Possible Uses of Rapid Switching Devices and

Induction RF for an LHC Upgrade

Frank Zimmermann, CERN

Thanks to Ulrich Dorda, Wolfram Fischer, Jean-Pierre Koutchouk, Peter McIntyre,

Kazuhito Ohmi, Francesco Ruggiero, Walter Scandale, Daniel Schulte, Tanaji Sen, Ken Takayama, Kota Torikai

Large Hadron Collider (LHC)proton-proton collider

next energy-frontier discovery machine

c.m. energy 14 TeV(7x Tevatron)

design luminosity1034 cm-2s-1(~100x Tevatron)

sector beam testend of 2006;start full ring commissioningin fall 2007;physics run 2008

outlineLHC upgradehigher-energy injectors stronger dipolesinteraction-region choiceslong-range beam-beam compensation by

pulsed electro-magnetic wiresrf crab cavitiessuperbunches & QCD Explorer

← RPIA’06

← RPIA’06← RPIA’06

← RPIA’06

LHC upgrade

European Accelerator Network on

road map for upgrade of European accelerator infrastructure (LHC & GSI complex)

technical realization & scientific exploitationaccelerator R&D and experimental studies

November 2004: 1st CARE-HHH-APD Workshop (HHH-2004) on ‘Beam Dynamics in Future Hadron Colliders and Rapidly Cycling High-Intensity Synchrotrons’, CERN-2005-006

September 2005: 2nd CARE-HHH-APD Workshop (LHC-LUMI-05)on ‘Scenarios for the LHC Luminosity Upgrade’http://care-hhh.web.cern.ch/CARE-HHH/LUMI-05/

High EnergyHigh Intensity

Hadron Beamshttp://care-hhh.web.cern.ch/care-hhh/

http://care-hhh.web.cern.ch/care-hhh/

stages• push LHC performance w/o new hardware

luminosity →2.3x1034 cm-2s-1, Eb=7→7.54 TeV• LHC IR upgrade

replace low-β quadrupoles after ~7 yearsluminosity →4.6x1034 cm-2s-1

• LHC injector upgradeluminosity →9.2x1034 cm-2s-1

• LHC energy upgradeEb→13 – 21 TeV (15 → 24 T dipole magnets)

LHC Upgrade Paths/Limitationspeak luminosity at beam-beam limit L~I/β*total beam intensity limitedby electron cloud, collimation, injectorsminimum crossing angledepends on intensity,limited by triplet aperturelonger bunches allow higher beam-beam limitfor Nb/εn, limited by Injectorsless e- cloud and rfheating for longer bunches;~50% luminosity gain forflat bunches longer than β*event pile up in physicsdetectors increases with Nb2

luminosity lifetime at beam-beam limit depends only on β*

electron cloud in the LHC

schematic of e- cloud build up in the arc beam pipe,due to photoemission and secondary emission

[Courtesy F. Ruggiero]

blue: e-cloud effect observedred: planned accelerators

schematic of e- motion during passage of long protonbunch; most e- do not gain any energy when traversingthe chamber in the quasi-static beam potential

[after V. Danilov]negligible heat load

superbunch

upgrade issues IR upgrade for lower β* & higher current

optics: quadrupole first or dipole firstheat load due to collision debris magnet technology & apertures & field

qualitycrossing angle & long-range collision

geometric luminosity lossdynamic-aperture reduction

electron cloudheat load, vacuum pressure, beam

lifetime, instabilities… → f

low ch

art

β*current

luminosity

IR magnettechnology

injectorupgrade

IR optics& layout

aperture

energydeposition

crossingangle beam

structurelong-rangecompensation

dynamicaperture

crab cavities

higher harm. rf

electroncloud long-range

beam-beam

upgrade roadmap → complex interdependence

higher-energy injectors

injector upgrade - motivationsraising beam intensity (higher bunch charge,

shorter spacing etc.), for limited geometric aperture, L~εN

reduction of dynamic effects (persistentcurrents, snapback, etc.)

