US LHC Accelerator Research Program berkeley brookhaven fermilab

US LHC Accelerator Research Program berkeley - brookhaven - fermilab - slac TAN Instrumentation for Optimization of LHC Luminosity W. C. Turner LBNL Presented at CERN TAN Instrumentation Meeting 9 -10 Jan 2006 TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Outline • Concept • Particle fluxes • Detector considerations • Integration time • Backgrounds • SPS H 4 tests TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

TAN and TAS absorbers in IPs 1 and 5 • The TAS absorbs ~200 W of forward collision products that have escaped the beam tube in front of Q 1 (mostly charged pions and photons) • The TAN absorbs ~ 200 W of forward neutral collision products (mostly neutrons and photons) and is placed in front of the outer beam separation dipole D 2 • Propose to instrument the TAN and TAS to measure and optimize the luminosity of colliding bunch pairs with 40 MHz resolution TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

TAN power deposition (W/kgm) • Peak pwr density 1 -10 W/kgm (location of ionization chamber) • A 3 m radiation hard cable will allow electronics to be located in a region with pwr density < 10 -5 W/kgm (100 Gy/oper yr) TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

TAN activation at 30 d/1 d (m. Sv/hr) • Contact dose < 0. 1 m. Sv/hr at outer r = 55 cm and back surfaces of the TAN (ok to stand in region per CERN guidelines) • Contact dose inside the inner absorber box exceeds 1 m. Sv/hr (requires remote handling per CERN guidelines) • Our goal is to design a detector that can be operated indefinitely without maintenance or replacement TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 5

The left-right asymmetry ratio is a sensitive function of the crossing angle - TAN 142 m from IP, Xing angle = 150 mrad – Measurement of the asymmetry ratio at the position of the TAN allows determination Xing angle TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 6

Incident particle fluxes on the TAN per pp interaction An example: TAN neutrons L = 1034 cm-2 s-1, sinel = 80 mb <n> = 0. 48 neutrons/pp int f = 40 MHz bunch Xing TAN Inst Mtg 9 -10 Jan 2006, CERN => 8 x 108 pp int/s => 3. 8 x 108 n/s => 9. 6 n/bunch Xing W. C. Turner – TAN Lumi Instrumentation 7

Design constraints for a detector placed near the shower maximum in the TAN • Very high peak radiation fluxes and high induced activation over many years of operation, 170 MGy (17 GRad)/oper yr, • Size limited to 80 x 80 mm 2 by beam-beam separation at the TAN • ~ 25 ns clearing time between bunch crossings • Sensitivity to a single pp interaction with good S/N ratio, ~ 270 mips in 40 x 40 mm 2/ppi TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Candidates considered for lumi detectors • A gas ionization chamber was our first choice - the simplest detector that can meet the requirements TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 9

Layout of Neutral Absorber ionization chamber Multi plate ionization chambers 4 ea 40 mmx 40 mm TAN inner absorber box 370 mm TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 10

Parameters for an ionization chamber prototype module tested at CERN SPS in 2001 Active area(1 quadrant) Plate gap No. of gaps Capacitance/gap Gas Gap voltage Electron gap transit time mip per pp int (3 W/kgm) mip per bunch xing@1034 Electron/ion pairs/cm-mip Ioniz e-/pp int Ioniz e-/bunch xing@ 1034 TAN Inst Mtg 9 -10 Jan 2006, CERN 40 mm x 40 mm 0. 5 mm 60 (electrically 6 series x 10 parallel) 28. 3 p. F Ar+N 2(2%), 4 x 760 Torr 300 V 15. 9 nsec 268 5. 35 x 103 388 5. 2 x 103 (1 gap) 5. 2 x 104 (10 gaps) 1. 04 x 105 (1 gap) 1. 04 x 106 (10 gaps) W. C. Turner – TAN Lumi Instrumentation 11

Concept for optimization of luminosity An intentional transverse sweep of one beam introduces a time dependent modulation of luminosity e = error offset amplitude d = intentional sweep amplitude • Define the detector current • Integrate to obtain the luminosity and error offset, 0 < t < T, TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 12

Integration times are sufficiently short to be practical even for the lowest luminosity envisioned (TOTEM) – Bunch by bunch measurements increase the integration times by the number of bunches (x 2808 for L = 1034, x 36 for TOTEM) – The practical sweep frequency needed for beam-beam separation measurements will determine the integration time at the highest luminosity TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 13

Estimated sources of luminosity background and systematic error are small compared to the pp inelastic collision rate Process Scaling Rate(sec-1) • pp inel collisions • beam-gas collision (10 -10 Torr) • beam-halo scraping (1: 6, 500 cleaning eff) • 1 mm slow drift of IP • 1 mrad slow drift of xing angle ~L ~L 1/2 8 x 108 3. 5 x 104 ~L 8 x 104 ~L ~L 8 x 103 1. 2 x 106 TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 14

Background due to activation • There are two sources of activation induced dark current – thermal neutron activation of the Ar ionization chamber gas – activation of the Cu absorber and ionization chamber plates • Both are estimated to produce a flux of ionizing particles that is small compared to the anticipated signal – At L = 1034 cm-2 sec-1, Fmip = 1. 3 x 1010 cm-2 sec-1 – Flux of ionizing e- due to Ar 41 decay ~ 105 cm-2 sec-1 – Flux of ionizing e- due to Cu activation ~ 106 cm-2 sec-1 TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation 15

Prototype tests in the SPS H 4 300 -400 Ge. V proton beam (unbunched) • The shower produced by a single 300 -400 Ge. V proton closely simulates the shower produced in a single pp interaction on LHC – ~231 mips/SPS p versus ~268 mips/LHC pp int (per quadrant) • The SPS tests demonstrated – Sensitivity to single pp interaction in LHC – Average pulse height in agreement with MARS simulations – Axial shower development in agreement with MARS simulations – N-1/2 scaling of noise – Linear scaling of pulse height with gas pressure up to 600 k. Pa with constant E = 600 V/mm – Left/right asymmetry measurement of the shower axis – Feasibility of a de-convolution approach to correct for pile-up in 40 MHz operation TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Waveform averaging improves proton shower S/N ratio • Pulse height 4. 2 m. V in good agreement with MARS prediction 4. 4± 0. 8 m. V TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Noise averages to zero Rms noise 1 event = 1. 28 m. V => S/N = 4. 2/1. 28 = 3. 3 raw events w/o averaging TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

N -1/2 scaling of rms noise ENC = 1. 28/0. 45 x 10 -3 = 2, 840 e TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Pulse height spectrum for proton triggers Noise spectrum due to non interacting proton fraction Spectrum of the interacting proton showers TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Fe absorber thickness scan, MARS data normalized to peak of experimental data TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation

Issues for discussion • Integration of Lumi, LHCf and ZDC installation and operation – Schedules – Hardware specifics – Documentation, exchange of drawings – Wood model • Stability of the TAN environment for luminosity measurement – Initial configuration – Removal of LHCf and/or ZDC as luminosity increases, Reinsertion at a later date? • Installation/removal/replacement of Cu bars • Parameters for initial commissioning and operation of LHC • Dedicated run requests • Protocols for coordination, synchronization and exchange of data TAN Inst Mtg 9 -10 Jan 2006, CERN W. C. Turner – TAN Lumi Instrumentation