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Satellites for ALICE ?

Satellites for ALICE ?. Could this be used ?. ALICE collisions with 50ns high intensity. 39 = 14 inter-train +23 from shifted 12b train +2 from probe-main. Reminder, currently colliding pairs for IP2: 50ns_1380b+1small_1318_39_1296_144bpi13inj 

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Satellites for ALICE ?

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  1. Satellites for ALICE ? Could this be used ?

  2. ALICE collisions with 50ns high intensity 39 = 14 inter-train +23 from shifted 12b train +2 from probe-main • 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

  3. Reminder: where do the main-main come from in IP2 • 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 no change for IP1/5 change in IP1/5

  4. What's happening at IP2 with 50ns spacing & 225ns gaps ? 225 ns IP2 • 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) To remove these, one must use 250ns gaps

  5. From the logbook: fill 1900 Courtesy Adam Jeff start of 1st train • 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) middle of 3rd train start of last train NB: ALICE informed of likely non-reproducibility. What is crucial is that we can reach 5e29. If more, we can always separate a bit.

  6. Size of 25ns satellites fills 1900 and 1901 Courtesy Adam Jeff • 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.

  7. 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

  8. Ramp-up after TS (based on rMPP) 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 • 1 physics fill with ~260b • 1 physics fill with ~840b • 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 / notOK injection checks of 7750ns ALICE confirm OK / notOK

  9. 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 preview at http://lpc-afs.web.cern.ch/lpc-afs/ FILLSCHEMES/ (working directory) Work for SPS. So... do not abuse

  10. Scheme 50ns_48b_9_0_36_36bpi2inj

  11. Scheme 50ns_264b_249_0_240_36bpi8inj

  12. Scheme 50ns_840b_807_0_816_108bpi12inj

  13. Scheme 50ns_1380b_1331_0_1320_144bpi12inj • 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 ? *please, check

  14. Work on injection courtesy Jan Uythoven et al. 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.

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