1. CLIC Technical committee
Machine Experiments, technical design and prototyping for the CLIC damping rings 
Yannis PAPAPHILIPPOU
Thanks to M. Barnes, S. Calatroni, P. Chiggiato, A. Grudiev, T. Lefevre, R. Maccaferri, M. Karppinen, G. Rumolo D. Schörling, H. Schmickler, M. Taborelli
June 15th, 2010

2. DR technology challenges
RF system
Baseline 1GHz system more conventional but transient beam loading is a challenge
Train recombination is needed
Concept for 2GHz powering system
Ultra-low vertical emittance
Tight alignment tolerances and challenging diagnostics for beam size monitoring
Ultra-low emittance and fast damping achieved with super-conducting damping wigglers
Demanding magnet technology combined with cryogenics and high heat load from synchrotron radiation (absorption)
Two stream effects
e--cloud reduced with vacuum chamber coatings (low photo and secondary emission yield)
Fast-ion instability avoided with low vacuum pressure
Multi-bunch effects
Low-impedance chamber design and dedicated feed-back system
Output emittance stability
Kicker and RF deflector technology
Design Parameters
CLIC
Energy [GeV]
2.86
Circumference [m]
420.56
Energy loss/turn [MeV]
4.2
RF voltage [MV]
4.9
Compaction factor
8x10-5
Damping time x / s [ms]
1.88/0.96
Number of arc cells / wigglers
100/52
Dipole/ wiggler field [T]
1.4/2.5

3. 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 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

4. Several wigglers similar to the MAX-Wiggler have been built recently
List of superconducting wigglers with period < 70 mm produced by Budker INP, Russia
Year
Magn.Field
[T] (max)
# of full size poles
Period
[mm]
Magn. Gap
Vert. Apert.
Liq. He Cons. [litre/hr]
Multipole wiggler for ELETTRA (Italy)
2002
3.7 45 64
16.5 11
≈0.5
Multipole wiggler for CLS (Canada)
2005
2.2 61 34
13.5
9.5
<0.05
Multipole wiggler for DIAMOND (England)
2006
3.75 60
Multipole wiggler -2 for CLS (Canada)
2007
4.34 25 48
14.5 10
2009
4.25
Multipole wiggler for LNLS (Brazil)
4.19 31
18.4 14
Multipole wiggler for ALBA-CELLSc(Spain)
2.1
117
30.15
12.6
8.5
Contact person at Budker INP, Novosibirsk: Nikolai Mezentsev,

5. Wiggler short prototypes
CERN
BINP
Regular coil
Corrector coils with
individual PS
Iron yoke
End coils to compensate the first
and the second integral

6. BINP NbTi Wiggler
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 evaluated by BINP and CERN magnet experts
Preliminary measurement results indicate that the peak field is reached

7. CERN prototype with NbTi wire
50 mm period
40 mm period
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

8. CERN DR Wiggler Prototype plan
M. Karppinen
MILESTONES:
Vertical race-track short NbTi model (2 periods) tested at CERN Nov 2009
Vertical race-track short Nb3Sn model (2 periods) conceptual design completed Dec 2009
Single Nb3Sn coil completed and tested at CERN Apr 2010
Short model fabrication design completed May 2010
Short 1/2-model completed and tested in mirror configuration at CERN Aug 2010
Short model completed Dec 2010
Long prototype (2 m, 50 periods) conceptual design completed (CDR) Dec 2010
Short model acceptance tests completed at KIT Feb 2011
Central and end module models completed and tested Oct 2011
Prototype design completed (TDR) Dec 2011
BUDGET:
1) CERN Staff (cat.2): S. Russenschuck replacing R. Maccaferri
2) Doc. Student (paid by Gentner funds): D. Schoerling
Budget (kCHF)
2010
2011 (TBC)
Material 20
Design office 18 15
Workshop 32 30
FSU 50
Misc (travel etc) 24 5
TOTAL
144
120
HR (FTE)
2010
2011
CERN Staff (cat. 2) (1
0.8
CERN Staff (cat. 3)
0.6
0.7
Student & Associates(2 1

