LHC Workshop - Chamonix XI LHC Workshop - Chamonix XI Intensity of the Pilot Bunch: Intensity of the Pilot Bunch: Injection Scenarios and Injection Scenarios and Consequences on Beam Consequences on Beam Instrumentation Instrumentation J-J Gras - SL/BI • Introduction • Assumed Injection Scenario • Consequences on BI • Conclusions and Wishes
LHC Workshop - Chamonix XI. Intensity of the Pilot Bunch: Injection Scenarios and Consequences on Beam Instrumentation J-J Gras - SL/BI. Introduction Assumed Injection Scenario Consequences on BI Conclusions and Wishes. Introduction. - PowerPoint PPT Presentation
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LHC Workshop - Chamonix XILHC Workshop - Chamonix XI
Intensity of the Pilot Bunch:Intensity of the Pilot Bunch:
Injection Scenarios and Consequences Injection Scenarios and Consequences on Beam Instrumentationon Beam Instrumentation
J-J Gras - SL/BI
• Introduction
• Assumed Injection Scenario
• Consequences on BI
• Conclusions and Wishes
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 2/17]
IntroductionIntroduction
The subject is to check if the functional The subject is to check if the functional requirements of our instrumentation in requirements of our instrumentation in ‘extreme’ conditions where the intensity ‘extreme’ conditions where the intensity signal to measure is the lowest are signal to measure is the lowest are reasonable.reasonable.
We imagined a possible injection scenario We imagined a possible injection scenario and deduced the precision requested for and deduced the precision requested for beam instrumentation.beam instrumentation.
19 January, 2001 Injection Scenario & Consequences on BI
Step 1: 5 10^9 protons. Pilot bunch operation will be ‘quench free’ at 450 GeV. Once we managed to close the Pilot bunch trajectory on itself, loss is spread over many
hundred turns (~500). It is then possible to tune the orbit and set the collimators to put the machine in a ‘safe’
state allowing a further increase of the tolerable intensity to 2.5 10^12 protons (~1% of
the total nominal intensity, ~25% of a nominal PS batch) using the heat reserve of the helium and keeping the same safety margin.
Step 2: 2.5 10^12 protons This intermediate intensity will be used to set the collimators at final positions. The LHC
should then be ready to welcome its first nominal SPS batch.
Step 3: First nominal SPS batch.
At collision energy (7 TeV), the Pilot bunch intensity is about 3 orders of magnitude above the quench limit and that no ‘full quench free’ study will be possible at this energy.
19 January, 2001 Injection Scenario & Consequences on BI
First injection and circulating beams should be established with a single Pilot bunch of 5.10^9 protons to prevent any damage due to uncontrolled persistent currents.
The aim of this stage is to: Close the orbit Establish circulating beams with a lifetime sufficient for standard
beam measurements Correct and stabilise the orbit Set the collimator system in the 'safe' stage mentioned in the
previous chapter.
19 January, 2001 Injection Scenario & Consequences on BI
It is possible now to inject up to 2.5 10^12 protons in total and : this intermediate beam should be upgradable towards nominal without taking too much
risks. Its bunch structure should not prevent the existence of the long-range beam-beam effect. It should allow beam instrumentation to provide a precision close to the one requested by
luminosity operation. It should be quick and easy to produce by the injectors.
This stage should allow to put collimators at final injection positions.
A good answer could be a PS batch ( 72 bunches/25 ns) with 3 10^10 protons per bunch (nominal structure, close to the foreseen 'Commissioning' beam definition at 1.7 10^10 protons per bunch and good measurement conditions).
It could also be a batch of 24 nominal bunches separated with 25 ns (or 75ns if necessary) (nominal bunch intensity and good measurement conditions).
19 January, 2001 Injection Scenario & Consequences on BI
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 10/17]
Consequences on BPM (3/3)Consequences on BPM (3/3)
The performance described in the LHC Beam Instrumentation Conceptual Design are adequate for the proposed scenario.
The performance measured today on the prototypes are in conformity with this conceptual design and will allow Q, Q’ measurements with the intermediate beam.
The BPM could potentially give information on intensity and help locating sudden losses (if an adequate post mortem is available).
The BPM system is NOT working below Pilot intensity. An efficient orbit feedback loop based on the BPM will be
necessary to ‘freeze’ the orbit in the cleaning sections in order to be able to use the collimation system. The necessary stability has been estimated (JB Jeanneret) to 1 σ at injection (~1 mm) but 1/10 of a sigma at top energy (~30 µm).
Such a feedback is a non trivial request.
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 11/17]
Consequences onConsequences on Beam Loss MonitorsBeam Loss Monitors
(‘LHC Beam Instrumentation Conceptual Design Report’ & ‘A BLM System for the LHC Ring’)(‘LHC Beam Instrumentation Conceptual Design Report’ & ‘A BLM System for the LHC Ring’)
The maximum sensitivity requirements will be at top energy so the system will be able to handle this injection scenario and protect the machine on the same bases (but different thresholds of course) than the one required at top energy.
