LHC Technical Committee, 23/05/2007 1 LHC Commissioning Phases Squeeze presented by Massimo Giovannozzi on behalf of the LHCCWG Particular thanks to S. Redaelli , G. Arduini, R. Assmann, R. Bailey, B. Goddard, V. Kain, M. Lamont, L. Ponce, J. Wenninger, EICs, LHCCWG members and ABP-LCU members
30
Embed
LHC Technical Committee, 23/05/20071 LHC Commissioning Phases Squeeze presented by Massimo Giovannozzi on behalf of the LHCCWG Particular thanks to S.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
LHC Technical Committee, 23/05/2007 1
LHC Commissioning Phases
Squeeze
presented by Massimo Giovannozzi
on behalf of the LHCCWG
Particular thanks to
S. Redaelli, G. Arduini, R. Assmann, R. Bailey, B. Goddard, V. Kain, M. Lamont, L. Ponce, J. Wenninger, EICs,
A.5 450 GeV, Increasing intensity: prepare the LHC for unsafe beam
A.6 450 GeV, two beam operation
A.7 450 GeV, collisions
A.8 Snap-back and ramp: single beam
A.9 Top energy checks
A.10 Top energy, collisions
A.11 Squeeze: commissioning the betatron squeeze in all IP's
A.12 Physics runs: physics with partially squeezed beams, no crossing in IP1 and IP5
Phases for full commissioning Stage A (pilot physics run)
Basic Objectives:• Master mechanics of squeeze• Control and protect aperture during optics change • Control orbit and optics during squeeze • Establish procedures and references (orbit, tune) for the feedback operation• Establish collimators settings during the squeeze (in particular TCTs to protect the triplet) as
well as TCDQ • Prepare for collisions with squeezed beams and physics
LHC Technical Committee, 23/05/2007 5
Squeeze – Overview of Steps Involved
Step Activity Priority
A.11.1Beam-based calibration of collimators for triplet protection and cleaning
Collimation Team
1
A.11.2 Load magnet settings into the hardware ABP/OP/PO 1
A.11.3Running the betatron squeeze with detailed measurements (beam parameters, optics, ...) for new beta*
ABP/OP 1
A.11.4 Preparation to bring the beams into collision ABP/OP 1
Priority categories (71th LTC):1. absolutely mandatory, 2. should be done if possible, 3. would be nice if it could be done
Iterative procedure for steps 1 to 3: to be repeated for each intermediate beta* stop point until we can get to the final value for physics.
Remark: The squeeze will be performed by changing gradients (linear interpolation) in between two matched optics.Recap of key parameters:
• Max 156 bunches
• No crossing angle
• beta* = 2 m
LHC Technical Committee, 23/05/2007 6
Squeeze - General commissioning approach
Goal: commission simultaneous squeeze of the IP1 and IP5, both beams
How can we get there during commissioning?
1. Start with a single pilot Beam 1 and squeeze IP1 without separation
2. Verify squeeze of one beam with parallel separation
3. Squeeze two separated pilot beams in IP1
4. Commission squeeze in IP5 with a single pilot Beam 1 (squeeze in 2 IP’s in parallel) - try with separation on
5. Try two beams in IP5 as well
• Remark: First commissioning done with detector magnets ON (input from their effect from collisions without squeeze, A.10). We should be ready to switch them OFF in case of difficulties.
• Remark: Squeeze of IP8 (and IP2) will follow in a similar manner.
LHC Technical Committee, 23/05/2007 7
Squeeze – Entry Conditions - IAssumption: The squeeze takes place with circulating beams at 7 TeV and does
not start at lower energies. • Beams separated, no crossing in IP1 and IP5 (works up to 156 on 156)
• Stable and well measured optics at 7 TeV for both - separated – beams (as exit of A.9):
– Reference "golden" orbit with beam-beam separation ON established for feedback. – Reference "golden" orbit established in the cleaning and dump insertions.– Beta-beating measured and under control in all the machine.
• Orbit and optics stable in the cleaning and dump insertions (1 sigma at 7 TeV).– If needed, the orbit feedback must be commissioned and operational, at least for local
orbit control at collimator locations (IR7 and IR6, maybe also IR3 if momentum cleaning is needed).
• Aperture measured at critical bottlenecks and corrected to acceptable levels (as exit of A.4 and A.9).
Aperture bottlenecks will appear during betatron squeeze: special measurements to be performed at 450 GeV.
Tolerance tables on beam parameters to be defined…
LHC Technical Committee, 23/05/2007 8
Squeeze – Entry Conditions - II• Collimators and dump protection elements (TCDQ) tuned to ensure
required cleaning and protection. – Cleaning collimators: after-ramp settings of injection optics at 7 TeV.
