CLIC main linac acc. structure

1
The new CLIC parameters
29.10.2007 Alexej Grudiev
2
Linear Collider major parameters

• Luminosity

• High Beam Power (several MWatts)
• Wall-plug to beam transfer efficiency as high as
  possible (several )
• Generation preservation of beam emittances at
  I.P. as small as possible (few nmrad)
• Beam focusing to very small dimentions at IP
  (few nm)
• Beamstrahlung energy spread increasing with c.m.
  colliding energies

3
CLIC overall layout
Drive Beam Generation Complex
CLIC overall layout 3 TeV
Main Beam Generation Complex
4
Old and new CLIC main parameters
Old (2005) New (2007)
Center-of-mass energy 3 TeV 3 TeV
Peak Luminosity 6.51034 cm-2 s-1 71034 cm-2 s-1
Peak luminosity (in 1 of energy) 3.31034 cm-2 s-1 21034 cm-2 s-1
Repetition rate 150 Hz 50 Hz
Loaded accelerating gradient 150 MV/m 100 MV/m
Main linac RF frequency 30 GHz 12 GHz
Overall two-linac length 28 km 42 km
Bunch charge 2.56109 3.72109
Bunch separation 0.267 ns 0.5 ns
Beam pulse duration 58.4 ns 156 ns
Beam power/beam 20 MW 14 MW
Hor./vert. normalized emittance 660 / 10 nm rad 660 / 20 nm rad
Hor./vert. IP beam size bef. pinch 60 / 0.7 nm 40 / 1 nm
Total site length 33 km 48 km
Total power consumption 418 MW 322 MW
http//clic-meeting.web.cern.ch/clic-meeting/clict
able2007.html
5
CLIC main linac optimization model
ltEagt, f, ?f, ltagt, da, d1, d2
BD
Bunch population
Cell parameters
N
Q, R/Q, vg, Es/Ea, Hs/Ea
Q1, A1, f1
Structure parameters
Bunch separation
BD
Ns
Ls, Nb
?, Pin, Esmax, ?Tmax
rf constraints
Cost function minimization
YES
NO
6
Optimization constraints

• 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 ltagt/?, ?a/ltagt, f
  and ltEagt because of short-range wakes
• Ns bunch separation depends on the long-range
  dipole wake and is determined by the condition
• Wt,2 N / ltEagt 10 V/pC/mm/m 4x109 / 150 MV/m

• RF breakdown and pulsed surface heating (rf)
  constraints
• ?Tmax(Hsurfmax, tp) lt 56 K
• Esurfmax lt 250 MV/m
• Pin/Cintp1/3 lt 18 MWns1/3/mm _at_ X-band
  (frequency dependent)

7
Frequency scaling of power constraint
Experimental data at X-band and 30 GHz become
available 2006
Scaled structures
Scaled structures show the same gradient at
X-band and at 30 GHz Eatp1/6 const
Pin/Cintp1/3f const
8
Optimization Cost functions
1. Luminosity per linac input power (performance)
Figure of Merit (FoM)
Collision energy is constant
2. Total cost parametric model (become available
2006) Investment cost Exploitation cost for
10 years Ct Ci
Ce
9
Optimization parameter space
N structures 7 14 2 24 60 61 4 -------------- 68.
866.560
All structure parameters are variable ltEaccgt
90 150 MV/m, f 10 30 GHz,
?f 120o, 150o, ltagt/? 0.09 - 0.21, ?a/ltagt
0.01 0.6, d1/? 0.025 - 0.1, d2 gt d1
Ls 100 1000 mm.
10
CLIC performance and cost versus gradient
Ecms 3 TeV L(1) 2.0 1034 cm-2s-1
Performance
Cost
Previous
Previous
New
New
Optimum

• Performance increases with lower accelerating
  gradient (mainly due to higher efficiency)
• Flat cost variation in 100 to 130 MV/m with a
  minimum around 120 MV/m

11
CLIC performance and cost versus frequency
Ecms 3 TeV L(1) 2.0 1034 cm-2s-1
Performance
Cost
New
Previous
Optimum
Previous
New
Optimum

• Maximum Performance around 14 GHz
• Flat cost variation in 12 to 16 GHz frequency
  range with a minimum around 14 GHz

12
CLIC Performance and Cost optimization
Performance (a.u.)
CLIC Old Parameters Accelerating field 150
MV/m RF frequency 30 GHz
CLIC New parameters Accelerating field 100
MV/m RF frequency 12 GHz
Total cost (a.u.)
13
Interplay between BD and RF
L1/N
BD optimum aperture ltagt 2.6 mm
Why X-band ? Crossing gives optimum frequency
RF optimum aperture ltagt/? 0.1 0.12
14
Summary

• CLIC main linac optimization model taking into
  account complex interplay between beam dynamics
  and rf performance has been developed over the
  past few years
• In 2006,
• new experimental data both at 30 GHz and at
  X-band have been obtained
• CLIC total cost parametric model has become
  available
• Optimization of CLIC frequency and gradient has
  been done which (together with some other
  considerations) resulted in major change of CLIC
  parameters from 150MV/m at 30GHz to 100MV/m at
  12GHz