CERN Mar Luminosity and longitudinal density W.C. Turner 1 Luminosity optimization and longitudinal density instrumentation W.C. Turner LBNL CERN Mar. 2002

CERN Mar Luminosity and longitudinal density W.C. Turner 2 TAN and TAS absorbers in IPs 1 and 5 The TAN and TAS each absorb ~200W of forward collision products Instrument the TAN and TAS to measure the luminosity of colliding bunch pairs with 40MHz resolution Applications –Bringing beams into collision –Use in feedback loop to maintain optimum luminosity –Segment to measure crossing angle and IP position

CERN Mar Luminosity and longitudinal density W.C. Turner 3 Constraints Very high peak radiation fluxes and high induced activation over many years of operation, 170 MGy (17GRad)/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

CERN Mar Luminosity and longitudinal density W.C. Turner 4 The technical solution... Segmented, multi-gap, pressurized gas ionization chamber constructed of rad hard materials 3-11 atmospheres Ar + 2%N 2 gas mixture, e - drift velocity 3.2 cm/  s Low noise bi-polar transistor pre-amplifier “cold” cable termination, ENC  ~ 1,824 e - Pulse shaper,  = 2.5 ns 3 m radiation hard cable between ionization chamber and front end electronics, radiation dose to electronics < 100 Gy/oper yr S/N ~ 5 for single pp interaction

CERN Mar Luminosity and longitudinal density W.C. Turner 5 Ionization chamber 60 gaps, 10 parallel x 6 series segmented into quadrants 0.5 mm gap spacing copper, ceramic construction

CERN Mar Luminosity and longitudinal density W.C. Turner 6 40 MHz capability of Luminosity Instrumentation Peaking time is less than the 25 ns bunch spacing Pulse train obtained by superposition of single pulses Un zipped amplitudes track the raw pulse heights

CERN Mar Luminosity and longitudinal density W.C. Turner 7 The right-left asymmetry ratio is a sensitive function of the crossing angle - TAN 142 m from IP, xing angle =  150 mrad – Measurement of the asymmetry ratios at the positions of the TAS and TAN on both sides of an IP may allow determination of IP pos. and xing angle - MARS simulations of D1 collimation and ATLAS/CMS magnetic fields are needed

CERN Mar Luminosity and longitudinal density W.C. Turner 8 Radiation hardness test On LHC the hadron energy incident on the TAN is ~ 1 GJ/yr; neutrons, = 2 TeV Simulate hadron showers with equivalent energy flux of SPS 450 GeV protons Compress 1 yr radiation exposure on LHC to ~ 1 wk on SPS extracted beam –Assume one slow 5.8 spill every 15.8s => ~5x10 11 p/spill, reasonable Periodically insert a collimator to reduce intensity to ~ 10 6 p/spill to verify single proton shower operation Investigating possibilities in ENH1 area (p0 and M2)

CERN Mar Luminosity and longitudinal density W.C. Turner 9 Longitudinal density measurement Applications –Debunched beam at injection –Population in abort gap –Ghost bunches –Beam centroid and shape Requirements (ref. C. Fischer, LHC-BSRL-ES rev 0.1 draft, 11 Nov 01)

CERN Mar Luminosity and longitudinal density W.C. Turner 10 Several methods are being investigated 1. Non-linear mixing of “synchrotron-undulator” radiation with a cw laser oscillator 2. A photodiode array with TDCs 3. Gated PMT for abort gap All utilize radiation from a 2-period undulator and D3 in IR4 RF system SC undulator Extraction mirror Q7 Q6 Q5 D4 D3

CERN Mar Luminosity and longitudinal density W.C. Turner 11 Extraction mirror and photon flux Beam Photons Mirror, 10mm x 50mm 5mm 30mm = 15  V 10m D3 Undulator V 1.48mrad Ref. Laurette Ponce PhD thesis in prep. Side View

CERN Mar Luminosity and longitudinal density W.C. Turner 12 ~ 50ps Rf clock, 40 MHz Delay generator Laser ~ 10W 40MHz, 50ps     +   PMT Synchrotron, wiggler radiation Crystal Filter Proton, 208 Pb +82 bunch rms length ~ 250ps ps samples/turn 25,000 ps nominal bunch separation 500 turns to map entire ring 50 turns to map nominal buckets Synchrotron period = 535 turns Non linear mixing of “synchrotron-undulator” radiation with a pulsed laser

CERN Mar Luminosity and longitudinal density W.C. Turner 13 Laser mixing abort gap integration time At 7 TeV, 5,400/10 11 ~ 5.4x10 -8 photons/p passage,  /  = 1 QE*  /  ~ Res req’d 2x10 4 p/ps x 50ps x 119 samples/rev= 1.2x10 8 p/rev Counts/rev = 5.4x10 -8 x x 1.2x10 8 = 6.5x10 -2 Integration time to get 4  2 counts = 61.5 rev = 5.5 ms << 100 ms Alternatively in 100 ms get 73  8 photons

CERN Mar Luminosity and longitudinal density W.C. Turner 14 Photodiode array measurement of bunch tails Single photon counting used to get 10 4 dynamic range time No. photons 10 x 10 diode arrayGrey filter TDC 100 ch protons 7 TeV QE ~ 1 P(0) = 0.90 ~ 100x0.1 = 10 photons/rev Integration time ~ 10 4 /10 ~ 10 3 rev ~ 90 ms << 10 s 5,400 photons/rev 0.5 <  < 1.0 

CERN Mar Luminosity and longitudinal density W.C. Turner 15 Summary Luminosity monitor –Data from SPS experiments indicate ionization chamber will work at 40 MHz –40MHz bunched beam and high radiation experiments in 2003, 2004 are highly desirable –MARS simulations needed to investigate: D1 collimation, ATLAS and CMS magnetic fields, sensitivity of TAS to transverse position of IP Longitudinal density –In early stage of development –Several applications and possibilities –May want to consider specialized instruments rather than one to do all –Laser mixing and photodiode approaches to be investigated on ALS at LBNL in 2002