A lattice with no transition and large dynamic aperture

In the case of a one-ring high-energy scheme for an advanced hadron facility, beam losses can be reduced if the ring lattice accommodates the beam from injection to maximum energy without crossing the transition. Since there is no synchrotron booster in such a scheme and the injection energy is relatively low, this requirement implies a negative compaction factor and an imaginary transition energy. This can be achieved by making the horizontal dispersion negative in some regions of the arcs so that the average value taken in the dipoles is globally also negative. Such a modulation of the dispersion may make it increasingly difficult to obtain a large enough dynamic aperture in the presence of sextupoles. A careful optimization is therefore necessary, and the possibility of modifying the linear lattice in order to include the requirements associated with chromaticity adjustments has to be studied. Work done along this line is summarized, with attention given to a racetrack lattice that can be used in a hadron facility main ring. An alternative lattice design which tends to minimize the effects of the nonlinear aberrations introduced by sextupoles and to achieve a large dynamic aperture, keeping the betatron amplitudes as low as possible, is described