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 => 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 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.

3

• 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

4

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)

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 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

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

• Initial scheduleBest = 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)

Pros/cons of upgrade paths, con’t

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

• Preferred Choice: TESLA shape– Performance and cost best understood

• Gradient Choice 31.5MV/mBased 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

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

13

• 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

Further Comments onstarting cavity gradient - 500GeV

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

25 30 35 40 45 50

36.9+/-1.85MV/m

42.3+/-2.12MV/m

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 acceptMost LL/RE cavities should be able to reach 40 MV/m acceptBut note there is a low energy tail that fails

3735