Introduction (user panel)
The MTCA based triggers have a jitter in the few ps range, the delay can be shifted in 9 ns steps, One can choose between 10 Hz triggers, Triggers connected to the (fast) FEL shutters, frequencies locked to the pulses (e.g. 1MHz) and the actual bunch patterns. A detailed description can be found in x2Timer manual (Design Paper).
- the triggers are for low impedance (~50 Ohm )
- signal level is + 5V - otherwise 0V (in the expert panel one can also invert the signal - base line is +5 V and trigger 0V)
- The trigger are send to the MTCA several ms before the first FEL pulse (3.1 ms for the "standard" trigger, 21.5 ms for the "early" trigger).
- The timer card can delay the trigger in 9 ns steps for more than 100 ms (an option to shift the trigger in 1 ns steps is available in the expert panel)
- The shown delay in µs is in respect to the first FEL pulse. negative delay: trigger comes before FEL, positive : trigger comes after the FEL.
- The desired delay has to be entered in the "delay to be set" field and as second step pressing the "set delay" sends the delay value to the timer card. Then the trigger delay will be changed and the "actual delay" will be updated.
- The trigger can be set to only provide a trigger signal if the FEL Fast shutter is open. One has to choose which FEL shutter to use.
- The trigger width can be adjusted from 9 ns to several ms in 9 ns steps
- The timer card can in addition to the 10 Hz triggers also provide frequencies which are linked to the FEL repetition rate and the actual burst pattern of the FEL. For details how to set these modes see below
- At the beamlines the triggers are provided with a BNC patch panel
The main control can be done with a simplified user panel which can handle the timing in respect to the FEL pulses (and not in respect to some arbitrary event time)
Choosing a FLASH1 trigger there are 2 options to be synchronized with the BL and the PG shutter :
A yellow background indicates that the trigger is synchronized to a fast shutter:
With the "Expert overview" one gets the overview over all channels available on the timing card and can configure the card. This is useful to look what channels are using clock settings or burst mode settings that one wants to change ... and using the other tabs one can set parameters for clocks and bursts (see below)
For each trigger channel there is in addition an "Expert panel" to set the properties of THIS channel
Set a constant frequency to a channel
The timer card provides the option to generate frequencies that are synched to the FEL reprate on the ps level. One can set 3 Clocks by deviding the reference frequency of 54.2 MHz by n. Please check (using the Expert overview ) before changing a frequency of it is used for some other channel !!
Since our main FEL frequency is 100.31 MHz the dividers are not straight forward:
|Clock frequency||Divider to be set|
|"1 MHz" (1000.31 kHz)||53|
|"500 kHz" (501.5 kHz)||107|
|"250 kHz" (250.8 kHz)||215|
|"200 kHz" (200.6 kHz)||269|
|"100 kHz" (100.3 kHz)||539|
General FLASH frequencies:
|Name ||Frequency ||Divider|
|1.3 GHz||1300.000000 MHz|
|108 MHz||108.333333 MHz||12|
|9 MHz||9.02777777 MHz||144|
|4.5 MHz||4.513888 MHz||288|
|1 MHz||1.003086 MHz||1296|
Once a clock is configured with the right frequency one can choose in the "expert panel" of the according channel the "FPGA clock" in the "input source select" chooser.
One has to set the delay to values less than the repetition rate ... (so for 1 MHz between 0 and 990 µs) and the trigger width also less than the rep rate ...
This results in a continuous train of pulses with the set trigger width.
Creating an (own) burst trigger
One can use now a SECOND trigger channel which is set to a regular 10 Hz trigger and gate the clock output to create a burst with defined start point and length,
For the example we use the FRONT.TRG2 (BL3 Trg5) as gate pulse which defines the length of the burst (set with the trigger width) and the (rough) starting point of the burst. This trigger is only used as gate and the physical trigger output is NOT used.
The second channel (here FRONT.TRG3 (BL3 Trg6) which is set to the clock frequency defines the reprate (by the FPGA clock setting) , the exact starting point of the first trigger ( by the delay ) and the width of the MHz/kHz triggers (width).
To get from the clock to the burst trigger one has to:
- set the "2nd source select" to the gate trigger ( here FRONT.TRG2) - this defines a second source to considder for the trigger output.
- and the "output source select" to "AND 2nd Ch." this finally only sends a trigger if on both inputs (clock and gate) we have a high signal.
Real bunch trigger - get a trigger for each FEL pulse
Sometimes it is convenient to get a trigger pulse for each pulse in the FEL. thus if the FEL number of bunches or reprate are changed, the trigger adapts accordingly.
For this one has to select the source of interest in the expert overview panel (tab: "Bunch pattern") ... well for us this is FLASH1 (FL1D) or FLASH2 (FL2D)
There are 6 different bunch pattern "channels" one can configure. Typically only 2 are needed ... And in each one there are 6 selectors to choose sources . We only need one - it does not matter in which one is used.
In the expert panel one can now choose the configured "Bunch Pattern" as "Input source select"
NOTE: To shift the burst in time one can no longer use the delay of the individual channel BUT the delay in the "Bunch pattern" tab in the expert overview! This now shifts all bursts ... so you better know what you are doing. typically the burst is already shifted to the actual FEL timing ... Shifting the timing should be discussed with the beamline scientist / local contact ...
Different trigger events (starting points)
one can configure each channel for an individual trigger event
|21||Trig16 + first bunch of FLASH1 - this trigger is shifted when FL1 starts later than "700"|
|180||shifts with the start time of FLASH1 as event 21 but comes 23 ms before the FEL|
|16||the MCA trigger 3.11 ms before the Flash1 pulses (same as A6 but more stable)|
|166||A6 event. still possible to use but less precise than 16|
|162||A2 event as earliest ( 24 ms before the FEL)|
|224||E0 event of the BL fast shutter ( 19 ms before the FEL) - to be switched off in 2020|
|225||E1 event of the PG fast shutter ( 19 ms before the FEL) - to be switched off in 2020|
|22||Trig116 + first bunch of FLASH2 - this trigger is shifted when FL2 starts at a different start time|
|181||shifts with the start time of FLASH2 as event 22 but comes 23 ms before the FEL|
from this trigger as starting point one can shift the timing in 9 ns steps first and finally in 0.9 ns steps for fine adjustment.
Info about the Fast shutter trigger
Since Jan 2020 the fast shutter trigger at FLASH1 is generated via local inhibit at the EXP1 and EXP2 crate and not via E0 and E1 events anymore
for details see Fast Shutter trigger inhibit system
Special trigger options for the fast shutter:
Fast shutter inhibit signal
It is possible to have the fast shutter inhibit signal (the signal coming from the fast shutter to the inhibit boxes connected to the X2 cards) directly available for users. For this one can select the output source as 2nd channel:
Inverse fast shutter trigger
If one wants to have an inverse fast shutter trigger (10 Hz signal that comes only if the fast shutter is CLOSED) one can use a T and a small Lemo cable to double the input from the fast shutter to another input at the inhibit box.
In the FL2 case input1 is the regular fast shutter channel and input2 is usually not used. for this additional input one can set the input configuration to inverse: