1. Vacuum Issues from the Beam Dynamics Point of View Marc Muñoz

2. Jul 05 Parameters and design approach Fixed budget for the whole project ~180 M€ Circumference limited to <270 m, due to the site and money. General layout: – Compact Lattice: Vertical focusing in the bending Only Doublets quads doublets Combined sextupole and correctors – Distributed dispersion – DBA-like structure. 16 Cells. 4-fold Symmetry 4×8 meters Long straight section 12×4.2 meters Medium straight section 8×2.6 meters Medium straight section

3. Jul 05 Parameters

4. Jul 05 Objectives Horizontal cross section < 150  m in the middle straight sections Vertical cross section < 10  m  x < 5 nm-rad Lifetime > 10 h Lattice energy acceptance > 3% As many as possible straight sections for users.

5. Jul 05 Design basics Expanded DBA structure Only doublets of quads, to save space, but more difficult fitting the optical functions Most of the vertical focusing in the bending magnets, due the inclusion of a large gradient ( 6 T/m) As many cells as possible (16) Short straight sections for IDs or instrumentation One long straight section for injection

6. Jul 05 Beam Sizes

7. Jul 05 Why we care about the vacuum system Three main reasons: – Lifetime. The pressure in the vacuum chamber is one of the determining parameters in the lifetime. For a good performance of the light source, we require a lifetime larger than 5 hours, and if possible close to 10 hours. – Impedance. The vacuum chamber determines the impedance, therefore the limits for the instabilities. – Lattice design. During the design period of the lattice, the needs of the vacuum system limit the position of the components. We should keep in mind the space needs for valves, tapes, flanges, etc.

8. Jul 05 Lifetime Touschek –6D tracking with Tracy, introducing a 1% coupling and vacuum chamber –For 400 mA:  T ~30.8 hours. –Limited by the RF Symmetric behavior of the energy acceptance for positive and negative dp. The limiting factor in both cases is the RF.

9. Jul 05 Lifetime-II The effect of quantum lifetime in all three directions is negligible Elastic scattering and bremsstrahlung lifetimes have been calculated for a residual N2 pressure of 1 nTorr Elastic scattering  78 h Bremsstrahlung  60 h Touschek  30 h Total 16 h Beam lifetime at 400 mA, including 1% coupling and the default vacuum chamber. The inclusion of a 3 rd harmonic cavity will increase it close to 25 h.

10. Jul 05 Lifetime III

11. Jul 05 Impedance The design of the chamber should be as smooth as possible in order to reduce the impedance. That can lead to open questions about the vacuum chamber material (Al, Steel, Cupper?). Particular care should be taken to avoid cavity like structures, where modes can resonate. One open question is what is the maximum opening for the slot of the vacuum chamber in the dipole. A larger slot simplifies the design, but can increase the impedance.

12. Jul 05 Other questions Vacuum chamber thickness in the sextupoles: In the ALBA case, the fast orbit correction is done by coils located in the sextupoles. In order to perform this correction at high frequency (over 100 Hz, and reaching values close to the 1 kHz, if possible), the chamber have to be as thin as possible.