R. Assmann - LTC Two Beam Operation R.W. Aßmann with W. Venturini and V. Kain LTC Acknowledgements to W. Herr, V. Previtali, A. Butterworth, P. Baudrenghien, J. Uythoven, J. Wenninger, … LHCCWG presentation on May 8 th

R. Assmann - LTC Commissioning Stage This concerns phase A.6: “450 GeV – Two Beam Operation” Essentially this means: –No crossing angle required (at maximum 156 bunches). Intensity: –Two beams should first be commissioned with safe beam in both rings. –Phase A.5 (“450 GeV, increasing intensity”) must be done before increasing intensity.

R. Assmann - LTC Entry Conditions With 5×10 9 p to 3×10 10 p: –Both beams have completed single-beam commissioning (phases A.1 to A.4): Orbit and optics have been adjusted. Instrumentation is operational for single beam. The two RF systems are operational. Aperture is understood at the mm level. Available n1 known. Stored beams are characterized and reasonably close to nominal behavior (lifetime > 5h, emittance < 3.75  m). –Injection bucket monitor application commissioned (for verification of injection) and “bucket tagging” done (A.2) for both rings (collision points known). –Radial position adjusted and consistent for both rings (A.2, A.3). –Separation bump knobs prepared in LSA. –Operational tools for “simultaneous” beam measurements in beam 1 and beam 2. At higher intensities: –Phase A.5 completed. –Automatic machine protection is operational (impossible to baby-sit two independent beams at all times).

R. Assmann - LTC Summary Commissioning Plan 1.Preparation and verification of injection. (A.6.1) 2.Clean up corrector settings in all IR’s to have consistent values for the two beams. (A.6.2) 3.IR set-up for and with two low intensity beams: a)Separation bump set-up. (A.6.3) b)“Common” beam diagnostics (BPM’s, BLM’s) commissioning and checks (A.6.5) c)Triplet alignment check. (A.6.4) d)IR aperture characterization and safety check. (A.6.3) e)Passive protection set-up: injection and tertiary collimators. (A.6.6) f)Machine protection set-up (e.g. software interlock on separation bumps) and verification. (A.6.3) g)RF phasing. (A.6.5) h)Collisions at 450 GeV. 4.Two-beam multi-bunch operation without crossing angles: a)Interleaved injection process. (A.6.7) b)Equalization of beam characteristics. (A.6.8)

R. Assmann - LTC 2 – Clean Up Corrector Settings Settings of common correctors might be different for the two beams after single beam commissioning. Zero or minimize settings of common correctors. If we cannot get through without common correctors, try beam1 corrector settings with beam2 or vice versa. Apply orthogonal beam1/2 orbit correction with 1 beam (enforce zero change for not filled beam). If problems encountered to store two beams (very unlikely): –Longitudinally separate the two beams (injection into different buckets). –Inject and correct on two beams (1000 turn data and/or orbit).

R. Assmann - LTC 3a – IR Set-up: Separation Already done in A.4.9? The two beams can collide in the IP´s (or close to them) without separation. Separation bumps must be set up before putting two beams. Can be done for individual single beams. Knobs for the different IP´s exist  can be put into place once the beam is centered in the triplet and once BPM offsets are known: –Base bump: Uses common correctors. Not orthogonal (separation in both beams). Is set up deterministically. –Tuning bumps: Orthogonal for beam1/2 and for x/y. Get correct orbit and separation. –Degrees of freedom (DOF) per IR: 5  around the ring 20 DOF for separation. Plenty of aperture should be available at injection (no crossing angle). Dispersion is changed. Check aperture after putting separation bumps. Separation constant in normalized coordinates (fields ramped with √  ) during the energy ramp.

R. Assmann - LTC X-planeY-plane

R. Assmann - LTC X-planeY-plane

R. Assmann - LTC Horizontal Dispersion with Separation Bumps

R. Assmann - LTC 3b – Commission Common Beam Diagnostics Common BPM´s: –There are no beam-beam effects or other electro-magnetic couplings expected between the two beams (low intensity, 156 bunches, no crossing angle). –Each beam during two beam operation should have the same position readings as the single beam. –Can be checked by dumping one of the two beams (avoids uncertainties from drifts). BLM‘s: –There can be cross-talk from beam losses to BLM‘s located for the other beam. –Effect should be measured and compared to expectations (small effect is predicted). Can have impact on BLM thresholds. Compare with single beam results for cross-talk.

