CNGS Target Area
Beam Position Monitors
OUTLINE
1. Recap of Requirements & Layout
2. Monitor Candidates- Secondary Emission Monitor- Pick-up in Air
3. Recent Results- Response of Pick-ups in air to an intense
proton beam
NBI2003 - Rh. Jones (CERN - AB/BDI)1

Layout of T40 Beam Diagnostics
Target position monitor fixed to target table & aligned wrt target
2nd BPM at 10m

Last two BPMs used to provide position and angle
Downstream secondary emission monitor (TBID) used tomeasure multiplicity, asymmetry and secondary beam haloNBI2003 - Rh. Jones (CERN - AB/BDI)

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T40 Beam Diagnostic Requirements--Measurement of Position and Angle of Proton Beam

Last 2 standard BPMs of the proton beam line

⇒ used to adjust trajectory angle⇒ 3 times less accuracy required for angle than for position at target

Final standard BPM of the proton beam line & target BPM⇒ used to provide position at the target⇒ setting up performed using final beam line BPM⇒ aiming at target rods verified & tracked using target BPM⇒ accuracy of measurement ±0.2mm in ±2mm central region.
⇒ accuracy of measurement ±0.5mm outside ±2mm central region.

NBI2003 - Rh. Jones (CERN - AB/BDI)

3Choice of Target Station Monitor
Advantages
TBIU
Upstream
secondaryemissionmonitor

BPKG
Position
Pick-up

Disadvantages
Requires vacuum⇒ Ti or Be windows⇒ vacuum pump
Carbon foils⇒ ageing not known
Complicated & heavy

9 Intensity & Position
9 Measured position
depends only onmechanical alignment

9 Simple construction
9 Radiation resistant
V No vacuum (⇒ tests)
V Little effect by 2ndary
particles (⇒ tests)

Chosen as baseline solution

NBI2003 - Rh. Jones (CERN - AB/BDI)Position only (+ intensity?)
Centre depends on electric& mechanical offset

4Pick-up ChoiceElectromagnetic Stripline
Coupler Pick-up

Electrostatic
Button Pick-up

Inductive Pick-up

NBI2003 - Rh. Jones (CERN - AB/BDI)5

Tests in the CERN-PS Booster
Test Conditions-Coupler & Button Pick-ups
installed in air in front of theBooster Dump

-Beam Type-

Measurements-Intensity: ~2.5E13 in 4 bunches of ~6.25E12 per bunch
Bunch length: ~230ns
Bunch spacing: 572 ns
Energy = 1.4 GeV
One plane connected
Passive Hybrid used to give Sum and Difference signals
Data acquired on digital oscilloscope
NBI2003 - Rh. Jones (CERN - AB/BDI)

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Stripline Coupler Test Results

Difference
SignalRaw Signal fromeach electrode(after 30MHz
Low Pass Filter)

NBI2003 - Rh. Jones (CERN - AB/BDI)7

Stripline Coupler Test Results
200

Difference
Signal (mV)

150
100
50Position (mm)0-30-20-100102030-50-100-150-200-250
NBI2003 - Rh. Jones (CERN - AB/BDI)

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0.2

Sum
Delta 0.15

Voltage (V)Button Pick-up Test Results
Expected Response~40mV

Differentiated
Pulse

0.1

0.05

-1.00E-07

00.00E+00

1.00E-07

2.00E-07

4.00E-07
Time (s)

-0.05

-0.1

3.00E-07

Expected Sum signal
NBI2003 - Rh. Jones (CERN - AB/BDI)

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Voltage (V)Button Pick-up Test Results
0.35

Air Ionisation Effects

0.3- Signal not differentiated- Signal level ~ 5-10 times higher- Consecutive bunch signals

0.25

increase as ionised cloud “hangsabout” after each bunch passage

0.2
0.15
0.1
0.05

-1.00E-06

00.00E+00-0.051.00E-06

2.00E-06

3.00E-06

4.00E-06
Time (s)-0.1
NBI2003 - Rh. Jones (CERN - AB/BDI)

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Delta/Sum (arb)

Button Pick-up Test Results
0.25

Button pick-up using airionisation is a very niceposition monitor!!

0.2
0.15
0.1
0.05
0-1.5

-1

-0.5

-0.05

00.5

1

1.5

Vertical Position (mm)

-0.1
-0.15
-0.2
-0.25
NBI2003 - Rh. Jones (CERN - AB/BDI)

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Conclusions
Button Electrode Monitor⇒ Sensitive to air ionisation• Mechanism for observed signal response still under investigation⇒ Position measurement possible BUT:

• Signal amplitude will depend non-linearly on beam intensity• Signal shape will change depending on the level of ionisation

Stripline Coupler Monitor⇒ Seems less sensitive to air ionisation than button⇒ Position measurement possible BUT:

• Noisy Signal observed (seems broadband – so possibly OK)• Tests using 200MHz structure CNGS beam required for final

verification• Add solenoid or HV for clearing ionised air cloud (?)

Inductive Monitor⇒ Tests yet to be performed
NBI2003 - Rh. Jones (CERN - AB/BDI)

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