LHC Workshop - Chamonix XI

1. 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

2. Introduction • The subject is to check if the functional requirements of our instrumentation in ‘extreme’ conditions where the intensity signal to measure is the lowest are reasonable. • We imagined a possible injection scenario and deduced the precision requested for beam instrumentation. Injection Scenario & Consequences on BI

3. Injection Scenario: Quench Protection(J-B. Jeanneret) • 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. Injection Scenario & Consequences on BI

4. Proposed Injection Scenario: Step 1(SL/BI Specification Board) • 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. Injection Scenario & Consequences on BI

5. Proposed Injection Scenario: Step 2(SL/BI Specification Board) • 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). Injection Scenario & Consequences on BI

6. 24 nominal bunches on h=84 Injection Scenario: 24 nominal bunches Injection Scenario & Consequences on BI

7. Proposed Injection Scenario: Step 3 & 4(SL/BI Specification Board) • A check should then be carried out with one full PS batch (72 bunches) of nominal intensity. • Finally, we should be able to proceed with the full injection with a check at each SPS batch injected. Injection Scenario & Consequences on BI

8. Consequences on BPM (1/3): WBN Noise vs Intensity (BI Day 2000) I already do my best around 4*10^10 protons per bunch Injection Scenario & Consequences on BI

9. Pilot Stability estimated today to +- 10% (R. Garoby PS/RF) Consequences on BPM (2/3): WBN - Bunch Intensity Influence (BI Day 2000) No measurement is guarantied below the Pilot Intensity Injection Scenario & Consequences on BI

10. Consequences on BPM (3/3) • The performancedescribed 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). • TheBPM 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. Injection Scenario & Consequences on BI

11. Consequences onBeam Loss Monitors(‘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 canlocate lossesand provide this information (if an adequate post mortem is available). But a sudden (one turn) single bunch losswill 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. Injection Scenario & Consequences on BI

12. Consequences onCollimation System(J-B Jeanneret, R Jung) • It seems today that: • The Collimation System will be set to a raw position based on the measured orbitand experienceon 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. Injection Scenario & Consequences on BI

13. Consequences on BCT’s (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. Injection Scenario & Consequences on BI

14. Consequences on Emittance Measurements(LHC Beam Instrumentation Conceptual Design Report) • 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 onlyinstrument 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. Injection Scenario & Consequences on BI

15. A Word about Ions(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. Equivalent to 5.5 10^9 protons per bunches for BPM’s Injection Scenario & Consequences on BI

16. Conclusions • BPM are NOTguaranteed 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?). • ... Injection Scenario & Consequences on BI

17. 1997 1998 1999 2000 2001 2002 2003 2004 2005 Request 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. Injection Scenario & Consequences on BI

18. Consequences on BPM (1/5): Pick-Up Transfer Function (D. Cocq SL/BI) My favorite playground is between + and - 5 mm of my center Injection Scenario & Consequences on BI

19. Consequences on BPM (4/5):Accuracy and Resolution(LHC Beam Instrumentation Conceptual Design Report) Injection Scenario & Consequences on BI