Transcript Update on Q2 Main linac starting gradient, upgrade gradient, and upgrade path • Results of WG5 discussions after feedback from plenary on Tuesday • New.

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 => 28 MV/m)
• Enhanced upgrade scenario
explorations for options 1 & 2
1
Three Upgrade Options
(with New Names)
1 : (same as last time)”Highest acceptable risk”based 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 risk”…based 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.
2
Pros/cons of upgrade paths
• Initial cost:
best = 3: (half-tunnel);
worst = Option 2: (20%margin)
– 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 (halftunnel).
– 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
3
WG5 Preferred Choice still is :
Option 1 (10% margin)
But Option 1 and Option 2 are getting closer !
– Cost Model estimates Option 2 (20%margin)
~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)
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A More Optimistic Upgrade Scenario
Based 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 risk”…based 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
5
MV/m..anticipate replacing 10% of existing cryomodules.
Note total tunnel length shortened by 2.5 km
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)
6
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
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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 ?
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END
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Pros/cons of upgrade paths, con’t
• 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)
10
Cavity Gradient/ Shape - 500GeV
• Shape Options (to be discussed by Saito)
– TESLA
– Low-Loss
– Re-entrant
– Superstructure
• Pros/Cons (to be discussed by Saito)
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Cavity gradient/ shape - 500GeV
Repeat 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
12
Further Comments on
starting cavity gradient - 500GeV
• R&D to address remaining risk
– Significant R&D 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
– R&D needed in BCD cavity processing & BCD material
(though other R&D efforts may prove beneficial e.g.
single crystal)
– This R&D effort needs to be organized internationally,
Discussions underway
– Must also address how to industrialize the processing
for reliable and reproducible performance
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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
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Assume cavities can reach avg of 90% of limit with 5%rms 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
31.5
35
37
41
47
10% s=5%
25
30
35
40
45
50
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