Tuning Techniques And Operator
Diagnostics for FACET at
SLAC National Accelerator Laboratory
Chris Melton
SLAC Accelerator Operations
FACET Tuning And Diagnostics
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What is FACET?
FACET Performance
Challenges
Operations Solutions
FACET Future
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What is FACET?
Facility for Advanced Accelerator Experimental Tests
• Design Criteria
• Facility overview
• Scientific mission
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FACET Beamline Overview
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FACET “W Chicane” Beamline
e- from Linac
Beam to User
Experiments
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FACET Experiment Beamline
e- from
W chicane
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FACET User Experiment Facilities
e- from
W chicane
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FACET Design Criteria
FACET is designed to deliver high energy, high peak current, short bunch length
electrons and positrons with low transverse emittance to user experiments.
The “Ideal Beam”
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23 GeV e- and e+ beams
30Hz pulses
3.2nC bunches
20 kA peak currents (Ipk)
20mm bunch length (sz)
20mm x 20mm spot size (sx,y)
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FACET Scientific Mission
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New research frontiers require larger, more expensive accelerators
New accelerating methods can reach higher energies in shorter distances
These methods leverage plasma wakes in dielectric & metallic structures
FACET was an ideal test facility for these new techniques due to
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The high charge of SLAC Linac beams
The high compression made possible by SLAC beamlines
High historical demand for electron / positron beams from the SLAC Linac
Success of the SLAC Final Focus Test Beam (FFTB) plasma experiments
FACET will serve the scientific community as a high energy physics user facility
for the exploration of novel methods of beam acceleration, related beam physics,
and development of related diagnostics, with specific applications to materials,
biological, energy, and plasma sciences.
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FACET Science
Plasma Wakefield Acceleration
How FACET generates high gradient acceleration with low energy spread:
• Send a bunch of electrons through Lithium (2011) or Rubidium (2012) plasma
• This drive bunch creates a ~ 50GeV/m acceleration gradient in the plasma
• A witness bunch then travels through the plasma and is accelerated
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FACET Performance
First beam to FACET dump on June 23, 2011
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What To Characterize and Tune? How?
Primary beam properties of interest
Tools for measurement
Charge
Toroid Charge Monitors
Position
Beam Position Monitors
Transverse Beam Size
Profile Monitors (YAG, OTR)
Transverse Emittance
Wire Scanners
Longitudinal Beam Size
Transition Radiation Monitors
If it were only that simple…
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Diagnostic Challenges - Linac
• Few measurements of bunch length (sz). Accuracy?
• Emittance (ex,y) and beam size (sx,y) measurements slow
• Lack of efficient and robust beta matching tools
• No dispersion characterization tools until end of 2012 run
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sz
ex,y,sx,y
sz
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ex,y,sx,y
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Diagnostic Challenges – Chicane & IP
• Densely installed magnets and experiment stations
- little room for BPMs, Wires, and Profile Monitors
• Few robust and convenient beam diagnostics after Linac
• Vertical ‘W’ Chicane dispersion not yet understood
• Beam Based Alignment very difficult (sextupole movers)
• Optical Transition Radiation damage at peak compression
• Beam waist location often unknown
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sz
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ex,y,sx,y
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SLAC Operations Finding What Works
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SLAC Operators start building software early
Proficiency in Matlab and EPICS is encouraged
Collaborative environment encourages revisions
Google Model: Build often; Failure is ok!
Operators have standardized a display format
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High contrast allows readability from across the room
Summary displays for subsystems by geography
Graphic overlays draw eye toward meaningful data
Information density balanced against interactivity
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SLAC Main Control Room
Can we do better?
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Yes!
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Including Klystron Displays
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Console Tuning and Diagnostics
FACET uses a hybrid control system: OpenVMS and EPICS
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Console Tuning and Diagnostics
Example: Investigating a Beam Containment System (BCS) Alarm
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Console Tuning and Diagnostics
Example: Investigating a Beam Containment System (BCS) Alarm
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Console Tuning and Diagnostics
Console driven high level tuning and diagnostic information
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Console Tuning and Diagnostics
Example: Measuring transverse beam size
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Console Tuning and Diagnostics
Example: Measuring transverse beam size
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New Tools For Better Performance
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What’s Next For FACET?
X-band Transverse Deflection Cavity
– Better bunch length diagnostics
– Commissioning started end of 2012 run
– Testing will continue during 2013 run
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What’s Next For FACET?
FACET-II ?
• FACET-II would be an R&D accelerator using the first 1/3 of the Linac
• Early FACET-II would be about January 2018 including construction
• Upstream of LCLS-II, which poses diagnostic constraints
- Final focus energy feedbacks will need different BPMs
- Space and budget constraints restrict profile monitors and wire scans
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Questions?
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