R. Assmann - LTC 3c – Determine BPM to QUAD Offsets in Triplets K-modulation in common triplets for the two beams (if not done before): –Relies on the fact that the beam orbit is insensitive to the quadrupole strength if the beam is in the magnetic center of the quadrupole! –Changes in quad strength (k-modulation) will reveal any beam offsets in the quadrupole. –Output are the BPM readings for beams in the magnetic center of the quadrupole: x 0,beam1, x 0,beam2, y 0,beam1 and y 0,beam2. –Output is also  * in the IR (tune measurement). Knowledge of this data will allow: –Centering beams in the triplet aperture. –Cross-check of BPM offsets for beam1 and beam2. –Deterministic set-up of separation bumps (relying on relative BPM readings). If problems  realign triplets!? Can be done manually or automatically.

R. Assmann - LTC 3d – IR aperture Characterization Minimum available IR aperture is easily determined via standard techniques: –Static closed orbit bumps until beam loss is measured (edge can be defined by collimators at x  ). –Separation bumps can be used. –Must be done with local bumps, as IR must not be the limiting aperture at injection. Does not mean a full determination of IR aperture versus s. Can be skipped if done carefully before this phase, if common BPM’s are performing well and if separation bumps are understood. Details not described here. See other presentations.

R. Assmann - LTC 3e – Adjust Two-Beam Collimators Two-beam collimators are common to two beams, collimating one in the vertical plane and leaving the other free. In IR 2 and IR 8: –Each IR has 1 two-beam collimator for injection protection (TCLIA). Even if not used at this stage, adjust their positions to the beam such that we get nominal aperture. –Each IR has 2 two beam collimators for triplet protection (TCTVB). Even if not required at injection, adjust their positions to the beam such that we get nominal aperture.

R. Assmann - LTC Procedure 2-Beam IR: Check Basics Up to 3×10 10 p (safe beam). Select IR (one IR at a time): Prepare and verify proper injection (correct buckets for collisions in selected IR, consistent radial offsets for both beams). Fill B1. Put in base separation bump and correct orbit B1 without common correctors. Dump B1. Fill B2. Correct orbit B2 without common correctors. Dump B2. Fill B1+B2. Perform common orbit correction. Dump B1. Check change in B2 meas. of common BPM’s and BLM’s in the IR’s. Dump B2. Fill B1+B2. Dump B2. Check change in B1 meas. of common BPM’s and BLM’s in the IR’s. Dump B1.

R. Assmann - LTC Procedure 2-Beam IR: Alignment, Orbit, Separation Fill B1+B2. Check offsets triplet magnetic center versus BPM’s (k-modulation). Triplet realignment if a bad surprise was encountered (preferably delay any needed realignment to planned access period). Fine tune separation bumps in x, y, B1, B2 to achieve nominal separation orbit. Measure dispersion. Record reference settings. Set up and/or check passive protection from IR collimators: TCTH, TCTVA, TCTVB, TCLIA, TCLIB, TDI. RF phasing. Collapse separation bump and observe changes in orbit and loss maps. Correct closed orbit and record required correction (incorporate in separation bumps, if strong corrections are needed). Parasitic collisions. Dump.

R. Assmann - LTC Procedure 2-Beam IR: Protection Checks IR Fill B1. Measure available IR aperture for B1. MP check: Try to put 7 TeV separation bump at 450 GeV. Abort before quench triggered from BLM system. If needed, adjust BLM thresholds. Fill B2. Measure available IR aperture for B2. MP check: Try to put 7 TeV separation bump at 450 GeV. Abort before quench triggered from BLM system. If needed, adjust BLM thresholds. Fill B1+B2. Start software interlock on separation bumps and check functionality. Ready for increased intensities.

R. Assmann - LTC 4a – Interleaved Injection Goal is to have two beams stored at 450 GeV with equal properties, like intensity and emittance. It is known: –Many beam parameters are functions of time. –Two stored beams can have inter-dependencies, especially for more than 156 bunches. It is therefore preferable to set up an interleaved injection process. Advantages also for machine protection (sanity of two beams constantly monitored during injection process). If this interleaved injection is prepared, it should be applied early on as a standard filling mode. Verification of procedure is logically included in this commissioning phase. Details: LHCCWG discussions (SPS supercycle with 2 LHC cycles or change supercycle, …)

R. Assmann - LTC 4b – Equalize Beam Characteristics Measure major beam characteristics (emittance, lifetime, intensity) and optical parameters (tune, chromaticity, …). Should be equal for two beams or one beam stored. Can be checked by dumping one of the two beams. Should be equal from one beam to the other. If unequal between the beams then equalize the two beams. Tolerances relaxed at lower intensities and larger beta* (much smaller beam-beam effect) but good to diagnose potential issues early on. Will facilitate the diagnostics of beam behavior during ramp, squeeze and collision. Important if unequal luminosity between experiments results.

