CLIC parameters at 500 GeV

A. Grudiev for CLIC study

02/09/2008

J.P.Delahaye CLIC design committee (26/08/08) 2

Strategy•3 TeV nominal parameters based on nominal beam

parameters•Emittances @ IP smaller than ILC by 15 in H, 2 in V for

5*smaller Qb•Paper design and prototypes of key components •No feasibility demonstration of all parameters by 2010 •Define (more) conservative beam parameters

(Emittances, Focusing, beam sizes at IP) which will have been addressed (or demonstrated) by 2010:•In facilities in operation or being approved for construction•In test facilities (ATF)•Base 500 GeV design (first stage) on more

conservative parameters•Strategy recommended at CLIC07 and supported by ACE•Increase credibility of the first stage (first to be built)•Larger beam dimensions at IP easier to achieve and measure•Relaxed stability tolerances

Conservative Final Focus parametersWhat is conservative after ATF2?

• Scaling ATF2 parameters (L*=1m, βx*= 4mm, βy*= 0.1mm ) to L*=4.3m gives βx*= 17mm, βy*= 0.43mm (ILC betas!)

• ATF2-based-conservatism is too bad for CLIC!• Why not lowering ATF2 betas?:• P. Bambade has already proposed a factor 2• Strategy: Join P. Bambade and push ATF2 betas as low as possible (and/or

push L* up).• Assuming ATF2 betas reach 2,0.05 mm (factor 2 lower than design). The

conservative CLIC betas would be • (8.6, 0.21)mm for L*=4.3m• (7.0, 0.17)mm for L*=3.5m

Rogelio Tomas Garcia Conservative FFS after the ATF2 ? 19/02/08

J.P.Delahaye CLIC design committee (26/08/08) 4

Vertical emittance from SLS

Swiss Light Source achieved 2.8pm, the lowest geometrical vertical emittance, at 2.4 GeV, corresponding to ~10nm of normalised emittance

Below 2pm, necessitates challenging alignment tolerances and low emittance tuning (coupling + vertical dispersion correction)

Seems a “safe” target vertical emittance for CLIC damping rings

Y. Papaphilippou

ph

ysic

al vert

ical em

itta

nce

[pm

]

J.P.Delahaye CLIC design committee (26/08/08) 5

5

Horizontal emittance scaled from NSLS II

PARAMETER Valuesenergy [GeV] 3

circumference [m] 791.5

bunch population [109] 11.8

bunch spacing [ns] 1.9

number of bunches 700

rms bunch length [mm] 2.9

rms momentum spread [%] 0.1

hor. normalized emittance [µm] 2.9

ver. normalized emittance [nm] 47

lon. normalized emittance [eV.m] 8700

coupling [%] 0.64

wiggler field [T] 1.8

wiggler period [cm] 10

RF frequency [GHz] 0.5 Scaling of emittance with beam

energy and bunch population including longitudinal emittance and IBS yields:

= 2.4µm In this respect, a normalised

horizontal emittance of 2µm is reasonable

Y. Papaphilippou

ph

ysic

al h

ori

zon

tal em

itta

nce [

nm

]

CLIC emittances: present and conservativeEpsx/Epsy NLC ILC CLIC 500 GeV CLIC 3 TeV

present Cons. present

Bunch population (109)7.5 20 3.72 3.72 3.72

DR: εx/εy (mm·rad/ nm·rad)

2.2/13 8/20 0.55/5 2/10 0.55/5

Mult Fact: FF/DR1.6/3 1.25/2 1.2/4 1.5/4 1.2/4

FF: εx/εy (mm·rad/ nm·rad)

3.6/40 10/40 0.66/20 3/40 0.66/20

bx* / by

* (mm)Scaled to l* = 4.3 m 8/0.11 20/0.4 15/0.1 8/0.1 4/0.09

Luminosity in 1% enegry (1034) 2 2 0.7 0.32 2

Factor 6 in luminosity is missing

C L I CC L I C

CLIC-ACE, 16 Jan. 2008Alexej Grudiev, Structure optimization.

Optimization constraints at 3TeV

Beam dynamics (BD) constraints based on the simulation of the main linac, BDS and beam-beam collision at the IP:

• N – bunch population depends on <a>/λ, Δa/<a>, f and <Ea> because of short-range wakes

• Ns – bunch separation depends on the long-range dipole wake and is determined by the condition:

Wt,2 · N / Ea= 10 V/pC/mm/m · 4x109 / 150 MV/m

RF breakdown and pulsed surface heating (rf) constraints:

• ΔTmax(Hsurfmax, tp) < 56 K

• Esurfmax < 250 MV/m

• Pin/Cin·(tpP)1/3 = 18 MW·ns1/3/mm

Difference in BD constraints for 3TeV and 500GeV

D. Schulte

Difference in BD constraints for 3TeV and 500GeV

D. SchulteL0.01/L = 0.4 at 3 TeV

Beam dynamics constraints at 500GeV and conservative emittance

Short range wake limits bunch charge

Long range wake amplitude on the

second bunch limits the bunch spacing:

Wt(2) * N / <Ea>

< 20 V/pC/m/mm * 4x109 / 150 MV/m

10 V/pC/m/mm has been used for 3TeV

εx,y = 3μm, 40nmβx,y = 8mm, 0.1mm

Other constraints• RF constraints remains the same as for 3TeV:

– P/C*tp1/3 < 18 Wu(MW/mm*ns1/3)

– Esmax < 260 MV/m

– ΔTmax < 56 K– RF phase advance per cell: 120 or 150 degree

• No 3TeV constraints:– Structure length Ls more than 200 mm; – Pulse length tp is free– Bunch spacing Ns is free

• 3TeV constraints Ns = 6:1. Ls = 230 mm; tp = 242 ns2. Ls = 480 mm; tp = 242 ns3. Ls = 480 mm; tp = 483 ns

Figure of Merit

CLIC_G@3TeV: 9.1

N

L

EeP

L b

cml

1

Rf-to-beam efficiency

Repetition rate for L1 = 2 [1034/s·cm2]

CLIC_G@3TeV: 50 Hz

If repetition rate is limited to 50 Hz

2

1

3

Case 2 has been chosen:• As close as possible to 100 MV/m• Cost considerations which were

not included in the optimization• Beam current in injectors is only

~2 times higher than for 3 TeV• RF constraints for PETS are the

lowest

Parameters of CLIC main linac in different cases

case3TeV nominal

0 1 2 3

Structure CLIC_G CLIC_G CLIC_G

Luminosity : L1[1034cm-2s-1] 2.03 0.31 0.53 1.00 1.92

Repetition frequency: frep[Hz] 50.0 50.0 50.0 50.0 50.0

RF input power: Pl [MW/linac] 50.4 8.4 12.0 12.2 17.5

RF energy per pulse: Pl /frep [kJ/linac] 1006 167 239 243 350

• Case 0: if we do not change anything then Luminosity reduction is ~6• Case 1: Changing the scheme but keeping CLIC_G. Reducing gradient to 67

MV/m but doubling pulse length results in Luminosity reduction only ~4. It implies twice less PETS per meter as well as twice less turn-arounds.

• Case 2: Keeping the nominal scheme but replacing only the accelerating structures. Luminosity reduction ~2.

• Case 3: Both the scheme and the structures are changed. Reducing gradient by 2 and increasing structure length and pulse length by 2. No luminosity reduction. It implies twice less PETS and turn-arounds.

Parameters of the structures for 500 GeV

Case3TeV nominal

0 1 2 3

Structure CLIC_G CLIC_G CLIC_G

Average accelerating gradient: <Ea> [MV/m] 100 100 67 80 50

rf phase advance: ∆φ[o] 120 120 120 150 150

Average iris radius/wavelength: <a>/λ 0.11 0.11 0.11 0.145 0.16

Input/Output iris radii: a1,2 [mm] 3.15, 2.35 3.15, 2.35 3.15, 2.35 3.97, 3.28 4.9, 3.1

Input/Output iris thickness: d1,2 [mm] 1.67, 1.00 1.67, 1.00 1.67, 1.00 2.08, 1.67 1.04, 1.04

Group velocity: vg(1,2)/c [%] 1.66, 0.83 1.66, 0.83 1.66, 0.83 1.88, 1.13 4.94, 1.21

N. of reg. cells, str. length: Nc, l [mm] 24, 229 24, 229 24, 229 19, 229 43, 480

Bunch separation: Ns [rf cycles] 6 6 6 6 6

Luminosity per bunch X-ing: Lb× [m-2] 1.22×1034 0.2×1034 0.13×1034 0.57×1034 0.47×1034

Bunch population: N 3.72×109 3.69×109 2.96×109 6.8×109 6.4×109

Number of bunches in a train: Nb 312 312 796 354 810

Filling time, rise time: τf , τr [ns] 62.9, 22.4 62.9, 22.4 62.9, 22.4 50.3, 15.3 64.7, 13.9

Pulse length: τp [ns] 240.8 240.8 482.8 242.1 483.1

Input power: Pin [MW] 63.8 63.6 30.4 74.2 69.7

Pin/CtPp

1/3[MW/mm ns1/3] 18 18 12 17 17

Max. surface field: Esurfmax [MV/m] 245 245 170 250 240

Max. temperature rise: ΔTmax [K] 53 53 35 56 56

Efficiency: η [%] 27.7 27.5 39.5 39.6 59.2

Figure of merit: ηLb× /N [a.u.] 9.1 1.5 1.8 3.3 4.4

Conclusions• Conservative set of parameters for emittances and final focusing

has been elaborated based on the existing or approved for construction facilities

• Based on this set, beam dynamics (BD) constraints has been modified.

• Optimization of CLIC main linac accelerating structure has been performed taking into account the modified BD constraints, the RF constraints (the same as for 3 TeV) and additional constraints coming from the compatibility to the 3TeV CLIC.

• As a result, new optimum structure with bigger aperture operating at 80 MV/m is proposed for 500 GeV CLIC. The use of this structure instead of CLIC_G increases the luminosity by factor 3.

• It also implies doubling the bunch charge which, on the other hand, seems to be feasible.

Beam power for L1 = 2 [1034/s·cm2]

CLIC_G@3TeV: 14 MW/beam

Input power for L1 = 2 [1034/s·cm2]

CLIC_G@3TeV: 50.4 MW/linac

If power loss per meter is limited to nominal

(Pl-Pb)*<Ea> = const