– Dump system fully commissioned for 7 TeV beams.
NB: collimators and dump protection elements (TCDQ) will require setting adjustments for every beta* step.
• Tertiary collimators (TCTs) hardware-commissioned and ready to move. Beam-based determination of closed orbit, beam size and divergence at each TCTs.
• Landau octupole circuits fully hardware-commissioned. • Ready-to-use magnet settings from MADX optics files and all timing
tables (trigger events/measurements). • Full commissioning of squeeze settings generation and trim (timing
tables) for insertion magnets.
A decision must be taken beforehand on the number of steps during the squeeze and on the final value of beta* for physics at each IP.
LHC Technical Committee, 23/05/2007 9
Squeeze – Entry Conditions - III• All instrumentation operational (no special requirements for squeeze).
Instrumentation commissioning done at phases A.3, A.6, A.10.
• All software operational (no special requirements for squeeze).
• Orbit monitoring + feedback available (commissioned for constant optics).
• Q, Q' monitoring + feedback available (commissioned for constant optics).
Need dedicated commissioning for feedback! Change of optics matrices for correction algorithm, triggered from sequencer or manual timing distribution, has to be operational. However, the algorithm proved to converge also with 100% beta-beating…
• Distribution of beta squeeze factor for machine protection commissioned.
• Roman Pots, VELO, LHCf OUT. Verification of the interlock signals. • Detector magnets ON
LHC Technical Committee, 23/05/2007 10
Squeeze – Stage A.11.1 – Setup of TCTs for triplet protection and cleaning - I
• Collimators settings based on measured apertures (phases A.4, A.9). • End-of-ramp settings for the collimators can be kept up to beta* ~ 6 m.• Then, TCT will be set such that the triplet aperture is protected for the
next beta* value. All the other collimators and TCDQ will be moved in to provide cleaning and protection for reduced aperture corresponding to next beta* value.
T. Weiler Collimation WG#85
Remarks: TCTs will always be used to ensure triplets protection (independently on intensity/beta* values).
LHC Technical Committee, 23/05/2007 11
Squeeze – Stage A.11.1 – Setup of TCTs for triplet protection and cleaning - II
RWA, 28/11/2006 21
2) Squeeze
• Squeeze reduces overall machine aperture, for * smaller than about 6 m!
• Triplets become the aperture bottleneck in the LHC (act as primary collimators risk of quench and damage)!
• Collimators must be closed before the actual squeeze to prevent this from happening!
• Very tight machine tolerances from collimators with small gaps: proceed in stepsto profit from larger tolerances as long as possible!
• Impedance will increase once collimators are being closed. Tune spread from octupoles is required to stabilize beam!
• Overall orbit and optics must be sufficiently under control to always ensure protection of the machine! Feedbacks will help to ensure this!
• Squeeze is a complex and dangerous process in the LHC…
R. Assmann LHCCWG#18
LHC Technical Committee, 23/05/2007 12
Squeeze – Stage A.11.1 – Setup of TCTs for triplet protection and cleaning - III
RWA, 28/11/2006 26
Reduced Procedure for Low Intensity
End of Ramp Measure tail population to 6
Correct machine
Switch off FB (transv)
Correct machine
Adjust coll IR3/7 for n1 of next * step (apply 1 margin)
Load the relevant functions of current versus time in the hardware, namely• Insertion quadrupoles• Lattice sextupoles to correct chromaticity during squeeze• Insertion correctors
21/11/2006 LSA 2006 2
Optics
•Machine Layouts in LSA database From layout database (Chris, Delphine)
•LOOP OVER MAD Perl (Marek)
•All optics in the LSA database Twiss, strengths, optics parameters
M. Lamont LHCCWG#18
Remark: the target for Stage A is beta* = 2 m. Nonlinear correctors in triplets are not needed above beta* = 1 m. Otherwise functions for these circuits should be loaded, too.
LHC Technical Committee, 23/05/2007 14
- As many functions as the foreseen beta* steps have to be generated.- Need to define the appropriate timing events for each step. - Functions loaded ~ 10 s before the squeeze, then triggered by timing
events. - Few minutes are needed to generate the settings on-line (including
matrices for feedback).
Squeeze – Stage A.11.2 – Load settings - II
21/11/2006 LSA 2006 6
GENERATION
•Optics versus time•Time from ΔI and dI/dt limits•Parabolic round in and round off
between optics Allowing stop in squeeze
M. Lamont LHCCWG#18
• Do one beam at a time, one IP at a time according to the pre-defined order.
