beam-beam effects and luminosity nlc and tesla concepts

May 30,2002 Nikolay Solyak , NLC&TESLA Overview 1

NLC/JLC and TESLA Overview

?Beam-beam effects and Luminosity?NLC and TESLA concepts?Damping Ring?Emittance Dilution in Main Linac ?Ground motion?Summary

Nikolay Solyak, Fermilab


Beam-beam effects and Luminosity

),(4 ,

2

0 yxDyx

b AHNn

fL ??? ?

???Luminosityf - pulse repetition frequency nb-number of bunches/pulse N -number of e-/e+ per bunch ? x,y –horiz (vertl) beam size in IP ? -cross angle A= (? z/? ) – beam divergency HD - Enhancement parameter

Beamstrahlung ? (energy spread and losses, background) ? flat beams - horizontal size

-vertical size

2

23

)(86.0

yxz

eE

Nr?????

??????

Ezx ds

?Nconst ???

)( zy ?? ????

? znyy ?

Dny

E

cms

beam HmradmmTeVE

MWPL ?

?????

)((%)

)()(

104 31

??Luminosity

(flat beams)

Pbeam –Beam power Ecms –Energy of c.m. ? ny –vert. norm. emittance ? E -beamstrahlung

Strong Focusing in IP


Pinch-effect and Luminosity EnhancementEnhancement Parameter HD depends of collision geometry (cross angle and beam divergency) and beam-beam dynamics in Interaction Point, which defined by Disruption parameter Dx,y (x/y-horiz/vert):

xyx

ze

yx

zyx

NrF

D?????

,,,

2?? ? z, / ? x,y, - longitudinal/transverse beam sizes, F-focusing length in oncoming beam; re- classical electron radius, ??=E/mc2 N-bunch population,


Kick-instability, when D > 40

0 10 20 30 40 50 600.0

0.5

1.0

1.5

2.0 e+e-A=0

e -e -

A=1

Enha

ncem

ent,

HD

Disruption parameter, D

No beam off-set(simulation errors only)

Off-set ? ?y? ? ?? ??0.0 0.5 1.0 1.5 2.00.0

0.5

1.0

1.5

2.0

Enha

ncem

ent,

HD

Beam-beam offset, ? y/?

D=10 D=0

D=40


Beam parameters at IP

---1.21.5# Photons per electron

NLC-II

33

Interaction Point

5.80.8 1.00.50.5Energy c.m.s. TeV

(?)140 / 2x6.9150/105 / 2x11.3Site / beam power, MW3012.633Two Linac Length, km3.42.0 3.4Luminosity *1034 cm-2*s-1

General Parameters

10.45.44.33.2 Beamshtahlung ? ? (%)

0.27950Bunch train, ? s1.4176337Bunch spacing, ns

13/0.118 / 0.1115 / 0.4Beta function ? x/? y, mm190 / 2.1

360/3.5800 / 1.51000/3Norm emittance ? ny/? ny, mm*mrad

4886 /41.4

1.5

55

1425Disruption parameter, Dy

391 / 2.8

35 48.523.4 Accelerating Gradient, MV/m11.4241.3RF Frequency GHz

1.432.0Pinch factor HD

0.110.3Longituinal beam size ? z, mm

0.752N/bunch, * 1010

192 / 1202820 /5# Bunches per train/ Rep. Rate

245 / 2.7553/5Transverse Beam size, ? ny/? ny nm

NLC-ITESLAParameter


JLC/NLC param


NLC RF Distribution System


Accelerating Gradient


TESLA. General Layout

33 km


TESLA RF Distribution System

(10MW, 1.5ms, 5Hz, 65%)

17 m


SC technology


Vertical emittance

• Are vertical emittance goals realistic ?

• Can we receive small emittance in DR?

• How to prevent emittance growth in main Linac, Beam Delivery System, Final Focus?


KEK ATF, Single buch emittanceN.Toge, KEK, LC’02


KEK/ATF, Multibunch emittanceN.Toge, KEK, LC’02

Emittance not normalized here ! ?n? ? ? ? ?=3.103

NLC TESLA


TESLA Damping Ring

Compression factor = 320 km / 17km = 17


NLC. Emittance Dilution and JitterMain Sources of Emittance Dilution and Beam Jitter :

?Trajectory and energy jitter- Sets quad vibration and RF stability

? Dispersion errors– Sets quad-to-bpm alignment? ? E errors: incoming ? E, E jitter, BNS energy spread.

