R Scrivens, CERN, ABI Workshop, 12/2008
The Feschenko Bunch Shape MonitorUser experience at CERN
• Developed by INR, Troitsk.• High resolution bunch shape monitor based on secondary
emission.• Various monitors in existence at CERN, SNS, DESY,
Argonne…
R Scrivens, CERN, ABI Workshop, 12/2008
• Accelerated beam strikes a wire (at ~ -5kV)• Produce secondary electrons, which same bunch structure as
primary beam.• Electrons pass through a set of slits and RF deflecting plate.• Only those electrons close to the RF zero crossing are
transmitted (and measured in a cup/electron multiplier). Hence measure at a defined beam/bunch phase.
• Shift the RF deflecting phase to the next pulse.• The deflecting plates are biased to make a focus onto the
second slit.
Vfocus
Vfocus
Detector (cup, electronmultiplier…)
R Scrivens, CERN, ABI Workshop, 12/2008
• CERN has used 3 different versions of the device:• Bunch Length and Velocity Detector – Linac 3 – Pb27+ @ 4.2 MeV/u• Bunch Shape Monitor – Linac 2 – p+ @ 10MeV and 30MeV• 3D Bunch Shape Monitor – Linac 2 – p+ @ 50MeV
R Scrivens, CERN, ABI Workshop, 12/2008
Bunch Shape Monitor – Linac 2 – p+ @ 10MeV and 30MeV
Detector Head
SEM tube feed
RF deflection power
Lens voltage
Inter tank
Target actuator not shown
R Scrivens, CERN, ABI Workshop, 12/2008
Detector Head
Target actuator
Inter tank cross section (from DESY model)
R Scrivens, CERN, ABI Workshop, 12/2008
-60 -50 -40 -30 -20 -10 0-220
-215
-210
-205
-200
-195
-190
-185
-180
-175
Measured data
Measured and simulated data for the variation ofbunch centre at the output compared to the inputphase of tank 1.
A=0.92A0 A=0.94A0 A=0.96A0 A=0.98A0 A=1.00A0 A=1.02A0 A=1.04A0 A=1.06A0 A=1.08A0 A=1.10A0
Bea
m o
utpu
t pha
se (d
eg)
RF Input Phase (degrees)
Uses: • Bunch shape measurement.• Limited halo investigation (wire cannot be used in beam centrethermal emission and wire damage).
• RF characterisation of the RF systems.
120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
B125 B130 B135 B140 B145 B150 B155 B120 B115 B110 B105 B100 B95In
tens
ity
Beam position (degrees)
R Scrivens, CERN, ABI Workshop, 12/2008Y.V. Bylinski et al, Bunch Length and Velocity Detector and its Application in the CERN Heavy Ion Linac, EPAC 94.
Bunch Length and Velocity Detector – Linac 3 – Pb27+ @ 4.2 MeV/u Beam sensitivity - 1uA (peak current) - using 0.1mm wirePhase Resolution: 0.4 degrees at 101MHz - 10psErrors 0.3% on velocity.
R Scrivens, CERN, ABI Workshop, 12/2008
Uses: •Measuring bunch profile and position
•Measurement of beam energy, Time of Flight, by moving the detector. (Error can arise due to magnetic field variation in time, or along the movement of the BLVD).
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 50 100 150 200 250
Inte
nsity
Phase
Measure bunch
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 50 100 150 200 250
Inte
nsity
Phase
Move detector -remeasure
R Scrivens, CERN, ABI Workshop, 12/2008
•Buncher cavity. Measure bunch centre as function of cavity phase and amplitude, Where position does not vary with amplitude, is the zero crossing.
•With a bunch cavity, measurement of the longitudinal emittance with the bunch rotation technique (buncher effective voltage must be known).
•The measurement effectively removes the need for a spectrometer magnet (must then rely on RF measurements for the cavity effective voltage).