→ improvement of turn-around time byfactor ~2, effective luminosity by ~50%

benefit to other CERN programmes(ν physics, β beams,…)

LHC injector upgradeSuper SPS

extraction energy 450 GeV →1 TeVSuper PS

extraction energy 26 GeV → 50 GeVSuper LHC

injection energy 450 GeV → 1 TeV[Super ISR is alternative to Super PS]

Space constraints in existing tunnels → incentive to develop more efficient kickers, i.e., by improving their technology reaching higher deflecting strength per unit! – opportunity for RPIA technology

present kicker parametersPS extr. SPS extr. LHC inj.

magnet length(mechanical)

0.22 m 1.674 m 3.4 m

aperture (diameter)

158x53 mm

38 mm

# units 4 5 4average field 0.07 T 0.0866 T 0.096 Tflat top length 5-12 μs 8-10 μs 8 μsflat top ripple

stronger dipoles

energy upgrade - motivationspredicting the energy for discovery is perilousfor a decade, after the discovery of the b quark we knewthere should be a companion t quark; predictions of itsmass over that decade grew 20→40→80→120 GeV4 colliders were built with top discovery as a goalfinally top was discovered by Fermilab at 175 GeV

mass of lightest two sparticles in MSSMconstrained by astrophysics & cosmology

Ellis et al,McIntyre PAC05

M. Mangano

production of W-like boson,at M>3.5 TeV, higher energy ispreferred

proposed design of 24-T block-coil dipole for “LHCenergy tripler”

P. McIntyre, Texas A&M, PAC’05

magnets are getting more efficient!

Super-SPS

Super-LHC

Super-PS

Super-Transferlines

Upgraded CERN Complex

IR choices

higher-luminosity IR opticsweb site http://care-hhh.web.cern.ch/care-

hhh/SuperLHC_IRoptics/IRoptics.html

Candidate solutions:Combined function NbTi magnets with large l* (O. Bruning)Dipole first options with Nb3Sn (CERN & FNAL)Quad 1st Nb3Sn (T. Sen)Quad 1st with detector-integrated dipole (J.-P. Koutchouk)Quad 1first flat beam (S. Fartoukh)Quad 1st plus crab cavities (in preparation)

Criteria: aperture, energy deposition, technology, chromatic correction, beam-beam compensation,…

http://care-hhh.web.cern.ch/care-hhh/SuperLHC_IRoptics/IRoptics.htmlhttp://care-hhh.web.cern.ch/care-hhh/SuperLHC_IRoptics/IRoptics.html

x

zcRσσθ

θ 2 ;

11

2≡Θ

Θ+= Piwinski angle

luminosity reduction factor

nominal LHC

maximum crossing angle

minimum crossing angle

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+≅

γεμ

σβεθ m75.3

103223 11*

bpardac

Nx

kd

beam-beam long-range collisions perturb motionat large betatronamplitudes, where particles come close to opposing beamcause ‘diffusive’ (or dynamic) aperture, high background, poor beam lifetimeincreasing problem for SPS collider, Tevatron, LHC,i.e., for operation with larger # bunches (9→70→120)

d: dynamic aperturekpar: # parasitic collisionsNb: bunch population

various approaches to boost LHC performance:1) increase crossing angle AND reduce bunch length

(higher-frequency rf & reduced longitudinal emittance)[J. Gareyte ~2000; J. Tuckmantel, HHH-20004]

2) reduce crossing angle & apply “wire” compensation[J.-P. Koutchouk]

3) reduce crossing angle & early separation dipole ‘D0’ inside detector [J.-P. Koutchouk, 2005]

4) crab cavities → large crossing angles w/o luminosity loss[R. Palmer for LC, 1988; K.~Oide, K. Yokoya for e+e- factories, 1989; 1st demonstration KEKB 2006;F. Zimmermann for LHC upgrade ~2000]

5) collide long super-bunches with large crossing angle[Ken Takayama et al, ~2000;F. Ruggiero, F. Zimmermann for LHC, ~2002W. Fischer for RHIC, ~2003?]

RPIAtechnology?

long-range beam-beam compensation by wire

wire compensation “BBLR”

SPS studiessimulations LHC situationRHIC experimentsUS LARPpulsed wire

SPS wire compensator

merits of wire compensation• long-range compensation was demonstrated

in SPS using 2 wires (lifetime recovery)• simulations predict 1-2σ gain in dynamic

aperture for nominal LHC • allows keeping the same – or smaller –

crossing angle for higher beam current→no geometric luminosity loss

challenges & plans• further SPS experiments (3rd wire in 2007)• demonstrate effectiveness of compensation

with real colliding beams (at RHIC) • study options for a pulsed wire

LHC bunch filling pattern

example excitation patterns (zoom)

not to degrade lifetime for the PACMAN bunches, the wire should be pulsed train by train

revolution period Trev(pattern repetition frequency)

