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.