PowerPointPrsentation

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• Development of non-intersecting
• transverse and longitudinal Profile Monitors
• P. Forck, A. Bank, W. Barth, C. Dorn, A. Peters,
  H. Reeg
• Gesellschaft für Schwerionenforschung, Darmstadt
• HIPPI Meeting 2005, Oxford
• Non intersecting methods for
• Preventing destruction of intersecting material
• Parallel observation at different locations
• Monitoring of possible time-varying processes
• Goal Same precision as intersecting methods
• Outline
• Transverse profile monitor by Beam Induced
  Fluorescence BIF
• Bunch Structure Monitor BSM based on residual gas
  electron spectroscopy
• Transmission control by transformers

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The UNILAC Facility at GSI
Achieved current for U-beam (tpulse 200 µs)
U73 2 emA
U28 5 emA
U4 16 emA
11.4 MeV/u
1.4 MeV/u
High Current Injector (RFQIH)
Alvarez DTL
Single Gap Resonators
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Basics of Beam Induced Fluorescence

• Physics of fluorescence for N2 residual gas p
  N2 ? p (N2) e- ? p N2 ? e-
• Excitation of residual gas molecules by beams
  energy loss
• Decay of N2 levels generate light, blue light
  390 nm lt ? lt 470 nm, lifetime ? 60 ns.
• Realizations at Los Alamos, CERN, Orsay/Saclay,
  Uni-Frankfurt, GSI, COSY .

Fluorescence of 200 keV p in N2 (1961)
LANL (D. Gilpatrick et al.) p at MeV in 510-5
mbar N2
Spectrum confirmed at CERN-PS/SPS from 1 to 450
GeV.
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Image Intensifier used at GSI-LINAC

• Technical realization of image intensifier at
  GSI
• Photo cathode S20 UV ?-e- conversion, 15 to 25
  efficiency, 200 nm lt ? lt 650 nm
• Two step MCP (25 mm diameter) 106 fold
  amplification
• P 46 phosphor e- -? conversion, 300 ns decay,
  500 nm lt ? lt 600 nm
• Minifying taper coupling to CCD chip (1/2) 7
  transmission
• Digital camera (Basler A311f) Firewire interface

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Test Setup at GSI-LINAC
Installation behind Alvarez at 11 MeV/u

Compact chamber with 150 mm insertion
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Typical Result at GSI-LINAC

• Features
• Single photon counting
• High resolution (here 0.3 mm/pixel),
• can easily be matched to application
• Low background (sometime larger
• contribution by neutrons and ?)
• Beam parameters at GSI-LINAC
• 4.7 MeV/u Ar10 beam
• I2.5 mA equals to 1011 particles
• One single macro pulse of 200 ?s
• Vacuum pressure p10-5 mbar (N2)
• bump restricted 1 m,
• ? no influence to beam detected

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Application of Beam Induced Fluorescence
Special application Variation during the macro
pulse detectable Switching of image
intensifier ? Exposure window during macro-pulse
Signal treatment Statistics offers offline
optimization statistics ? integration time ?
resolution
Beam parameter Ar10 at 11 MeV/u with 8 mA
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In Preparation Digital Interface for Firewire
Digital camera offers no loss of data-quality,
versatile trigger, variable exposure
time CCD-camera Basler A311f featuring 649x494
pixels, 12 bit, 50 frames/s, IEEE
1394b Iris/MCP-gain variation Remote controlled
iris by local, ethernet based DAC Readout HUB ?
optical fiber ? real-time controller running
RT-LabVIEW (NI) Status DAQ in preliminary design
phase
DAQ System
LabVIEW Software
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Novel Device for non-intersecting Bunch Shape
Measurement

• Bunch-Shape seldom measured !
• Scheme for novel device
• Secondary electrons for residual gas
• Acceleration by electric field
• Target localization by apertures
• and electro-static analyzer
• (?y 0.2 to 2 mm, ?z0.2 to 1 mm)
• rf-resonator as time-to-space converter
• same as intersecting method (INR-Moscow)
• Readout Ø70 mm MCP Phosphor CCD
• Measurement done within one macro-pulse
• (not yet achieved due to back-ground)

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Realization for Bunch Shape Monitor at UNILAC
E-field and the energy-analyzer
Installation for beam based tests

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First Results from Bunch Shape Measurement at
UNILAC
Time information carried by the residual gas e-
is transferred to spatial differences

• Features
• ? Single electron detection
• ? Recorded within few
• macro-pulses
• ? Resolution better
• 50 ps 20_at_108MHz
• ? Pressure bump required
• Back-ground should be
• suppressed
• Beam parameters
• Ni14 at 11.4 MeV/u
• I1.5 mA, 200 µs macro pulse
• Average 8 macro pulses
• Pressure p210-6 mbar
• Deflector power P15 W

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First Application from Bunch Shape Measurement

• Variation of buncher
• Bunch shape was determined,
• influeneced by buncher
• Pick-up No measurable influence
• Emittance determination possible
• Beam parameters
• Ni14 at 11.4 MeV/u
• I2 emA, 200 µs macro pulse
• Average 4 macro pulses
• Pressure p10-5 mbar

