“Bringing the first LHC beams into collision at all 4 IP's”

25 January 2006 Chamonix 2006 - Divonne Les Bains

“Bringing the first LHC beams into collision at all 4 IP's”

“Bringing the first LHC beams into collision at all 4 IP's”

E. BravinCERN AB-BI

Many inputs from W. Turner and A. Ratti

LBNL US-LARP

25 January 2006 Chamonix 2006 - Divonne Les Bains 2

• The aim of LHC is to produce collisions inside the 4 detectors: ATLAS, ALICE, CMS and LHC-b

• For ATLAS and CMS the collision rate should be as high as possible

• For ALICE and LHC-b the rate should be set and kept at optimal levels

Introduction


The collisions rate at an interaction point (IP) is proportional to the Luminosity and depends on many machine parameters

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Beam offsetsBeam parameters

Due to the large number of variable parameters it is very difficult to compute L from beam observables like currents, emittances and machine parameters like beta functions Need a dedicated monitor

LuminosityAn offset of 1

produces a 20% reduction in luminosity


Monitor the collisions rate by detecting the flux of forward neutral particles generated in the interactions

Collision Rate Monitors(aka “Luminosity monitors”)


The range of operation

Full specifications in LHC document LHC-B-ES-0007 rev 1.0

Day 1


The nominal performances

Full specifications in LHC document LHC-B-ES-0007 rev 1.0


LBNL is committed to develop and install fast ionization chambers in the 4 TANs around IP1 and IP5

CERN will install solid state CdTe detectors produced by CSA-LETI around IP2 and IP8

The challenge of these detectors is to be sufficiently radiation hard to survive 20 years of LHC operation (this means several GGy of integrated dose) and to be sufficiently fast and sensitive to allow the bunch by bunch measurement for luminosities in the range 1028 1034

The Monitors


History of Ionization Chamber


The LBNL Ionization Chamber


The LBNL Ionization Chamber

Courtesy of Berkeley lab


Status of LBNL detector

• The Ionization chamber final design will be ready soon

• First chamber will be delivered by end 2006, remaining 3 chambers by mid 2007

• Front end electronics well advanced and on track (most sensible item now.) B-by-B resolution is just right…

• Acquisition system based on the DAB card and FBCT integrators mezzanine. Programming of on board FPGA not yet started (potential source of worries)

• Gas system to be designed and installed, seeking help from CERN (TS+PH), contacts already established. AB/BI is following this up for the time being…


The LETI CdTe detector


Status of CdTe detector

• The design of the detector has been ready for a while… Technology stretched to the limit in terms of rad-hardness can not be used in IP1 and IP5

• Decision to proceed with this technology taken only at the end of 2005… trying to make it for the March FC…

• LETI needs about 12 months to produce 4 monitors… looks just ok

• Front end electronics could be off the shelf, in any case it is just a simple linear preamplifier

• For the acquisition system we hope to use the DAB as for the IC thus profiting from the development done by LBNL


The quest for a place in the TAN

• Until 2003 it was planned to install the IC as replacement of the 3th copper bar of the TANs

• Since then several other detectors have made their appearance and will replace more copper bars… In fact there is no more space for Cu bars in the TANs

• These detectors are: ATLAS-ZDC + LHCf at IP1 and CMS-ZDC at IP5… There is also the ALICE-ZDC at IP2 but this is another story…

• Not all detectors are in a design state suited for integration. There are interferences with the operation of the lumi, especially with LHCf


Colliding beams...“The final approach”

• Set up beams using BPM near Q1. Expected overlap incertitude ~200m

• This leaves 13 separation at m and 2 separation at =18m

• The collision rate is quite small there…

• Perform a raster scan around this position and find the position where the signal from the luminosity monitors is max

Easy…


But…

• At =18m luminosity is low even at best conditions: L=~1026 with 1 pilot bunch per beam

• Many unknowns about background

• Detector signals will have to be “understood” at this moment (not much can be done beforehand without beam for this…)

• Scans can be lengthy


Background

Estimated event rates for 2808 nominal bunches =0.5m and for 1 pilot bunch =18m

Vacuum pressure of 10-10 Torrs


… Background

• At high beta the ratio between pp collisions and unwanted effects like beam-gas and beam losses is much worse

• It might be necessary to use coincident detection on both sides of the IP. The system is currently not designed for that, but it should not be to difficult to implement… under investigation


Conclusions / Remarks

• BI and LBNL know the objective and the way to get there… the way is still steep…

• Insufficient resources on both sides of the Atlantic have delayed the lumi project, there is no slack… schedule is tight… no margin for error now!

• The TAN, once a lonely, awkward place is now much sought after… interferences between the different detectors are unavoidable… TAN workshop march ‘06

“Bringing the first LHC beams into collision at all 4 IP's”

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