The UC Simulation of Picosecond Detectors

1
The UC Simulation of Picosecond Detectors

• Pico-Sec Timing Hardware Workshop
• November 18, 2005
• Timothy Credo

2
TOF Detection

• Current method bars of scintillator several
  meters long
• Signal amplified in PMT at each end
• Relevant length scale is 1 in, which governs time
  resolution (100 ps)
• 1 picosecond resolution requires scale on the
  order of 300 microns

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A Picosecond TOF Detector

• Light produced in the window of MCP-PMT shines on
  a photocathode
• Signal amplified in MCP, and summed in the anode
• Electronics measure pulse from four collection
  points

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Summing Multianode

• Multilayer circuit board collects MCP signal
• 16x16 125 micron pads each routed to electronics
  by equal-time impedance-matched traces
• 4 central collection points deliver signal to
  electronics
• Mismatched impedances cause signal reflections

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Simulations (Window, MCP)

• Cherenkov emission, transmission, chromatic
  dispersion, and quantum efficiency simulated in
  ROOT (started by R. Schroll)
• Simulations use MCP time spread and gain (1e6)
  for single photons to estimate the signal
  arriving on the anode
• These data were input into an HSPICE simulation
  of the summing anode

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Window Thickness and Material

• Simulations evaluated the time resolution of the
  window and MCP for different window materials and
  thicknesses
• MgF2 is transparent further into the ultraviolet
  and offers better performance
• Larger windows generate more photons, providing a
  better average over TTS

Window Width (mm) RMS Jitter (picoseconds) RMS Jitter (picoseconds) Number of Photoelectrons Number of Photoelectrons
Window Width (mm) Silica MgF2 Silica MgF2
1.0 15.31 12.88 16.3 21.6
2.0 10.21 8.74 32.4 42.6
3.0 8.39 7.22 48.2 63.0
4.0 7.12 6.06 63.6 83.2
5.0 6.80 5.71 78.2 102.6
6.0 6.34 5.18 93.0 122.0
7.0 5.71 4.85 109.0 141.0
8.0 5.29 4.59 121.9 159.4
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Time Resolution (Window, MCP)

• The time resolution of the window and MCP depend
  on the number of photons detected and on the TTS
  of the MCP
• With the Burle Planacon MCP, simulations indicate
  a 6 picosecond resolution
• A smaller TTS (already achieved in smaller area
  MCPs) would make 1 ps resolution possible

Average timing of signals arriving at the anode,
for different MCPs
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Simulations (Anode)

• The performance of the multianode was simulated
  in HSPICE using a spice model generated from the
  board design using HyperLynx
• With a 50 O termination, ringing decayed with a
  time constant of t 5.5 ns
• With 60 ps TTS, pulse had average rise time of 80
  ps, and average height .25 V
• With 10 ps TTS, average rise time was 25 ps, and
  average height 1.2 V

Voltage vs. time plots of anode simulations,
with 60 ps TTS (top) and 10 ps TTS (bottom)
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Ten Simulated Pulses (60 picosecond TTS)
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Ten Simulated Pulses (10 picosecond TTS)
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Time Resolution (Anode)

• With a large TTS (s 60 ps), the pulse shape is
  not consistent
• With this anode a resolution of around 10 to 20
  picoseconds could be achieved for a large TTS
• With a faster MCP, the pulse shape is more stable
• Picosecond resolution may be possible, but not
  without a fast large area MCP (TTS comparable to
  smaller area MCPs)

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Future Plans

• Custom summing board mates with standard 32x32
  Burle anode
• Glue boards to Burle PMT with Planacon MCP using
  conductive epoxy (Greg Sellberg, Fermilab)
• Solder component board with fast comparators
• Use commercial TDC(?) and test several tubes in a
  beam at Fermilab or Argonne

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Conclusion and Questions

• A picosecond TOF detector could be developed, but
  would rely on a fast large area MCP and fast
  electronics
• Is the MCP response to a single photoelectron a
  good approx. to its behavior in the case of many
  photoelectrons?
• Will the particle create a pulse as it passes
  through the anode and the electronics, and what
  effect will this have?