9. DR radiation parameters
Synchrotron radiation
DR radiation parameters DR
Power per dipole [kW]
1.2
Power per wiggler [kW]
16.1
Total power [MW]
1.3
Critical energy for dipole [keV]
19.0
Critical energy for wiggler [keV]
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)

10. Damping wiggler experiments
Need to test the wiggler on real beam conditions
Validate cryogenic performance, reliability and heat load evacuation (absorber)
Test quench performance under presence of beam and synchrotron radiation (especially for Nb3Sn)
Validate measured field quality (wiggler should be transparent to beam stability)
Can be combined with vacuum chamber tests (photo-emission yield, desorption)
Experimental set-up
Storage ring with available straight section of ~3m for installing wiggler and absorber downstream of a dipole or other insertion device
Ability to install the cryogenic system
Average current of ~200mA for testing absorber in similar radiation conditions
For using wiggler as an X-ray user insertion device, K-parameter can be adjusted by reducing wiggler field (need to have good field quality at lower currents)
Candidates
ALBA (interested for a full experimental program), ATF (reducing horizontal emittance for higher fields and IBS), CESRTA (positrons and IBS measurements), MAXIII (long experience with SC wigglers), SLS (TIARA-SVET work-package for ultra-low vertical emittance studies almost approved),…

11. 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)
Experimental program for testing coated vacuum chambers
SEY in CESRTA
PEY and desorption in a storage ring
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 11

12. Coatings for e- Cloud Mitigation
M. Taborelli LER2010
Bakeable system
NEG gives SEY<1.3 for > 180C
Evolution after many venting cycles should be studied
NEG provides pumping
Conceivable to develop a coating with lower activation T
Non-bakeable system
a-C coating provides SEY< 1 (2h air exposure), SEY<1.3 (1week air exposure)
After 2 months exposure in the SPS vacuum or 15 days air exposure no increase of e-cloud activity
Pump-down curves are as good as for stainless steel
No particles and peel-off
Very good results obtained at CESR-TA (although contaminated by silicon from kapton adhesive tape)
bare Al
CESRTA e+
TiN
TiN new
a-C CERN

13. Experimental Program for the Vacuum of CLIC-DR
P. Chiggiato
The vacuum chambers of the DR are bombarded by synchrotron radiation, electrons-positrons and ions. Such collisions induce gas desorption and photoelectron emission.
The most critical vacuum chambers are those in the wiggler magnets because the energetic particle deposition is coupled with the cryogenics constraints.
The experimental program should follow three lines:
1- Design, production and static vacuum measurement of the wiggler beam pipe in cryogenic conditions.
2- Definition of the best surface treatment to fulfill the machine requirements (a-C, new NEG, conditioning). The characterization will be given by electron stimulated desorption in our labs.
3- For the chosen geometry of the DR beam pipes, measurements by a synchrotron radiation facility are proposed: desorption yield and photoelectron yield should be measured at a critical energy not far from the expected DR values. A collaboration with ESRF is being prepared. The aim is the installation of a dedicated bench in sector 31, using the large spectrum of the bending magnet. Preliminary test have been already carried out in 2009.
The next slides give an idea of the kind of measurements we would like to perform.
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

14. Electron Stimulated Desorption
P. Chiggiato
The system is baked at 300°C (24h); the sample is measured unbaked and after 2 h heating at some selected temperatures
Electron energy: 500 eV --Bombarding current: 1 mA--Estimated bombarded area: 200 cm2
Measurement taken after 100 s of bombardment
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

