1. ILC Beam Switchyard: Issues and Plans
Based on ongoing discussions with Deepa Angal-Kalinin, Grahame Blair, Brett Parker, Tom Mattison, Andrei Seryi, PT, and others
September 13, 2005
ILC BDS Meeting

2. What is the “BSY”? Skew correction and emittance diagnostic section
BCD: “Diagnostics Section”, G. Blair, M. Woodley
Fast extraction system and tuneup dump line
BCD: “Tuneup Extraction Line, MPS, Energy Diagnostics”, T. Mattison, M. Woodley, D. Angal-Kalinin
Big Bend system (for 2 mrad IR)
BCD: “Beam Switchyard”, M. Woodley
IR transport lines
September 13, 2005
ILC BDS Meeting

3. Issues (1) skew correction system coupling correction philosophy
Paul Emma’s NLC design (writeup/refs)
coupling correction philosophy
projected vertical emittance optimization (writeup/refs)
emittance diagnostic section
σy at laserwires too small (modify optics)
detection of laserwire signals in chicane … synchrotron radiation?
need integrated skew correction and emittance tuning performance simulations (a la LET)
September 13, 2005
ILC BDS Meeting

4. Issues (2a): fast extraction
detection of “runaway” beam very near to fast extraction system is required
number of errant bunches allowed to reach collimation system spoilers: off-energy and betatron oscillations (writeup/refs)
energy spread measurement not required here
< 1% ISR emittance 1 TeV cm (reasonable?)
ignore critical energy of ISR photons (?)
another iteration of the design is needed
timing: detection of betatron oscillations in diagnostic section and energy offsets in chicane, propagation, processing
kicker strength
Brett’s initial design and TESLA kickers not very different (in-vacuum electrodes vs yoked magnets)
assume (somewhat optimistic) 10 μrad/m (with septa?)
kicker rise time
100 nsec in TDR; 150 nsec in Brett’s initial design
for 150 nsec bunch spacing, wait until after 2nd bunch passes before triggering kickers
faster kickers means weaker kickers … optimum?
kicker flattop duration
abort signal propagation back to DR
80 μsec in TDR; 150 μsec for 0.9c propagation to upstream end of 1 TeV cm linac
September 13, 2005
ILC BDS Meeting

5. September 13, 2005 ILC BDS Meeting
BSY Diagnostic Chicane Issues & Questions (M. Woodley, August 25, 2005)
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- functional requirements
1) detection of off-energy bunches and abort triggering
2) location of detectors for BSY diagnostic section laserwires
3) measurement of energy and energy spread
- issues
1) distance from energy BPM to FEXL kickers (how many bunches get through?)
2) ISR emittance growth
3) total chicane length
4) magnet technology (H-bends? C-bends?)
5) energy offset resolution
6) resolution of dispersion/betatron motion discrimination
7) minimum beam size for laserwire ~ 3 um
8) need vacuum window and line-of-sight to laserwire photon detectors (one near center of chicane for upstream
emittance laserwires, one after central chicane bends for energy spread laserwire)
9) minimum clearance for laserwire detectors ~ 1 inch
- beam parameters
1) normalized emittance emitxn = 10e-6 m
2) energy spread (dP/P) = GeV, GeV (PT) ... undulator?
3) minimum dispersion determines chromatic spot size ... etax = 20 mm gives GeV, GeV
4) for energy spread resolution, need geometric spot size (at most) equal to chromatic spot size ... betax = 5 m
gives Gev, GeV
5) sigmax = GeV, GeV
- questions/comments
1) ISR emittance growth limits: 500 GeV? 0.1 % ? 250 GeV?
2) kickers in 2nd leg of chicane? (issue 1) ... if so, must have QD (or no quad at all) at exit of chicane which
makes optics tricky given 5 m betax at center of chicane and chicane length needed to preserve emittance
3) quadrupoles in chicane?
4) "bad beam" threshold: +- 2% dP/P, GeV, GeV
5) threshold for incoming betatron oscillations?
September 13, 2005
ILC BDS Meeting

6. from Brett …
September 13, 2005
ILC BDS Meeting

7. Issues (2b): dump line energy acceptance of dump line (±20%)
beam size on dump window needs to be increased (modify optics)
rastering system (add to design)
energy/energy spread diagnostics (add)
designs for special magnets (“coil pocket” quads, septum quads, Panofsky quads)
another iteration of the design is needed
need performance and tuning simulations (a la LET)
September 13, 2005
ILC BDS Meeting

8. Issues (3) choice of combined-function FODO lattice
compare with TESLA DBA, TME (writeup/refs)
need performance and tuning simulations (a la LET)
September 13, 2005
ILC BDS Meeting

9. Other Issues deflection cavities for diagnostics?
deflection cavities for fast extraction?
acceptance of post-linac systems
linac aperture is 7 cm
BSY aperture is 1.2 cm
September 13, 2005
ILC BDS Meeting

10. My Plans (such as they are … )
try to nail down the functional requirements
allowable emittance growth
required bandwidth
response time (how many bunches get through?)
instrumentation resolution
magnet specifications
redesign emittance diagnostic section optics
larger vertical beam size
redesign diagnostic chicane
smaller dispersion, larger betas, shorter system
redesign fast extraction system
10 μrad/m kickers downstream of chicane
maybe a (more conservative) TDR-like system, too?
redesign dump line
bigger spot on dump window
add rastering system
do system performance simulations
September 13, 2005
ILC BDS Meeting