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Personal Perspectives on the ITRP Recommendation and on the Next

Steps Toward the International Linear Collider

Barry BarishPAC Annual MeetingKnoxville, Tennessee

16-May-05

16-May-05 PAC 05 - Barish 2

Why e+e- Collisions?

• elementary particles• well-defined

– energy,– angular momentum

• uses full COM energy• produces particles

democratically• can mostly fully

reconstruct events


A Rich History as a Powerful Probe


The Energy Frontier


Why a TeV Scale?

• Two parallel developments over the past few years (the science & the technology)

– The precision information e+e- and ν data at present energies have pointed to a low mass Higgs; Understanding electroweak symmetry breaking, whether supersymmetry or an alternative, will require precision measurements.

– There are strong arguments for the complementarity between a ~0.5-1.0 TeV ILC and the LHC science.


ElectroweakPrecision Measurements

e+e+ and neutrino scattering results at present energies strongly point to a low mass Higgs and an energy scale for new physics < 1TeV

0

2

4

6

10020 400

mH [GeV]

Excluded Preliminary

∆αhad =∆α(5)

0.02761±0.000360.02747±0.00012Without NuTeV

theory uncertainty

Winter 2003


Why a TeV Scale e+e- Accelerator?


– The precision information from LEP and other data have pointed to a low mass Higgs; Understanding electroweak symmetry breaking, whether supersymmetry or an alternative, will require precision measurements.

– There are strong arguments for the complementarity between a ~0.5-1.0 TeV LC and the LHC science.


Linear Collider Spin Measurement

LHC should discover the Higgs

The linear collider should measure its spin

LHC/ILC Complementarity

The process e+e– → HZ can be used to measure the spin of a 120 GeV Higgs particle.

The Higgs must be spin zero


Extra Dimensions

Linear collider

LHC/ILCComplementarity

Map extra dimensions: study the emission of gravitons into the extra dimensions, together with a photon or jets emitted into the normal dimensions.


Why a TeV Scale e+e- Accelerator?


– Designs and technology demonstrations have matured on two technical approaches for an e+e-

collider that are well matched to our present understanding of the physics.


GLC GLC/NLC Concept

• The main linacs operate at an unloaded gradient of 65 MV/m, beam-loaded to 50 MV/m.

• The rf systems for 500 GeV c.m. consist of 4064 75 MW Periodic Permanent Magnet (PPM) klystrons arranged in groups of 8, followed by 2032 SLED-II rf pulse compression systems


TESLA Concept

• The main linacs based on 1.3 GHz superconducting technology operating at 2 K.

• The cryoplant, is of a size comparable to that of the LHC, consisting of seven subsystems strung along the machines every 5 km.


Which Technology to Chose?

– Two alternate designs -- “warm” and “cold” had come to the stage where the show stoppers had been eliminated and the concepts were well understood.

– A major step toward a new international machine required uniting behind one technology, and then working toward a unified global design based on the recommended technology.


ICFA/ILCSC Evaluation of the Technologies

The Report Validates the Readiness of L-band and X-band Concepts

BUT, IT DID NOT MAKE A CHOICE


International Technology Review Panel


The Charge to the International Technology Recommendation Panel

General Considerations

The International Technology Recommendation Panel (the Panel) should recommend a Linear Collider (LC) technology to the International Linear Collider Steering Committee (ILCSC).

On the assumption that a linear collider construction commences before 2010 and given the assessment by the ITRC that both TESLA and JLC-X/NLC have rather mature conceptual designs, the choice should be between these two designs. If necessary, a solution incorporating C-band technology should be evaluated.

Note -- We interpreted our charge as being to recommend a technology, rather than choose a design


ITRP Schedule of Events• Six Meetings

– RAL (Jan 27,28 2004)

– DESY (April 5,6 2004)

– SLAC (April 26,27 2004)

– KEK (May 25,26 2004)

– Caltech (June 28,29,30 2004)

– Korea (August 11,12,13)

– ILCSC / ICFA (Aug 19)– ILCSC (Sept 20)

Tutorial & Planning

Site Visits

Deliberations

Exec. SummaryFinal Report

Recommendation


Evaluate a Criteria Matrix

• The panel analyzed the technology choice through studying a matrix having six general categories with specific items under each:– the scope and parameters specified by the ILCSC; – technical issues; – cost issues; – schedule issues; – physics operation issues; – and more general considerations that reflect the

impact of the LC on science, technology and society


The Recommendation

• We recommend that the linear collider be based on superconducting rf technology

– This recommendation is made with the understanding that we are recommending a technology, not a design. We expect the final design to be developed by a team drawn from the combined warm and cold linear collider communities, taking full advantage of the experience and expertise of both (from the Executive Summary).

– The superconducting technology has several very nice features for application to a linear collider. They follow in part from the low rf frequency.


Some Features of SC Technology• The large cavity aperture and long bunch interval

reduce the complexity of operations, reduce the sensitivity to ground motion, permit inter-bunch feedback and may enable increased beam current.

• The main linac rf systems, the single largest technical cost elements, are of comparatively lower risk.

• The construction of the superconducting XFEL free electron laser will provide prototypes and test many aspects of the linac.

• The industrialization of most major components of the linac is underway.

• The use of superconducting cavities significantly reduces power consumption.


The Technology Recommendation

• The recommendation was presented to ILCSC & ICFA on August 19 in a joint meeting in Beijing.