15. ESD of a-C films P. Chiggiato
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

16. Photon Stimulated Desorption
P. Chiggiato
Angle of incidence = 25 mrad
C coated chamber
Critical Energy
20.5 KeV
Angular acceptance
4.234 mrad
Photon Flux (E>10eV)
2.94x1015 photons (s mA)-1
Beam Energy
6 GeV
Typical Beam Current
185 mA 31
The system is baked at 300°C (24h). The sample is not baked.
The sample is separated from the rest of the system by a gate valve (at the diaphragm position, not pictured in the drawing); it is pumped by an auxiliary TMP during the bakeout of the system.
At the end of the bakeout, the gate valve is opened.
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

17. Photon Stimulated Desorption
P. Chiggiato
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

18. Photon Stimulated Desorption of a-C films
P. Chiggiato
The photon desorption yield of the unbaked C coated sample is lower than that of uncoated stainless steel.
CO and CO2 are the two leading gases; on the contrary, for stainless steel, H2 is the main desorbed gas.
In progress: measurement of baked carbon coated samples.
Paolo Chiggiato, AVS 56th, San Jose, November 11, 2009

19. RF system RF frequency of 2GHz
A. Grudiev
CLIC DR parameters
Circumference [m]
420.56
Energy [GeV]
2.86
Momentum compaction
8x10-5
Energy loss/turn [MeV]
4.2
RF voltage [MV]
4.9
4.4
RF frequency [GHz]
1.0
2.0
Peak/Aver. current [A]
0.66/0.15
1.3/0.15
Peak/Aver. power [MW]
2.8/0.6
5.5/0.6
RF frequency of 2GHz
R&D needed for power source
High peak and average power introducing strong transient beam loading to be handled by non-conventional LLRF system
The 1GHz frequency eases beam dynamics and drives the RF system to more conventional parameters for power source and LLRF
Extra complication with train recombination and RF deflector stability
Some schemes with longer bunch trains for 1TeV operation of the collider are not compatible with this bunch structure and PDR circumference
Choose as baseline in the RF frequency of 1GHz
Conceptual design for the 2GHz RF system has to be undertaken in parallel as a back-up solution

20. RF prototyping and experiments
A. Grudiev
Conceptual design of both systems should be ready for CDR
A second decision of the final RF frequency should be made in the course of the technical design ( )
RF deflector stability measurements in CTF3, for validating the train recombination
RF design including powering scheme and LLRF for both frequencies
Prototyping based on the final RF design parameters ( )
Design and build 1-2 RF modules and test them in the lab
Experimental program for validation ( )
High power RF design (high average and peak power level) 
LLRF system to provide beam stability (voltage and phase stability tolerances from RTML)
RF system itself in the presence of strong beam loading (both transient and the steady-state)
Experimental set-up
Install RF modules in storage ring with highest possible beam current and energy loss/turn
Bunch frequency should compatible 1 (or 2) GHz (may be used as a higher harmonic cavity)
Important to be able to fill ring unevenly for studying transient effects.
Necessary beam instrumentation allowing beam size and bunch length measurements down to the level of CLIC DR stability requirements

21. Kicker design Kicker jitter is translated in a beam jitter at the IP
M. Barnes
Kicker jitter is translated in a beam jitter at the IP
Stability Tolerance remains typically to a few 10-4
Double kicker system relaxes requirement, i.e. ~10 reduction
Striplines required for achieving low longitudinal coupling impedance
An “n-cell” inductive adder has been identified as a possible method for controlling pulse shape and achieving high reliability (redundancy of switches)
Significant R&D needed for switch, transmission cable, feed-throughs, stripline mechanical stability, terminator (PhD thesis student at CERN, collaboration with CIEMAT)
Y.P., 10/03/2010
CELLS meeting

22. Kicker experimental program
Purpose
Test kicker stability with beam
Validate low impedance design
Test double kicker system performance
Experimental set-up
Need available space to install kicker ( around 3m) without limiting geometrical acceptance
Low horizontal beam size is necessary for validating stability requirements
50Hz operation may be required for testing kicker reliability
Important to be able to reproduce damping ring train length and gaps for kicker flat top and rise time
High single bunch currents for validating low-impedance design
Necessary beam instrumentation allowing beam size jitter measurements
Extraction transfer line with adjustable well controlled optics for testing double kicker system
Candidate
ALBA, ATF (especially due to experience with the double kicker system)