The BLM can locate losses and provide this information (if an adequate post mortem is available). But a sudden (one turn) single bunch loss will induce only one count in the concerned pin-diodes foreseen around the quadrupoles.( 1 count per 5 10^5 protons lost at 450 GeV but with a maximum counting rate of 40 MHz). ACEM and Ionisation chambers will provide more quantitative information in the cleaning sections.
The BLM will be used to set properly the collimators once the orbit will have been stabilized. The requirements for this phase in terms of sensitivity and strategy still have to be discussed.
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 12/17]
Consequences onConsequences on Collimation SystemCollimation System
(J-B Jeanneret, R Jung)(J-B Jeanneret, R Jung)
It seems today that: The Collimation System will be set to a raw position based on the
measured orbit and experience on its accuracy. The Collimation System will then be set carefully to the aimed position
based on the cleaning section beam loss monitors. This relies on an adequate control of the orbit stability.
A given set of Primary and Secondary collimators will have to move ‘at the same time’ and be ‘linked’ to the machine state, mode and energy (these ‘at the same time’ and ‘linked’ will have to be clarified).
The requested resolution of the collimators (around 10 µm needed at top energy) can be achieved.
The problem may come from Thermal Dilatation (~1µm/º). This could lead to a ‘cercle vicieux’ and require a (slow) feedback loop based on the BLM.
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 13/17]
Consequences on BCT’sConsequences on BCT’s (LHC Beam Instrumentation Conceptual Design Report) (LHC Beam Instrumentation Conceptual Design Report)
The DC BCT is foreseen to have a resolution of 1 µA (~5 10^8 p.) over the whole dynamic of 10^6 (21 bits ADC) to reach nominal intensity (~3 10^4 p.). Thus, around 10% of a Pilot Bunch .
The Bunch to Bunch BCT should have a better resolution equivalent to 2% of a pilot bunch (10^8 p) over a dynamic range of 2 10^3 (12 bits ADC).
LEP experience showed that DC BCT’s are good for absolute measurements and BtB BCT’s for relatives measurements.
These performances are adequate for our injection scenario requirements.
No ‘good’ lifetime measurement will be possible with one Pilot. BtB based lifetime measurement should be available for the
intermediate beam. 20 h. lifetimes should be measured with a precision of 10% within 10s.
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 14/17]
Consequences on Consequences on Emittance MeasurementsEmittance Measurements
The Wire Scanners will be the reference for transverse profile measurement in LHC. They can only be used with limited intensity (~10^13 p) but will be fully operational for our intermediate beams probably even for selected bunch by bunch measurements with an accuracy on beam sizes better than 5%.
If accepted, the new Low Energy (< 2 TeV) Synchrotron Light monitors will allow a cross calibration check at the intermediate stage and take over during full SPS batches injection. This would also be the only instrument allowing non destructive turn by turn measurements at these low intensities and energies.
Both equipment will be installed close to each others. Cross calibration should then be possible without ß function knowledge.
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 15/17]
A Word about IonsA Word about Ions(P. Collier’s SLI Web Pages)(P. Collier’s SLI Web Pages)
BPM are at the limit with 6 10^7 Lead Ions per bunch. (What about Ions Pilot Bunch Intensity and quench levels?)
A proton beam with the same structure than the ions one could be helpful to prepare the machine.
OTR, IPM integrated over 20ms will be OK. Wire Scanners OK. SL monitors to be investigated at 450 GeV (again low energy one is mandatory).
Lifetime, Q, Q’ measurements to be investigated.
Species Z A 10^7 ions/b Nb of Bunches
Lead, Pb 82 208 6.8 608Tin, Sn 50 120 28 608Kripton, Kr 36 84 55 608Argon, Ar 18 40 220 608Oxygen, O 8 16 1200 608
Equivalent to 5.5 10^9 protons
per bunchesfor BPM’s
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 16/17]
ConclusionsConclusions
BPM are NOT guaranteed below Pilot bunch intensity per bunch.
No 'full safe' operation will be possible at top energy. Other devices (like BCT) should also be able to signal
rapidly these sudden loss events. We need information/confirmation on Ion Beam
Intensities for our functional specifications. An efficient control system (GUI, feedback, post
mortem, middleware, timing…) will be mandatory already the first day (sector test with beam or not?).
...
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 17/17]
Request and WishRequest and Wish
Take software constraints and potential into account as soon as possible and don’t hesitate to involve software responsible in related discussions.
Would it be possible, if reasonable, to have a reviewed and updated version of the LHC Conceptual Design document in addition to the Web reference.
1997 1998 1999 2000 2001 2002 2003 2004 2005
19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 18/17]
Consequences on BPM (1/5): Consequences on BPM (1/5): Pick-Up Transfer Function Pick-Up Transfer Function (D. Cocq SL/BI)(D. Cocq SL/BI)
Pick-Up Transfer Function
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10
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Beam Position [mm]
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With 5th Order Polyniomal Corrrection
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19 January, 2001 Injection Scenario & Consequences on BI
Chamonix XI - [S. 19/17]
Consequences on BPM (4/5):Consequences on BPM (4/5):Accuracy and ResolutionAccuracy and Resolution