AAP Review Oxford, January Introduction to SB2009 Nick Walker Marc Ross Akira Yamamoto

Outline Accelerator Design & Integration (ADI) goals Straw-man Baseline 2009 Working Assumptions Primary Focus of SB2009 (Themes) Other SB2009 Aspects Cost Differential Physics Scope Impact N. Walker - AAP Review (Oxford)

ADI Goals Overall cost –All reasonable cost savings should be adopted Improved cost balancing –Providing margin for future cost increases Improved understanding of system functionality –Critical review of requirements and system performance (more than just cost reduction) More complete and robust design –Many system layout and CFS related design elements are now more mature → better design Re-optimised R&D plans –Feedback from ADI process to TD Phase 2 R&D Plans N. Walker - AAP Review (Oxford) 3

Straw-man Baseline 2009 Working Assumptions (WA) N. Walker - AAP Review (Oxford)

SB2009 Proposal 1.A Main Linac length consistent with an average accelerating gradient of 31.5 MV/m and maximum operational beam energy of 250 GeV –together with a High-Level RF distribution scheme which optimally supports a spread of individual cavity gradients. 2.A single-tunnel solution for the Main Linacs and RTML, with two possible variants for the High-Level RF (HLRF): –Klystron cluster scheme (KCS); –Distributed RF Source scheme (DRFS) N. Walker - AAP Review (Oxford) 5

SB2009 Proposal 3.Undulator-based positron source located at the end of the electron Main Linac (250 GeV), in conjunction with a Quarter-wave transformer as capture device. 4.A lower beam-power parameter set with the number of bunches per pulse reduced by a factor of two (n b = 1312), as compared to the nominal RDR parameter set N. Walker - AAP Review (Oxford) 6

SB2009 Proposal 5.Reduced circumference Damping Rings (~3.2km) at 5 GeV with a 6 mm bunch length 6.Single-stage bunch compressor with a compression ratio of Integration of the positron and electron sources into a common “central region beam tunnel”, together with the BDS, resulting in an overall simplification of civil construction in the central region N. Walker - AAP Review (Oxford) 7

SB2009 Themes N. Walker - AAP Review (Oxford) 8

SB2009 Themes N. Walker - AAP Review (Oxford) 9 Direct Physics Scope Impact

SB2009 Primary Themes N. Walker - AAP Review (Oxford)

CFS: Primary Cost Driver Assumed primary advantage of SB2009 options is reduced CFS scope –Underground tunnel / volume –Reduced cooling requirements –… Focus of 2009 activities was to assess impact on CFS solutions –Removed, added, modified SB2009 reduces underground tunnel length by ~27km N. Walker - AAP Review (Oxford) Reduction in CFS Risk

Single Main Linac Tunnel Primary RDR arguments for a separate service tunnel: –Safety egress –Availability N. Walker - AAP Review (Oxford) 12

High-Level RF Solution Seen as critical component for one-tunnel solution. Two solutions for ILC: –Distributed RF Source (DRFS) Small 750kW klystrons/modulators in tunnel One klystron per four cavities ~1880 klystrons per linac Challenge is design for manufacture (cost reduction) –Klystron Cluster Scheme (KCS) RDR-like 10 MW Klystrons/modulators on surface Surface building & shafts every ~2 km Challenge is novel high-powered RF components (needs R&D) N. Walker - AAP Review (Oxford)

Distributed RF Source N. Walker - AAP Review (Oxford) 750kW Modulated Anode Klystron (MAK)drives 4 SCRF cavities >100k Hours lifetime expected 13 RF sources (52 cavities) driven by common modulator and power supply High-Availability requires redundancy for modulator/power- supply

Distributed RF Source N. Walker - AAP Review (Oxford) All RF power source components in single tunnel

Klystron Cluster Scheme 16 All active RF power source components moved to surface buildings N. Walker - AAP Review (Oxford)

KCS N. Walker - AAP Review (Oxford) 17 # of KCS per main linac9 # of (RDR) RF units per system32 # of cryomodules per system96 # of cavities per system832 # of klystrons/modulators per system19 (36) peak rf power per system (MW)170 (340) R&D required on HLRF distribution components (peak power handling) RF control of effective 1km RF unit TE 01 -mode Coaxial Tap-Off (CTO) with wrap-around power extraction

KCS – CFS impact 18 Four additional surface stations N. Walker - AAP Review (Oxford)

