Minutes of 84th FFIR/BDSIM and 7th ILC-Asia WG4 meeting on 11/24/2004

The 7th meeting was held on Nov.24 10:00 am at rm.425 bldg no.3.

Discussion on slides prepared for 1st ILC WS.

(1) gamma-gamma option (Takahashi)

  (a) GoalFDemonstrating gamma beam production
     Stable collision between electron beam and laser light.
     Continuous production of Compton photon.
     --> high luminosity photon beam
     (i) We need
        * mode-lock laser
        * cavity
     (ii) R&D items
        * stable high-power pulsed laser (cavity, laser)
        * timing control (electron bunch & laser, < 1 psec)
        * pointing stability

  (b) Monitoring produced photon beam
        * Intensity, energy, polarization
        * Can we monitor electron after Compton scattering?
        * How to measure polarization of high-energy photon directly
        * Monitor system fast enough for feed back

  (c) Optical system for cavity is the most challenging
        * Demonstration of build up
        * Controlling circumference, temparature and vibration of 100-m ring cavity.
        * Adaptive optics
        * Radiation damage

  (d) Requirement
        * electron beam (bunch separation >>1.4nsec, 337ns)
        * Stable mode-lock laser

  (e) ATF laser wire group
        * Cavity (L=40cm, 80cm)
        * pulse build-up: order of 10^3 for L=80cm, ~100 for L=40cm)
        * No focus at interaction point
        * Phase control error in feedback for circumference limits the build-up
        * No plan for a larger cavity

  (f) World-Wide activity
        * Jeff Gronberg (LLNL) may try to get R&D budget for Pol.positoron-cavity.
        * Not yet consider electron beam.
        * We don't have a design of laser pol.positoron source yet.

  (g) Discussion
        * If the price of laser system drops dramatically, we may not need a cavity system.
        * R&D for cost reduction of laser system will be done by industry or laser fusion group.
        * build-up technique is developed for LIGO, TAMA300 (large system, CW only) and ATF(small system).
        * R&D process
          (i) low power laser + small cavity
          (ii) high power laser + large cavity
          (iii) electron beam and laser collision
          We can start (i), if we have more manpower.
        * We need a core teem at KEK
        * We have to make a core team at KEK and/or Univ.
          before we discuss laser system with experts in other fields.

  (h) To do (Takahashi):
        * Start discussion about R$D program with Jeff Gronberg(US), Valery Telnov, Klaus Moenig, Albert de Roeck (Europe).
        * Hold meetings at KEK in Dec. and at SLAC in Jan. to discuss g-g option.
        * Try to start discussion with gravitational-wave people.

(2) "ATF2" proposal
     To be discussed at ATF2 mini-workshop (2005.1 SLAC)
Table of contents (very tentative)
1. Introduction

1.1 Goal
      Ensure collisions between nanometer beams to achieve high 
luminosity enough for ILC physics.

1.2 Background
      Relation to the SLAC-FFTB; achievements and remaining issues

1.3 Study item
    (a) FF compact optics  (focus)
          - Primary Goal: Realize 35nm-spot-size beam. Proof of principle: local correction
          - Beam (E=1.54GeV, emittance 1 x 10^-11) is different from that of ILC. However,
            magnet tolerance is compatible. ATF2 should have an impact on ILC.
          - Beam size monitor (Shintake monitor) at IP is indispensable.
          - For 35nm beam, the beam extracted from ATF should be stabilized at same order of beam size.
          - Secondary Gaol: Maintenance of 35nm-spot-size beam.
               Requirement: 3-5? HzAsingle bunch  or  2-3 bunches with sb=300-100nsec is enough
               DiscussionFWe need more intense beam because of slow response of Shintake monitor?
          - emittance  - x-y coupling?      3 times of DR emittance at present
               The smaller coupling, the better. But current coupling is small enough for R&D.

    Discussion: We have to control beam size as well as orbit at nm-level at ILC.
                At ATF2, beam size is 35nm and beam orbit shift of nm is tolerable.
                Still, is ATF2 a good test facility or not.

    (b) nanometer stabilization at IP
          - NanoBPM    goal 2nm,   (replace Shintake monitor with nanoBPM)
          - Requirement on ATF extracted beam jitter is <1/20 sigma
                Current Status:
                -DR    10% (best) beam jitter at the laser wire position (dispersion free)
                -EXT   must use the double kicker system (Imai's Dr thesis)
                       The extraction kicker will come next summer from SLAC.
                       feed-forward system consisting of DR and EXT BPM's and kicker.
                       active mover system for the final doublet

     (c) with the ILC-style beam  ( 20 bunches with sb=300nsec )
          - require completetion of fast extraction kicker
          - intra-pulse feedback  (active feedback)

2. Schedule
     before TDR: verification of the optics
     after TDR: adjustment of optics configuration with the ATF2 experience (tuning)
                education of young scientists

    optional  -  laser facility

* To be discussed
        - 1.3(a)&(b) is relevant to ILC design ?
        - cost performance  ( tuning training,  education of young scientists )
        - risk reduction?
        - There are still R&Ds after the TDR.

* Official schedule CDR in 2005 and TDR in 2007.
* This is a boundary condition ? We can ignore it, because it is impossible.
* If the official schedule is a boundary condition, "ATF2" is not worth construction ?
* In the latter case, ATF2 is very important to start good physics with high lum. beam soon after ILC construction.
* Even if TDR is finished in 2007, the design of ILC will not be fixed completely. Especially, BDS will be modified just before its construction.

The next meeting will be on 1 December, 2004,10:00 - at 3 gokan, 425 .