CLIC: RF and Beam dynamics constraints in cavity designing

Vasim

CLIC: Basic parameters

• CLIC aims at operating frequency of 12 GHz and an average accelerating gradient of 100 MV/m

• For X-band frequency the aperture radii of the cells are comparatively smaller and need to withstand high gradients for efficient acceleration.

• This gives RF and beam dynamics constraints to designing a cavity.

Constraints

RF constraint

1)

2) Pulsed surface heating

3) Cost factor

Beam dynamics constraints

1)For a given structure, no. of particles per bunch N is decided by the <a>/λ and Δa/<a>2)Maximum allowed wake

Rest of the bunches should see a wake less than this wake(i.e. No recoherence).

mMVEsur /260max

KT 56max

mmnsMWCP inpin33 18

N

XmXmmpCVWt

9

1

104///667.6

Power and field in a tapered structure

PIQ

R

vQv

P

dz

dP

gg

'

gv

P

Q

RE

'

Solving eq.1 numerically we get power at any given point (dist.) in the structure and using eq.2 we get field at that pont.

1) 2)

IP parameters

Power and field in a CLIC_ZC structureBeam loadedUnloaded

<Eacc>=130.7 MV/m<Eacc>=100 MV/m

Surface fields and pulse heatingUnloaded condition

Beam loaded condition

CLIC_ZC: Efficiency & FOM

..65.83

96.03.27

10

10%

%03.27..

..

076.11..

994.2..

96.05.0

1563126

57

9

34%1

uaX

N

LuFOM

EP

EB

JttPEP

JLtEaccIEB

AnsNqI

nsfXt

nsvLt

BeamRF

BeamRF

fbin

b

accb

gf

Structure CLIC_G CLIC_ZC

Bunch population 3.7X109 3.0X109

Bunch separation 6 6

Filling time (ns) 62.9 57

Input power (MW) 63.8 52

Pin Tp1/3/C (MWns1/3/mm) 18 15.32

Max. Esur (MV/m) 245 275

Max. temp/. rise ΔTmax(K) 53 15

Efficiency (%) 27.7 27

Luminosity (in1%) 1.22X1034 9.6X1033

FOM (a.u.) 9.1 8.65

Comparison

Next• I am working on next ZC structure in which

surface electric field will be below the limit.• It should be noted that these calculations are

based on zero crossing of wake and assuming 0.5 ns bunch spacing.

• In near future I would like to explore the structure with 2 GHz bandwidth, Q~200, bunch spacing will be appro. 0.667 ns (8 cycles).

• These parameters will take care of wakes without affecting the efficiency significantly but surface fields will be a real problem.