Post LS1 operational envelope & MPS implications MPP Workshop March 2013 Post LS1 operational envelope & MPS implications Thanks to: C.Bracco, OP team, S.Redaelli, B.Salvachua, R.Schmidt, B.Todd, R.Tomas, J.Wenninger

outline Changes in LHC commissioning at 7 TeV Operational envelope after LS1 and possible improvements Conclusions

Commissioning strategy Beam intensity below which beam is considered safe (some interlocks can be masked) Without compromising machine protection, this possibility makes it easier (and faster) to commission the machine as: It allows to use a given fill for multiple actions It limits the risk of fill dumps due to non critical problems (i.e. spurious interlock or operational mistakes) Setup beam allows to mask the following channels on the BIC: BLM (maskable) IR6 BPM RF COLL movements AC dipole PIC (maskable) Setup beam is (mainly) used for: Chroma measurements COLL alignment Optics measurements Ramp/squeeze commissioning Loss maps Asynchronous BD

The safe beam Dump Screen HOW WAS THE INTENSITY BEAM LIMIT DEFINED? The effect of a high intensity beam impacting on equipment is not easy to evaluate, as it depends strongly on impact angles, beam size,… Controlled beam experiment for the LHC was performed (in 2005), by impacting a 450 GeV beam orthogonally on a target (multiple layers of Tin, Steel, Copper) installed in an SPS transfer line. Dump Screen 30 cm 108 plates 6 cm

The safe beam A B D C Controlled experiment with 450 GeV beam: A: no effect on copper (beam intensity ~1.2×1012 p) B: visible effect on copper, but no melting (beam intensity ~2.4×1012 p) ORTHOGONAL IMPACT! C: copper is damaged but no hole created (beam intensity ~4.8×1012 p) D: copper is melted with beam intensity ~7×1012 p (no damage on stainless steel) Results agree with simulations Shot Intensity / p+ A 1.2×1012 B 2.4×1012 C 4.8×1012 D 7.2×1012 A B D C

The safe beam flag

5x1011 p (factor 2) due to the small emittance The safe beam flag 5x1011 p (factor 2) due to the small emittance THE SAFE BEAM FLAG

The name SAFE beam made no longer sense -> SETUP BEAM FLAG(S) The setup beam flag For operational purposes there was a need of having at least 1 nominal bunch in the machine at high energy; moreover, as the possibility of an orthogonal impact is negligible some layers of safe beam flag were defined. The name SAFE beam made no longer sense -> SETUP BEAM FLAG(S) NORMAL RELAXED VERY RELAXED NORMAL is now a factor 2 above the damage limit at high energy RELAXED has been established to allow 1 nominal bunch at high energy (resulting in a factor 5 higher than the normal, thus becoming a factor 10 above the damage limit at high energy) VERY RELAXED has been established to allow 3 nominal bunches at high energy (resulting in a factor 13 higher than the normal, thus becoming a factor 26 above the damage limit at high energy)

The safe/setup beam at 7 TeV (maintaining the curves) After LS1 the LHC will be operated at an energy close to 7 TeV. The value of the normal setup beam flag would in this case allow an intensity of ~1x1010 (pilot beam) 4 Tev 7 TeV (maintaining the curves) Allowed intensity Factor (wrt normal) NORMAL 2.5x1010 1x1010 p RELAXED 1.2x1011 5 4.8x1010 p VERY RELAXED 3.26x1011 13 1.26x1011 p

The safe/setup beam at 7 TeV After LS1 the LHC will be operated at an energy close to 7 TeV. The value of the normal setup beam flag would in this case allow an intensity of ~1x1010 (pilot beam) 4 Tev 7 TeV (maintaining the curves) (maintaining the concept) Allowed intensity Factor (wrt normal) NORMAL 2.5x1010 1x1010 p RELAXED 1.2x1011 5 4.8x1010 p 1.2x1011 p 13 VERY RELAXED 3.26x1011 1.26x1011 p 3.26x1011 p 34 PLUS THE ε FACTOR It’s clear that we should review the concept of relaxed and very relaxed beam flag! Can we accept the same risk level as for 4 TeV operation? If so, a beam flag allowing 1 nominal bunch at 7 TeV can be defined!