• Obviously this will not be the case for standard operation but we should start simple.
• dI/dt limits: Q4 is usually the limiting circuit for the squeeze
t for each beta* step: max of t for each insertion quadrupole circuit.
LHC Technical Committee, 23/05/2007 15
Squeeze – Stage A.11.3 – Run the squeeze - IOnce functions for the first beta* step are loaded and ready in the
hardware, the squeeze can be triggered by timing events sent out by the operators. Before this…
1. Switch ON continuous monitoring of tune and chromaticity (BBQ, PLL).2. Monitor beam losses around the ring, in particular in the IP and in the
cleaning IR's. 3. Continuous monitoring of the orbit. Feedback working (cleaning
insertions, dump region AND IP that is being squeezed). 4. If it is available, start a monitoring of the local orbit at the TCTs (H + V).
Save data for later analysis.
Then…
1. Trigger the change to the first beta* value by sending the appropriate timing event.
2. Ready to dump if something goes wrong.
LHC Technical Committee, 23/05/2007 16
Squeeze – Stage A.11.3 – Run the squeeze - II
In case everything goes well…
1. Perform the required measurements (optics, aperture, ...) at the new beta* value.
•Detailed measurement program and its procedures to be defined.•Define appropriate check procedures for optics and orbit in collimation and
dump regions.2. If necessary, adjust beta* with optics knobs (MADX on-line model).
3. Check losses and beam halo / adjust cleaning collimators and TCDQ for next step, if needed (changes only required for beta*< ~ 6 m).
4. Set the tertiary collimators to ensure an adequate level of MQX protection (later, with higher intensities, also to ensure cleaning!).
5. Record optimum collimator settings in the appropriated databases for the generation of the time functions of settings.
LHC Technical Committee, 23/05/2007 17
Squeeze – Stage A.11.3 – Run the squeeze - III
Ready to move to the next beta* value.
1. Load functions for new beta* step for the insertion magnets.2. Load updated settings for the main sextupole families. 3. Update the octupole settings if needed (depends on collimator settings/transverse feedback).
Trigger the next beta* step.
In case something goes wrong and the beam is dumped, try to understand where is the problem (post mortem analysis) and restart.
LHC Technical Committee, 23/05/2007 18
LHCCWG - November 29th 2006 6
Squeeze (3/4)
Quadrupole gradients [T/m] in the Dispersion Suppressor (Q7-Q10) as a function of : beam1 (left) beam2 (right)
Rather smooth except for 1 m << 2 m
S. S. FartoukhFartoukh, 23 LTC meeting, 23 LTC meeting
Squeeze – Stage A.11.3 – Run the squeeze on paper - I
LHC Technical Committee, 23/05/2007 19
Squeeze – Stage A.11.3 – Run the squeeze on paper - II
LHCCWG - November 29th 2006 7
Squeeze (4/4)
Quadrupole gradient [T/m] in the trim quadrupoles (QTL11,-QT12,QT13) as a function of : beam1 (left) beam2 (right)
Smooth/monotonous for beam1 but more “erratic’’ for beam2, with unavoidable zero-crossing for both beams (matching procedure could be optimised if needed)
S. S. FartoukhFartoukh, 23 LTC meeting, 23 LTC meeting
LHC Technical Committee, 23/05/2007 20
LHCCWG - November 29th 2006 11
BehaviourBehaviour of optical parameters during of optical parameters during squeeze of IR1 squeeze of IR1 -- IIII
Squeeze – Stage A.11.3 – Run the squeeze with real magnets - I
Position of the problem
From a magnet standpoint, the low squeeze is a sequence of current ramps, eventually with changes of sign and stopsfor beam measurements and corrections
There are two possible implications, i.e.Hysteresis crossing
Decay and snapback
Both change the actual field produced for a given current (transfer function)
W. Venturini LHCCWG#21
LHC Technical Committee, 23/05/2007 24
Max setting errors,from hysteresis loops
(without modeling hysteresis crossing)
• MQM ~ 30 units at 320 A, 10 units at 1000 A, 5 units at 2000 A
• MQY ~ 25 units at 200 A, ~10 units at 300 A
• MQTL ~ 90 units at 17 A, ~ 25 units at 34 A, etc..
