CNGS Target Area Beam Posit ion Monit ors OUTLI NE 1. Recap of Requirements & Layout 2. Monitor Candidates - Secondary Emission Monit or - Pick-up in Air 3. Recent Results - Response of Pick-ups in air t o an int ense prot on beam 1 NBI2003 - Rh. Jones (CERN - AB/BDI)
Layout of T40 Beam Diagnost ics Target posit ion monit or f ixed t o t arget t able & aligned wrt t arget 2 nd BPM at 10m Last t wo BPMs used t o provide posit ion and angle Downst ream secondary emission monit or (TBI D) used t o measure mult iplicit y, asymmet ry and secondary beam halo 2 NBI2003 - Rh. Jones (CERN - AB/BDI)
T40 Beam Diagnost ic Requirement s Measurement of Position and Angle of Proton Beam - Last 2 st andard BPMs of t he prot on beam line ⇒ used t o adj ust t raj ect ory angle ⇒ 3 t imes less accuracy required f or angle t han f or posit ion at t arget - Final st andard BPM of t he prot on beam line & t arget BPM ⇒ used t o provide posit ion at t he t arget ⇒ set t ing up perf ormed using f inal beam line BPM ⇒ aiming at t arget rods verif ied & t racked using t arget BPM ⇒ accuracy of measurement ± 0.2mm in ± 2mm cent ral region. ⇒ accuracy of measurement ± 0.5mm out side ± 2mm cent ral region. 3 NBI2003 - Rh. Jones (CERN - AB/BDI)
Choice of Target St at ion Monit or Advant ages Disadvant ages Requires vacuum TBI U ⇒ Ti or Be windows � I nt ensit y & Posit ion ⇒ vacuum pump Upst ream � Measured posit ion secondary depends only on Carbon f oils emission ⇒ ageing not known mechanical alignment monit or Complicat ed & heavy � Simple const ruct ion Chosen as baseline solution BPKG � Radiat ion resist ant Posit ion only (+ int ensit y?) � No vacuum ( ⇒ t est s) Posit ion Cent re depends on elect ric � Lit t le ef f ect by 2ndary Pick-up & mechanical of f set part icles ( ⇒ t est s) 4 NBI2003 - Rh. Jones (CERN - AB/BDI)
Pick-up Choice Elect romagnet ic St ripline Coupler Pick-up Elect rost at ic But t on Pick-up I nduct ive Pick-up 5 NBI2003 - Rh. Jones (CERN - AB/BDI)
Test s in t he CERN-PS Boost er Test Conditions - Coupler & But t on Pick-ups inst alled in air in f ront of t he Boost er Dump - Beam Type - I nt ensit y: ~2.5E13 in 4 bunches of ~6.25E12 per bunch - Bunch lengt h: ~230ns - Bunch spacing: 572 ns - Energy = 1.4 GeV - Measurement s - One plane connect ed - Passive Hybrid used t o give Sum and Dif f erence signals - Dat a acquired on digit al oscilloscope 6 NBI2003 - Rh. Jones (CERN - AB/BDI)
St ripline Coupler Test Result s Dif f erence Signal Raw Signal f rom each elect rode (af t er 30MHz Low Pass Filt er) 7 NBI2003 - Rh. Jones (CERN - AB/BDI)
St ripline Coupler Test Result s 200 Difference Signal (mV) 150 100 50 Position (mm) 0 -30 -20 -10 0 10 20 30 -50 -100 -150 -200 -250 8 NBI2003 - Rh. Jones (CERN - AB/BDI)
But t on Pick-up Test Result s 0.2 Voltage (V) Expected Response Sum ~40mV Delta 0.15 Dif f erent iat ed Pulse 0.1 0.05 0 -1.00E-07 0.00E+00 1.00E-07 2.00E-07 3.00E-07 4.00E-07 Time (s) -0.05 Expect ed Sum signal -0.1 9 NBI2003 - Rh. Jones (CERN - AB/BDI)
But t on Pick-up Test Result s 0.35 Voltage (V) Air I onisat ion Ef f ect s 0.3 - Signal not dif f erent iat ed - Signal level ~ 5-10 t imes higher 0.25 - Consecut ive bunch signals 0.2 increase as ionised cloud “hangs about ” af t er each bunch passage 0.15 0.1 0.05 0 -1.00E-06 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 -0.05 Time (s) -0.1 10 NBI2003 - Rh. Jones (CERN - AB/BDI)
But t on Pick-up Test Result s 0.25 Delta/Sum (arb) Button pick- up using air 0.2 ionisation is a very nice 0.15 position monitor!! 0.1 0.05 0 -1.5 -1 -0.5 0 0.5 1 1.5 -0.05 Vertical Position (mm) -0.1 -0.15 -0.2 -0.25 11 NBI2003 - Rh. Jones (CERN - AB/BDI)
Conclusions Button Electrode Monitor ⇒ Sensit ive t o air ionisat ion • Mechanism f or observed signal response st ill under invest igat ion ⇒ Posit ion measurement possible BUT: • Signal amplit ude will depend non-linearly on beam int ensit y • Signal shape will change depending on t he level of ionisat ion Stripline Coupler Monitor ⇒ Seems less sensit ive t o air ionisat ion t han but t on ⇒ Posit ion measurement possible BUT: • Noisy Signal observed (seems broadband – so possibly OK) • Test s using 200MHz st ruct ure CNGS beam required f or f inal verif icat ion • Add solenoid or HV f or clearing ionised air cloud (?) I nductive Monitor ⇒ Test s yet t o be perf ormed 12 NBI2003 - Rh. Jones (CERN - AB/BDI)
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