linear colliders lecture 4 the real designs€¦ · international linear collider (ilc)...

John Adams Institute Frank Tecker Linear Colliders

Frank Tecker – CERN

Linear Colliders Lecture 4

The real designs

  The designs   Parameter Overview   NC/SC driven differences   Damping rings   CLIC two beam scheme

John Adams Institute Frank Tecker

Generic Linear Collider

  We have seen the different sub-systems in the previous lectures

  Now let’s look at the real designs in a bit more detail…

C.Pagani

Electron Gun Deliver stable beam current

Damping Ring Reduce transverse phase space (emittance) so smaller transverse IP size achievable

Bunch Compressor Reduce σz to eliminate hourglass effect at IP

Positron Target Use electrons to pair-produce positrons

Main Linac Accelerate beam to IP energy without spoiling DR emittance

Final Focus Demagnify and collide beams


Linear Collider Designs   TEV Superconducting Linear Accelerator (TESLA)

  Based on 1.3 GHz superconducting cavities developed by DESY   Japanese Linear Collider / Next Linear Collider (JLC/NLC)

  Based on 11.4 GHz normal conducting RF system promoted by SLAC/KEK

  Compact Linear Collider (CLIC)   Multi-TeV study based on 12 GHz (30 GHz previously) normal conducting RF

using a Two-Beam RF generation concept developed at CERN

  International Linear Collider (ILC)   International technology choice after review and evaluation of different designs

⇒ Based on SC cavities, 500 GeV → 1 TeV   International groups are reviewing the design   Reference Design Report (like Technical DR) released

http://www.linearcollider.org/cms/?pid=1000437


First LC: SLC

T.Raubenheimer


Parameter comparison

SLC TESLA ILC J/NLC CLIC Technology NC Supercond. Supercond. NC NC

Gradient [MeV/m] 20 25 31.5 50 100

CMS Energy E [GeV] 92 500-800 500-1000 500-1000 500-3000

RF frequency f [GHz] 2.8 1.3 1.3 11.4 12.0

Luminosity L [1033 cm-2s-1] 0.003 34 20 20 21

Beam power Pbeam [MW] 0.035 11.3 10.8 6.9 5

Grid power PAC [MW] 140 230 195 130

Bunch length σz* [mm] ~1 0.3 0.3 0.11 0.03

Vert. emittance γεy [10-8m] 300 3 4 4 2.5

Vert. beta function βy* [mm] ~1.5 0.4 0.4 0.11 0.1

Vert. beam size σy* [nm] 650 5 5.7 3 2.3

Parameters (except SLC) at 500 GeV


Accelerating gradient

  Normal conducting cavities have higher gradient with shorter RF pulse length

  Superconducting cavities have lower gradient (fundamental limit) with long RF pulse

SC WARM


SC Technology

  In the past, SC gradient typically 5 MV/m and expensive cryogenic equipment

  TESLA development: new material specs, new cleaning and fabrication techniques, new processing techniques

  Significant cost reduction

  Gradient substantially increased

  Electropolishing technique has reached ~35 MV/m in 9-cell cavities

  Still requires essential work

  31.5 MV/m ILC baseline

⇒

Chemical polish Electropolishing


ILC design

Achieved accelerating gradients   Recent progress by R&D programme to systematically

understand and set procedures for the production process   goal to reach a 50% yield at 35 MV/m by the end of 2010

  already approaching that goal   90% yield foreseen later

2007

2009


Warm structures

  Need conditioning to reach ultimate gradient

  RF processing can melt field emission points ⇒ higher fields

  More energy: electrons generate plasma and melt surface

  Molten surface splatters and generates new field emission points!

  Excessive fields can also damage the structures

  Design structures with low Esurf/Eacc

  Study new materials (Mo, W)

Damaged CLIC structure iris longitudinal cut


Warm structure conditioning

  Increase input power gradually

NLC structure processing CLIC structure conditioning


Bunch structure   SC allows long pulse, NC needs short pulse with smaller bunch charge

ILC

2625 0.370

970

0.156

312

20000

ILC

12

0.0005

0.37


Warm vs Cold RF Collider

  Normal Conducting   High gradient ⇒ short linac

  High rep. rate ⇒ GM suppression

  Small structures ⇒ strong wakefields

  Generation of high peak RF power

  Superconducting   long pulse ⇒ low peak power

  large structure dimensions ⇒ low WF

  very long pulse train ⇒ feedback within train

  SC structures ⇒ high efficiency

  Gradient limited <40 MV/m ⇒ longer linac (SC material limit ~ 55 MV/m)

  low rep. rate ⇒ bad GM suppression (εy dilution)