? Short-range wakefields- BBU ? BNS –required rf energy overhead- Sets tolerances on structure-to-beam alignment for ? ?

? Long-range wakefields- BBU ? wake reduction –sets dipole frequency errors- Sets internal structure alignment tolerances- Sets charge tolerances

? Other (coupling, bookshelf, slow ground motion)


BBU

BNS ? to suppress single-bunch BBU Detuned+Damped Structure? Multi-bunch BBU


Long-Range Wakefield Suppression?Multibunch BBU stronger than for single bunch

?Needs Suppression by factor of 100? Detuning+Damping

Example of Long-Range Transverse Wakefield for H60VG3 with Manifold Damping and Three-Fold Interleaving

*Red-bunch locations


Emittance and Jitter Budgets for NLC-I

0.0353.6At IP0.033.3After Linac0.0223.2After BC0.023Emittance from DR??x??x

0.25%0.510.22At IP-0.250.1From FD-0.30.1From BDS

0.2%0.30.1From Linac0.1%0.10.1From BC0.1%0.10.1F rom DR? ? /E? y/? y? x/? x

Jitter Budget for NLC Stage 1 Parameters

Emittance Budget for NLC Stage 1 Parameters


NLC Emittance Budget

25%

1%

7%

1%4%

3%

4%

2%

1%

1%

1%


TESLA wake-fields and emittance dilutionSingle-bunch (short range) wake-fields

• Longitudinal wake is small (induced energy spread <10-3, can be minimize to 3·10-4 by running at the optimal RF phase +5?)

• More serious 2.5% energy spread at injection energy (chromatic effects), ? ??? =15%• Transverse wake ? 1/a3 ? no BNS damping necessary, only 2.5% emittance growth due

to wake-field & 7% - due to 0.5 mm cavity misalignment.• One ? y injection error yields ? ? y?? y =6 %

Multi-bunch (long range) wake-fields• Longitudinal wake is almost negligible due to natural frequency spread in longitudinal

HOM. Bunch-to-bunch energy spread after feed-back suppression (Lorentz force) < 5·10-4.

• Transverse wakes should be detuned and damped to suppress BBU instability. Natural HOM frequency spread due to fabrication errors helps. For damping needs Q< 105. In TTF found dipole mode 2.58 GHz with high Q> 106 (need redesign HOM coupler).

• Fast intra-train orbit correction system can remove BBU effects. (loose 3.5% bunches).• Jitter due to ground motion has to be corrected by fast intra-beam correction to 0.1 ? y• Slow drift (diffusive ground motion) ? re-alignment once/month.


TESLA HOM dumping (HOM couplers)Transverse long range wake

36 cavity average , 0.1% energy spread • Natural HOM frequency spread enough for detuning.

•All HOM modes should be damped below Q=105

but … .(see below)

NLC: W_T~105 V/pC/m2

TTF Trapped mode Experiment


Ground motion Studies

SLAC site A=5x10-7 ? m2/m/sHERA site A= 6x10-6 ? m2/m/s

Where: A=10-4 -:- 10-8

Large wavelength. Good correlation

Level 1-2 nm


Luminosity Degradation and realignmentSimulation of Luminosity Degradation in 1 TeV NLC due to quad misalignments driven by diffusive ground motion in BDS. * Final doublet quads are always stabilized (1nm) by using beam-beam collision stabilazation feed-back

Magnet Jitter and Drift tolerances for NLC-II Beam Delivery System


Summary

? Luminosity ~(2-3)1034 requires beams with 7-11 MW average power and extremely low normalized vertical emittances ? ?? 3?10-8 m.

? ATF/KEK demonstrate single bunch emittances close to LC goal. Needs more studies for multibunch beams with high charge. TESLA approach with fast kicker not demonstrated yet.

? Alignment tolerances for NLC tighter than for TESLA.Fast intra-train feed-back in TESLA helps to reduce alignment tolerances: 2? m vs. 300? m ? quads, 30? m vs. 500? m? structures.

? Diffusive ground motion is similar for both NLC and TESLA. Needs to re-align Accelerator every month.

beam-beam effects and luminosity nlc and tesla concepts

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