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