1380b 50ns schemes

LBOC 23-Aug-2011 CERN Massimiliano Ferro-Luzzi 1

1380b 50ns schemes1380b 50ns schemes

12b staggered, LR encounters in IP8 ALICE satellite-main collisions in 50ns physics


The "standard" 2011 1380b schemeThe "standard" 2011 1380b scheme

The intermediate 12b batch is shifted by 25ns such as to collide in IP2 (not IP8)


LR collisions at 3.75mLR collisions at 3.75m

The intermediate 12b gives staggered crossings in IP8: 12b make LR encounters in IR8 at 3.75m instead of usual 7.5m– with negative LHCb polarity (net angle of 40urad), the encounters are

closer than with the positive (1040urad). Is this an issue for operation / performance ? Note that most bunches make such LR collisions at 3.75m in IR2 This 12b staggered pattern in IR8 can be removed

– either in the standard scheme (remove 24 collisions from ALICE and add them to LHCb), not very nice for ALICE

– or by using the IR2 sat-main scheme (clearly preferred if we would have to make a choice)

7.5m 7.5mcollidingcolliding staggeredstaggered


12jul to 26jul12jul to 26jul

48b48b

264b264b

840b840b

1092b1092b

1380b N=1.051380b N=1.051380b1380bmain-sat IP2 collisionsmain-sat IP2 collisions

normal schemenormal scheme


Size of 25ns satellitesSize of 25ns satellites

Shown hear relative to average main bunch population

Scaling from 1.2e33 Hz/cm2 at IP1 (* = 1.5m) and assuming 2x1300 collisions in IP2 and homogeneous emittance, we need

Nsat25ns = 0.14%Nmain

for reaching 5e29 Hz/cm2 at IP2 (* = 10m), head-on.

Caveat: absolute value of measured fraction has systematics (under study) related to baseline subtraction.

Courtesy Adam JeffCourtesy Adam Jeff

fills 1900 and 1901fills 1900 and 1901


ALICE sat-main with 48bALICE sat-main with 48b

ATLAS/ALICE 9.5/0.007 = 1360ATLAS/ALICE 9.5/0.007 = 1360

expect 2600 for 0.1% sat fractionexpect 2600 for 0.1% sat fraction

main-sat IP2: ~23main-main IP1: 9main-sat IP2: ~23main-main IP1: 9


ALICE sat-main with 264bALICE sat-main with 264b

ATLAS/ALICE 250/0.054 = 4630ATLAS/ALICE 250/0.054 = 4630


main-sat IP2: ~427main-main IP1: 249main-sat IP2: ~427main-main IP1: 249


ALICE sat-main with 840b and 1380bALICE sat-main with 840b and 1380b

840b840b

1380b1380b

best lumi ratio ATLAS/ALICE = 5000best lumi ratio ATLAS/ALICE = 5000

"best" lumi ratio ATLAS/ALICE = 8800"best" lumi ratio ATLAS/ALICE = 8800




Rough summaryRough summary

IP2 lumi signal clearly visible, but on low side

Unfortunately: – no LDM measurement (?)

– no AFS summary files from ALICE (coming ?) NB: was ALICE asking/hoping for 2e30 Hz/cm2 ???

(was never advertised for a 0.1-0.2% sat fraction) Prospects:

– improved control of sat fraction in PS ?

– smaller emittance,

Bunches expected(0.1% sat)

seen expected/seen

48b 2600 1360 1.9

264b 3900 4630 0.84

840b 4000 8800 0.45

1380b 4000 5000 0.8

caveat: very coarsecaveat: very coarse


1380b with sat-main collisions in IP21380b with sat-main collisions in IP2

250ns gaps in SPS

all bunches are staggered in IR2, hence each main collides with an "empty" 25ns slot... unless there is a satellite at that place!


Why bother ?Why bother ?

Benefits:– ALICE luminosity diluted over all 25 ns slots: perfect, minimize pile-up!

– More collisions in ATLAS (1%), CMS (1%) and LHCb (2%)

– SPS 250ns gap: "more relaxed operation" w.r.t. 225ns gaps

– And... (but is this really a benefit ?) no more LR encounters at 3.75m for the 12b in IP8

Prospects:– PS RF (Steve Hancock): potentially could control the 25ns satellite

intensity!

– Next year: could squeeze ALICE according to achievable population of 25ns satellites,

e.g. b*=1m would allow operating with current satellite populations

– Upgrade: if choose 50ns and if 3 main-main collisions are too much, this trick would maybe allow upgrade operation with ATLAS / CMS / LHCb (5e34, 5e43, 2e33 lumies)

all small gains, but all realall small gains, but all real

1380b 50ns schemes

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