Triggering of MIL Based Equipment

Informative: Triggering of FAIR-style White Rabbit based equipment has already been considered, see approved technical concept, Meeting October 2021. The B2B already distributes all information via the White Rabbit network since January 2021.

This section just deals with a solution in the context of the bunch-to-bucket system (work package 2.14.10.12). It does not aim at an overall solution to solve issues with MIL timing related to the FAIR General Machine Timing (GMT) system (work package 2.14.10.3).

Introduction and Issues in the 2021 Beam Time

Triggering of MIL based equipment has multiple issues

• no information for event numbers 256 and higher
• existing TIFs and dedicated electronics has evolved over the years and can't be changed easily
• MIL timing is event based and TIFs do not allow generating pre-triggers (negative offset)

In the 'old control system', the kickers are triggered using the following procedure

• the 'Timing Generator' is triggered by EVT_KICK_START1/2
• the 'Timing Generator' locks to the RF-signal
• the 'Timing Generator' generates a kicker trigger based on the RF-signal
• (an additional delay is introduced to the kicker itself)
• (an additional dealy is added by the signal propagation time in copper cables)

The triggering concept of MIL based beam instrumentation (and other equipment) is the following

• everything is event based
• data acquisition starts with EVT_KICK_START1/2 (sometimes an additonal delay is added)
• equipment uses 100us or 500us integration time
• the integration time includes
  • processing time of 'Timing Generator'
  • kicker delay

Figure: Triggering with the B2B system in 2021. Green lines: Scheduled deadline for events issued by the Data Master (DM) and the B2B system. Event numbers are EVT_KICK_START (EKS), CMD_B2B_TRIGGEREXT/INJ (KTE/KTI) and CMD_B2B_DIAGKICKEXT/INJ (KDE/KDI). Boxes indicate the time window of the kicker trigger (green), beam passage (orange), beam instrumentation integration window for MIL based equipment (light blue) and other actions (light pink). The figure is not to scale. Details see text.

The triggering concept of the B2B system is not event based but time based and tightly integrated into the White Rabbit timing system. For the 2021 beam time, the B2B system is triggered by EVT_KICK_START1/2. As an obvious result, the extraction time with the B2B system no longer coincides with EVT_KICK_START1/2 (plus a minor delay) and the beam passage in the transfers line is outside the integration time of beam instrumentation equipment.

The figure above shows the situation with triggering in the 2021 beam time. The beam passage happens roughly 1 millisecond after EVT_KICK_START1/2. For quipment with MIL based timing there is no possibility to add a negative offset to the event deadline and the beam is not detected within the integration window, see here. As a temporary experimental workaround for the 2021 beam time, two new events (0x112 and 0d192) were introduced that use the same deadline as the trigger messages for the kickers. However, this did not work out for multiple reasons that are not discussed here and this workaround will be discontinued.

Solution for the 2022 Beam Time

Figure: Triggering with the B2B system in 2022. Green lines: Scheduled deadline for events issued by the Data Master (DM) and the B2B system. Event numbers are EVT_KICK_START (KS), CMD_B2B_TRIGGEREXT/INJ (KTE/KTI), CMD_B2B_DIAGKICKEXT/INJ (KDE/KDI) and a new event number CMD_B2B_START(B2BS). Boxes indicate the time window of the kicker trigger (green), beam passage (orange), beam instrumentation integration window for MIL based equipment (light blue) and other actions (light pink). The figure is not to scale. Details see text.

The figure above depicts the proposal for the 2022 beam time. As the main difference to the 2021 beam time, the triggering of the B2B system is decoupled from the triggering of other equipment. This is achieved by using two distinct messages both having a dedicated unique event number. Coincidence between the beam passage (triggered by the B2B system) and the existing MIL based equipment is achieved at the model / LSA layer by shifting the deadline of the B2B start message relative the one of EVT_KICK_START1/2. No change is required for triggering equipment based on MIL based timing.

Update (December 2021): Shifting the deadlines of EVT_KICK_START1/2 (SIS18, ESR) and CMD_EXTR_KICKER_START (CRYRING) relative to the earliest deadline of CMD_B2B_TRIGGEREXT can be done via the ParamModi parameter Kick Start Event Verschiebung .

NB: It is highly recommended that all equipment based on White Rabbit timing is migrated to the new timing and triggering scheme provided by the B2B system.

Drawbacks and Mid Term Perspective

The main drawback of the '2022 proposal' described above is the lack of triggering MIL based equipment when using the true bunch-to-bucket transfer. There are two alternatives.

• Migrate primary equipment to White Rabbit based timing. Here, it is straight-forward to apply negative offsets for pre-triggerin or compensating latency.
• If MIL based timing remains a must, a solution could be developed, where the precise timing of 'old' MIL events played during transfer is not planned on the model/LSA layer but is set on-the-fly. In case this is required, such a solution should be implemented within the GMT. This has to be worked out, but it is expected that the Data Master anyhow undergoes a major change in the coming years ('injector timing', 'cluster', 'A10').

-- DietrichBeck - 9 December 2021