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Chopper wheel PowerPoint Presentation
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Chopper wheel

Chopper wheel

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Chopper wheel

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  1. Stanford DG535(Repetition Rate) This unit sets the macropulse repetition rate by inhibiting the 100 Hz timing signal from the chopper wheel Quantum Composer 8-Channel timing unit This unit is triggered by the Repetition Rate DG535, and takes a clock input from the 81.25 MHz RF reference. On triggering, it waits for the next RF clock cycle, then cascades trigger signals to the Mechanical Shutter (selecting a specific macropulse), and to the Macropulse LengthDG535 to set the macropulse length. Additional trigger signals are provided to the rack room and the TW laser. AΠB Trig Sync 81.25 MHz A B C D E F G H TW Laser Rack Room 1 Streak Camera 7 Mechanical Shutter The mechanical shutter selects specific macropulses from the 100 Hz macropulse train to define the 1, 2, 5, 10 or 20 Hz repetition rate Stanford DG535(Macropulse Length) This unit provides trigger to the Pockels cell driver to define the macropulse length Chopper wheel Rotates at 100 Hz and contains a timing photodiode to signal position on each turn. A slot cut in the disc passes a 130 ms laser pulse train every turn. 4 3 A B C D T Pockels Cell Driver

  2. Quantum ComposersTiming Unit Settings Incorrect timing settings which do not drive EMMA RF correctly due to a 20 ms offset in the main R trigger, changed 2011 02 25 Gate: Mode (Chan Menu) –Level - 2.50 V; Clock: Rate - 81.25 MHz; Level - 0.1 V; Ref. out - To pulse; Ext. Opt. - Force OFF; T0 clock rate - 0.010000000 Trig: Mode – Triggered; Level – 1.00 V; Edge – Rising Edge

  3. Quantum ComposersTiming Unit Settings New timing settings established to drive EMMA RF correctly using timingsensor located on the left-hand side of the chopper wheel, set 2011 02 25 Gate: Mode (Chan Menu) – Level - 2.50 V Clock: Source Ext. w/PLL;Rate - 81.25 MHz; Level - 0.1 V; Ref. out - To pulse; Ext. Opt. - Force OFF; T0 clock rate - 0.010000000 Trig: Mode – Triggered; Level – 1.00 V; Edge – Rising Edge * = Value changed from 27.37 ms to 26.37 ms on May 23 following shutdown work. ** = Value changed from 27.31 ms to 26.41 ms (noted on 28/8/12 – not sure when change was actually made)

  4. DG535 Unit Settings:Macro Pulse Length (Pockels Cell) Values correct, as of October 25th Channel ‘A’ adjusted slightly to capture beam following shutdown work Trig: Ext.; Threshold = +0.16 V; Slope (+/-) = +; Trigger term = High Z Output: AB; AB & -AB Loads = High Z; AB: TTL