ILC Accelerator: Luminosity Production

1
ILC Accelerator Luminosity Production

• Peter Tenenbaum
• HEP Program Review
• June 15, 2005

2
Introduction SLC and ILC

• SLC luminosity in 1998 2 x 1030
• ILC luminosity targets
• Instantaneous 2 x 1034
• Integrated 500 fb-1 in 4 years
• Implications
• High beam power (10 MW)
• Small beam sizes everywhere
• Deliver luminosity 75 of the time
• Do not allow beam to damage accelerator

3
Luminosity Production

• Luminosity goals ? ILC operation
• Algorithms, instruments, correction devices for
  emittance tuning and feedback
• Design and operations approach which minimize
  unwanted downtime
• System which prevents beam damage but permits
  luminosity operation
• Approach put these operational issues into the
  design on equal footing with cost and CM Energy
• Design requires quantitative and realistic
  studies which show that emittance preservation,
  stabilization, availability, machine protection
  goals will be achieved
• Tolerances and specifications of components will
  be driven by these operational requirements
• What have we done so far and what are we doing
  now?

4
Tuning and Stabilization Studies Tools

• Developed simulation tools to permit modeling of
  beam transport from Damping Ring exit to IP
• Beam optics, acceleration, wakefields, beam-beam
  interaction
• Misalignments, errors, beam instrumentation (with
  realistic limitations), ground motion, feedbacks
• In regular use to model tuning and operation of
  ILC and estimate luminosity performance
• Understand how varying parameters impacts
  luminosity
• Compare tuning and feedback algorithms
• Determine required performance from beam
  instrumentation
• Model interactions between subsystems and
  regions, escape tyranny of the Gaussian
• SLAC in collaboration with CERN, Cornell, DESY,
  LBL, Queen Mary University London (QMUL)

5
ILC Bunch Compressor Design

• TESLA TDR called for compression from 6 mm to 300
  µm in 1 stage
• Marginal performance large energy spread drives
  BC and linac emittance growth
• No margin for longer bunch in damping ring
• No path to shorter final bunch lengths
• Solution multi-stage BC with acceleration
  between the stages
• Studied a first set of candidate designs
• _at_ 300 µm final length, emittance growth reduced
  by 50 compared to TDR design
• 150 µm final length achievable
• Developing optimized 2-stage design using results
  from first study
• SLAC in collaboration with LBL
• Cornell coming on board this month

6
Main Linac Emittance Tuning

• CW in 2001 Emittance preservation trivial in
  low-frequency, SC main linac
• Result not carefully studied
• CW in 2005 Main linac emittance goals hard to
  achieve
• Large energy spread from BC
• Large apertures ? poor BPM resolution
• Component alignment in cryomodules poor
• Major effort developing and evaluating emittance
  tuning procedures
• Several candidates which have desired
  performance
• Different approaches have different limitations
  and make different demands on main linac hardware
• Pushing the algorithms for better performance
• Studying the limits of each algorithm
• Considering implications on linac design
  (Stronger or weaker lattice desired? BPM
  resolution? Laser-straight linac required?
  Tolerance to stray fields? Benefits from RF
  cavity HOM BPMs?)
• Initiating experimental study of SC quadrupole
  center stability
• SLAC in collaboration with Cornell, FNAL, KEK
• CERN and DESY involvement in past, maybe again in
  future

7
BDS Tuning and Feedback

• Tuning and alignment issues more complicated than
  in BC or linac
• Feedback orbit through collimators and
  sextupoles, colliding nanobeams
• Lots of experience at SLAC (SLC FF and FFTB)
• Performed simulation studies of extremely
  sophisticated collision feedback
• Optimizes IP offset/angle vs lumi within 1 train
• Beginning studies on static alignment and tuning
  of BDS
• Work on more complete feedback
• Several components (steering, optics, energy,
  collision)
• Several timescales (microseconds to minutes)
• Extends back into BC and linac
• SLAC in collaboration with QMUL

8
Availability and Downtime Modeling

• More to it than just MTBF and MTTR
• Written a time-domain simulation
• MTBF and MTTR
• Impact of failure (down for repairs, colliding at
  reduced luminosity, need to spend time tuning
  around, etc)
• Impact of accelerator segmentation
• Availability of people to perform repairs
• Lumi recovery/tuning time after repairs
• Recovery sequence
• Impact of machine development (MD) programs

9
Availability and Downtime (2)

• Applied program to study big ticket issues and
  get quantitative answers
• Impact of putting repairable items like
  klystrons in accelerator tunnel
• DR and linac in same tunnel vs separate tunnels
• Conventional vs undulator vs undulator weak
  conventional e source
• What sorts of MTBF and MTTR values needed for
  magnet power supplies etc?
• How much improvement in uptime for given level of
  redundancy in RF system? How much penalty for
  lack of redundancy where impractical?
• SLAC in collaboration with DESY

10
Machine Protection

• Studied extensively for NLC design
• Just getting started on ILC studies
• Already have good understanding of the main
  issues from NLC work
• Current work classifying scenarios which lead
  to single-pulse or single-train damage
• Starting point to determine mitigation strategies
• Results will influence ILC design
• Special instrumentation or algorithms to trap
  faults?
• Sacrificial collimators?
• Balance between beam signals, other signals, and
  passive protection
• SLAC in collaboration with DESY

11
SLAC Role in ILC Luminosity Production Study

• SLAC has a lot of experience in this area
• SLC and FFTB
• Intense area of study for NLC
• Led to current approach
• operations issues are part of the design on equal
  footing with cost and energy reach
• Strong early participants in ILC design
• SLAC group is leading collaborations with
  worldwide membership
• Still growing
• Several regular phone / video meetings on various
  topics