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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