1. Kicker and RF systems for Damping Rings
CLIC Technical Committee
Kicker and RF systems for Damping Rings
F. Antoniou, M. Barnes, T. Fowler, A. Grudiev, Y. Papaphilippou
February3rd, 2009

2. Design optimisation for CDR (2010) M. Korostelev, PhD thesis, 2006
Outline
CLIC damping rings (DR) layout and parameters
DR injection and extraction optics
DR septa and kicker parameters
DR RF system specifications
Pre-damping rings (PDR) parameters
Kicker and RD considerations for PDR
Summary
CLIC parameter note 2005
CLIC parameter note 2008
Design optimisation for CDR (2010)
M. Korostelev, PhD thesis, 2006
03/02/09
CTC, YP

3. CLIC damping ring layout
03/02/09
M. Korostelev, PhD thesis, EPFL 2006

4. DR bunch structure and timing
CLIC DR timing parameters
Old
(2005)
New
(2008)
Repetition rate [Hz]
150 50
Number of bunches
110
312
Number of trains 4 1
Bunch spacing [ns]
0.533
0.500
Revolution Time [μs]
1.2
>1.2
Machine pulse [ms]
6.67 20
H/V/L damping times [ms]
2.8/2.8/1.4
1.5/1.5/0.76
Reduction of repetition rate from 150 to 50Hz leaves enough time for the emittances to reach their equilibrium
Bunch spacing increased almost to same level as for the interleaved train scheme
Interleaved train scheme abandoned
Extraction kicker rise time relaxed
Injection and extraction process simplified
312 bunches with 0.5ns spacing, fill 13% of the rings 4

5. DR injection/extraction optics
Injection and extraction system placed at the same area, upstream of the super-conducting wigglers
Kickers placed at maximum beta functions for minimum deflection angle
Septa and kickers share the same cell
Additional cells to be added in order to increase available space for elements and protection system
Phase advance between injection (extraction) septa and kickers of around π/2
M. Korostelev, PhD thesis, EPFL 2006
03/02/09
CTC, YP

6. DR Septa parameters
DR septa parameters
SEP-1
SEP-2
Effective length [m]
0.4
0.5
Bending angle [mrad] 13 42
Field integral [T.m]
0.11
0.34
Blade thickness [mm] 5
Same parameters for injection/extraction elements due to optics mirror symmetry
Septum parameters are scaled from NLC damping rings
Two DC modules with blade thickness of 5 and 13mm
Effective length can be increased to 2m if additional cells are added
Larger septa blade thicknesses and smaller peak field
03/02/09
CTC, YP

7. DR Kicker parameters Rise and fall time significantly increased
Effective length can be increased to 2m
Smaller peak field
Kicker stability refers to field uniformity and pulse-to-pulse stability
Tolerance of 0.1σx beam centroid jitter
DR kicker parameters
Old
New
Rise and fall time [ns] 25
1000
Flat top [ns]
142
~160
Repetition rate [Hz]
150 50
Effective length [m]
0.4
0.4-2
Aperture [mm] 20
Kick [mrad]
2.45 3
Field [Gauss]
500
<610
Kicker stability
inj
ext
Second kicker in transfer phase advance of π for jitter compensation (as in NLC/ATF)
Achieved 2.8x10-4 at ATF for shorter rise/fall times and flat top
Third kicker, delay line and RF deflector are removed
Contribution to beam impedance should be addressed (budget of a few MΩ/m in transverse and a few Ω in longitudinal) –external circuit may be important