  Large number of e+ per pulse

  very large (unconventional) DR


Damping rings   TME (theoretical minimum emittance) lattice

  NLC: similar to existing synchroton light sources

Low dispersion and horizontal beta function in the dipole

High field in dipole vertical focusing

Sextupoles at high dispersion points, with separated betas

300 m Main Damping Ring 3 Trains of 192 bunches

1.4 ns bunch spacing

231 m Predamping Ring

2 Trains of 192 bunches

30 m Wiggler

30 m Wiggler

Injection and RF

Circumference Correction and

Extraction

110 m Injection

Line

110 m Transfer

Line

90 m Extraction

Line

Spin Rotation


TESLA/ILC damping ring   Long pulse:

950µs × c = 285 km!!

  Compress bunch train into 17 km (or less) “ring” kick individual bunches

  Min. circumference by ejection/injection kicker speed (≤20 ns)

  “Dog bone” ring with ≈ 400m of 1.67 T wigglers

  6.7 km circular rings in the baseline ILC design

  Very demanding kicker rise+fall time < 6 ns


DR test at ATF

  ATF at KEK in Japan tests DR issues

ATF, 3rd gen. SRS, SLC

“Laser Wire”


Damping Ring emittance

SLC

ATF achieved

ILC

ATF Design

CLIC DR design

CLIC 500 GeV CLIC

3 TeV

NSLS II scaled

SLS

0.001

0.010

0.100

1.000

10.000 0.1 1 10 100

Vert

ical

nor

m. E

mitt

ance

(µra

d-m

)

Horizontal norm. Emittance (µrad-m)


CLIC scheme

  Very high gradients (>100 MV/m) possible with NC accelerating structures at high RF frequencies (30 GHz → 12 GHz)

  Extract required high RF power from an intense e- “drive beam”

  Generate efficiently long pulse and compress it (in power + frequency)

Long RF Pulses P0 , ν0 , τ0

Short RF Pulses PA = P0 × N1 τA = τ0 / N2 νA = ν0 × N3

Electron beam manipulation Power compression

Frequency multiplication

‘few’ Klystrons Low frequency High efficiency

Accelerating Structures High Frequency – High field

Power stored in electron beam

Power extracted from beam in resonant structures


Transfer lines

Main Beam Drive Beam

CLIC TUNNEL CROSS-SECTION

CLIC two beam scheme

  High charge Drive Beam (low energy)   Low charge Main Beam (high collision energy)   => Simple tunnel, no active elements   => Modular, easy energy upgrade in stages

Main beam – 1 A, 156 ns from 9 GeV to 1.5 TeV

Drive beam - 101 A, 240 ns from 2.4 GeV to 240 MeV

4.5 m diameter

power-extraction and transfer structure (PETS)

accelerating structures

quadrupole quadrupole

RF

BPM

12 GHz, 68 MW

(c)FT


(c)FT

TA radius = 120 m

BC2

delay loop1 km

decelerator, 24 sectors of 876 m

326 klystrons33 MW, 139 µs

CR2

CR1

circumferencesdelay loop 73.0 mCR1 146.1 mCR2 438.3 m

BDS2.75 km

IPTA r=120 m

BC2

245 m

delay loop1 km

326 klystrons33 MW, 139 µs

drive beam accelerator2.38 GeV, 1.0 GHz

CR2

CR1

BDS2.75 km

48.3 kmCR combiner ringTA turnaroundDR damping ringPDR predamping ringBC bunch compressorBDS beam delivery systemIP interaction point dump

drive beam accelerator2.38 GeV, 1.0 GHz

BC1

245 m

e+ injector,2.86 GeVe+

PDR 398 m

e+ DR

493 m

booster linac, 6.14 GeV

e+ main linac

e– injector,2.86 GeV e–

PDR 398 m

e– DR

493 m

e– main linac, 12 GHz, 100 MV/m, 21.02 km

Main Beam Generation Complex

Drive beam

Main beam

Drive Beam Generation Complex

CLIC – overall layout – 3 TeV


140 µs train length - 24 × 24 sub-pulses 4.2 A - 2.4 GeV - 60 cm between bunches

240 ns

24 pulses – 100 A – 2.5 cm between bunches

240 ns 5.8 µs

Drive beam time structure - initial Drive beam time structure - final

CLIC RF POWER SOURCE LAYOUT

Drive Beam Accelerator efficient acceleration in fully loaded linac

Power Extraction

Drive Beam Decelerator Section (24 in total)