88.9 μs +/- 0.0002 μs(variation with beam energy)

maximum strength 120 Ammaximum current (smaller currents will also be needed)

120 A(1m)

60 A(2m)

0→max ramp up/down time 374.25 nslength of max. excitation 1422.15 nslengths of min. excitation(larger min. times may be needed too)

573.85 ns & 598.8 ns

length of abort gap (could vary) 2594.75 nsnumber of pulses per cycle 39average pulse rate 439 kHzpulse accuracy with respect to ideal 5%turn-to-turn amplitude stability (relative to peak) 10-4

turn-to-turn timing stability 0.04 ns

parameters of pulsed beam-beam compensator for LHC

issues: high repetition rate, jitter & turn-to-turn stability tolerance

( )22

20

21

14

11

⎟⎟⎠

⎞⎜⎜⎝

⎛+

Δ−≈

ξπ

σε

ε g

xsfdtd

xrev

emittance growth from noise → jitter toleranceincluding decoherence & feedback (Y. Alexahin):

g~0.2 feedback gain, ξ~0.01 total beam-beam parameter,s0~0.645 related to the fact that only a small fraction of the energy received from a kick is imparted on the continuumeigenmode spectrum1% emittance growth per hour ↔ Δx=1.5 nm with feedback ↔ Δx=0.6 nm w/o feedback (σx*=11 μm)

rmsw

w

NIP

wwp

rms II

ecnnlIrx

⎟⎟⎠

⎞⎜⎜⎝

⎛ Δ=⎟

⎠⎞

⎜⎝⎛ Δ

εσ2

beam jitter from wire jitter:for Iwlw=120 Am, jitter tolerance for 1% emittance growth w/o FBper hour becomes ΔIw/Iw~1x10-4

crab cavities

Crab Cavities

KEKB s.c. crab cavity production

RF Deflector( Crab Cavity )

Head-onCollision

Crossing Angle (11 x 2 m rad.)

Electrons PositronsLERHER

1.41 MV

1.41 MV

1.44 MV

1.44 MV

Super-KEKB crab cavity scheme

2 crab cavities / beam / IP

first crab cavities will be installedat KEKB in early 2006

Palmer for LC, 1988Oide & Yokoya for storage rings, 1989

crab cavities

• combine advantages of head-on collisions and large crossing angles

• require lower voltages than bunch shortening rf systems

• but tight tolerances on phase jitter to avoid emittance growth

crab voltage compared with bunch-shortening rf

crab voltage required for Super-LHC

zoom

crossing angle 0.3 mrad 1 mrad 8 mrad

800 MHz 2.1 MV 7.0 MV 56 MV

400 MHz 4.2 MV 13.9 MV 111 MV

200 MHz 8.4 MV 27.9 MV 223 MV

crab cavity voltage for different crossing angles & crab rf frequencies

*800 MHz would be too high for nominal LHC bunch length

( )c

rfrf

ccrab Rfe

cERfe

cEV θππ

θ

12

0

12

0

422/tan

≈=

R12=30 m

KEKB Super-KEKB

ILC Super-LHC

σx* 100 μm 70 μm 0.24 μm 11 μm

θc 22 mrad 30 mrad 10 mrad 1 mrad

Δt 6 ps 3 ps 0.03 ps 0.002 ps

IP offset of 0.2 σx*

IP offset of 0.6 nm, ~5x10-5 σ*

comparison of timing tolerance with others

cIPcnxtθmax2Δ≤ΔΔxmax=0.6 nm from Y. Alexahin’s formula

Δxmax=0.5 nm scaled from strong-strong beam-beamsimulation by K. Ohmi (HHH-2004), for 1% ε growth per hour

Gupta: Quad Pairs for (not so) Large Crossing Angle, 4mrad, why not 8 mrad?

Minimum X-ing angle is determined by how close the other beamline can come

Consider the two counter-rotating beams with the first going through a quad.How close can the second beam be?

Displaced quads with the first beam in the quad and counter rotating beam just outside the coil in a field free region.

50 m free space !, 45 cm lateral[H. Padamsee, US LARP IR meeting October 2005]

I.R. 20

I.R. 90

I.D. 188

I.D. 120

I.D. 30

I.D. 240

Input Coupler

Monitor Port

I.R.241.5

483

866Coaxial Coupler

scale (cm)

0 50 100 150

KEKB crab cavity, ~1.5 MV@500 MHz

radial size 43 cmTM2-1-0 (x-y-z) rect. mode (=TM110 cyl.)

