ILC Beam Switchyard: Issues and Plans

1
ILC Beam SwitchyardIssues and Plans

• Based on ongoing discussions with Deepa
  Angal-Kalinin, Grahame Blair, Brett Parker, Tom
  Mattison, Andrei Seryi, PT, and others

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

3
Issues (1)

• skew correction system
• Paul Emmas NLC design (writeup/refs)
• coupling correction philosophy
• projected vertical emittance optimization
  (writeup/refs)
• emittance diagnostic section
• sy 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)

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
• lt 1 ISR emittance growth _at_ 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
• Bretts 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 Bretts 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

5
BSY Diagnostic Chicane Issues Questions (M.
Woodley, August 25, 2005)
-
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) 0.06 _at_
250 GeV, 0.03 _at_ 500 GeV (PT) ... undulator?
3) minimum dispersion determines chromatic spot
size ... etax 20 mm gives 12 um _at_ 250 GeV, 6 um
_at_ 500 GeV 4) for energy spread resolution, need
geometric spot size (at most) equal to chromatic
spot size ... betax 5 m gives 10.1 um _at_
250 Gev, 7.1 um _at_ 500 GeV 5) sigmax 15.7 um _at_
500 GeV, 9.3 um _at_ 500 GeV - questions/comments
1) ISR emittance growth limits 1 _at_ 500 GeV?
0.1 ? 1 _at_ 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, 25 sigmax _at_ 250 GeV,
43 sigmax _at_ 500 GeV 5) threshold for incoming
betatron oscillations?
6
from Brett
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)

8
Issues (3)

• choice of combined-function FODO lattice
• compare with TESLA DBA, TME (writeup/refs)
• need performance and tuning simulations (a la LET)

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

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