bruno muratori astec daresbury laboratory · bruno muratori astec daresbury laboratory (m. bowler,...
TRANSCRIPT
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Optics considerations for ERL test facilities Bruno Muratori
ASTeC Daresbury Laboratory
(M. Bowler, C. Gerth, F. Hannon, H. Owen, B. Shepherd, S. Smith, N. Thompson, E. Wooldridge, N. Wyles)
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Overview
Optics Layout strategy for ERLP MAD8
Space Charge for the ERLP Analytical ASTRA GPT
Start to End (S2E) models for the ERLP MAD8 ELEGANT GENESIS
Beam Breakup for the ERLP BI
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ERLP Building Layout
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Energy Recovery Linac Prototype
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Parameters for ERLP
4 ps long bunches, 80 pC
8.35 MeV Injection line (TL2) between 10 m and 15 m
35 MeV Beam Transfer System (BTS)
Initial emittance (norm) between 1 mm mrad and 2 mm mrad
Transverse beam size ~ 1-16 mm
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Beta Functions for ERLP
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Dispersion for the ERLP
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Injection & Extraction Chicanes (from JLab with thanks)
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Alignment: Arc Dipole Magnet with Chamber
EBPMs
Survey Target Holders
30 deg. extraction port
Arc Dipole Magnet
0 deg. extraction port
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Compression Chicane (from JLab with thanks)
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JLab Wiggler
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JLab Wiggler – Testing
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JLab Wiggler Model – Beta Functions
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ASTRA & Drifts - Analytical Approach
Horizontal focusing given by (equivalent for vertical)
Sigma matrix transformation
New emittance
Gaussian bunch (in s)
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Results & Comparisons for ASTRA & Drifts – 1 mm mrad
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ASTRA & Quadrupoles for TL2 – Long model
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ASTRA & Quadrupoles for TL2 – Short model
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GPT & Quadrupoles for TL2 – Short model
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ASTRA & Quadrupoles for TL2 – Short model
ASTRA distribution from gun and booster (CG & FH)
Emittance outside transverse plane
Gaussian good approximation for emittance growth estimate
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GPT
All results so far in good agreement
Different algorithms also agree
Emittance increase appears to be comparable to the analytical estimate in all cases considered
Dispersion may be left out for a rough estimate
Next: Include bends …
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GPT & TL2 with dipoles (short model) – first results
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GPT & Quadrupoles for TL2 – Short model
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Problem: Fringe Fields, Solution: Enge Function
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Transfer Line 2 / Linac
Lattice matching with MAD8- keep Twiss parameters at reasonable values (e.g. β < 50m)- Dispersion free after injection/extraction bends and arcs- 1st arc: isochronous- 2nd arc: R56 = -R56 bunch compressor- Only exact matching point in transverse and longitudinal phase space is at the entrance of the FEL
Tracking with elegant (TL2: E = 8.35MeV, l = 15m, 4 dipoles, 12 quads)Space charge effects ignored
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Start to End Model
Booster to FEL8.35/35MeV
Elegant
FEL to Dump8.35/35MeV
Elegant
FEL Interaction
GENESIS250k particles
Gun to Booster0 to 8.35MeV
ASTRA250k particles 250k particles106 particles
Lattice MatchingMAD8
Lattice MatchingMAD8
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1
23
4
S2E Simulation
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Sextupole Linearisation
• Sextupoles in the outward arc help to achieve the shortest possible bunch length
• Can actually make bunch length too short for lasing! (in theory)
• Adjustable in real machine to optimise lasing properties
• In practice we are likely to see disruptive effects not apparent in the model
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Beam Breakup and the ERLP
Initial calculations & running the code BI (E. Wooldridge)
Assume TESLA HOM’s
Threshold current 5.12 mA
Beam Breakup not a problem for ERLP at this low current
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Conclusions
Optics with no real problems so far Good agreement between ASTRA and GPT and analytical
result for drifts (provided flow is laminar) All to be redone with dipoles correctly modelled Can analytical estimate be used as an upper bound in all
cases ? or at least a reasonable 'rough guess' ? Try to take into account space charge by rematching at
several stages in injector line. However, this cannot take into account transverse & longitudinal coupling
BBU not a problem Start to end simulations only real answer to see if bunch is
acceptable for lasing at FEL (to be redone with dipoles)
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Daresbury Laboratory - Tower Building
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Internal shielding complete
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External shielding in construction
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Inside Control Room
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Assembly Building
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Class 100 (ISO 5) Clean Room
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Magnet Test Room
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Control Room
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TRACE-3D
Include z component for E field Update continuously (no
averaging) Would be nice to take into
account longitudinal dispersion 1) Match transfer matrix cpt.
R16 (dispersion) to zero 2) Match R26 (angular
dispersion) to zero 3) Match R15 (bunch spatial
width) to zero 4) Match R25 (bunch angular spread) to zero Usually only first two done (e.g. in MAD8)