Driver Accelerator Design D. Douglas, G. Krafft, R. Li, L.
Merminga, B. Yunn
Slide 2
31 May, 20002 System Parameters
Slide 3
31 May, 20003 Design Issues/Requirements Source/Injector
Performance Delivery of appropriate beam to FEL Energy Recovery
Peculiarities of SRF environment Geometric, schedule
constraints
Slide 4
31 May, 20004 Source/Injector Performance Must run source &
injector at original IR Demo design parameters (135 pC) with
doubled repetition rate (37.5 75 MHz) Traditional concerns:
transverse/longitudinal emittances at high charge cathode lifetime
injector characterization injector operability
Slide 5
31 May, 20005 Source/Injector Performance Status: have had
successful initial run at 135 pC emittance, momentum spread scoped
out emittance marginal (20-30 mm-mrad), momentum spread okay
(~0.1%?), bunch length unknown cathode lifetimes > 0.6 kC;
present wafer at > 2 kC injector increasingly well characterized
still need some calibrations, polarity corrections, modeling
injector operability constantly improving (scripting,
procedures)
Slide 6
31 May, 20006 Delivery of Appropriate Beam to FEL Transport
& transverse/longitudinal matching Beam quality preservation:
space charge other wakefield/collective effects CSR
Slide 7
31 May, 20007 Energy Recovery Transport,
transverse/longitudinal matching and acceptance Space charge BBU
FEL/RF interaction
Slide 8
31 May, 20008 Peculiarities of SRF Environment Cavity focussing
HOM coupler-driven skew coupling RF drive system
characteristics
Slide 9
31 May, 20009 Geometric, Schedule Constraints Machine must fit
in existing vault Machine must be installed around IR Demo
(physically and temporally)
Slide 10
31 May, 200010 Design Concept Direct evolution of IR Demo to
higher energies: energy recovering CW SRF linac
Slide 11
31 May, 200011 Design Concept Evolutionary path: 10 MeV/5 mA
injector 10 MeV/10 mA injector 35-48 MeV linac (1 cryomodule)
80-210 MeV linac (3 cryomodules) FEL insertion following linac
(CSR) FEL insertion in backleg Have existence proof narrower,
longer significant fraction can be installed while IR Demo still
operable
Slide 12
31 May, 200012 Aside: Need for Design Code Driver in an unusual
regime - large acceptance SRF linac with recirculation
acceleration, RF focussing, large momentum offsets - bordering on
non-perturbative Most design codes are perturbative/do not model
acceleration, or are particle pushers with limited beamline
modeling capability (no optimization or analysis) At present, using
DIMAD but cross-referencing with direct numerical integration
Slide 13
31 May, 200013 Runge-Kutta Integrator Integrate test ray
response to ambient magnetic fields Use lab frame coordinates -
nonperturbative
Slide 14
31 May, 200014 Exact/DIMAD comparison
Slide 15
31 May, 200015 Design Features 3 module linac high gradient
7-cell module in center slot (reduce over- focussing induced
mismatch) Quad telescopes match into/out of recirculator Bates
end-loops FODO backleg transport to FEL insertion FEL insertion
quad telescopes matching to/from wiggler two embedded optical
cavities Longitudinal phase space management identical to that in
Demo
Slide 16
31 May, 200016 Longitudinal Matching Requirements: short bunch
(high peak current) at wiggler small momentum spread at dump E E E
E E longitudinal phase space through acceleration cycle
Slide 17
31 May, 200017 Longitudinal Matching - cont. E E longitudinal
phase space during energy recovery
Slide 18
31 May, 200018 Layout
Slide 19
31 May, 200019 Beam Envelopes linac FELarc
Slide 20
31 May, 200020 arc FEL
Slide 21
31 May, 200021 Aberrations - Linac to FEL
Slide 22
31 May, 200022 Aberrations - FEL to Linac
Slide 23
31 May, 200023 Simulation of Energy Recovery Tracking with
large momentum spread longitudinal matching/energy compression
should work, but requires octupoles larger linac final to to energy
ratio (20 to 1) makes energy recovery/compression more difficult 30
mm-mrad emittances dicey skew quad - last module imposes much of
effect; might not be far greater than in demo
Slide 24
31 May, 200024 Reinjection
Slide 25
31 May, 200025 Mid-1st Module
Slide 26
31 May, 200026 Between 1st & 2nd Modules
Slide 27
31 May, 200027 Mid-2nd Module
Slide 28
31 May, 200028 Between 2nd & 3rd Modules
Slide 29
31 May, 200029 Mid-3nd Module
Slide 30
31 May, 200030 End
Slide 31
31 May, 200031 End - octupoles on
Slide 32
31 May, 200032 End - skew quad effect included
Slide 33
31 May, 200033 Space Charge Initial application of PARMELA
modeling to injector provided successful operation at 135 pC per
bunch Ongoing refinement must occur improved RF calibration factors
benchmarks against machine behavior to verify model and determine
parametric sensitivities Certified model will be applied to design
from gun to dump
Slide 34
31 May, 200034 SRF Issues Upgrade module RF drive control new
control module needed to take full advantage of upgrade module
design capabilities existing RF control module adequate (with
appropriate parametric choices for, e.g., cavity coupling) for
energy gains up to 67 MeV 7-cell cavity model HOM effects coupler
driven skew coupling BBU longitudinal HOM power-induced
heating
Slide 35
31 May, 200035 BBU Certification TTBBU benchmark against IR
Demo in progress Analysis will employ measured 5-cell HOM Qs and
frequencies and give BBU threshold as function of 7-cell Qs provide
a specification for damping of 7-cell HOMs
Slide 36
31 May, 200036 Wakefields/Impedance Stewardship Initial
estimates suggest momentum spread induced by IR Demo-like impedance
budget (2 chamber, multiple viewers, BPMs) may be marginally
acceptable Characterization ongoing as vacuum system design evolves
Plan use of shielded components upstream of wigglers, considering 3
chamber throughout system
Slide 37
31 May, 200037 CSR Certification Detailed CSR model in advanced
stage of development being benchmarked against CERN measurements
cross-checks planned with IR Demo design concept will be simulated
to certify performance Rudimentary model suggests Bates endloop
design may be acceptable, but Results depend on details of phase
space distribution, so careful analysis with detailed model is
necessary
Slide 38
31 May, 200038 Rudimentary Simulation
Slide 39
31 May, 200039 FEL/RF Interaction Initial studies on IR Demo
under way Ongoing work will characterize Upgrade system behavior
and performance Need a more fully developed model of the FEL
Slide 40
31 May, 200040 What to do? Develop definitive injector model
Analyze space charge effects Complete conceptual design beam optics
model incorporate best knowledge magnetic fields (fringe, roll-off,
etc) certify skew quad effects Develop engineering design beam
optics model diagnostic, correction systems error
tolerances/component specifications alignment, powering, field
homogeneity requirements
Slide 41
31 May, 200041 What to do? CSR benchmark model using Demo
certify upgrade design BBU benchmark TDBBU using Demo certify
upgrade design FEL/RF interaction benchmark model using Demo
certify upgrade design Continue impedance stewardship
Slide 42
31 May, 200042 What to do? Machine modeling cavity model HOM
driven skew coupling 7-cell cavities non-perturbative model for
large acceptance linac operational modeling RF drive system
controls - continue work on control module analysis, design
Commissioning planning