Beam Commissioning Workshop 9 th December 2010 Strategy

Beam Commissioning Workshop, 9 th December 2010 Strategy for Luminosity Optimization S. White 1

Same Time Last Year • First experience with collisions at 450 Ge. V: Þ Initial optimization with BPMs. Þ “Manual” optimization. Low rates, very lengthy (~ 40 minutes/plane). R. Jacobsson • Example of LHCb: Þ Only three points / plane Þ Established communication protocol with experiments, test software and procedure. • Conclusions from last year: Þ Move on to an automated procedure and include in routine operation. Þ Assess impact on machine protection. 2

Progress in 2010 • Slowly moved on to a fully automated procedure: • April 2010: Þ L ~ 5. 0 x 1027 cm-2 s-1. Þ Automated scan operational. Þ Optimization in series, full procedure ~ 45 minutes. • November 2010: Þ Ions physics fill. Þ Optimization in parallel. Þ Full procedure few minutes. Þ Operational efficiency significantly improved. 3

Fill-to-fill Reproducibility • Amplitude of the corrections (B 1 -B 2) applied. Fills since 10 A/s ramp: Statistics over all fills excluding IP 2: Dxrms Dxmax Dyrms Dymax 41 mm 180 mm 21 mm 90 mm Þ Fill-to-fill reproducibility: in general within +/- 60 mm. Sufficient to find collision point with actual beam parameters (s ~ 60 mm). Þ Horizontal plane worse than vertical plane. Þ Nominal LHC: s ~ 16 mm. Could become more difficult. Þ IP 2: large differences due to offset collisions. 4

IP 2 • Amplitude of the corrections for IP 2 ONLY: Þ Separation applied in the horizontal plane. Þ Vertical plane, most of the time no corrections. Optimizing the vertical plane systematically would help control the orbit. 5

Fill Stability • Optimization performed only at the beginning of fills. Few checks done at the end of fills: Fill Nb. 1366 1372 1373 1393 1450 IP 1 X (mm) IP 1 Y (mm) IP 5 X (mm) IP 5 Y (mm) 3 3 2 10 1 -4 7 -2 6 16 -5 -3 -5 -1 -2 4 -2 - -5 - Þ Done only for IP 1 and IP 5. Þ No significant orbit (separation) drift observed within a fill. Þ Corrections could have been applied in a few cases (gain few %). Þ Need more systematic checks: try mini-scans every hour to confirm (could be done during regular physics fill). 6

Procedure to bring beams into Collision • Beams are brought into collision with a ‘PHYSICS’ beam process: Þ Ramps down the injection separation bumps (all IPs). Þ Loads the corrections from last fill. Þ Optimization scans launched manually by the operator. Þ Now done in ‘ADJUST’, no physics data acquired. • Latest fills: Þ Once all the bumps are loaded it takes ~10 minutes to go in STABLE BEAM. Þ From logbook: orbit corrections + lumi-scans. ~ 10 minutes Þ How can we optimize further? Can’t we declare STABLE BEAM earlier? 7

Collapsing the Separation Bumps • ‘PHYSICS’ beam process takes 108 seconds: Þ Procedure well optimized. Þ Duration scales with energy, constrained by slowest magnet. Duration can be further optimized with optics matching: Þ Example of IP 1 (linear approximation). Gain ~ 30 seconds. Þ Limited by MCBX. Initial specifications 5 A/s. Down to 20 seconds. • Alternative solution: split the strength between MCBXs, existing scheme for IR 8 (E. Laface). • Separation bumps are ramped down from 2 mm. Could be reduced during other operation phases. 8

Is the Machine safe during Luminosity Optimization? Example of an IP bump with and without MCBX: Þ Creates a large offset in the TCT region. Þ MCBX magnets not used for luminosity optimization. Þ Split the amplitude between beams. Þ Changing the orbit at the TCT cannot be avoided. Þ Collimators settings based on reference orbit. A large deviation from this reference can affect the hierarchy and the triplet protection. Þ Define the available margins (see talk by R. Bruce). Þ Quantify what is needed for luminosity optimization. Þ Set limits accordingly / find alternative solutions (move the TCTs? ). 9

Displacement at the TCT • Displacements at the TCTs from the scans ONLY: Beam 1 Statistics over all fills excluding IP 2 (beam 1): Beam 2 Dxrms 0. 08 s Dxmax 0. 29 s Dyrms 0. 05 s Dymax 0. 24 s Þ In general, within +/- 0. 2 s. Few cases above. Þ IP 2: goes up to 0. 5 s in the horizontal plane due to offset collisions. Þ 3. 5 m optics : well within margin in all cases (~ 2. 5 s). 10

Orbit at the TCT Horizontal plane Vertical plane Technical stop • Difference with respect to the reference orbit at the TCTs in STABLE BEAM (includes scans + other sources): Þ From the beginning several 0. 1 s offset (reaches ~1. 5 s in IR 2). Þ No significant orbit drift observed. Þ In some cases, fill-to-fill fluctuations >> 0. 2 s. Larger than what is expected from the scans. Þ The horizontal plane is worse than the vertical plane: consistent with the scans observations. 11

Projection for next Year (4 Te. V) • Three scenarios considered for next year (see talk by R. Bruce): b* = 2 m b* = 0. 8 m b* = 1. 5 m b* (m) Margin Dxmax 2. 0 2. 5 s 0. 23 s 1. 5 s 0. 2 s 0. 8 0. 5 s 0. 15 s Dxrms 0. 06 s 0. 05 s 0. 04 s Þ Contribution from the scans well within margin in all cases. 12

Moving the TCT with the beam? • Requested by the collimation team, several cases should be considered: • Luminosity optimization: Þ Done on a daily basis. Orbit variations at the TCT within tolerances. Þ Not necessary, would imply dynamic orbit reference. • Luminosity calibration (to be discussed in more details at Chamonix): Þ Done over larger separation, few times a year. Þ Required for +/- 6 s scan range. • Luminosity leveling (strategy to be defined). In case we use separation: Þ Experience from IP 2 shows large fluctuations: could become necessary (or use MCBXs? ) in case of large dynamic range. Þ Would give more flexibility in general for MDs and specific measurements. 13

Controls • Operational functionalities: Þ Automated single / parallel optimization. Þ Manual IR steering. Þ Automated calibration scans. Þ Online analysis. • To be added: Þ Moving the TCTs with the beam when necessary. Implementation ready in LSA (P. Meira). Requires specific RBAC rights, difficult to test and develop. How do we use/operate them? Þ Luminosity leveling: implement a set method? Same software? To be defined based on the outcome of Chamonix. • Maintenance and development: Þ Daily maintenance and debugging should be handled by OP. Þ New developments and strategy to be discussed within LPC+LBS. 14

Summary • Reproducibility and stability: Þ Good fill-to-fill reproducibility: in general < +/- 60 mm. Could become more difficult with smaller beams. Þ No significant drifts during a fill observed (to confirmed). Þ The horizontal plane is worse than the vertical plane. • Procedure to collide: Þ Declare STABLE BEAM as soon as possible. Þ Displacement at the TCT due to the scans well within tolerances. Þ Optimization can be done in STABLE BEAM. • Software: Þ Main functionalities operational. Þ Move the TCTs with the beam: Required for calibration scans (luminosity leveling? ). Strategy to be defined. Þ Luminosity leveling: requested by ALICE and LHCb. New tools required. Specifications, procedure and strategy to be defined. 15