  The goal for future neutrino facilities is the determination of the
$[U_{e3}]$ mixing and CP violation in neutrino oscillations. This will require
precision experiments with a very intense neutrino source. With this objective
the creation of neutrino beams from the radioactive decay of boosted ions by
the SPS of CERN from either beta or electron capture transitions has been
propossed. We discuss the capabilities of such facilities as a function of the
energy of the boost and the baseline for the detector. We conclude that the SPS
upgrade to 1000 GeV is crucial to have a better sensitivity to CP violation if
it is accompanied by a longer baseline. We compare the physics potential for
two different configurations. In the case of beta beams, with the same boost
for both $\beta^+$ (neutrinos) and $\beta^-$ (antineutrinos), the two setups
are: I) $\gamma=120$, L=130 Km (Frejus); II) $\gamma=330$, L=650 Km (Canfranc).
In the case of monochromatic EC beams we exploit the energy dependence of
neutrino oscillations to separate out the two parameters $U(e3)$ and the CP
phase $\delta$. Setup I runs at $\gamma=90$ and $\gamma=195$ (maximum
achievable at present SPS) to Frejus, whereas Setup II runs at $\gamma=195$ and
$\gamma=440$ (maximum achievable at upgraded SPS) to Canfranc. The main
conclusion is that, whereas the gain in the determination of $U(e3)$ is rather
modest, setup II provides much better sensitivity to CP violation.