Single Tunnel: Safety Tunnel safety regulations have been reviewed in all three regions –[references to reports/documents] Acceptable single-tunnel solutions exist –However, solutions vary from region to region N. Walker - AAP Review (Oxford) 19 AsiaAmericasEurope HLRF scheme examined so far Primarily DRFS.Primarily KCS.Primarily KCS Isolation of incident location Firewalls / doors every 500 m along the tunnels, and selective closure of the airflow. Utilize caverns at the vertical shaft bases for isolating oil-filled equipment. Firewalls / doors every 500 m along the tunnels Safe pathwaysRest of the tunnels.Most of the tunnels.Rest of the tunnels.

Single Tunnel: Availability ADI/SB2009 focus is on finding acceptable HA solution for the single Main Linac tunnel –Primarily (but not only) driven by HLRF considerations. Availability Task Force established –Monte Carlo simulations using AVAILSIM –Maintenance model scenarios –Development of HA solutions for HLRF –Review of state-of-the-art (MTBF numbers) N. Walker - AAP Review (Oxford) 20 RDR → SB2009: ~1% downtime

Reduced Parameter Set Reduction of beam current (beam power) –Reduced peak RF power ⇒ Reduced klystron/modulator count Reduce bunch number per pulse (n b ) –Increase bunch spacing ⇒ reduced current –Charge per bunch (N) remains 2×10 10 Reduced DR circumference (WA 5) –Scale as n b –No change in DR beam current (collective effects) N. Walker - AAP Review (Oxford) 21

Impact Longer RF pulse length (fill time) Higher Q ext (more control overhead) Lower RF-to-beam power efficiency More aggressive beam-beam parameters Higher disruption → stability Larger beamstrahlung However – no show stoppers N. Walker - AAP Review (Oxford) 22

Damping Ring Low-P Considerations Reduced (  2) bunch number  Reduction in DR circumference by same fraction –Current remains constant –Inj/ext kicker specs remain the same –e-cloud issues remain ~unchanged Can we double the number of bunches in a 3.2km ring? –Double current in ring –Kicker timing OK (needs R&D, but part of RDR spec.) –e-cloud is likely major bottleneck → R&D N. Walker - AAP Review (Oxford)

Central Region Integration RDR solution complex (CFS) Three tunnel concept Looked for consolidated solutions –Simplification of civil engineering scope N. Walker - AAP Review (Oxford)

6/22/2016 AAP Review 25 e - wiggler and rf injection/extraction e - BDS e + BDS e + wiggler and rf Central Region Systems Integration Undulator E+/- Warm Accel E+ Tgt + Capture + Accel 5GeV Injector Booster 5 GeV Boosters share tunnel with BDS E- Gun and injector share tunnel with BDS Undulator + Aux Injector + E+ Tgt-Capture-Accel + Booster share tunnel with BDS No Independent Keep Alive source and only two tunnels, beam + support

Undulator-Based e + Source (WA 3) Goal: Consolidate all sources into central region Requires moving undulator-based source to the end of the Main e - linac (250 GeV). –RDR solution has source located at the 150 GeV point in the electron Main Linac –Considered a fixed-energy point, independent of centre-of-mass energy Primary motivation is in shared infrastructure and reduction in CFS scope However, source must now be operated at varying electron beam energies –Depending on required centre-of-mass energy N. Walker - AAP Review (Oxford) 26

Benefits for e+ source Shared Machine Protection System with BDS Better integration with BDS lattice All energy acceptance limiting apertures now in central region. Low-energy e + transport line shortened by several km Consolidation of ‘high-radiation’ sources in central region –Constrained environmental impact Large energy overhead –(No energy overhead in RDR solution) –Risk reduction during early commissioning N. Walker - AAP Review (Oxford) 27

Other Aspects of SB2009

Accelerating Gradient (WA 1) Gradient has the highest cost-leverage of any single parameter Global R&D into SCRF remains highest-priority focus for TDP-2 Re-evaluation of the design accelerating gradient is required during TDP-2, based on –Statistical cavity performance (R&D results), i.e. expected/projected yield for cost-optimised mass production –Required operational overhead of installed cavities in linac (under full beam loading) Published R&D goals currently remain unchanged N. Walker - AAP Review (Oxford) 29