R. Assmann - LTC Summary Commissioning Plan 1.Preparation and verification of injection. (A.6.1) 2.Clean up corrector settings in all IR’s to have consistent values for the two beams. (A.6.2) 3.IR set-up for and with two low intensity beams: a)Separation bump set-up. (A.6.3) b)“Common” beam diagnostics (BPM’s, BLM’s) commissioning and checks (A.6.5) c)Triplet alignment check. (A.6.4) d)IR aperture characterization and safety check. (A.6.3) e)Passive protection set-up: injection and tertiary collimators. (A.6.6) f)Machine protection set-up (e.g. software interlock on separation bumps) and verification. (A.6.3) g)RF phasing. (A.6.5) h)Collisions at 450 GeV. 4.Two-beam multi-bunch operation without crossing angles: a)Interleaved injection process. (A.6.7) b)Equalization of beam characteristics. (A.6.8)

R. Assmann - LTC Exit Conditions Two 450 GeV beams safely stored with lifetime of 5-10 h. Separation bumps fully commissioned with common correctors. Beam calibrated separation bumps including corrections. Triplet alignment checked. IR aperture fully characterized and safe for both beams (n1 > 7). Passive protection (collimators) in place for both beams. The injection  * of 11m fully proven. Else fallback to 17 m (very unlikely). Automatic machine protection checked with safe intensities (e.g. “7 TeV separation bumps” in IR’s). Interleaved injection process commissioned. Beams reasonably equalized: –∆ Emittance ≤ 40% –∆ Intensity ≤ 20% Up to 156 bunches possible in the IR.

R. Assmann - LTC Conclusion This is not the most complicated stage of commissioning but will certainly be very exciting. This commissioning step can be performed quickly (even too quickly) but should be done properly to have a good and safe base for further work (I estimate 3-4 shifts per IR, 3-4 days in total). Goal: Understand the IR’s early on and fix problems (alignment) if machine access is possible. It will be the first time that we must have a detailed look at the experimental IR’s: this will come back with more stringent requirements later. Full safety of the IR’s assessed and proven with dedicated MP tests. Remember: Special risks associated with IR orbits and bumps! First 450 GeV collisions in every IR possible without significant overhead. Two-beam operation (450 GeV and 7 TeV) will become challenging with more than 156 bunches, high intensities and lower beta*: long-range beam-beam, crossing angles, reduced aperture, beam-beam effects, …

R. Assmann - LTC Backup

R. Assmann - LTC 5 – Equalize Radial Offsets It is assumed that the same RF frequency and harmonic number is set up for the two beams (see presentation by G. Arduini). This means that the two beams have the same revolution frequency. Any different ∫BdL or path length for the two beams will then result in a momentum offset and a corresponding radial offset: 1 cm  C  1.5 mm  x in the arc Offsets in the two beams should be of equal magnitude. Equalize if necessary (see talks by A. Butterworth and G. Arduini). Implications on injection.

R. Assmann - LTC 6 – Adjust Injection Timing LHC has 2 independent RF systems. LHC is the master. The bunches in beam1 and beam 2 need to be injected into the right RF buckets. Requirement: Bunches collide at the IP. Final phasing will be done with feedback from experiments. Rough phasing done here: –Observe beam induced pickup signals in a common BPM and adjust the delays. Ideally done with two common BPM‘s symmetrically at both sides of the IP, using same cable length (ideal phasing condition: beam 1 left arrives at same time as beam 2 right). –Alternatively, do rough phasing with single beam wall-current monitors in IR4 (known cable length). –Details by P. Baudrenghien in June. Monitor of injection buckets (foreseen from fast BCT) should be operational.

R. Assmann - LTC 7 – Verify and Adjust Separation Bumps After detailed adjustments (radial offsets, injection timing, equalization, BPM offsets) check again crossing bumps. If needed fine-adjust to the target bumps. Determine the aperture in the triplets in absolute and normalized terms. Separation constant in normalized coordinates (fields not ramped) during the energy ramp.