Applications of psec TOF in proton and heavy-ion accelerators

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Applications of psec TOF in proton and heavy-ion
accelerators

• Peter Ostroumov
• Pico-Sec Timing Hardware Workshop
• November 18, 2005

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Outline

• TOF measurements in accelerators
• Rare Isotope Accelerator Facility
• Accelerated bunched beam velocity (energy)
  measurements based on induced rf signals
• Bunch time profile measurements with resolution
  10 picoseconds based on streak camera
• Improvement of time resolution of the existing
  BLD
• Bunch time structure measurements using X-rays
• High resolution is obtained by using streak
  cameras
• Examples of TOF technique application in nuclear
  physics experiments at ATLAS mass and nuclear
  charge identification of radioactive ions using
  gas-filled magnet

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TOF systems

• High-power (hundreds of kilowatts) accelerators
  such as RIA driver linac
• Require high-precision control of beam energy
• Maintain short bunches (40-100 picoseconds)
• Beams of rare isotopes must be analyzed by
  detecting individual particles. Fast time
  measurements (20 picoseconds resolution) are
  necessary to control bunched beam quality
• Absolute energy measurements based on TOF system
• Required for many experiments
• Non-destructive, cheap compared to magnet
• Well suited for beam velocities lt0.5c
• Very high accuracy can be obtained
• Wide range of beam currents starting from 0.3 nA
  (1010 particles/sec) can be analyzed

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Absolute energy measurement using resonant TOF
system
48.505 MHz
FEE
FEE
FEE
f48.505-48.500 5 kHz
Phase meter
Beam frequency 48.500 MHz Resonator frequency
48.500 MHz
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Absolute energy measurement using resonant TOF
system
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Absolute energy measurement using resonant TOF
system

• Precision of TOF measurements
• Signal noise ratio
• Phase jitter due to vibration, some thermal
  effects
• Major contribution beam phase jitter

Phase advance over 9 m 5400 deg of 48.5
MHz Phase meter precision 0.2 deg TOF300
nsec

• Accuracy of beam energy measurements
• Additional effect is the distance between the
  detectors
• Typical number is ??E/E2?10-4

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High accuracy is achieved by using

• Chain of bunches, signal is integrated in the
  resonator (msec)
• Mixing of two frequencies in the resonator helps
  to avoid extra noise that can be accumulated in
  external circuits
• The bunch phase at 48.5 MHz is directly
  translated to 5 kHz and minimizes phase meter
  errors
• Front End Electronics
• Amplitude detection
• Narrow band-pass filter (5 kHz)
• AGC (automatic gain control) amplifier

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Bunch Length detector
4 5 6

• 1-tangstin target wire, 2-collimator, 3-plates of
  the rf deflector, 4-MCP, 5-phosphor screen, 6-CCD
  camera,.

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Electron beam trajectories with no RF applied
(streak camera)
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Electron beam image on the phosphor with no RF
applied
Focused electron beam profile Resolution is 15
pixels Bunch width 10 deg at 97 MHz290
picoseconds 15 pixels corresponds to 10
picoseconds resolution
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RF on, bunch image
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Bunch time profile

• 58 Ni bunch profile (a) inferred from
  scintillator signal (b).

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Time resolution

• The time required for the emission of secondary
  electrons
• The time difference, due to the different arrival
  times of the secondary electrons originating from
  different points of the wire, at the rf deflector
• The contribution to the detector resolution from
  the angular and energy distributions of the
  secondary electrons
• The time of flight of the electrons through the
  electrostatic field of the plates.
• Finally the RF voltage and rf phase jitter is a
  very important factor in determining the time
  resolution of the detector.

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Improvement of time resolution of the existing BLD

• Reduce both the entrance and exit slits size down
  to 0.2 mm
• Use single electron mode of measurements. In the
  single electron mode the problem associated with
  the finite size of the SE beam will be minimized.
• Reduce the diameter of the wire to 0.03 mm
• Increase the voltage applied to the wire up to 15
  kV
• Increase the rf voltage to have large sweeping
  amplitude on the exit slit
• Improve electron beam optics to obtain more
  isochronous trajectories
• Improve phase jitter of the rf deflector by
  introducing an external RF synthesized signal
  generator with a high stability.

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Heavy-ion bunch time structure using X-rays
Focusing spectrograph for picosecond time
resolution of ion beam (adapted from 1)
Streak camera
BEAM
1 O.N. Rosmej et al. 30th EPS Conference on
Contr. Fusion and Plasma Phys., St. Petersburg,
7-11 July 2003 ECA Vol. 27A, O-1.9C
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Typical streak camera being used at electron
synchrotrons
Time resolution of streak cameras can be less
than 1 picosecond
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Heavy-ion bunch time structure using X-rays
(proposal)

• Ions penetrate the thin target ( 0.1-0.2 mm) and
  undergo multiple collisions with target atoms.
• Excitation of bound electrons followed by
  radiative decay gives rise to projectile and
  target radiation. Decay time 10 femtosec
• Focusing specrograph with spatial resolution
  provides high spectral and spatial resolution of
  the K-shell spectra.
• Streak camera measures the temporal structure of
  the beam with picosecond resolution.

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ATLAS Layout
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Mass and nuclear charge identification using
gas-filled spectrograph

• Difficulty
• The masses are very close
• The same q/m, velocity

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TOF for mass and charge identification
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Time-of-Flight Measurement with the Storage Ring
in the Isochronous Mode (Milan Matos
presentation)
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Signals from the Detector
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Time-of-Flight Spectrum
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Conclusion

• Time resolution of 3-5 picoseconds is required to
  tune and operate high-power heavy-ion linacs
• So far the technique remains complex and
  expensive to provide high resolution
• TOF is a common technique for identification of
  mass and nuclear charge of rare isotopes.
  Currently several large facilities are being
  constructed worldwide to produce beams of exotic
  nuclei.
• High resolution MCPs can help to reduce the cost
  of storage rings or spectrographs in future rare
  isotope accelerator facilities