1. Status of CTC activities for the Damping rings
CLIC Technical Committee
Status of CTC activities for the Damping rings
Yannis PAPAPHILIPPOU
February 23rd, 2010

2. DR parameters and challenges
High-bunch density
Emittance dominated by Intrabeam Scattering, driving energy, lattice, wiggler technology choice and alignment tolerances
Electron cloud in e+ ring imposes chamber coatings and efficient photon absorption
Fast Ion Instability in the e- ring necessitates low vacuum pressure
Space charge sets energy, circumference limits
Repetition rate and bunch structure
Fast damping achieved with wigglers
RF frequency reduction considered due to many 2GHz (power source, high peak and average current)
Output emittance stability
Tight jitter tolerance driving kicker technology
Positron beam dimensions from source
Pre-damping ring challenges (energy acceptance, dynamic aperture) solved with lattice design
Target Parameters
NLC
CLIC
bunch population (109)
7.5
4.1
bunch spacing [ns]
1.4
0.5
number of bunches/train
192
312
number of trains 3 1
Repetition rate [Hz]
120 50
Ext. hor. norm. emittance [nm]
2370
<500
Ext. ver. norm. emittance [nm]
<30
<5
Ext. long. norm. emittance [keV.m]
10.9
<4
Inj. hor. norm. emittance [μm]
150 63
Inj. ver. norm. emittance [μm]
1.5
Inj. long. norm. emittance [keV.m]
13.18
1240
Design Parameters
CLIC
Energy [GeV]
2.86
Circumference [m]
493.2
Energy loss/turn [Me]
5.8
RF voltage [MV]
7.4
Compaction factor
6e-5
Damping time x / s [ms]
1.6 / 0.8
Number of arc cells / wigglers
100/76
Dipole/ wiggler field [T]
1.4/2.5

3. Wiggler prototypes Two wiggler prototypes
2.5T, 5cm period, built and currently tested by BINP
2.8T, 4cm period, designed by CERN/Un. Karlsruhe
BINP prototype did not reach target performance (new prototype)
CERN prototype 40mm period) reached field performance target 1.9K or 50mm)
On-going work on Nb3Sn mock-up
Nb3Sn SC
wiggler
NbTi SC
BINP PM
50 mm period
40 mm period
Parameters
BINP
CERN
Bpeak [T]
2.5
2.8
λW [mm] 50 40
Beam aperture full gap [mm] 13
Conductor type
NbTi
Nb3Sn
Operating temperature [K]
4.2

4. Radiation absorption scheme
K. Zolotarev, CLIC09
A 4-wigglers scheme
Gap of 13mm (10W/m)
Combination of collimators and absorbers
Terminal absorber at the end of the straight section (10kW)
Mechanical design and impedance estimation for CDR
Implication with cryogenics 4

5. Coatings for e- Cloud Mitigation
M. Taborelli LER2010
Amorphous carbon coating showed reduction of e-cloud activity in CESRTA (better than any other coating)
Continue coating characterization with additional chambers
Understand photo-emission yield and pressure curves (work also in the SPS)
Identify collaborations in light source community for chamber tests (SOLEIL, ALBA)
bare Al
CESRTA e+
TiN
TiN new
a-C CERN

6. RF system RF frequency of 2GHz
R&D needed for power source
High peak and average power of 6.6 and 0.6MW
Strong beam loading transient effects
Beam power of 6.6MW during 156 ns, no beam during other 1488 ns
Small stored energy at 2 GHz
Wake-fields and HOM damping should be considered
1GHz frequency being evaluated (2 trains with 1ns bunch spacing)
Easier extrapolation from existing designs (e.g. NLC)
Lowering peak current and thus transient beam loading
Delay line for train recombination
A. Grudiev, CLIC08
CLIC DR parameters
Circumference [m]
493.2
Energy [GeV]
2.86
Momentum compaction
0.6x10-4
Energy loss per turn[MeV]
5.9
Maximum RF voltage [MV]
7.4
RF frequency [GHz]
2.0
Decision on RF frequency by end of March 2010
Conceptual design including HOM damping to be done for CDR (external collaboration)

7. Kicker stability
M. Barnes CLIC09
Kicker jitter translated in beam jitter in IP, withσjit ≤0.1σx
Tolerance typically ~10-4
Double kicker system relaxes requirement, i.e. ~3.3 reduction
Striplines required for achieving low longitudinal coupling impedance
Significant R&D needed for PFL (or alternative), switch, transmission cable, feedthroughs, stripline, terminator (PhD thesis student at CERN)
Should profit from collaboration with ILC and light source community
Y.P., 03/02/2010
ACE 2010