1. 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

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

3. 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

4. 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

5. 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

6. The safe beam flag

7. 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

8. 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)

9. 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

10. 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!

11. 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

12. 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 am

13. Commissioning at 7 TeV Signal TimingRF s
IR6 BPM s
MSK BLM 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

14. 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)

15. 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)

16. 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

17. 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?

18. Possible improvements
MD settings management

19. 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)

20. 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)

21. 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

22. 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