LHC Workshop - Chamonix XI

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.



Injection Scenario: Quench ProtectionInjection Scenario: Quench Protection(J-B. Jeanneret)(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.



Proposed Injection Scenario: Step 1Proposed Injection Scenario: Step 1(SL/BI Specification Board)(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.



Proposed Injection Scenario: Step 2Proposed Injection Scenario: Step 2(SL/BI Specification Board)(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: 24 nominal Injection Scenario: 24 nominal bunchesbunches

24 nominalbunches on

h=84



Proposed Injection Scenario: Step 3 & 4Proposed Injection Scenario: Step 3 & 4(SL/BI Specification Board)(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.



Consequences on BPM (1/3): Consequences on BPM (1/3): WBN Noise vs IntensityWBN Noise vs Intensity (BI Day 2000) (BI Day 2000)

WBTN - 2nd PrototypeRMS Noise versus Beam Intensity

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1E+09 1E+10 1E+11 1E+12

Number of Protons per Bunch

RM

S N

ois

e [

mm

]

Noise 0

Noise 1

Noise 2

Pilot Nominal Ultimate

I already do my best around

4*10^10 protonsper bunch



Consequences on BPM (2/3): Consequences on BPM (2/3): WBN - Bunch Intensity InfluenceWBN - Bunch Intensity Influence (BI Day 2000) (BI Day 2000)

WBTN - 2nd PrototypeLinearity versus Beam Intensity (Period = 89 ms)

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1E+09 1E+10 1E+11 1E+12

Number of Protons per Bunch

Lin

ea

rity

De

via

tio

n [

mm

]

Lin 0

Lin 1

Lin 2

Pilot Nominal Ultimate

No measurementis guarantied below the Pilot

Intensity Pilot Stability estimated today

to +- 10%(R. Garoby PS/RF)



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.



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.



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.



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.



Consequences on Consequences on Emittance MeasurementsEmittance Measurements

(LHC Beam Instrumentation Conceptual Design Report)(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 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.



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



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?).

...



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



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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Beam Position [mm]

Me

as

ure

d B

ea

m P

os

itio

n [

mm

]Without Correction

With 5th Order Polyniomal Corrrection

My favorite playground is between

+ and - 5 mm ofmy center



Consequences on BPM (4/5):Consequences on BPM (4/5):Accuracy and ResolutionAccuracy and Resolution

(LHC Beam Instrumentation Conceptual Design Report)(LHC Beam Instrumentation Conceptual Design Report)

Bunch Type Pilot Bunch Bunches of Nominal IntensityMode ofOperation

Trajectory(singleshot)

Orbit(224 turnaverage)

Trajectory(single shot,

single bunch)

Trajectory(single shot,average of all

bunches)

Orbit(average of all

bunches over 224turns)

Resolution 200mm 20mm 50mm 5mm 5mm

EL

EC

TR

ON

ICS

Accuracy 500mm

AlignmentError

700mm

ME

CH

AN

ICA

L

Residualafterk-modulation

~50mm

Documents

LHC Workshop - Chamonix XI