Commissioning at 7 TeV Activity Comment Result Betatron loss maps It can be done with unsafe beam, adjusting the ADT parameters such that we lose a pilot equivalent intensity Not affected by the change in allowed intensity value Off momentum loss maps It could be done with a pilot, but only 1 LM per fill (see next slide for details) COLL alignment It must be done with nominal bunches (orbit)…need 3 for collisions The process done with unsafe beam would add complexity (and time consumption) Optics measurements (always done with safe beam) can be done with 1 pilot only More fills required as some intensity can be lost Chroma measurements Always done with pilot Asynchronous BD Often done with pilot

Commissioning at 7 TeV It’s theoretically possible to do off-momentum loss maps without losing the full beam (Belen’s slides) This would reduce the number of commissioning fills (it needs nominal beam) But in practice… OFF-MOMENTUM loss maps of April 3rd 2012 @4:47:42 am

Commissioning at 7 TeV Signal Timing RF - 1.149 s IR6 BPM - 0.405 s MSK BLM - 0.216 s UNMSK BLM The definition of a “relaxed” setup beam flag would allow to use this method If unsafe beam is used, 3 interlocks are potentially problematic: RF – the interlock can probably be changed (it looks like 150/200 Hz could do it (Belen’s slides) IR6 BPM (to be studied if it comes late enough!?) Maskable BLM (maybe coming late enough?!) Belens’s slides

The safe/setup beam at 7 TeV Some ideas/comments… With the same risk level taken in 2012 operation up to 1 nominal bunch at 7 teV would be allowed For asynchronous beam dump there is no difference between 1 and few (2/3) nominal bunches (as long as they are far away from each other!) If we ensure the protection of the cold aperture (always leaving the TCSG in IR6 inside at, say, 15 sigma margin and make sure the TCDQ is not moved out (should we removed it from the maskable inputs?))…could we eventually allow few nominal bunches (at least at flatop)? We should study the value with simulations (see Roderick and Alessandro) A distinction has to be made between global and bunch intensity (for failure scenarios, 3 nominal bunches are not quite the same as 30 pilots) We can think about 2 scenarios: “Standard” commissioning (loss maps, COLL alignment,…) with well-know configurations and centered orbit MDs or not well-known situations A warning could be generated if interlocks masked while changing SBF from relaxed to normal (for efficiency purposes)

7 TeV (“NON-standard”) operation Ramp&squeeze Settings have not yet been fully generated (ongoing); however we are confidents that squeezing to 3m (from 11 m) is possible and maybe even further squeezing is feasible Many operational challenges have to be faced (COLL function generation, PC settings, tune and chroma corrections,…) Nevertheless there is no machine protection related problem (COLL alignment strategy has to be carefully studied) From a MP point of view there is no problem to go for this option (potential problem on TCT alignment at intermediate optics)

7 TeV (“NON-standard”) operation Beta* leveling Beta* leveling could start at the end of the ramp or after a short squeeze Beta* leveling with fixed configurations - easy to manage and does not have MP implications UNfixed configurations – it could be not feasible, as: The number of MP checks would drastically increase (together with the number of possible configurations) The beta beat corrections in the arc would not be effective each time a further local squeeze is performed, as they use correctors in the IRs In order to allow stable beams declaration with non-fixed beta* values we need to: …either make a change in SMP to eliminate the beta* value from the safe stable beam flag inputs …or broaden the beta* limit values, basically resulting in having just an upper limit

7 TeV (“NON-standard”) operation Lower beta injection (9/7 m) Injection at lower beta would allow to consistently reduce the time spent in the squeeze Some machine protection implications have to be taken into account In particular we would go for a solution where the available aperture in the IT is used for smaller beta* without reducing the global bottleneck (thus avoiding changes in collimators settings at injection)…is this acceptable?

Possible improvements MD settings management

Possible improvements Settings management Ensure reproducibility of settings and limit the risk of erroneous trims: Implementation of an orbit-correctors-like system by creation of frozen BPs (non- trimmable copies of the original ones) against which checking the settings in critical phases of operation (i.e. with state machine)…static behavior! Implementation of a dynamic settings check (i.e. for COLL) Improve the usage of BP categories and active/resident cases Limitation on “non-CCC based” trims “Standardize” the bump management: The value of the bump interlock limit is presently based on the max RT trim bump allowed – duplicating the interlock would allow to have different interlock levels Definition of a clear margin in unit sigma (interlock)

Possible improvements Settings management Possibility to create some fixed "non-standard" COLL configurations to be used for MDs. If feasible, this could result in: Limiting manual operation on collimators Reducing the work load on COLL team (overloaded by constant presence in CCC during commissioning/MD) Re-enforcing machine protection It would require change in energy limit thresholds Implementation of an operation oriented tool to move COLL in case of "standard" needs, avoiding to use the expert tool (too powerful)

Possible improvements Some time has to be spent to classify at least frequent modification scenarios A clear test procedure has to be defined (and documented) for each of them A serious approach is needed to avoid the risk of operating a non qualified machine A tracking of the requalification is also important

CONCLUSIONS The concept of setup beam flag has to be ri-discussed in view of the gained experience and simulations The definition of a “relaxed” setup beam flag can be considered; this would help the commissioning process and be important for MDs (the AC dipole and TCQD movement could be removed from the maskable inputs) There is no a priori showstopper (from MP point of view) to go for ramp&squeeze and/or beta* leveling Lower beta injection has to be carefully studied! Some improvements can be done on settings management and HW re-validation to increase the reliability/reproducibility of the machine