C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Design and Tests of a New Rest Gas Ionization Profile Monitor Installed in the SPS as a Prototype for the LHC BIW04 May 3-6, 2004 –Knoxville, Tennessee C. Fischer, J. Koopman, D. Kramer, R. Perret, M. Sillanoli CERN – Geneva - Switzerland

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Acknowledgements §AT/VAC/SL: monitor conditionings §ES/MME & PH/TA1: coatings §D. Cornuet and Co.: magnet measurements §G. Arduini: monitor insertion in SPS §A. Beuret: magnet power supplies §A. Guerrero: software requests §B. Dehning, F. Roncarolo: wire scanner data §and all others….

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Outline §The New Monitor magnet central detector tank and assembly §Commissioning in 2002 §The year 2003 problems & cures results §Preparation & Perspectives for 2004

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor §Encouraging results were got since the installation in 1999 of a prototype provided by DESY and modified to use signal from electrons. §It has been decided to equip the LHC with 4 gas monitors (one H, one V, in each ring). §Continuous profile measurements also needed in the SPS for the LHC era. §Prototype design compatible with LHC requirements: transverse space contingencies compactness impedance budget no big discontinuities in the tank smooth transitions, §e- signal B field required §Conventional magnet found with 200 mm gap, fulfilling space requirements new gas monitor designed accordingly, manufactured in 2001 and installed in the SPS for the 2002 run

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor: the magnet (1) §magnet recuperated from LEP with following characteristics: I max = 55 A B max = 0.25 T Strength = 0.14 Tm Gap width : 200 x 200 mm 2 Overall length 680 mm section: 681 x 646 mm 2 §hole drilled through the yoke for the light signal extraction 3D view top view 200 mm

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor: the magnet % Relative B variation along z with y=o at different x Relative B variation along z with x=o at different y B linearity I (A) B (mT)

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor: mechanical design The central detector 166 mm 84 mm cross section view top view 3D view e-e- light MCP prism light

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor: mechanical design The tank within its magnet 200 mm =84 mm Light signal cross section view 3-D view Light signal 680 mm e - signal side view

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee New Rest Gas Monitor Picture of the assembled central detector As installed in the SPS with 2 corrector magnets used at - B/2 (3 magnet bump) Electric field map e_e_

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Results from commissioning in 2002 encountered problems: high noise level §electron cloud effect with LHC type beam evidence : signal increase after injection of 3 rd batch effect : electrode DC voltage fluctuations signal fluctuations §high frequency modes generated by the LHC beam structure inside the detector and in cables effect : HV instabilities, signal loss remedies during 2003 stop § NEG application (TiZrV) on HV electrodes to lower SEY §RF absorbers (filters) close to HV supplies §series resistors close to detector feed-throughs §view port conducting cover plate installed for better image current conduction

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee The 2003 campaign (1) encountered problems and cures: §bad electrical contacts on phosphor screen after bake-out at 200 C (needed for NEG activation ) insertion of thin CuBe frame with flexible contacts §aging of MCP central region due to high output signal (test of a fast but less sensitive phosphor) MCP gain decreased and image intensifier added, bump applied to the beam orbit to avoid bad area §limited resolution camera lens diaphragm opening reduced by 50% § lightening on phosphor screen with shortest bunch length series resistors removed §image tilt due to stray B field (through the magnet hole ) on the image intensifier intensifier wrapped with metal sheets magnet used at 50% of B max

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Results from 2003 (1) Pilot: pNominal: p = 0.88 mm 450 GeV = 0.83 mm E= 450 GeV LHC type beams from pilot to nominal investigated; dynamic in current 10 4 n = m

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Results from 2003: analysis (3) limitations: electron cloud effect still there (from 3 rd batch) signal increase saturation of MCP at 450 GeV Profile Norm evolution along the cycle

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Results from 2003: analysis (4) Limitations, ctn limited resolution, show-up at 450 GeV for low beam dimensions (s 0.7 mm) 75 ns LHC beam: n = m pilot bunch: n = m 26 GeV – IPM = 1.5 mm 450 GeV - th IPM = 0.36 mm meas IPM = 0.57 mm 450 GeV - th IPM = 0.53 mm meas IPM = 0.64 mm 26 GeV – IPM = 2.2 mm Error contribution: 0.35 m m Sources : intensifier residual tilt tails optics: 247 m /pixel

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Cures implemented during the 2004 stop (1) §Electron cloud: MCP input face NEG coated §MCP aging and saturation: MCP replaced by a new one, will be operated at lower gain coupled with Low Light Level camera lower MCP output current suppression of 2 stage amplification better S/N ratio and resolution more sensitive phosphor layer on new prism: lower MCP output current CdS:In Y 3 Al 5 O 12 :Ce (P46) variable gain to be applied during acceleration cycle to avoid saturation §Resolution limitation: general cleaning of different detector parts replacement of external RF absorbers close to power supplies number of wires on cathode grid decreased by factor 3 contribution to tails non reflective treatment of support surfaces to suppress parasitic reflections new optics in front of the camera improved opening

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Cures implemented during the 2004 stop (3) new optical bench LLL camera PM tube

C. Fischer-BIW04-May 3-6, Knoxville, Tennessee Perspectives for 2004 With these improvements and a few other upgrades of the control software, all efforts will made during the year 2004 to bring the monitor to an operational stage for the LHC era. A second monitor working in the H plane is approved and is expected for the 2006 SPS start-up. Thank you for your attention