Courtesy K. Akai

Solutions

• plane of separation need not be the plane of crossing

• new fundamental mode 2-beam crab cavity [H. Padamsee]

• compact induction rf crab cavity?

Forwardbeam

ReturnBeam

RF CavityTM010 (cyl)

TM 1-1-0 (rect)

Can This Work (Maybe 2 Cavities if necessary)

Dampers Dampers

[H. Padamsee, US LARP IR meeting October 2005]

superbunches & QCD Explorer

x-y crossing or 45/135 degree crossing

K. Takayama et al.,PRL 88, 14480-1 (2002)

superbunch hadron collider

superbunches for LHC

+ negligible electron-cloud heat load + no PACMAN bunches + reduced IBS + higher luminosity for same tune shift

& smaller beam current

- huge event pile up

example parameter sets (HHH-2004)

baseline ‘Piwinski’ super-bunch

joint statement by LHC ATLAS & CMS experiments on super-bunches

at CARE-HHH-2004 workshop

“based on the physics motivation for an upgrade of the LHC luminosity by an

order of magnitude, it is not seen how in case of the super-bunch scenario, this

increase in the luminosity could be exploited by an upgraded ATLAS or CMS

detector”

ATLASALICE

LHC-B

CMSLHCQCDE

CLIC-1

QCD Explorer based on LHC and CLIC-1

QCD Explorer based on LHC and CLIC-1

some key points• extends reach of HERA by 2 orders of magnitude• as fundamental for QCD as the Higgs for electro-

weak interaction• highest-energy linac-ring collider• optimum luminosity L>1031 cm-2 s-1 is achieved

with proton superbunch• e- beam emittances relaxed from CLIC goal

filling patternswith nominalLHC proton beam

filling patternswith LHC proton superbunch

luminosity maximized by concentrating p’s over length of e- train

� � � � � � � � � � � � � � � �

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� � � � � � � �

� � � � � � � � � � � �� � � � � � � � �

schematic IR layout

vertical and horizontal dipoles combine and separate the two beams

parameter e- Pbeam energy Eb 75 GeV (or higher) 7 TeVbunch population Nb 2.56x109 6.5x1013

bunch length σz 31 μm (rms) 18 m (full)Spacing Lsep 0.267 ns N/A# bunches nb 220 1effective line density λb 3.2x1010 m-1 2.1x1012 m-1

IP beta β∗ 0.25 m 0.25 minteraction length lIR 2 mcollision frequency Fcoll 150 Hz luminosity L 1.3x1031 cm-2 s-1

beam-beam tune shift ξx,y N/A 0.006rms norm. emittance γεx,y 73 μm 3.75 μmIP spot size σx,y 11 μm 11 μm

QCDE parameters

conclusions

RPIA’06 issues @ LHC upgrade:

pulser for long-range beam-beam compensation

crab-cavity optimizationstronger kickers at Super-PS/SPS/LHCsuperbunches for QCD Explorer

tentative milestones for future machine studies

• 2006: installation of crab cavities in KEKB, validation of KEKB beam-beam performance with crabbing; installation of a long-range compensator in RHIC

• 2007: experiments with three dc beam-beam compensators at SPS; dc compensation experiments with colliding beams in RHIC; also at RHIC installation of a pulsed compensator (LARP)

• 2008: experiment with pulsed beam-beam compensation in RHIC; installation of crab cavity in hadron machine (also RHIC?) to validate low rf noise and emittance preservation; studies of electron lenses in RHIC?

Francesco Ruggiero

thank you for your attention!

outlineLHC upgrade stagesupgrade issues higher-energy injectorsLHC injector upgradepresent kicker parametersstronger dipolesproposed design of 24-T block-coil �dipole for “LHC�energy tripler”IR choiceshigher-luminosity IR opticslong-range beam-beam compensation by wirecrab cavitiescrab cavitiesGupta: Quad Pairs for (not so) Large Crossing Angle, 4mrad, why not 8 mrad?Solutionssuperbunches & QCD Explorerjoint statement by LHC ATLAS & CMS experiments on super-bunches�at CARE-HHH-2004 workshopconclusionsRPIA’06 issues @ LHC upgrade:tentative milestones for future machine studiesthank you for your attention!