Machine Protection for LCLS Injector Commissioning

(IMPS)Howard Smith

For the MCC Operations GroupNovember 29, 2006

Overview of content

• Splitting of LINAC TIU• Splitting of LINAC PLIC• “IMPS”• LCLS Injector Layout

– A Comment about Linguistics– Modes of Operation

• “BASII”• Beam Shut Off Mechanisms• Single Shot Mode• Burst Mode• AP20 Processor and some concern• A comment about the screens• Acknowledgements• Disclaimer: Most of the sketches in this presentation are not rigorously

representative of any actual configuration. Rather, they are intended to provide adequate indication of their role in the overall system.

“Split TIU”To be activated by some administratively controlled switch.

Breaks system into two systems, one encompassing sector 21-30, the other encompassing sectors 0-20.

New transmitter in sector 21 for the 0-20 system - will use existing sector 0 receiver.New receiver in sector 20 - will pick up the existing transmitter signal.

New receiver tied to AP20 LDIM for MPS shut off as appropriate (LCLS beams if TD11 out, CID beams if BASII out).

A few signals in the 21-30 branch (LINAC PLIC electronics in MCC ok) still needed for sector 0-20 protection. These to be repeated to LI20 chassis for shut off of CID beams.

“Split PLIC”Existing system counts pulses above threshold.

3 bad pulses within 0.8 seconds invokes 1 Hz rate limit (via MPG IDIM module).After that, 7 bad pulses within 1.6 seconds invokes “backup trip” (a.k.a. “SLAM” a.k.a.

“PPYY RELAY”)Areas of known expected loss or big signal (with other PIC MPS protection) are

desensitized by a gated offset derived from PDU triggers (gates are shot-to-shot).

“Split PLIC”New features added for LCLS.

When triggered by PDU, entire back end of signal (from sector 21-30) is desensitized by a gated offset.

LCLS beam losses should never exceed existing threshold for invoking MPG rate limit (via IDIM) or backup trip when gate is turned on.

Translation: LCLS LINAC PLIC should not bother PEP.

“Split PLIC”Three new comparator thresholds are now made for just the back end (sectors 21-30) of

the signal (when the LCLS PDU trigger is given).Rather than counting pulses above threshold, new system faults an output every time a

pulse above threshold is seen. These faults persists for one second.These output bits then drive 1553 MPS LDIM channels.

MPS algorithm to do the following:One or more Level 1 bad pulses in last second ? Force 10Hz rate limitOne or more Level 2 bad pulses in last second ? Force 1 Hz rate limitOne or more Level 3 bad pulses in last second ? Force zero rate.

(Last condition will ratchet zero to one Hz effectively 0.5 Hz)

Interim Machine Protection System

• LCLS undulator protection will ultimately require a new system:– Needs to stop beam pulse N when a fault is detected between beam

pulse N-1 and N (<8ms response).• New system is in the design stages.• For Injector Commissioning, an interim system is needed.• Interim system uses existing VME MPS system (“new MPS”)

– Signals detected with CAMAC modules (LDIM & PICP)– CAMAC 1553 serial link reports information to AP micros– AP micros report information via 1553 link to MPS Supervisor– MPS Supervisor shares memory with MPG. MPG invokes rate limiting.

• Existing system is not fast (enough)– A fault detected on pulse N allows a few more pulses N+1, N+2,...N+M

to occur.– M = ...(I’m not sure)?– Terms in M include 3/360th MPG pipeline plus whatever beam is already

stored in damping ring.

LCLS Injector Layout

Types of Devices:

• Obstructions:– vacuum valves– beam stoppers – alignment mirrors

• Magnet Power Supplies– on and at set point– completely off– derived from EPICS magnet control IOC– used as MPS Stoppers for algorithm branching

• Profile Monitor Screens• Toroids

– Gun peak current monitor– throughput comparators (level 1 <90% transmission; level 2 <50% transmission)

• Flow Switch and klixon on CE11 collimator• LASER joule meter• EPICS heartbeat• LINAC PLIC and TIU• Ion Chambers

– Standard PICP modules with standard SLC DB• Complete list available as excel spreadsheet on LCLS Sharepoint database

A comment about the “Lingo”All of these beam line devices have EPICS names

Example: Gun Spectrometer Dipole is known as MAG_BEND:IN21:BL231, but is referred to in speech by it’s common name from MAD deck “BXG”. “SLC aware” IOC also has an SLC database, BEND IM20 unit 231.

OPS would be well served to study up on some of these “common names” and start to formulate the “Lingo” that is ultimately used in the control room.

Printed maps on trailer 5C wall (outside Zev & Sonya’s office) are a good place to start.

For MPS translation string purposes (the messages which come up on the MPS CUD), I have tried to refer to devices by their common name (as I understand them to be).

