A beam current of 250 mA was stored in the machine for the first time in 2001. However, the radiation induced outside the shielding exceeded the authorised level and tests were temporarily interrupted. After a campaign of systematic shielding reinforcement, experiments resumed in April 2003. Stable beam at 250 mA was stored in one-third filling mode. With this partial filling (330 bunches) of the circumference, the periodic beam loading of the cavities induces a spread in synchrotron frequencies along the bunch train that prevents the constructive built-up of Higher Order Mode (HOM) driven coupled bunch instabilities. The machine is now operated at this current during the restart period following each shutdown, in order to speed up the vacuum conditioning time required by the installation of new vacuum vessels. In the uniform filling mode, the stabilisation of the longitudinal coupled bunch instabilities is more difficult and has to be performed by a precise temperature optimisation of the RF cavity temperatures. A beam current of 250 mA was also achieved in that filling pattern but the HOM driven instabilities still need to be mastered in the whole [0 ­ 250 mA] current range. The final assessment of operating conditions will be performed in the forthcoming months.

As far as vacuum and heat load are concerned, the one-third filling mode is the most demanding. No abnormal pressure or temperature rise on critical components like ceramic chambers, crotches, bellow flat absorbers or RF windows was observed when ramping the current from 200 to 250 mA. The lifetime is in excess of 55 h in uniform filling mode (to be compared to 80 hours at 200 mA). This lifetime reduction is due to the higher residual pressure in the ring, the higher density of electrons in the bunch (Touschek lifetime) and to the increase in the chromaticity in order to stabilise the resistive wall instability.