• ICFA unanimously endorsed the ITRP’srecommendation on August 20


The Community then Self-Organized

Nov 13-15, 2004


The First ILC Meeting at KEK

The Global Design Effort

Formal organization begun at LCWS 05 at Stanfordin March 2005 when I became director of the GDE


GDE – Near Term Plan

• Staff the GDE– Administrative, Communications, Web staff– Regional Directors (each region)– Engineering/Costing Engineer (each region)– Civil Engineer (each region)– Key Experts for the GDE design staff from the world

community (please give input)– Fill in missing skills (later)

Total staff size about 20 FTE (2005-2006)



• Schedule• Begin to define Configuration (Aug 05) • Baseline Configuration Document by end of 2005-----------------------------------------------------------------------• Put Baseline under Configuration Control (Jan

06) • Develop Conceptual Design Report by end of

2006

• Three volumes -- 1) Conceptual Design Report; 2) Shorter glossy version for non-experts and policy makers ; 3) Detector Concept Report



• Organize the ILC effort globally– First Step --- Appoint Regional Directors within the

GDE who will serve as single points of contact for each region to coordinate the program in that region.

– Make Website, coordinate meetings, collaborative R&D, etc

• R&D Program– Coordinate worldwide R & D efforts, in order to

demonstrate and improve the performance, reduce the costs, attain the required reliability, etc. (Proposal Driven to GDE)


Starting Point for the GDE

main linacbunchcompressor

dampingring

source

pre-accelerator

collimation

final focus

IP

extraction& dump

KeV

few GeV

few GeVfew GeV

250-500 GeV

Superconducting RF Main Linac


Parameters for the ILC

• Ecm adjustable from 200 – 500 GeV

• Luminosity ∫Ldt = 500 fb-1 in 4 years

• Ability to scan between 200 and 500 GeV• Energy stability and precision below 0.1%• Electron polarization of at least 80%

• The machine must be upgradeable to 1 TeV


Experimental Test Facility - KEK• Prototype Damping Ring for X-band Linear Collider

• Development of Beam Instrumentation and Control


Final Focus Test Faclity - SLAC


TESLA Test Facility Linac - DESY

laser driven electron gun

photon beam diagnostics

undulatorbunch

compressor

superconducting accelerator modules

pre-accelerator

e- beam diagnostics

e- beam diagnostics

240 MeV 120 MeV 16 MeV 4 MeV


Towards the ILC Baseline Design


Specific Machine Realizationsrf bands:

L-band (TESLA) 1.3 GHz λ = 3.7 cm

S-band (SLAC linac) 2.856 GHz 1.7 cm

C-band (JLC-C) 5.7 GHz 0.95 cm

X-band (NLC/GLC) 11.4 GHz 0.42 cm

(CLIC) 25-30 GHz 0.2 cm

Accelerating structure size is dictated by wavelength of the rfaccelerating wave. Wakefields related to structure size; thus so is the difficulty in controlling emittance growth and final luminosity.

Bunch spacing, train length related to rf frequency

Damping ring design depends on bunch length, hence frequency

Frequency dictates many of the design issues for LC


Cost Breakdown by Subsystem

cf31%

structures18%rf

12%

systems_eng8%

installation&test7%

magnets6%

vacuum4%

controls4%

cryo4%

operations4%

instrumentation2%

Civil

SCRF Linac


RF SC Linac ChallengesEnergy: 500 GeV, upgradeable to 1000 GeV

• RF Accelerating Structures– Accelerating structures must support the desired

gradient in an operational setting and there must be a cost effective means of fabrication.

– ~17,000 accelerating cavities/500 GeV

– Current performance goal is 35 MV/m, (operating at 30 MV/m)• Trade-off cost and technical

risk.

1 mRisk

Cos

t

~The

oret

ical

Max


Electro-polishing(Improve surface quality -- pioneering work done at KEK)

BCP EP• Several single cell cavities at g > 40 MV/m

• 4 nine-cell cavities at ~35 MV/m, one at 40 MV/m

• Theoretical Limit 50 MV/m


Gradient

Results from KEK-DESY collaboration

must reduce spread (need more statistics)

single

-cel

l m

easu

rem

ents

(in

nin

e-ce

ll ca

vities

)


New Cavity Shape for Higher Gradient?

TESLA Cavity

• A new cavity shape with a small Hp/Eacc ratio around35Oe/(MV/m) must be designed.

- Hp is a surface peak magnetic field and Eacc is the electricfield gradient on the beam axis.

- For such a low field ratio, the volume occupied by magneticfield in the cell must be increased and the magnetic densitymust be reduced.

- This generally means a smaller bore radius. - There are trade-offs (eg. Electropolishing, weak cell-to-cellcoupling, etc)

Alternate Shapes


Parameters of Positron Sources

rep rate # of bunches per pulse

# of positrons per bunch

# of positrons per pulse

TESLA TDR 5 Hz 2820 2 · 1010 5.6 · 1013

NLC 120 Hz 192 0.75 · 1010 1.4 · 1012

SLC 120 Hz 1 5 · 1010 5 · 1010

DESY positron source 50 Hz 1 1.5 · 109 1.5 · 109


Positron Source

• Large amount of charge to produce

• Three concepts:– undulator-based (TESLA TDR baseline)

– ‘conventional’– laser Compton based


Strawman Final Focus


Conclusions

Remarkable progress in the past two years toward realizing an international linear collider:

important R&D on accelerator systemsdefinition of parameters for physicschoice of technologystart the global design effortfunding agencies are engaged

Many major hurdles remain before the ILC becomes a reality (funding, site, international organization, detailed design, …), but there is increasing momentum toward the ultimate goal --- An International Linear Collider.

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