Overview of 2012 mib in alice
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Overview of 2012 MIB in ALICE. A. Alici (INFN), A. Di Mauro (CERN) LBS #43, 28/01/2013. Introduction.

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Overview of 2012 mib in alice

Overview of 2012 MIB in ALICE

A. Alici (INFN), A. Di Mauro (CERN)

LBS #43, 28/01/2013


Introduction

Introduction

  • As already reported in previous LBS meetings (#35, #37 and #40), vacuum conditions in LSS2 limited significantly ALICE running and data taking in 2012. In particular, probably due to a not perfect bake out at the end of the intervention during the 2011/12 winter stop, the TDI has shown a vacuum performance worst than 2011 (contrarily to LHCb TDI).

  • ALICE cannot ramp up most of gaseous detectors when the total LSS2P is larger than ~ 3E-8 mbar, corresponding to bkgd contamination up to 50%; ideal operating conditions would be P < 7E-9 mbar

  • Some basic observations:

    • The pressure in the TDI increases during injection when the jaws are closed and when the total beam charge is larger than 1.4E11 p, the longer this condition is kept the larger the pressure increase

    • At the end of injection when the TDI jaws are opened the pressure decreases slowly, the larger the starting value the longer the recovery time; if the starting value is larger than ~3E-8 mbar the decrease is followed by a bump of several hours which further delay the vacuum recovery

  • After our proposal (LPC, 03/09/12) the injection procedure has been modified since Sept 4 in order to minimize the time spent with closed jaws with circulating Beam 1: B1 is injected first, then TDI jaws are opened and finally B2 is injected. However, the TDI (and Left LSS2) pressure during a given fill is affected also by total beam intensity and condition at the beginning of the fill (cumulative effect if short delay between consecutive fills) .

LBS#43


Alice vs lhcb tdi

ALICEvsLHCbTDI

With proper conditioning/bakeout acceptable behaviour, good hopes for post LS1…

LBS#43


Left lss2 p overview 08 12 2012

Left LSS2 P overview 08-12/2012

TDI p generally > 10E-8 mbar

TDI

ID800

VGPB.123

LBS#43


Id800 recombination chambers

ID800 recombination chambers

ALICE magnets polarity reversal

LBS#43


Fill 2997 bad

FILL 2997 (Bad)

LBS#43


Fill 2997 bad1

FILL 2997 (Bad)

Example of large P bump, no data taking in ALICE (bkgd rate >200 KHz during all fill)

LBS#43


Fill 3027 ok

FILL 3027 (OK)

First FILL with modified injection

LBS#43


Fill 3027 ok1

FILL 3027 (OK)

Start data taking at SB declaration

LBS#43


Bkgd rate measurements

Bkgd rate measurements

Correlation between Left bkgd rate measured by V0 trigger detector and product of beam intensity times sum of LSS2 pressure.

KHz

FILL 2858

LBS#43


Outlook

Outlook

  • Beam-gas simulation results were performed with R. Appleby’s and D. Brett’s help using a simplified FLUKA model of LSS2 for fill 2117 (2011) vacuum, results were presented in LBS#32.

  • In 2nd half of 2012 a new detailed model of LSS2 has been created by A. Lechner (EN/STI) and E. Leogrande (ALICE)

  • 2 M “20 m scoring planes” containing secondaries from beam-gas interactions in LSS2 for FILL 2736 vacuum have been generated during last weeks and will be used to produce events inside ALICE and x-check measured bkgd

LBS#43


Overview of 2012 mib in alice

BACKUP SLIDES

LBS#43


Fill 2736

FILL 2736

LBS#43


Alice vacuum layout

ALICE vacuum layout

A

C

A side

70 m

69.7 m

VGPB.623.4L2

VGI.500.4L2

120m

C side

70 m

69.7 m

VGPB.623.4R2

VGI.500.4R2

120m

LBS#43

14


Alice layout

ALICE layout

Beam 1

BCM-A

8 sensors

z = + 6 m, r = 10 cm

Beam 2

BCM C

7 sensors

z = -18.5 m, r=10 cm

LBS#43

15


The v0 detector

The V0 detector

ITS

V0A

rin=8 cm rout=100 cm

V0C

rin=8 cm rout= 76 cm

SPD

V0C

V0A

340 cm

90 cm

Two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection

LBS#43

16


V0 timing properties

V0 timing properties

V0A

V0C

IP

beam2

beam1

340cm

~11.3ns

90cm

~3ns

V0A+V0C ≈ 14.3ns

V0A-V0C ≈ 8.3ns

collisions

IP

beam1

Beam background from beam2

~-11.3ns

~3ns

V0A+V0C ≈ -8.3ns

V0A-V0C ≈ -14.3ns

Bkgd1 (BGA)

Beam background from beam1

IP

satellites

beam2

~11.3ns

~-3ns

V0A+V0C ≈ 8.3ns

V0A-V0C ≈ 14.3ns

Bkgd2 (BGC)

LBS#43


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