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
-30 -20 -10 0 10 20 30
Ener
gy
Phase
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
-30 -20 -10 0 10 20 30
Ener
gy
Phase
Measurement of emittance with a buncher cavity and BSM
R Scrivens, CERN, ABI Workshop, 12/2008
3D Bunch Shape Monitor – Linac 2 – p+ @ 50MeV
S.K. Esin et al, A three dimensional bunch shape monitor for the CERN proton Linac, Linac 1996, Geneva, Switzerland,
• The second slit is replace with an linear array detector, with a sandwich of secondary electron emission electrodes (like an RF streak camera).
• The wire can be stepped across the beam.• The slit can be stepped vertically, to provide a vertical resolution.• The array detector can be read out as a function of time during the beam pulse.
R Scrivens, CERN, ABI Workshop, 12/2008
Uses: •The bunch form can be measured as a function of a H and V. The3D bunch volume density is measured (averaged over many bunches).
•Projections allow any of the 3 real space measurements:• For the bunch length, use for bunch profile, and (with a cavity) a longitudinal emittance measurement.
• In the H & V plane, use as a wire scanner (profile and emittance with a quadrupole).
• Investigation of the halo (e.g. different phase structure).
R Scrivens, CERN, ABI Workshop, 12/2008
5
8
11
14
17
2023
-0.5
0
0.5
1
1.5
2
2.5
3
1 3 5 7 911 13 15
1719
2123
2527
29
Time during pulse
Channel Number / Phase
3D BSM measurement of the bunch structure, as a function of time during the Linac 2 proton beam pulse.Beam is distorted in RF phasestabilization regime.
R Scrivens, CERN, ABI Workshop, 12/2008
01
23
4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1357911131517192123252729H axis (mm)
Channel Number - Phase
3D BSM measurement of the bunch structure (50MeV), as a function of horizontal beam position (in the stable part of the pulse).Bunch core intensity increases towards centre.Bunch tail is quite constant in intensity (suggesting tail has a differentbeam size).
R Scrivens, CERN, ABI Workshop, 12/2008
What could be done better (@ CERN)•At CERN, we did not manage to drive them from the CERN control system.
• The application also dealt with the real time measurements, conversion to CERN architecture required software and hardware modifications.
• The local control system was kept, and used non-standard cards (e.g. still some Camac cards, and a unique PC->VME controller). No maintenance was followed up.
• =>The BSMs are no longer operational at CERN. Renovation is not worthwhile for last years of operation.
R Scrivens, CERN, ABI Workshop, 12/2008
• BSMs are powerful bunch measurement systems, with high phase resolution.
• At CERN, the BLVD was heavily used during accelerator commissioning.
• Variants measure:• Bunch shape• Position• Beam velocity• Bunch 3D density• Transverse emittance (with quadrupole)• Longitudinal emittance (with buncher cavity)
Summary
R Scrivens, CERN, ABI Workshop, 12/2008
Some useful reading:Y.V. Bylinski et al, Bunch Length and Velocity Detector and its Application in the CERN Heavy Ion Linac, EPAC 94.S.K. Esin et al, A three dimensional bunch shape monitor for the CERN proton Linac, Linac 1996, Geneva, Switzerland,A.V. Feschenko et al, Study of Beam Parameters of the CERN Proton Linac Using a Three Dimensional Bunch Shape Monitor, Linac96, Geneva, Switzerland.P.N. Ostroumov, Review of Beam Diagnostics in Ion Linacs, Linac98, Chicago, ILN. Y. Vinogradov et al, Bunch Shape Measurement of CW Heavy Ion Beam, Linac2002, Gyeongju, KoreaA.V.Feschenko et al, Bunch Shape Monitors for the DESY H- Linac, PAC 1997Hurd J.W. et al. Bunch Shape Monitor for SSCL Linac. Proc of the 1993 Particle Acc. Conf., Washington, May 17-20, 1993S.K.Esin, A.V.Feschenko, P.N. Ostroumov. INR Activity in Development And Production of Bunch Shape Monitors, Proc. Of the 1995 PAC and Int. Conf. on High-Energy Accelerators, Dallas, 1-5 May, 1995, V.4, pp. 2408-2410A.V.Feschenko, V.A.Moiseev, Space Charge Effects in Bunch Shape Monitors, Linac2000, Monterey, Ca.
This slide is not for displaying