No decay, or if any, below measurement noise (pretty high in this particular case)
Small loop
Squeeze – Stage A.11.3 – Run the squeeze with real magnets - III
W. Venturini LHCCWG#21
LHC Technical Committee, 23/05/2007 26
Squeeze – Stage A.11.3 – Run the squeeze with real magnets - IV
W. Venturini LHCCWG#21
Concluding remarks (1) Δk = f(k) can be extracted from hysteresis loops These errors due to hysteresis add to global uncertainty
on gradients, with the present FIDEL model FIDEL modeling of hysteresis crossing should bring
errors in the range of few units, but this gets harder at low currents
Very low settings for MQTL and MQT, difficult to manage: transfer functions diverge, it is difficult to get the desired field
No decay in MQT and MQTL On MQM and MQY full decay characterization needs
more data (measurement foreseen in 2007) Data are available at the median injection current, which is only indicative.
LHC Technical Committee, 23/05/2007 27
Squeeze – Stage A.11.4 – Preparation to bring the beams into collision
Assume that we are able to squeeze both beams separately for beta* values down to the value agreed for physics runs. Settings for movable devices are also defined.
Then, after this (details in A.10):
• Inject both beams, ramp and squeeze them both (with separation still ON).
• Once both beams are squeezed, load into the power supplies of the orbit correctors the functions to set the separation OFF (get them from MADX model).
• Switch OFF the orbit feedback (local orbit correction at the IR(s) that is(are) being squeezed) and trigger the event "go in collision“ (next phase…).
LHC Technical Committee, 23/05/2007 28
Squeeze – Exit Conditions• Betatron squeeze commissioned in all relevant IPs in a defined number
of step points.– Goal: define the maximum amount of losses and the required beam quality
(emittance blow-up, final beta* value) after squeeze.
• Definition of time-dependent settings for all the movable devices (collimators and TCDQ) versus beta* values and versus beam-beam separation, to be used later for automatic squeeze triggered by sequencer. This includes also interlocks position functions.
• Definition of reference orbits in the experimental insertions versus beta*.
• Definition of procedures for feedback operation – reference orbit– when to switch it on/off
• Definition of procedures for Q, Q' feedback operation.
• Definition of procedures for using Landau octupoles (expected to be needed only for higher beam intensities).
LHC Technical Committee, 23/05/2007 29
Summary• Phase A.11 :
– Squeeze beams
• Main focus is on:– Control the mechanics of the squeeze– Control and protect the aperture during the squeeze– Control the orbit and the optics during the squeeze– Protection of triplets using TCTs– Define the actual procedure/sequence to squeeze the various
insertions
• At the end of this phase:- beams can be brought in collision…
Squeeze criteria & requirements – Chamonix XIV [O. Brüning] What is required to safely get the beam out of the LHC – Chamonix XV [B. Goddard] Beam commissioning of the collimation system – Chamonix XV [R. Assmann]
• LHCCWG presentations:Collimation During Ramp and Squeeze, LHCCWG#18 [R. Assmann]Squeeze mechanics, LHCCWG#18 [M. Lamont] Squeeze optics and power converter settings, LHCCWG#18 [S. Fartoukh, M. Giovannozzi, J. Jowett, Y. Papaphilippou]Commissioning Procedures, LHCCWG#21 [S. Redaelli] 450 GeV Optics: IR Aperture and IR Bumps, LHCCWG#13 [Y. Papaphilippou] 450 GeV Optics – Mechanical Aperture and Momentum Aperture, LHCCWG#11 [S. Redaelli], Overview of Feedbacks and Implications for Commissioning, LHCCWG#6 [R. Steinhagen]Response Matrix Measurements and Analysis, LHCCWG#9 [J. Wenninger] Behaviour of the magnets through the squeeze, LHCCWG#21 [W. Venturini]Optics measurements needed at top energy, LHCCWG#22 [F. Zimmermann]Two-beam operation, LHCCWG#25 [R. Assmann]
• Other presentations:IR1 & IR5 optics updated for the LHC V6.5, LTC 31/03/2004 [S. Fartoukh]V6.5 optics development in IR2 & IR8, LTC 31/03/2004 [O. Brüning]Requirements in ramp & squeeze, LHC MAC 9-11/12/2004 [O. Brüning]Squeeze of the crossing scheme in IR1 & IR5, ABP-LOC 11/10/2005 [S. Fartoukh]Discussion of the operational procedure for squeezing the beams, ABP-LCU 12/02/2007 [S. Redaelli]Progress in IR8 matching for beta* squeeze, ABP-LCU 26/02/2007 [Y. Papaphilippou]Final squeeze solution for IP8, ABP-LCU 21/05/2007 [Y. Papaphilippou]LHC ramp commissioning, LTC 9/5/2007 [M. Lamont]LHC Orbit Stability during β* Squeeze, LHC Collimation WG 27/11/2006 [R. Steinhagen]