PMT ID Numbers

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The PMT ID numbers as defined in NuWa offline software are explained.


In counting PMT IDs the number zero is reserved as illegal.

In the software, PMTs are addressed using a single bit-packed int which is packed/unpacked by the "Conventions/Detectors.h" classes. This number provides a globally unique The packing is:

Byte 1
site ID ("Conventions/Site.h")
Byte 2
detector ID ("Conventions/DetectorId.h")
Bytes 3 & 4
local PMT ID ("Conventions/Detectors.h")

Local PMT ID is unique within the detector subsystem.


AD PMTs are addressed by a cylindrical coordinate system made up of a grid of PMT rings and PMT columns.


Main AD PMTs

The AD PMT local ID bytes are:

Byte 3
rings number, 1-8 counted from bottom to top.
Byte 4
column number, 1-24 counted counter-clockwise looking down at the AD cylinders.

Note: in G4dyb and pre-validated DetSim the convention is that column 1 is at 0 degrees (on positive X-axis). The real ADs will have column 1 at +7.5 degrees.

AD Calibration PMTs

There are 6 calibration PMTs which are packed by giving them the illegal ring number (zero) and column numbers:

  • 1: top, target-viewing
  • 2: bottom, target-viewing
  • 3: top, gamma-catcher-viewing
  • 4: bottom, gamma-catcher-viewing
  • 5: top, mineral-oil-viewing
  • 6: bottom, mineral-oil-viewing

PMT Indices

This packing above will produce a sparse set of numbers. When a compact set is needed, for example to index an array, the convention is followed that the numbers 1-192 are given mapped such that

  • ring-1, column-1 is PMT #1
  • counting continues around the ring counter-clockwise up to PMT #24
  • ring-2, column-1 is PMT #25
  • ...
  • PMT #192 is ring-8, column-24

The calibration PMT indices are:

  • 193: top, target-viewing
  • 194: bottom, target-viewing
  • 195: top, gamma-catcher-viewing
  • 196: bottom, gamma-catcher-viewing
  • 197: top, mineral-oil-viewing
  • 198: bottom, mineral-oil-viewing

Ladder-based Numbers

The offline does not know about ladders but they are used by some people, particularly during commissioning. Laddder-based counting uses:

  • Ladder numbers 1-8 starting with #1 just above the x-axis (holding offline column numbers 1-3) and proceeds counter-clockwise.
  • LadderColumn numbers 1-3, progressing counter-clockwise w/in one ladder. Note, this is a different "column" convention than what offline uses.
  • Ring numbers 1-8, same convention as offline.

Ladder-based numbering is usually expressed like:


Conversion between Ladder-based numbering and Offline convention is as follows (note, integer division)

Lx = (column-1)/3 + 1
Cy = (column-1)%3 + 1


column = (Lx-1)*3 + Cy

Pool PMTs

Fixme: This needs work.


Fixme: This needs work.

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