PS2 beam parameters and proposal for aperture strategy

1. PS2 beam parameters and proposal for aperture strategy M. Benedikt Beams and apertures, M.Benedikt

2. PS2 design aspects • The upgrade of the CERN injector complex is motivated by LHC operation and the therefore the LHC requirements define the main design choices. • The injector complex should however provide flexibility and the potential for non-LHC physics applications • Design philosophy for the PS2 is to start optimization from LHC requirements and to keep other options open wherever in line with main requirements or not requiring important deviations. Beams and apertures, M.Benedikt

3. LHC requirements • The injector complex upgrade should provide a significantly higher beam brightness for LHC operation than presently available from the existing machines. • The maximum transverse emittances for the LHC beam are fixed because of aperture limitations at LHC injection energy in the LHC itself and its injection transfer lines. • Therefore beam brightness can only be increased by an intensity increase (assuming unchanged emittances) • Design goal for injectors: • Provide beams for LHC with up to twice higher brightness than the present “ultimate” beam: 3.4E11 instead of 1.7E11 protons per bunch (for 25 ns spacing) • PS2 has to provide an additional intensity reserve of ~20% 4E11 ppp. • Fixes injection energy to ~ 4GeV to have acceptable incoherent space charge tune shifts of DQ < 0.2. Beams and apertures, M.Benedikt

4. LHC beam in PS2 and PS Beams and apertures, M.Benedikt

5. PS2 potential for high intensity beams • The total intensity of the LHC beam in the PS2 is 6.7E13 protons per cycle, which is significantly beyond the SPS record of 5.3E13. • The LPSPL as PS2 injector provides a macro pulse of peak current 32 mA and 1.2 ms length. With a chopping ratio of 0.5 this translates into a total intensity of 1.2E14 per pulse. • Therefore a potential peak intensity of 1E14 protons per pulse could be envisaged and the impact on the PS2 design is analysed. • The bunch intensity (assuming 25 ns spacing) has to increase from 4E11 (LHC beam) to 6E11 to reach the peak intensity of 1E14. • Assuming identical longitudinal parameters and brightness as for the LHC beam, the norm. transverse emittances have to be increased by the same factor 1.5: • Transverse emittances norm. rms: ≥ 4.5 pmm (in both planes) • This has to be compared to 15/8 pmm (h/v) in the PS! Beams and apertures, M.Benedikt

6. Comparison of PSB-PS and LPSPL-PS2 • PSB – PS LHC beam: • PSB (h=1 at injection), 2E12/bunch, DQvert ~ 0.5, • Transfer PSB - PS at 1.4 GeV, h=1 (PSB) to h=7 (PS) • PS (h=7 at injection), 2E12/bunch, enorm,rms (h/v)=2.5 pmm, DQvert ~ 0.2, • Both machines space charge limited. • PSB – PS high intensity beam: • PSB (h=1 at injection), 8E12/bunch, DQvert ~ 0.6, bunch splitting before ejection • Transfer at 1.4 GeV to PS on h=2 (PSB) to h=8 (PS) • PS (h=8 at injection), 4E12/bunch, DQvert ~ 0.12, • Only PSB space charge limited because of bunch splitting before transfer to PS. • Nearly a factor 2 lower space charge at PS injection compared to LHC beam. • This difference between HI and LHC beams at PS injection originates from the production schemes, not from limitations in the PS. • This margin for operation should be (at least partially) exploited in the PS2 to produce high intensity beams within smaller norm. emittances (i.e.higher brightness), hereby reducing the aperture requirements. Beams and apertures, M.Benedikt

7. Aperture concept for PS2 – LHC beam • Use aperture formula as quoted by Javier/Yannis as basis • Aperture = nsigma√(e∙(b+Db))+D∙(Dp/p) total +COmax√b/bmax • Add radially space for chamber (2.5mm), alignment (1mm), heating jacket (5 mm). • Calculate number of sigmas for LHC beam as function of outside dimensions of vacuum system and closest points of magnet poles: Beams and apertures, M.Benedikt

8. Aperture concept for PS2 – HI beam • Assume transverse emittances of 9/6 pmm (h/v) for highest intensity beam to have lower space charge than for LHC beam. • Calculate number of sigmas for HI beam as function of outside dimensions of vacuum system and closest points of magnet poles: Beams and apertures, M.Benedikt

9. Apertures as function of intensity - HI beam • Assume emittances of 9/6 pmm (h/v) for beam with 1E14 protons and scaling of intensity with emittance (const. phase space density) • Calculate number of sigmas for HI beam as function of intensity: Beams and apertures, M.Benedikt

11. Main magnet aperture and aperture layout • Proposal for outer dimensions of vacuum system (incl. alignment and heating jacket) in the main magnets: • Dipoles half sizes: 60 mm horizontal, 40 mm vertical • Quadrupole half sizes: 65 mm horizontal, 45 mm vertical • Typical apertures for LHC beam: >6 / >5 sigmas (horizontal/vertical) • Typical apertures for HI beams: >3.5 sigmas (horizontal/vertical) • Comfortable situation for LHC beam with large operation margin • Apertures for HI beam (sigmas) smaller depending on intensity but offering the potential to reach 1E14 ppp with operation experience. • Best balance between space charge reduction, emittance increase and beam loss management will have to be established with increasing operation routine. • Collimation system with primaries at 2.5 – 3 sigmas for highest intensities, secondaries at 3 – 3.5 sigmas and around 0.5 sigma of margin to aperture limit. • All critical elements should be another 0.5 sigma in the shadow of the main magnets. • More informations needed on PS2 physics beams to estimate yearly beam power for beam loss considerations. Beams and apertures, M.Benedikt

12. Next steps • Feedback and discussion • Consolidate beam parameters, verify space charge calculations • Transverse beam distribution from painting • Consequences of smaller normalised emittances of HI beams for PS2 (MTE extractions, slow extraction) and for SPS • Stronger multipoles to excite beam for MTE, SE • Aperture requrirements for extractions • Need for emittance exchange to SPS? Minimum extraction energy • Detailed aperture concept for complete machine and collimation study • Injection and low-energy losses, intermediate energies, extraction losses for various beam emittances from LHC to HI for fixed/variable collimation settings. • Number of sigmas and space for collimation at low/high energies • Quadrupole chambers • Aperture requirements for kickers and other sensitive elements • More information on HI physics requests hopefully from May workshop on fixed target physics. Beams and apertures, M.Benedikt