8. DR RF system RF frequency of 2GHz
A. Grudiev
CLIC DR parameters
Circumference [m]
365.2
Energy [GeV]
2.42
Momentum compaction
0.8x10-4
Energy loss per turn[MeV]
3.9
Maximum RF voltage [MV]
4.115
RF frequency [GHz]
2.0
RF frequency of 2GHz
Power source is an R&D item at this frequency
High peak and average power of 5 and 0.7MW
Strong beam loading transient effects
Beam power of ~5 MW during 156 ns, no beam during other 1060 ns
Small stored energy at 2 GHz
Wake-fields and HOM damping should be considered
High energy loss per turn at relatively low voltage results in large φs of 72o (see also LEP)
Bucket becomes non-linear
Small energy acceptance of 0.8%
RF voltage increased to 5MV (energy acceptance of 2.6%)
As longitudinal emittance is decreased (3.5 keV.m), horizontal emittance increased to 470nm
03/02/09
CTC, YP

9. PDR working parameters
F. Antoniou
Parameter [unit]
Value
beam energy [GeV]
circumference [m]
bunch population [E+09]
bunch spacing [ns]
bunches per train
rms bunch length [mm]
rms momentum spread [%]
hor. Emittance w/o IBS [nm]
no. of arc bends
arc-dipole field [T]
length of arc dipole [m]
number of wigglers
wiggler field [T]
length of wiggler [m]
wiggler period [cm]
mom. compaction [10-5]
RF frequency [GHz]
energy loss/turn [MeV]
RF voltage [MV]
h/v/l damping times [ms]
Revolution time [ns]
Repetition rate [Hz]
2.424
260.1
4.5
0.5
312
0.2
0.3
13000 30
1.7 1 20 2
4.7
1.54 16
2.7/2.7/1.35
870 50
312 bunches with 0.5ns spacing, fill 18% of the pre-damping rings
Designed for large momentum acceptance and fast damping
Large RF voltage, small momentum compaction factor
Injected Parameters e- e+
Bunch population [109]
4.4
6.4
Bunch length [mm] 1 5
Energy Spread [%]
0.1
2.7
Hor.,Ver Norm. emittance [nm]
100 x 103
9.3 x 106
PDR Extracted specs
Value
Bunch length [mm] 10
Energy Spread [%]
0.5
Hor. Norm. emittance [nm]
63000
Ver. Norm. emittance [nm]
1500 9

10. PDR injection/extraction optics
Kickers
Septa
PDR kicker parameters
Value
Rise and fall time [ns]
700
Flat top [ns]
~160
Repetition rate [Hz] 50
Effective length [m] 2
Aperture [mm] 20
Kick [mrad]
Field [Gauss]
150
Kicker stability
inj
ext
Injection and extraction system placed at symmetric points of the matching area, upstream of the super-conducting wigglers
Kickers placed at maximum beta functions with available space of around 2m
Phase advance between septa and kickers of around π/2
Kicker stability at extraction as DR injection
03/02/09
CTC, YP

11. PDR RF system RF frequency of 2GHz
Power source is an R&D item at this frequency
Peak and average power of 2.1 and 0.4MW
Transient beam loading effects
Beam power of ~2MW during 156 ns, no beam during other 710 ns
Wake-fields and HOM damping should be considered
Peak and average current of 1.4 and 0.24A
High RF voltage of 16MV in order to assure large momentum acceptance of 21%
Especially for longitudinal stacking of polarized positrons
CLIC PDR parameters
Circumference [m]
260.1
Energy [GeV]
2.42
Momentum compaction
0.5x10-4
Energy loss per turn[MeV]
1.5
Maximum RF voltage [MV] 16
RF frequency [GHz]
2.0
Space reserved in the FODO straight section upstream of the wigglers and the matching section
Geometrical acceptance of around 40mm
03/02/09
CTC, YP

12. Summary DR injection and extraction systems DR RF system
Extraction process simplified (1 train)
Main issues the kicker stability
DR RF system
RF voltage increased for larger energy acceptance
Main issue the RF frequency (power source) and transient beam loading
PDR kickers are more conventional
PDR RF system
RF frequency of 2GHz is the main issue
Large RF voltage needed (space)
Design should target for low impedance and general impact to collective effects (HOM damping) should be addressed
03/02/09
CTC, YP