Accelerating Gradient (WA 1) SB2009 WA is to maintain the RDR value of 31.5 MV/m (Q 0 ≥ ) pending final and thorough review of R&D status –Determines length of main linac (CFS requirements) Unlike RDR, propose to adopt variable power distribution for HLRF to allow for spread in accelerating gradient of individual cavities –Maximise average accelerating gradient (better ‘yield’) –Has impact on required RF power overhead and efficiency –Expect overall cost benefit Acceptable performance spread of cavities about the average still remains to be determined –Expect approximately ±(10-20) % N. Walker - AAP Review (Oxford) 30

Single-Stage Bunch Compressor Adoption of 6mm bunch length in DR allows us to consider a single- stage compressor with compression factor 20 Overall simpler system Single stage compressor saves ~300m of tunnel (including reduction in SCRF accelerator) Expected to have better beam dynamics performance Loss of tuning flexibility (  z restricted to nominal 300  m) N. Walker - AAP Review (Oxford) 31

Further Aspects Electron Source –No fundamental change to design –Main SB2009 modifications are integration aspects into shared beamline tunnel with BDS Positron Source (in addition to proposed relocation) –RDR Flux Concentrator capture device has been replaced with a more conservative Quarter-Wave Transformer magnet (risk reduction) –Reduction in capture efficiency has been compensated by longer undulator Beam Delivery System –Main focus has been integration of e+ source –Additional lattice modifications have also been incorporated –1 TeV upgrade geometry is maintained –Inclusion of crab cavities to implement ‘travelling focus’ N. Walker - AAP Review (Oxford) 32

Physics Scope Impact of SB N. Walker - AAP Review (Oxford)

Physics (Luminosity) Impact Two elements of proposed baseline have direct impact on the potential physics scope –Low beam power option (WA-4) –Re-location of e+ source to the end of the electron Main Linac (WA- 3) Consider impact in two steps: 1.At E cm = 500 GeV (primary focus of design work to-date) 2.At lower centre-of-mass energies (200 GeV ≤ E cm < 500 GeV) Note that no formal or optimised parameter sets exist other than for E cm = 500 GeV N. Walker - AAP Review (Oxford) 34

E cm = 500 GeV Reduction in P beam by 50% requires more aggressive focusing of the beams at the IP to achieve RDR peak luminosity Two scenarios studied –High-disruption parameter set, achieving 1.5×10 34 cm -2 s -1 (25% reduction) –Adoption of the “travelling focus” concept first proposed by Balakin to recover the full RDR luminosity of 2×10 34 cm -2 s N. Walker - AAP Review (Oxford) 35

Comparison to RDR “Parameter Plane” N. Walker - AAP Review (Oxford) 36 Proposed parameters push working point to one extreme of the parameter plane Only Disruption for Travelling Focus significantly exceeds original RDR specifications

Lower Energy Running Primary impact is positron source performance (yield) as electron beam energy is reduced Critical area is blow E cm = GeV At E cm = GeV an alternate pulse scheme is proposed to drive the source –Pulse 1 drives positron source at E beam ≥150 GeV –Pulse 2 produces luminosity with E beam = GeV N. Walker - AAP Review (Oxford) 37 Full e+ charge at 2.5Hz

Source Yield N. Walker - AAP Review (Oxford) 38 Design point

Estimated Cost Reduction Cost differentials (wrt to RDR) have been estimated using RDR unit costs (ILCU) Exceptions are hardware costs not relevant to RDR –DRFS klystrons and modulators –KCS distribution waveguides and associated components –… No new ‘bottoms-up’ estimate has been made for this analysis Current expected cost reduction is 13% of the published RDR VALUE estimate Further iterations/optimisations are expected to increase this during TDP-2 –By a few % N. Walker - AAP Review (Oxford) 39

Conclusions Initial Accelerator Design & Integration effort has successfully concluded –Approximately 1 year study Publication “on-time” of proposed baseline modifications. 7 primary SB2009 Working Assumptions –Wide-ranging impact on accelerator design –Core technologies remain the same as RDR Three primary themes ($$$) –Single tunnel for Main Linac (including new HLRF solutions) –Low-power parameter set –Central region integration Initial studies have demonstrated feasibility –But clearly more detailed design work is required in TDP2 Impact on luminosity acknowledged and requires further study Estimated 13% reduction in RDR value estimate N. Walker - AAP Review (Oxford) 40