Particle Detector: Position and Time
Sensitive
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The particle detector consists of a chevron MCP and a hex-anode DLD.
The MCP is a plate with a grid of tubes (or channels) with diameter on
the order of 10 micrometers. An incoming particle will reach the front MCP and
enter a channel. The channels on the front MCP are angled so that the particle
will collide with the wall of the channel. This collision releases electrons
which also collide with the wall and release more electrons. This process
continues until a shower of electrons exits the channel. Typically one particle
will yield an electron shower of approximately 103 electrons. The chevron
MCP consists of two plates with their channels aligned at an angle. Each
electron emitted from the first MCP causes an electron shower in the second
MCP. Therefore the chevron provides a gain of approximately 106. The front MCP is held at -20V and the back MCP at 2000V. When the
front MCP emits an electron shower its voltage suddenly increases. This voltage
increase provides the timing signal for the arrival of a particle. The timing
of every particle reaching the detector in a given event is measured from the
laser pulse that began that event.
Behind the chevron is a hex-anode DLD which is held at a higher voltage
than the second MCP and attracts all the emitted electrons. The DLD is a grid
of three wires (u,v
and w wires)The electron shower generates an
electrical signal on each wire. This signal travels down each wire in both
directions. The times that the signal arrives at the ends of each wire are
recorded. From the difference in arrival times for a given wire the position of
the electron shower can be calculated. This position is interpreted as the position
of the incident particle.
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