This document is a guide for ACR staff and anyone else on shift for the current best practices when operating the FACET-II linac. For recent news and links to ops procedures visit the MCC wiki FACET-II hot page (requires SLAC intranet access).

Beam Delivery

Supporting FACET-II users

  • Don't assume that users are OK with/aware of any abnormal beam condition you observe. Make sure they're aware of any issues with the machine as they arrive.
  • When shifts end, verify explicitly with users that they have retracted/made-safe any experimental devices on the beamline, and restored any machine configuration changes
  • <more babysitting advice goes here>

Loss monitoring

During beam delivery, losses & secondary radiation should be kept ALARA

  • BCS LIONs, BPMs, toroids, the PLIC, S20 PMTs and RDMs should all be monitored during MDs and user delivery
  • Significant losses should be investigated and tuned out
  • Occasionally, experiments (e.g. E300 PWFA) will generate significant radiation in S20
    • ensure before any experiment work begins that beam transport is clean
    • continue to monitor loss signals for increases above your baseline expectation

Critical software & controls infrastructure

There are a number of background processes that must remain operational for the controls system to function

  • Alpha ← mainframe for all SLC micros, if this dies it will take all the SLC-era controls system with it, so you should know if something is wrong
  • SLC → AIDA-PVA → EPICs communication
    • You can check on the aidapva, aida_slcklys, aida_slcbpm statuses in the SCP under network micro index
  • Watcher processes
    • in EPICS, physics apps → GOTO watcher
    • everything on this panel should be green, if a watcher is off/dead/not needed it should be bypassed by its owner
  • MDL feedforward
    • Keeping the main drive line phases consistent is key to
  • S20 differential pumping system (DPS)
    • DPS watcher and upstream & downstream turbopump statuses are on the S20 CUD

On-call physicist

The FACET-II MD schedule lists the current on-call physicists for the day. This person is the first point of contact for any technical questions & issues regarding beam delivery. The phone numbers for all accelerator physics & beam operations (APBO) group members are in the ACR phone tool and the SLAC directory.

  • This does not replace the usual escalation mechanisms for requesting help from support engineering groups & communication with the LAF program deputy
  • If you're unable to reach the on-call person for a blocking issue, attempt to contact other members of the APBO group

Standard machine characterization

Periodically, the following set of measurements should be taken & logged to characterize beam quality. Up-to-date beam measurements are critical for making informed decisions when running the accelerator.

  • Save machine configuration
    • SCORE save-the-world
    • SCP config macros
    • reference orbit (from the orbit display)
  • Emittance measurements in the following areas:
    • L0 (injector)
    • L2 (LI11)
    • L3 (LI19)
  • Measure the beam size at the final focus
    • IPWS1 X and Y measurements
    • XTCAV bunch length (recommend taking >3 measurements to get a sense of per-measurement error)
  • Record beam images from the following screens:
    • PR10571
    • PR11375
    • SYAG
    • DTOTR2

Beam Tuning

  • Table of target machine parameters should go here
  • Should have different values for pencil/short-bunch/2bunch as needed & note what is and is not operating-mode dependent

Loss reduction

  • In general, maintaining clean transport of the e- beam is more important than having the best possible measured beam quality. If you notice losses rising while tuning, you should identify & walk back changes that caused them

Transverse

Injector

  • steering
  • SOL121
  • quads 10361, 10371

Linac

  • BC11 launch/exit
  • CQ11317, CQ11352
  • steering

S20

  • steering

Longitudinal

  • Compressions scan (link to wiki)
  • complementary phase adjustments in L1 & L2




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