberg states interacts with cooled trapped antiprotons. Since the charge exchange cross section depends on Ps velocity and quantum number, the velocity distribution of Ps emitted by a positron-positronium converter as well as its excitation in Rydberg states have to be studied and optimized. In this thesis Ps cooling and emission into vacuum from nanochannelled silicon targets was studied by performing Time of Flight measurements with a dedicated apparatus conceived to receive the slow positron beam as produced at the Trento laboratory or at the NEPOMUC facility at Munich. Measurements were done by varying the positron implantation energy, the sample temperature and the nanochannel dimensions, with the aim of finding the best parameters to increase Ps fraction having velocity lower than 5 10^4 m/s. Preliminary data were analyzed in order to extract the Ps velocity distribution and its average temperature. More, an original method for evaluating the permanence time of Ps inside the nanochannels before being emitted into vacuum, was described. A first rough evaluation based on the performed measurements is reported and this result will be useful to investigate the Ps cooling process and to synchronize the laser pulse for Ps excitation in the AEgIS experiment. In order to perform measurements of Ps excitation in Rydberg states, a new apparatus for bunching positron pulses, coming from the AEgIS positron line, was designed and built. COMSOL and SIMION softwares were used for designing a magnetic transport line and an electron optical line, which extracts positrons from the magnetic field and focus them on the nanochanneled Si sample. More, a buncher device, which spatio-temporally compresses the positron bunches, was built and a fast circuit for supplying the 25 buncher electrodes with a parabolic shaped potential was designed and tested. According to the simulations, at the target position the device will deliver positrons with an energy ranging from 6 to 9 keV, in bunches of 5 ns duration and a spot of 2.5 mm in diameter. By using this apparatus, first measurements for the optimization of Ps excitation in Rydberg states and studies on the Ps levels with and without magnetic field will be performed. At a later stage investigations of Ps spectroscopy or of Ps laser cooling with the same apparatus could be achievable for the first time.