1. WG1: Overall Design personal highlights report by Nick Walker First ILC@DESY project meeting 2/12/2004 conveners: Kiyoshi Kubo (KEK) Tor Raubenheimer (SLAC) Daniel Schulte (CERN)

2. Scope for WG1 First- and second-stage energy and the accelerating gradient. First- and second-stage energy and the accelerating gradient. Review of machine parameters Review of machine parameters Two-tunnels versus single-tunnel for LINAC Two-tunnels versus single-tunnel for LINAC Damping ring design: Damping ring design: Dog-bone housed in LINAC tunnelDog-bone housed in LINAC tunnel Ring design(s) in separate tunnels.Ring design(s) in separate tunnels. Positron source: Undulator-based vs conventional designs. Positron source: Undulator-based vs conventional designs. Priority of the polarised positrons?Priority of the polarised positrons? Beam crossing angle at the interaction point. Beam crossing angle at the interaction point. Beam dynamics issues. Tolerances. Beam dynamics issues. Tolerances.

3. Main Highlights (IMO) Cost Optimisation: $ vs MV/m Cost Optimisation: $ vs MV/m what should be the baseline gradient?what should be the baseline gradient? Luminosity Parameters Luminosity Parameters what should be the baseline beam parameters?what should be the baseline beam parameters? Commissioning & Reliability Commissioning & Reliability One or Two LINAC tunnels?One or Two LINAC tunnels? Conventional vs Undulator e + sourceConventional vs Undulator e + source Damping ring tunnelDamping ring tunnel

4. Luminosity Parameters Review of TESLA CDR & TDR parameters [NJW] Review of TESLA CDR & TDR parameters [NJW] How and why a factor 6 luminosity was achievedHow and why a factor 6 luminosity was achieved

5. CDR TDR TDR General Parameters # of bunches p.p. 1130 2820 2820 pulse length [  s] 800 800 950 950 bunch spacing  t b [ns] 708 708 337 337 bunch charge N e [10 10 ] 3.63 3.63 2.0 2.0 pulse current [mA] 8.2 8.2 9.5 9.5 av. beam power [MW] 8.3 8.3 11.3 11.3 emittance at IP  x,y [10 -6 m] 14, 0.25 14, 0.25 10, 0.03 10, 0.03  x,y at IP [mm] 25, 0.7 25, 0.7 14, 0.4 14, 0.4 spot size at IP  x,y [nm] 845, 19 845, 19 550, 5 550, 5 bunch length at IP  z [mm] 0.7 0.70.3 beamstrahlung  B [%] 2.5 2.5 3.0 3.0 vert. Disruption D y 18 18 25 25 luminosity [10 34 cm -2 s -1 ] 0.6 0.6 3.4 3.4 CDR vs TDR Parameters (500GeV) Factor  0.8 Emittance factor  0.7, 0.1 Demag. Factor  0.6, 0.6 Beam size factor  0.7, 0.3 Luminosity factor  5.8 Enhancement: factor ~1.2 Luminosity: 5.7

6. Luminosity Parameters Review of TESLA CDR & TDR parameters [NJW] Review of TESLA CDR & TDR parameters [NJW] How and why a factor 6 luminosity was achievedHow and why a factor 6 luminosity was achieved TDR 3.410 34 cm -2 s -1 needs high beam- beam disruption parameter TDR 3.410 34 cm -2 s -1 needs high beam- beam disruption parameter unstable collisionunstable collision peek luminosity very ambitious.peek luminosity very ambitious. Reduction of beam-beam effects and some Luminosity safety margin desirable. Reduction of beam-beam effects and some Luminosity safety margin desirable.

7. Baseline Luminosity Some example parameter sets by Tor Raubenheimer

8. Baseline Luminosity Some example parameter sets by Tor Raubenheimer Lower Bunch Charge L  210 34 cm -2 s -1

9. Baseline Luminosity Some example parameter sets by Tor Raubenheimer Larger  y * L  210 34 cm -2 s -1

10. Baseline Luminosity Some example parameter sets by Tor Raubenheimer Lower average P L  210 34 cm -2 s -1

11. Baseline Luminosity Some example parameter sets by Tor Raubenheimer L  210 34 cm -2 s -1 A good compromise Still achieves physics requirement goals of 500 pb -1 in first 4 years

12. Baseline Luminosity Some example parameter sets by Tor Raubenheimer Push the limits!!! L  510 34 cm -2 s -1

13. RF Cost Optimisations H. Padamsee, C. Adolphsen, K. Kubo presented estimates of optimum gradient, based on scaling from TESLA numbers Important is assumption about Q 0 (g) All speakers concluded: g ~ 35-40 MV/m is cost optimum

14. Simple Scaling Laws Relative Cost Gradient MV/m

15. Energy Upgrade Different Scenarios 500 GeV  1 TeV Different Scenarios 500 GeV  1 TeV Dig tunnel for 1 TeV @ 35 MV/m: fill half for 500 GeV machine (US favoured option) Dig tunnel for 1 TeV @ 35 MV/m: fill with linac at ~18 MV/m for 500 GeV machine (close to TDR solution) 2 nd option more expensive, but would allow ~900 GeV operation at reduced L with no additional hardware installation. Some discrepancies in cost models: scenarios need review.

16. Reliability / Operability Talks by Talks by Tom Himel (SLAC) on tunnel scenariosTom Himel (SLAC) on tunnel scenarios Nan Phinney (SLAC) on commissioning strategies (impact of choice of e+ source)Nan Phinney (SLAC) on commissioning strategies (impact of choice of e+ source) Probably most controversial of all subjects dealt with Probably most controversial of all subjects dealt with much religion still exists heremuch religion still exists here

17. Tunnels Second tunnel is 5% cost increase [US costing, T. Himel] Comparable availability in single tunnel may be achieved by better components (3% more cost [T. Himel]) But risk in achieving better performance No agreement on this point, to be discussed further too much religion

18. e + source (N. Phinney) Conventional positron source is technically challenging, but it can be commissioned earlier decouples positrons and electrons Wiggler based source at fixed energy (150GeV) may ease operation US view: not discussed in WG1 further [US preference is clearly for conventional source] impact of commissioning scenarios too severe in their view.

19. WG1 Conclusions Creation of interim working groups: Group to define parameter ranges in the next two months Group on construction schedule, commissioning and availability; positron source, tunnel configurations Group on LET including failure modes Group on instrumentation

20. My Conclusions An excellent start! An excellent start! Good working atmosphereGood working atmosphere Everybody positively focused on ILCEverybody positively focused on ILC Contentious issues still exist Contentious issues still exist see choice of suggested working groupssee choice of suggested working groups We We reduce the TDR luminosity by ~30%reduce the TDR luminosity by ~30% reduced the working gradient from 35-30 MV/mreduced the working gradient from 35-30 MV/m and nobody blinkedand nobody blinked