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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

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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.

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• 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 (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

Pros/cons of upgrade paths

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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)

WG5 Preferred Choice still is :

Option 1 (10% margin)

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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 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 MV/m..anticipate replacing 10% of existing cryomodules.

• Note total tunnel length shortened by 2.5 km

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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)

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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 ?