This thesis reports on low-energy injection studies, considering a multi-shot and multiturn injection method in radial phase space, using only one kicker magnet. A new model is presented in which the coupling between the radial and longitudinal phase space significantly increases the injection efficiency at low energies. Coupling with the longitudinal phase space takes place if the energy of the injected beam is different from the equilibrium ring energy and if there is dispersion at the septum position. Coupling with the vertical phase space, introduced by skew quadrupole fields, also increases the injection efficiency. A computer program, MCIS, has been written in order to make quantitative predictions from the new model. Calculations are presented for HELIOS, a superconducting synchrotron with a final electron energy of 700 MeV. The present injection energy is 200 MeV. The calculations show that if injection were to take place off-energy by δ _m ≈ 1 %, then the injection energy could be lowered to a minimum of about 35 MeV. This prediction only takes into account single particle beam dynamics. The effect of most other parameters on the injection efficiency is also calculated. Experimental studies of the injection process were performed during the commissioning period of Helios, which was carried out by a team under the author's direction. Data obtained at an injection energy of 100 MeV are compared with calculations. A precise measurement of the relative energy deviation of the injected beam δ_m has been made. The agreement with the model is good and it proves the presence of longitudinal coupling for the optimum injection conditions. The measurement of the optimum kicker strength also agrees with the model, as does the general behaviour of injection as a function of several parameters. The measurements lead to a high level of confidence in the model presented. The belief in the general validity of the model is reinforced by its agreement with the overall injection behaviour of accelerators other than HELIOS, which inject successfully at low energies.