Update on Q2 Main linac starting gradient, upgrade gradient, and upgrade path

1
Update on Q2 Main linac starting gradient,
upgrade gradient, and upgrade path

• Results of WG5 discussions after feedback from
  plenary on Tuesday
• New Option 2 (16 MV/m gt 28 MV/m)
• Enhanced upgrade scenario explorations for
  options 1 2

2
Three Upgrade Options (with New Names)

• 1 (same as last time)Highest acceptable
  riskbased on 10 margin
• Build tunnel long enough (41km) for one TeV, but
  install only 500 GeV worth of cryomodules in
  first 22 km of tunnel for 500 GeV phase.
• 35 MV/m installed gradient, 31.5 MV/m operating
  gradient for 500 GeV (gradient choice rationale
  discussed earlier).
• Fill second part of tunnel (19 km) with 36 MV/m
  cavities (gradient choice discussed earlier),
  install more RF/refrigeration
• 2 NEW Lower riskbased on 20 margin
• 500 GeV phase Build tunnel long enough for one
  TeV (41 km). Populate 24.4 km of tunnel with
  cavities (35 MV/m installed gradient ) Operate
  cavities at 20 margin (i.e. 28 MV/m). Increase
  gradient to 31.5 MV/m over Phase I lifetime,
  energy climbs to 560 GeV.
• Upgrade Add 36 MV/m cavities in remaining 16.6
  km, and add RF and refrigeration for upgrade.
• 3 Half-Tunnel (same as last time)
• Build first half of tunnel for 500 GeV (22km)
  and fill it with full gradient cavities (35 MV/m
  installed gradient, 31.5 MV/m operating gradient,
  discussed later).
• Build second half of tunnel (19km) and add 36
  MV/m cavities and RF/refrigeration for upgrade.

3
Pros/cons of upgrade paths

• Initial cost
• best 3 (half-tunnel) worst Option 2
  (20margin)
• Cryomodules RF Refrigeration 2Tunnel
  guiding model costs
• Option 1 1.16, Option 2 (1.6) 1.22, Option 3
  1.0
• Option 2 is less risky, most flexible for physics
  through higher initial energy reach
• Upgrade cost
• best Option 2 (20 margin) worst Option 3
  (half-tunnel).
• Option 1 0.7, Option 2 (0.4) 0.63, Option 3
  0.9
• Total cost (initial upgrade)
• worst 3 (20 margin)
• . Option 1 1.85, Option 2 (1.97) 1.85,
  Option 3 1.9

4
WG5 Preferred Choice still is
Option 1 (10 margin)

• But Option 1 and Option 2 are getting closer !
• Cost Model estimates Option 2 (20margin) 1.05 x
  Option 1 (10 margin)
• ( Linac RF Cryo 2tunnels)
• Cost Model estimates Option 1 1.16 x Option 3
• Option 3 (Half-tunnel) Upgrade viability may be
  questionable, physics impact of digging new
  tunnel in vicinity of machine (this is a higher
  level discussion topic than WG5)

5
A More Optimistic Upgrade ScenarioBased on
Weeding out Scheme (Still under discussion)

• 1 ..Highest acceptable risk..based on 10
  margin
• Build tunnel (41km 38.5 km) for one TeV, but
  install only 500 GeV worth of cryomodules in
  first 22 km of tunnel.
• 35 MV/m installed gradient, 31.5 MV/m operating
  gradient for 500 GeV (gradient choice rationale
  discussed earlier).
• Upgrade Fill second part of tunnel (19 km 16.5
  km) with 36 MV/m cavities (gradient choice
  discussed later), install more RF/refrigeration.
• Replace the lowest performing cryomodules during
  upgrade with new cryomodules so that all Phase I
  modules perform at 35 MV/m..anticipate replacing
  10 of existing cryomodules.
• Note total tunnel length shortened by 2.5 km
• 2 Lower riskbased on 20 margin
• Build tunnel long enough for one TeV (38.5 km).
  Populate 24.4 km tunnel with cavities in phase1
  (35 MV/m installed gradient ) Operate cavities at
  20 margin (at 28 MV/m) in 500 GeV Phase 1.
  Increase gradient of installed cavities to 31.5
  MV/m over Phase I, energy climbs to 563 GeV.
• Upgrade Add 36 MV/m cavities in 14.1 km, and
  add RF and refrigeration for upgrade.
• Replace the lowest performing cryomodules during
  upgrade with new cryomodules so that all Phase I
  modules perform at 35 MV/m..anticipate replacing
  10 of existing cryomodules.
• Note total tunnel length shortened by 2.5 km