Several Modes of Operation (Beam Destinations):

• Electron beam to Gun Spectrometer:– All downstream devices are ignored. – Initiated by MPS Stopper bit BXG magnet on and trimmed

(derived in EPICS magnet control reported to AP20 LDIM).– Requires vacuum device “BXG Wakefield Shield” retracted. This

device assures a smooth vacuum impedance for beam headed toward LINAC, but needs to be removed (would be an obstruction) to allow beam to be bent into Gun Spectrometer.

Several Modes of Operation (Beam Destinations):

• Electron beam to Injector Spectrometer:– All downstream devices are ignored. – Initiated by MPS Stopper bit BX01/BX02 magnet completely off.

(derived in EPICS magnet control reported to AP20 LDIM).– Enables protection of MPS devices in the Injector Spectrometer

Beam Line (these devices otherwise ignored).– In principle, this mode should allow simultaneous/interlaced

operation with ~30GeV beams from CID to BSY (SABER, ESA). In practice, there might be problems. Such interlacing requires LCLS devices downstream of Dogleg 1 to be in an okay state for ~30GeV beam.

Several Modes of Operation (Beam Destinations):

• Electron beam to BC1 and TD11:– All devices downstream of TD11 are ignored. – Initiated by MPS Stopper bit TD11 in.– When LINAC is configured for LCLS operation, we need to keep

30GeV beam from CID away. This is done by shutting off scavenger, A Line, and SABER rate limiting areas unless BASII is in (or unless the LCLS stuff is okay for 30GeV beam).

Several Modes of Operation (Beam Destinations):

• Electron beam to BSY 52SL2:– New “split LINAC TIU” system will be used to protect LINAC

devices from LCLS beam. – New “split LINAC PLIC” system will be used to protect LINAC

from LCLS beam losses without interrupting PEPII Operations.– For 2007, LCLS beam past TD11 will probably occur only for

brief periods. There is great interest in using 29-4 transverse deflector to understand longitudinal distribution and for tuning of BC1.

– Small complication involving BASII stoppers 950/960 in sector 28. These stoppers generate a TIU fault, but removing them also removes BASII at 20-1, shutting down PEP. R.P. doesn’t want us to touch logic...we’ll probably shut off air supply to BASII 20-1.

“BASII”Use of this term calls for clarification

• “BASII” is a term which describes a mode of operation for the LINAC and BSY PPS.– Allows beam in LINAC with access in Sector 30, BSY, and beyond.– Requires that a list of PPS stoppers be “in”.– Also effects mode of operation for MPS and BCS.

• “BASII” is the name of a beam stopper (and associated scatterer) at 20-1.– a.k.a. “BASII dump” or “BASII dump and scatterer”– a.k.a. “Swing dump”.

• “BASII” is a term associated with a pair of stoppers at LINAC sector 28-9.– ST950– ST960

• “BASII” is a term associated with stoppers in sector 10 PEP HE electron extraction.– HE EXT ST4046– HE EXT ST4048– HE EXT magnet B2 power supply– HE EXT magnet B3 power supply– HE EXT magnet PM1 power supply

• “BASII” is a term associated with stoppers in sector 4 PEP LE positron extraction.– LE EXT ST6426– LE EXT ST6427– LE EXT magnet B1 power supply– LE EXT magnet PM1 power supply

• “BASII” is a term associated with PPS for the LCLS injector.– Author awaiting training program...

“BASII”Use of this term calls for clarification

• “BASII” is a term which describes a mode of operation for the LINAC and BSY PPS.– Allows beam in LINAC with access in Sector 30, BSY, and beyond.– Requires that a list of PPS stoppers be “in”.– Also effects mode of operation for MPS and BCS.

• “BASII” is the name of a beam stopper (and associated scatterer) at 20-1.– a.k.a. “BASII dump” or “BASII dump and scatterer”– a.k.a. “Swing dump”.

• “BASII” is a term associated with a pair of stoppers at LINAC sector 28-9.– ST950– ST960

• “BASII” is a term associated with stoppers in sector 10 PEP HE electron extraction.– HE EXT ST4046– HE EXT ST4048– HE EXT magnet B2 power supply– HE EXT magnet B3 power supply– HE EXT magnet PM1 power supply

• “BASII” is a term associated with stoppers in sector 4 PEP LE positron extraction.– LE EXT ST6426– LE EXT ST6427– LE EXT magnet B1 power supply– LE EXT magnet PM1 power supply

• “BASII” is a term associated with PPS for the LCLS injector.– Author awaiting training program...

Small complication involving BASII stoppers 950/960 in sector 28. These stoppers generate a TIU fault, but removing them also removes

BASII at 20-1, shutting down PEP. R.P. doesn’t want us to touch logic...we’ll probably shut off air supply to BASII 20-1.

LCLS MPS beam shut off mechanism

Shutter trigger and pockel’s cell trigger originate from CAMAC PDU programmed with conditional expressions such as:~shutter_perm ->deact

BCS shutter is a backup fault if MPS shutter does not close.

