Satellites for ALICE ?

LPC at LBOC 05-Jul-2011 CERN Massimiliano Ferro-Luzzi 1

Satellites for ALICE ?Satellites for ALICE ?

Could this be used ?


ALICE collisions with 50ns high intensityALICE collisions with 50ns high intensity

Reminder, currently colliding pairs for IP2:

50ns_1380b+1small_1318_39_1296_144bpi13inj

ALICE was hoping for same luminosity with >100 colliding pairs (lower pile-up). Not "easily achievable" in the current scheme...

Alternative: use collisions between satellite and main bunches ? Only possibe if:

– satellites at 25ns are substantial enough => luminosity (in head-on orbit) can be sufficiently large (>5e29 Hz/cm2)

this means: Nsat25ns > ~0.14% Nmain on average (approximately)

– we remove all main-main collisions in IP2 and run head-on this requires 250ns gaps instead of 225ns between trains

39 = 14 inter-train+23 from shifted 12b train+2 from probe-main

39 = 14 inter-train+23 from shifted 12b train+2 from probe-main


Reminder: where do the main-main come from in IP2Reminder: where do the main-main come from in IP2

no change for IP1/5no change for IP1/5

change in IP1/5change in IP1/5

The exact four-fold pattern would be

Q1 Q2 Q3 Q4

RF buck X +0 +8910 +17820 +26730

Maximizing IP8 after IP1/5 is done by adding on top of the above and to both rings (not really needed for 75ns, but crucial for 50ns)

beam1 +0 +30 +60 -30

beam2 +0 +30 +60 -30 To give non-colliding bunches to IP1/5 while optimizing number of collisions

in IP8, one adds (instead of previous)

beam1 +0 +30 +60 -30

beam2 +0 +30 -60 -30

LHCb: beam1-beam2 = +30 (ATLAS/CMS: beam1=beam2)

ALICE: isolated collisions when |beam1-beam2| = 90 buckets


What's happening at IP2 with 50ns spacing & 225ns gaps ?What's happening at IP2 with 50ns spacing & 225ns gaps ?

if using 225 ns spacing between two PS batches in the SPS, then collisions will occur between the last bunch of a train and the first bunch of subsequent train of other beam – corollary: there must be at least 2 trains in the batch

– Note: 225ns = 9*25ns (90 RF buckets) PRO: gives isolated collisions (spaced by at least ~2us) CONTRA: only few of these (max ~16 with 1380 bunches)

IP2225 ns


From the logbook: fill 1900From the logbook: fill 1900

Satellite bunch measurements with LDM for beam 2.Large satellite 5 ns after the bunch. size varies from bunch to bunch, from 0.5% of main bunch to 2.5%. See attached screenshots.

For beam 1, the satellite 5 ns after the bunch is partly masked by the instrument response, but looks like it is slightly smaller (0.5 - 1.5% of main bunch)

start of 1st trainstart of 1st train

middle of 3rd trainmiddle of 3rd train

start of last trainstart of last train

Courtesy Adam JeffCourtesy Adam Jeff

NB: ALICE informed of likely non-reproducibility. What is crucial is that we can reach 5e29. If more, we can always separate a bit.

NB: ALICE informed of likely non-reproducibility. What is crucial is that we can reach 5e29. If more, we can always separate a bit.


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


Any work at injection ?Any work at injection ?

Prepare / test SPS trains with 250 ns gaps– new patterns prepared by Delphine (Thank you!)

Note: Length of 50ns/144b with 225ns: 7675ns Length of 50ns/144b with 250ns: 7750ns Length of 25ns/288b with 225ns: 7775ns the one used for testing Last injectable bucket remains 31181, no issue with AGK.

To be checked: Verify that can correctly inject the 50ns/144b with 250ns

length = time between first and last bunch


Ramp-up after TS (based on rMPP)Ramp-up after TS (based on rMPP)

If OK with you:If OK with you: Scenario to bring back the LHC to 1380b operation after the

Technical Stop is:– 1 test ramp with 1 pilot/beam

– 1 physics fill with Single_2_1_1_1(_wp?), loss maps (?)

– 1 physics fill with ~50b



– back to physics at 1380b

Remarks:– "1 fill" of course assuming everything's OK

– Fills with 2b, ~50b, ~260b can be short stable beams request by the expts: ~3h for the 50b and 260b fills

– The 840b fill could be normal (potentially ~1e33 Hz/cm2 !).

test ALICE sat-main: OK / notOKtest ALICE sat-main: OK / notOK

injection checks of 7750nsinjection checks of 7750ns

ALICE confirm OK / notOKALICE confirm OK / notOK


Two possible paths (pending decision on Path A proposal)Two possible paths (pending decision on Path A proposal)

Path A: satellite-main collisions in ALICE

(probe overinjected, 250ns SPS gaps, IP2 head-on) – 1 fill with 50ns_48b_9_0_36_36bpi2inj

– 1 fill with 50ns_264b_249_0_240_36bpi8inj

– 1 fill with 50ns_840b_807_0_816_108bpi12inj

– lumi produc 50ns_1380b_1331_0_1320_144bpi12inj

Path B: normal main-main collisions in ALICE

(probe kept, 225ns SPS gaps, IP2 separated) – 1 fill with 50ns_48b+1small_10_13_36_36bpi3inj

– 1 fill with 50ns_264b+1small_250_25_216_36bpi9inj

– 1 fill with 50ns_840b+1small_802_31_792_108bpi13inj

– lumi produc 50ns_1380b+1small_1318_39_1296_144bpi13inj

One can change from one path to the other (reversible)

new filling schemes to be created

new filling schemes to be created

Work for SPS. So... do not abuse

preview at http://lpc-afs.web.cern.ch/lpc-afs/FILLSCHEMES/(working directory)

preview at http://lpc-afs.web.cern.ch/lpc-afs/FILLSCHEMES/(working directory)


Scheme 50ns_48b_9_0_36_36bpi2injScheme 50ns_48b_9_0_36_36bpi2inj



*please, check

SPS: 250ns gaps in trains Inject probe into bucket 3601*

(for example), then it's overinjected by the first 144b train but not by the intermediate 12b batch

Beams head-on in IP2

NB: could move back all trains by 360 buckets. Any reason for that ?NB: could move back all trains by 360 buckets. Any reason for that ?


Work on injectionWork on injection

1. Lengthen the MKI pulse length by 75 ns.

2. Take an SPS beam with two probes. One at position 1 and one at 7775 ns + 3 * 25 ns = 7850 ns (before the test was done with 7775 ns). Inject the first bunch at position 31181 in the LHC.

3. Dump the beam and check that the last bunch is not touched by the rising edge of the MKD.

4.a If all is ok, no further modifications are required.

4.b If not OK:

a. Lengthen the AGK length set (set to about 11 us). This can be done from the CCC and takes about half an hour.

b. Find the new `last bucket' one can inject at, this will be smaller than the present limiting bucket 31181.

c. Inject two SPS probes spaced by 7850 ns and check the dump.

d. If ok, modify the value set for the last bucket in SIS and IQC.

e. If not ok re-iterate step 5.

courtesy Jan Uythoven et al.courtesy Jan Uythoven et al.

Satellites for ALICE ?

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