6
Estimated Cost Impact

• Upgrade cost
• Option 1 0.7 0.66, Option 2 0.63 0.57,
  Option 3 0.9 0.82
• Total cost (initial upgrade)
• Option 1 1.85 1.82, Option 2 1.85 1.78,
  Option 3 1.9 1.82
• (Includes cost of replacement modules)

7
Attractive Features of Weeding Concept

• Low gradient cryomodules identified during Phase
  I running
• Keep cavity and cryomodule production factory
  running at low rate to produce 10 replacement
  modules over lifetime of 500 GeV Phase
• About 100 - 120 modules (1200 - 1500 cavities)
• Avoids factory production halt and start up
  problems for upgrade production

8
Requests to Other Groups

• What is the effect of 10, 20 margin on
  reliability?
• What is the effect of 10 or 20 margin on cost?
  
• Guiding model suggests 10 extra margin has
  initial project cost penalty of 5 (on linac cost
  only).
• All costs need more detail analysis
• How attractive is the weeding out scheme in
  feasibility, cost, and upgradability ?

9
END
10
Pros/cons of upgrade paths, cont

• Initial schedule
• Best 3 half-tunnel, worst 2 lower risk
• Option 3 takes longer to start up due to largest
  module production and installation
• Upgrade schedule
• best 2 lower risk worst 3 half-tunnel.
• Option 2 The extra RF to upgrade half-gradient
  can be installed while ILC is running if there
  are 2 tunnels.
• Option 2 does not require interruption for module
  production and installation,
• Option 2 does not take advantage of gradient
  advances to come
• Upgrade viability
• worst 3 half-tunnel. Has civil
  construction. Need to check if tunnel boring
  machines vibrate the ground too much to allow
  tunneling during running. If so, upgrade is not
  viable.
• Need to move certain installed systems (e.g
  undulators)

11
Cavity Gradient/ Shape - 500GeV

• Shape Options (to be discussed by Saito)
• TESLA
• Low-Loss
• Re-entrant
• Superstructure
• Pros/Cons (to be discussed by Saito)

12
Cavity gradient/ shape - 500GeVRepeat of Friday
Summary - Proch

• Preferred Choice TESLA shape
• Performance and cost best understood
• Gradient Choice 31.5MV/m
• Based upon
• Critical field 41MV/m (TESLA shape)
• Practical limit in multi-cells 90 critical
  field 37MV/m (5 sigma spread)
• Lower end of present fabrication scatter ( 5)
• TESLA shape 35 MV/m
• Vert dewar acceptance criteria 35MV/m or more
  (some cavities must be reprocessed to pass this)
• Operating gradient 90 x installed gradient
  31.5MV/m
• Allows for needed flexibility of operation and
  commissioning
• Gives operating overhead for linac and allows
  individual module ultimate performance.
• Choice of operating gradient does not include
  fault margin
• e.g 2 - 5 additional cryomodules to be
  determined by availability considerations

13
Further Comments onstarting cavity gradient -
500GeV

• RD to address remaining risk
• Significant RD necessary to achieve the
  specified module gradient and spread.
• System tests and long-term tests of 35 MV/m
  modules needed as spelled out by R1 and R2 of TRC
  
• RD needed in BCD cavity processing BCD
  material (though other RD efforts may prove
  beneficial e.g. single crystal)
• This RD effort needs to be organized
  internationally, Discussions underway
• Must also address how to industrialize the
  processing for reliable and reproducible
  performance

14
Upgrade gradient choice(depends on shape)
discussed on Friday Summary - Proch

• Theoretical RF magnetic limit
• Tesla shape 41 MV/m
• LL,RE shape 47 MV/m
• Practical limit in multi-cell cavities -10
• TESLA shape. 37 MV/m
• LL, RE shape expected 42.3 MV/m
• Lower end of present fabrication scatter (- 5)
• TESLA shape 35 MV/m
• LL, RE shape 40 MV/m
• Operations margin -10
• TESLA shape 31.5 MV/m
• LL, RE shape 36 MV/m

15
Assume cavities can reach avg of 90 of limit
with 5rms in Vert dewar
Most Tesla cavities should be able to reach
35MV/m accept Most LL/RE cavities should be able
to reach 40 MV/m accept But note there is a low
energy tail that fails
36.9/-1.85MV/m
42.3/-2.12MV/m
41
47
31.5
37
35
s5
10
Eacc MV/m