1. Follow-up on Damping Ring design
CLIC Technical Comittee
Follow-up on Damping Ring design
Yannis PAPAPHILIPPOU
March 9th, 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. Schematic layout e- Damping Ring e+ Damping Ring e- Pre-damping Ring

4. PDR design
F. Antoniou, CLIC09
Injected Parameters e- e+
Bunch population [109]
4.4
6.4
Bunch length [mm] 1 10
Energy Spread [%]
0.1 8
Hor.,Ver Norm. emittance [nm]
100 x 103
7 x 106
Main challenge: Large input emittances especially for positrons to be damped by several orders of magnitude (large energy acceptance and dynamic aperture)
Fast damping achieved with conventional hybrid PM wigglers (PETRA III)
No major technological challenges apart from RF system (as for the DR), extraction kickers (relaxed tolerance but still challenging) and maybe vacuum technology (coatings)
Y.P., 09/03/2010
CTC

5. DR layout Racetrack shape with
S. Sinyatkin, et al., LER 2010
Racetrack shape with
96 TME arc cells (4 half cells for dispersion suppression)
38 Damping wiggler FODO cells in the long straight sections (LSS)
Space reserved upstream the LSS for injection/extraction elements and RF cavities
Y.P., 09/03/2010
CTC

6. Arc cell magnets
S. Sinyatkin, et al., LER 2010
2.36m-long TME cell with bends including small gradient (as in NLC DR and ATF)
Drift space and magnet lengths rationalised
Preliminary design of main magnets already available
Y.P., 09/03/2010
CTC 6

7. Power supplies
Power estimated as magnet design not yet fully available
Mostly conventional parameters
Y.P., 09/03/2010
CTC 7

8. Wigglers’ effect with IBS
Stronger wiggler fields and shorter wavelengths necessary to reach target emittance due to strong IBS effect
Current density can be increased by different conductor type
Nb3Sn can sustain higher heat load (potentially 10 times higher than NbTi)
Two wiggler prototypes
2.5T, 5cm period, built and currently tested by BINP
2.8T, 4cm period, designed by CERN/Un. Karlsruhe
Mock-ups built and magnetically tested
Prototypes to be installed in a storage ring (ANKA, CESR-TA, ATF, ALBA) for beam measurements
Nb3Sn SC
wiggler
NbTi SC
BINP PM
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

9. Permanent magnet performance
Pure permanent magnet not able to reach very high field (i.e. 1.2T for Sm2Co17)
Pole concentrators used (e.g. vanadium permendur) to enhance pole field to a max value of 2.3T
Not more than 1.1T reached for 40mm period and 14mm gap
Higher field of 1.8T reached for 100mm period
Max field of 2.3T can be reached for a gap/period ratio of ~0.1, (140mm period for 14mm gap)
In that case, output emittance gets more than doubled (>800nm)
In order to reach target DR performance, number of wigglers has to be increased by more than a factor of 2, i.e. ~40% of ring circumference increase
Only way to reach high field for high gap/period ratio is by using super-conducting wigglers
Simulations by P. Vobly
Scaling by Halbach

10. Wiggler short prototypes
CERN
BINP
Regular coil
Corrector coils with
individual PS
Iron yoke
End coils to compensate the first
and the second integral
Y.P., 09/03/2010
CTC

11. BINP NbTi Wiggler
Present design uses NbTi wet wire in separate poles clamped together
Wire wound and impregnated with resin and prototype assembled including corrector coil and quench protection system by spring 2009
Field measurements in June showing poor performance (reaching 420 instead of 660A) due to mechanical stability problems (GFP separators)
Magnet delivered at CERN for further measurements and verification
New design under evaluation by BINP and CERN magnet experts

12. CERN prototype with NbTi wire
50 mm period
40 mm period
R. Maccaferi et al.
Crash test program at CERN with 40mm mock-up using NbTi wire
Reached peak field of 2.5T at 1.9K (2T at 4.2K)
Current density extrapolated to 50mm, provides more than 2.5T field
Currently continuing with Nb3Sn winding tests and first results expected during this summer

13. Collective effects in the DR
G. Rumolo
Electron cloud in the e+ DR imposes limits in PEY (99.9% of synchrotron radiation absorbed in the wigglers) and SEY (below 1.3)
Cured with special chamber coatings
Fast ion instability in e- DR, molecules with A>13 will be trapped (constrains vacuum pressure to around 0.1nTorr)
Other collective effects in DR
Space charge (large vertical tune spread of 0.19 and 10% emittance growth)
Single bunch instabilities avoided with smooth impedance design (a few Ohms in longitudinal and MOhms in transverse are acceptable for stability)
Resistive wall coupled bunch controlled with feedback (100s of turns rise time)
Chambers
PEY
SEY ρ
[1012 e-/m3]
Dipole
1.3
0.04
1.8 2
0.0576 7 40
Wiggler
0.6
0.109 45
1.5 70 80
ρwig = 5x1012 m-3, ρdip = 3x1011 m-3
Y.P., 09/03/2010
CTC 13

14. 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

15. DR radiation parameters
Synchrotron radiation
DR radiation parameters
PDR DR
Power per dipole [kW]
3.3
1.2
Power per wiggler [kW]
15.2
16.1
Total power [MW]
0.7
1.3
Critical energy for dipole [keV]
16.0
19.0
Critical energy for wiggler [keV]
9.3
13.6
Radiation opening angle [mrad]
0.11
Synchrotron radiation power from bending magnets and wigglers
Critical energy for dipoles and wigglers
Radiation opening angle
90% of radiation power coming from the 76 SC wigglers
Design of an absorption system is necessary and critical to protect machine components and wigglers against quench
Radiation absorption equally important for PDR (but less critical, i.e. similar to light sources)
Y.P., 09/03/2010
CTC

16. Radiation absorption scheme
A 4-wigglers scheme
Gap of 13mm (10W/m)
Combination of collimators and absorbers (similar to PETRAIII)
Terminal absorber at the end of the straight section (10kW)
K. Zolotarev, CLIC09 16

17. 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 (CTF3 experience)
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)

18. 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., 09/03/2010
CTC

19. Alignement
M. Boege, LER2010
Present tolerances not far away from ones achieved in actual storage rings
SLS achieved 2.8pm emittance
DIAMOND claim 2.2pm and ASP quoting 1-2pm (pending direct beam size measurements)
Participate in low emittance tuning measurements in light sources (SLS) and CESR-TA
Y.P., 09/03/2010
CTC

20. Technology issues beyond CDR
Detailed magnet design and wiggler measurements
Instrumentation
Measurement of very low vertical emittance (beam sizes of a few microns) quite challenging, especially in a bunch-by-bunch mode for wide dynamic range
Cryogenics
Does not seem a problem but wiggler technology and performance depends on it
Timing stability tolerances
Need to evaluate phase jitter (LLRF system)
Detailed vacuum chamber design
Impedance, implications of “cold” vacuum chambers
Girders, vibrations and stabilisation
Feedback system
Especially challenging in bunch-by-bunch mode at 2GHz
CLIC machine protection using the DR (or PDR)
Blow-up (orbit, coupling, kickers?) for dumping a “safe” beam
Y.P., 09/03/2010
CTC