Combiner Ring × 3

Combiner Ring × 4 pulse compression &

frequency multiplication

pulse compression & frequency multiplication

Delay Loop × 2 gap creation, pulse

compression & frequency multiplication

RF Transverse Deflectors

CLIC Drive Beam generation


Lemmings Drive Beam

Alexandra Andersson


Fully loaded operation

  efficient power transfer from RF to the beam needed “Standard” situation:

 small beam loading  power at structure exit lost in load

“Efficient” situation:   high beam current   high beam loading

  no power flows into load   VACC ≈ 1/2 Vunloaded


Fully loaded operation

  Disadvantage: any current variation changes energy gain

at full loading, 1% current variation = 1% voltage variation at 20% loading, 1% current variation = 0.2% voltage variation

  Requires high current stability

  Stable beam successfully demonstrated in CTF3

  > 95% efficiency

Beam on ~ 0 MW

Output power from accelerating structure

1.6 µs compressed RF pulse

Beam off ~ 24 MW


Frequency multiplication

  basic principle of drive beam generation   transform very long pulses into short pulses with

higher power and higher frequency

  use RF deflectors to interleave bunches  ⇒ double power  ⇒ double frequency


Delay Loop Principle   double repetition frequency and current   parts of bunch train delayed in loop

  RF deflector combines the bunches (fdefl=bunch rep. frequency)

  Path length corresponds to beam pulse length


3rd

λo/4

4rd

2nd

Cring = (n + ¼) λ injection line

septum

local inner orbits

1st deflector 2nd deflector

1st turn

λo RF deflector field

  combination factors up to 5 reachable in a ring

RF injection in combiner ring

Cring has to correspond to the distance of pulses from the previous combination stage!


Demonstration of frequency multiplication


CTF 3

CLEX

30 GHz “PETS Line”

Linac

Delay Loop – 42m Combiner Ring – 84m

Injector

Bunch length chicane

30 GHz test area

TL1

TL2

RF deflector

Laser

4A – 1.2µs 150 MeV

32A – 140ns 150 MeV

  demonstrate remaining CLIC feasibility issues, in particular:

  Drive Beam generation (fully loaded acceleration, bunch frequency multiplication)

  CLIC accelerating structures

  CLIC power production structures (PETS)


  combined operation of Delay Loop and Combiner Ring (factor 8 combination)

  ~26 A combination reached, nominal 140 ns pulse length

  => Full drive beam generation, main goal of 2009, achieved

Current from Linac

Current after Delay Loop

Current in the ring

30A

DL CR

Drive beam generation achieved


  must extract efficiently >100 MW power from high current drive beam

  passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power

  periodically corrugated structure with low impedance (big a/λ)

  ON/OFF mechanism

Power extraction structure PETS

Beam eye view

The power produced by the bunched (ω0) beam in a constant impedance structure:

Design input parameters PETS design

P – RF power, determined by the accelerating structure needs and the module layout. I – Drive beam current L – Active length of the PETS Fb – single bunch form factor (≈ 1)


Frequency: 11.424 GHz Cells: 18+2 matching cells

Filling Time: 36 ns

Length: active acceleration

18 cm

Iris Dia. a/λ 0.155~0.10

Group Velocity: vg/c 2.6-1.0 %

Phase Advace Per Cell 2π/3

Power for <Ea>=100MV/m

55.5 MW

Unloaded Ea(out)/Ea(in) 1.55

Es/Ea 2

Present best structure performance   2 structures T18_VG2.4_disk

(no damping)

  tested at SLAC and KEK

  Exceeded 100 MV/m at nominal CLIC breakdown rate

Impr

ovem

ent b

y co

nditi

onin

g

CLIC nominal


Summary   Linear e+/e- Collider the only realistic approach to higher energy   Many challenges!!!   Efficient acceleration

  RF system   High gradient

  Extremely small beam sizes   Damping ring performance is crucial   Emittance preservation   Alignment and stabilisation

  Much interesting work left to do!!!   Much more detailed lectures at last ILC school

http://ilcagenda.linearcollider.org/conferenceTimeTable.py?confId=3475


Documentation about CLIC   General documentation about the CLIC study:

http://cern.ch/CLIC-Study/

  CLIC scheme description: http://preprints.cern.ch/yellowrep/2000/2000-008/p1.pdf

  CLIC Physics http://clicphysics.web.cern.ch/CLICphysics/

  CLIC Test Facility: CTF3 http://ctf3.home.cern.ch/ctf3/CTFindex.htm

  CLIC technological challenges (CERN Academic Training) http://indico.cern.ch/conferenceDisplay.py?confId=a057972

  CLIC Workshop 2009 (most actual information) http://indico.cern.ch/event/45580

linear colliders lecture 4 the real designs€¦ · international linear collider (ilc)...

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