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Beam Space Charge Contribution
The residual gas e- are influenced by beams
E-field in addition to the monitor E-field ?
Simulation of influence for different currents

Simulation method e- trajectory calc. inside
beam pipe linear optics for energy
analyzer Simulation parameter Ekin 11.4
MeV/u Parabolic bunch shape 0.5 ns
longitudinal root points 5 mm transversal root
points Variation of current (as for Ni14
) Simulation result ? stronger influence as for
standard method, but still
acceptable
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Dynamic Transmission control at UNILAC

• Variation of maximal loss
• via software input
• 8 different input thresholds
• ? 8 different macro-pulse duration
• by electric chopper in front of RFQ
• Save protection of equipment.
• FPGA-electronics
• ACCT ? V/f-converter ?
• Up/down-counter 1st ACCT ?, 2nd ?
• ? Digital comparator ? chopper

ACCT clamping
Integration window
ACCT signal
40 µs/div
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Conclusion and Outlook
Beam Induced Fluorescence BIF First
prototype in operation for single photon
counting, usable during UNILAC operation Data
acquisition in design phase (responsible engineer
just hired) More investigation with high
current required possible problems
broadening by space charge field, two-step
excitation. Non-intersecting Bunch Shape
Monitor Prove-of-principle performed,
resolution lower than 50 ps 20 _at_ 108 MHz
Improvements for back-ground suppression in
preparation ?beam test necessary Calculations
and measurements of signal deformation due to
beam space charge required Device in
experimental condition ? engineering design for
operation required Dynamic Transmission control
System design finished Hardware in operation
Improvements of operation control required

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Comparison for different Gases at p Source
(Saclay)

• Choice of fluorescence gas
• High fluorescence yield at optical wave-length
• Short lifetime of excited level
• Good vacuum pumping
• Results
• ? Profile is independent of gas
• Care
• Long lifetime (N2 60 ns) ?
• broadening by beam space charge
• Light emitted by primary ions
• e.g. p N2 ? H N2
• (only important for Ekinlt1 MeV)
• At large N2 density (pgt10-3 mbar) Two-step
  processes e.g. N2 e- ? N2 e- possible

Example Ion source 100 keV, 100 mA protons P.
Ausset et al. (Orsay/Saclay)
N2, Ne Ar, Kr Xe
Profiles from different gasses
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Non-intercepting Profile Measurement based on
Energy Loss

• Standard monitors SEM-Grid, Wire-Scanner,
  Scintillation Screen, OTR-Screen
• Disadvantage intercepting,
• problems for time-varying processes
• Non-intercepting profile measurement
• Large beam power can destroy the material
• Synchrotron Monitoring during full cycle
• LINAC Monitoring at different locations,
• variation during the macro-pulse
  
• Physics electronic stopping power
• Bethe-Bloch formula
• - dE/dx const Zt ?t /At Zp2
  1/ß2 ln(const ?2ß2/I) ß2

M. Plum et al. p in N2 at CERN-PS
cross section a dE/dx
pc GeV

1/Ekin (for Ekingt 1GeV nearly constant)
Target e--density
Strong dependence on projectile charge

• Profile determination from ionization and
  excitation of residual gas.

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Technical Realization Possibilities for BIF
Single MCP - lower 103-fold amp.
higher resolution Example CERN-SPS (160
µm/pix), R. Jung et al.
Double MCP single photon, 106-fold amp.
- resolution limited (MCP-channels) Example
GSI-LINAC (300 µm/pixel)
Photo-cathode Only for required wavelength
interval to avoid dark currents, e.g. S20UV
200lt?lt650 nm ? dark rate 500 e-/cm2/s, S25red
300lt?lt900 nm ? 30000 e-/cm2/s Phosphor Fast
decay ? lower sensitivity e.g. P47 t 0.1 µs,
P43 t 1000 µs ? IP43 4 IP47 Problem
Radiation hardness of CCD camera
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BIF at Synchrotrons
Example CERN SPS and PSB,PS (R. Jung, M. Plum et
al.) Photon yield scales like Bethe-Bloch energy
loss ?E d for p with 100
MeV lt E kin lt 450 GeV

Method fluorescence decay by 5 ns long bunches
Comparison to wire scanner at SPS
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Realization of Bunch Shape Monitor at UNILAC

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Standard Bunch Shape Determination
Standard intersecting method developed by
INR-Moscow (A. Feschenko, P. Ostrumov et al.)

? Insertion of a 0. 1 mm wire at 10 kV ? Emission
of e- within lt 0.1 ps ? Acceleration toward 1mm
slit ? Rf-deflector as time-to-space
converter ? Detection with SlitCup or MCP ?
Resolution better 1o or 10 ps
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Dynamic Transmission control at UNILAC
Verification for transmission control Artificial
beam loss by quadrupole variation ?
chopper window decrease
40 µs/div
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High Current Transmission control at UNILAC
FPGA