10 Hz on virtual cathode all the time (continuous rate to LASER steering feedback).

Special hardware box for negotiating shutter/ pockel’s cell triggers, backup fault, and Single Shot Mode

Combination of MPS shutter controls and pockel’s cell controls.

What is this Single Shot Mode?

• Explicitly requested by LCLS Physicists• Allows one (and only one) beam pulse to happen.• Useful for diagnosing problems or bootstrapping.• “Driven” by master beam control buttons.• Master beam control buttons talk to shutter/pockel’s cell control box,

which in turn sends the status to AP20 MPS.• Two bits: Single Shot Mode, and Single Shot Request.• AP20 MPS treats the Single Shot Mode bit as an MPS stopper,

forcing branching which requires Single Shot Request bit to be true. Single Shot Request can only stay true long enough for one beam pulse to happen (one MPS transition from zerorate to 1 Hz then back to zerorate).

• Single Shot Mode bit (button) will be a true toggle; well suited for Master Beam Control.

• Single Shot Request is more like a strobe than a toggle, so Master Beam Control button will be a weird way to control it.

What is this Single Shot Mode?

• Single Shot Mode bit (button) will be a true toggle; well suited for Master Beam Control.

• Single Shot Request is more like a strobe than a toggle, so Master Beam Control button will be a weird way to control it.

What is this Burst Mode?

• Single shot mode was so popular that augmentation having a burst of pulses was also desired.

• Allows MPS to transition from zerorate up to 10Hz (as allowed by other devices) for a specified duration of time (or total number of pulses).

• Useful for limiting exposure of sensitive profile monitor cameras and screens to only pulses intended to be measured.

• “Driven” by EPICS controls.• EPICS digital output tied to AP20 LDIM MPS.• Two bits: Burst Mode, and Burst Request.• AP20 MPS treats the Burst Mode bit as an MPS stopper, forcing branching

which requires Burst Request bit to be true. Burst Request only stay true long enough for the requested burst to be delivered.

• While Single Shot Mode has relaxed MPS device state requirements, no such relaxation is included for Burst Mode.

• Plans in place to interface Burst Mode with High Level Software Applications.

What does AP20 do?

• Each interrupt (360Hz), AP20 looks for a package from SP00.

• This package identifies a pulse as having ratelimit area, ratelimitstate, and stopper configuration.

What does AP20 do?

• Each interrupt (360Hz), AP20 looks for a package from SP00.

• This package identifies a pulse as having ratelimit area, ratelimitstate, and stopper configuration.

• AP20 then finds it’s algorithm branch which matches this set of information.

What does AP20 do?

• Each interrupt (360Hz), AP20 looks for a package from SP00.

• This package identifies a pulse as having ratelimit area, ratelimitstate, and stopper configuration.

• AP20 then finds it’s algorithm branch which matches this set of information.

• Once it has the right algorithm branch, it compares it to it’s CAMAC inputs. Based upon it’s CAMAC, it recommends a new rate.

What does AP20 do?

• Each interrupt (360Hz), AP20 looks for a package from SP00.

• This package identifies a pulse as having ratelimit area, ratelimitstate, and stopper configuration.

• AP20 then finds it’s algorithm branch which matches this set of information.

• Once it has the right algorithm branch, it compares it to it’s CAMAC inputs. Based upon it’s CAMAC, it recommends a new rate.

• It then tells the Supervisor what new rate AP20 will allow.

Some concern about AP20.

• With 5 MPSTs there are 2^^5=32 possible configurations. It turns out 13 of these are interesting.

• With 13 stopper configurations and 4 rate limit states, algorithm has 52 branches (just for LCLS).

• This is about five times more branching than we have ever done in an AP.

• Can the AP keep up? CTL SW think the bottleneck is in the CAMAC evaluation, not the branch lookup.

• Algorithm running in AP20 now. No smoke yet, but MPS is not really in a condition to jump around between states with MPG.

A quick comment about screens.

• As mentioned, there is tremendous concern about protecting the profile monitor cameras and radiators.

• Present specification requires that if any screen is not out, (unless behind a stopper) that only Single Shot is allowed.

• Expectation is that this requirement will be relaxed to allow Burst Mode with screens in. (Requires a moderate code change, but hooks are in place (commented out).

Acknowledgements

• Patrick Krejick– Specification and clarification of system requirements.

• Stephen Norum, Arturo Alarcon– Keep track of all the signals and what they need to do.

• Nancy Spencer– Translated the above list into SLC control system database.

• Geoff Milanovich– Reviewed/validated the MPSL code

• Anthony Tilghmann, Sony Nguyen– Build and maintain the hardware infrastructure (including TIU modifications)

• Bob Simmons– Engineered and built the LINAC Devised PLIC system modifications.

• Andy Gioumousis– Engineered and built the MPS Control box for negotiating Shutter and Pockels cell triggers,

Single Shot Mode, and Shutter Fault.• You!

– As with any protection system, this one’s ultimate effectiveness relies on the people who use it.