23. Damping Rings diagnostics
Turn by turn transverse profile monitors (X-ray?) with a wide dynamic range:
Hor. geometrical emittance varies from injection to extraction and the vertical from 270pm.rad to 0.9pm.rad.
Capable of measuring tails for IBS
This would probably be the most challenging item
Longitudinal profile monitors
Energy spread of 0.5% to 0.1% and bunch length from 10 to 0.1mm.
Note that the dispersion around the ring is extremely small (<12mm).
Fast beam loss monitoring and bunch-by-bunch current measurements
E-cloud + ion diagnostics
300PUs, turn by turn (every 1.6μs)
10μm precision, for linear and non-linear optics measurements.
2μm precision for orbit measurements (vertical dispersion/coupling correction + orbit feedback).
WB PUs for bunch-by-bunch (bunch spacing of 0.5ns for 312 bunches) and turn by turn position monitoring with high precision (~2μm) for injection trajectory control, and bunch by bunch transverse feed-back.
PUs for extraction orbit control and feed-forward.
Tune monitors and fast tune feed-back with precision of 10-4, critical for resolving instabilities (i.e. synchrotron side-bands, ions)

24. Instrumentation experimental program
T. Lefevre
Most important, turn by turn, bunch by bunch profile monitor
Necessitates storage ring with ultra-low emittance or very small optics functions (small beam sizes), i.e. in combination with demonstration of ultra-low vertical emittance e.g. SLS (see TIARA-SVET)
Diagnostics based on X-rays, need space not only in the ring (~1m) but also for building a small optical line
Feed-back systems may be part of the package
Need space for feed-back kicker and stripline BPM (most storage rings already have this)
High-intensity beam conditions (typical for B-factories) for triggering instabilities (e.g. SOLEIL is limited by FII at top current of ~500mA)
Storage rings may be good test beds not only for DR diagnostics but for CLIC in general

25. LER collaboration
Low emittance rings workshop revealed necessity for strengthening collaboration among light source, damping rings, b-factories
Established a list of collaboration subjects
Collaboration coordinators: R. Bartolini (DIAMOND), M. Biagini (INFN/LNF), M. Palmer (Cornell) and YP (CERN)
Subject
Coordinators 1
Low emittance cells design
M. Borland (APS), Y. Cai (SLAC) 2
Non-linear optimization
R. Bartolini (DIAMOND/JAI), C. Steier (LBNL) 3
Minimization of vertical emittance
M. Boege (PSI), R. Dowd (Australian Synchrotron), K. Kubo(KEK) 4
Integration of collective effects in lattice design
R. Nagaoka (SOLEIL), Y. Papaphilippou (CERN), K. Harkay (APS) 5
Insertion device, magnet design and alignment
S. Prestemon (LBNL), E. Wallen (MAXlab), E. Levichev (Budker), PETRAIII 6
Instrumentation for low emittance
M. Palmer (Cornell), G. Decker (APS), B. Hettel, T. Lefevre (CERN) 7
Fast Kicker design
P. Lebasque (Soleil), C. Burkhardt (SLAC), M. Ross (FNAL) 8
Feedback systems (slow and fast)
A. Drago (INFN/LNF), B. Podobedov (BNL), T. Nakamura (JASRI/SPring8) 9
Beam instabilities
G. Rumolo (CERN), R. Nagaoka (SOLEIL) 10
Impedance
K. Bane (SLAC), S. Krinsky (BNL), E. Karantzoulis (Elettra), M. Zobov (INFN) 11
Vacuum
Y. Suetsugu (KEK), O. Malyshev (Cockroft), Schulze (PSI), M. Taborelli (CERN) 12
RF design
F. Perez (ALBA), Novokatchki (SLAC), KEKB, P. Marchand (SOLEIL) R. Rimmer (JLAB)