BEAM QUALITY MONITORING IN THE
CERN ANTIPROTON DECELERATOR (AD)Abstract
The CERN Antiproton Decelerator (AD) has now reached a stable mode of operation,
regularly delivering batches of 100 MeV/c antiprotons to the ATRAP, ATHENA
and ASACUSA collaborations.
Experience during the commissioning and initial physics runs revealed difficulties inachieving design goals and maintaining stable performance levels.
This paper will deal with the specific difficulties in monitoring and improving beam
quality in a slow cycling machine operating with low beam intensities of a few
10^7 circulating particles.

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WAO2003 T. Eriksson, CERN

Contents• Introduction• Performance review 2000-2002• Monitoring and improving beam quality– Beam intensity– Beam emittances– Stability of orbit and ejection trajectory• Conclusion

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WAO2003 T. Eriksson, CERNAD Ring and Hall
Stoch. Cooling kicker
Protons via
loop (TTL2)
Target Area: 26GeV/c protons ->3.57 GeV/c pbars,
yield ~ 4 10-6

4 dispersion freestraight sections:S-cool, E-cool,RF, diagnostics

4 arcs: chromaticity
correction, dispersionsuppression

ExperimentalArea

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Electron CoolingStoch. Cooling pick-up
WAO2003 T. Eriksson, CERN

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Performance review
Intensity at 3.5 GeV/c (*10^7)
Intensity at 100 MeV/c (*10^7)
Deceleration efficiency (%)
Cycle repetition rate (s)Flux (10^5 pbars/s)

2000
3.0
2.0
65
140-110
1.8End2001
3.2
3.0
95
96
3End2002
3.3
3.0
90
86
3.5

Design
5.0
1.2
2560
2

4

1

1

12

1

11

1.5
30
600

1202201890

117200Emittances at 100 MeV/c (85% beam)εh (π.mm.mrad)
εv (π.mm.mrad)∆p/p(after cooling, *10^-4)∆p/p(bunched, after rotation *10^-4)
Minimum extracted bunch length (ns)14/3/2003

WAO2003 T. Eriksson, CERNMonitoring and improving beam quality
Beam intensity and trajectory at injection:• Proton production beam in injection line (1.5*10^13) measured
with current transformers and screens/TV:s• Only 3-4*10^7 pbars after target – no measurements possible– “blind” steering through dogleg– Secondary electrons/pions injected in ring together with pbars helps tosome extent– Scanning dipoles is extremely slow and other machine parameters candrift in the meantime

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WAO2003 T. Eriksson, CERNCirculating beam intensity• Longitudinal Schottky analysis using DSP is necessary tomeasure a few 10^7 down to 100 MeV/c
PULong.

PU H
Transv.

PU V
Transv.

N o isegenerator
RFSYSTEM

fR E VA D C clock
generation

ADCfS

D R X b oard

POW ER PC

DSP + 8 DDCs

W O RKSTATION

VMEbusE thernet

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Measured intensity throughout the cycle

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Beam emittances• Beam cooling at low energies need constant attention• Scanning of electron/pbar beam trajectories with destructive
measurements is extremely slow but the only way at present

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WAO2003 T. Eriksson, CERN

Vertical beam profiles before and after stochastic
cooling at 3.5 GeV/c

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Non-destructive emittance measurements

•
••
•
•

Beam Ionization Profile Monitor
Emittance and beam center msmnts
Measures throughout AD cycle
Local pressure bump needed
More development work needed

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WAO2003 T. Eriksson, CERN

Beam width evolution [mm]SmoothedSignal [mm]Beam centre evolution [mm]Horizontal and vertical beam widths and centres
during the cycle as seen with the beam ionisation
profile monitor

1510

50020

4060

80time [s]14/3/2003

WAO2003 T. Eriksson, CERNMonitoring Schottky scan visually• Schottky observation via commercial FFT-analyzer• Extremely useful for :–––––

Beam distribution (shape).
Intensity.
Cooling speed and centering.
Initial and final momentum spread.
Losses during the cycle.

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WAO2003 T. Eriksson, CERN

Stability of orbit and ejection trajectory• Improvements were made in 2002 after much suffering frominstabilities at 100 MeV/c• Initially it was foreseen to measure orbits at low energy withprotons…
• Thanks to improved closed orbit measurement system, we
can measure accurate orbits at 100MeV/c with as little as
1E7 particles

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WAO2003 T. Eriksson, CERN

Conclusion
Initial setup problems were encountered due to the low beam
intensities and slow cycle. Beam monitoring and improvements
turned out to be more difficult than foreseen.
The long startup period and subsequent improvements and tuneups have made it possible for the operation team to get to know
the AD quite well. Not always using the latest or most high-techdiagnostic equipment makes things slower, but it can be moreinteresting for the operator, giving opportunities to learn more
about accelerator physics.

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Machine tunes• Presently, BTF measurements are done on flattops using acommercial network analyzer• The machine needs to be stopped at desired energy• Beam is blown up• Difficult at low energies due to weak signals and limited
beam lifetime

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WAO2003 T. Eriksson, CERNDSP tune measurements• For optimization of ramps and shorter cycle
AD Horizontal tunes 3.5 - 0.3 GeV/c
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

Revolution frequency[MHz]
Measured qCtime[ms31 ]00
32 00034 00048 05050 00052 00057 00059 00057 050
00.47
0.45
0.43
0.41
0.39
0.37
0.35

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WAO2003 T. Eriksson, CERN