1. Beam Instability in High Energy Hadron Accelerators and its Challenge for SPPC
Liu Yu Dong

2. Content
Some Serious Instabilities measured in several hadron accelerators
SPS: Microwave Instability
LHC: TRANSVERSE COUPLED-BUNCH INSTABILITY MEASUREED
SINGLE-BUNCH TRANSVERSE INSTABILITY
Head-Tail Instability
Tevatron: Transverse Head-Tail Instability
Electron Cloud Instability: in PS, SPS and LHC
The Instability Challenges for SPPC

3. Some Serious Instabilities measured in several hadron accelerators
Microwave Instability
Caused by broad-band impedance corresponding to the short range wake field. In proton accelerators this instability is shown as a fast increase of the bunch length.
Keil-Schnell Criterion can be used to decide the threshold of instability.
Increasing the beam current I0, bunch lengthen will be appearance.
The limitations on beam intensity by microwave Instability was seen in CERN-SPS

4. Observed Microwave Instability in SPS
Source for microwave instability:
Impedance from vacuum pump flanges.
Solution: The higher value of Δp/p, the higher threshold.
Threshold of the instability
Accelerate ramp process
The two operating modes of the double RF system , namely the bunch shortening mode (BSM) and the bunch-lengthening mode
(BLM) , the phase between the two RF systems is and 0
T. Argyropoulos, Proceedings of HB2014

5. TRANSVERSE COUPLED-BUNCH INSTABILITY MEASUREED IN LHC
Beam parameters: bunch spacing by 50 ns, Nb=1.2e11
Observed TCBI in LHC
Simulated result onTCBI with HEADTAIL
N. Mounet, E. M´etral, G. Rumolo. et.al,proceeding of IPAC2012, 3087

6. Source of the TCBI in LHC
Resistive wall impedance:
(1) collimators; (2) copper-coated beam screen; (3) broad band impedance of smooth transition
Solution method:
(1) Chromaticity
(2) Octupole
N. Mounet, E. M´etral, G. Rumolo. et.al,proceeding of IPAC2012, 3087

7. SINGLE-BUNCH TRANSVERSE INSTABILITY MEASUREED IN LHC
Single bunch with population 1.5x1011
Frequency domain
Time domain
E. Métral, N. Mounet, ProceedingsofIPAC2011
Source of the instability:
Impedance from the numerous collimators with very small gaps ~5σ

8. Otupole: An effective method to depress the head-tail instability
E. Métral, Proceedings of Chamonix 2011 workshop on LHC Performance

9. Beam Instabilities in the Tevatron
Transverse Head-Tail Instability
P. M. Ivanov#, J. Annala. et al., Proceedings of the 2003 PAC

10. Source and cures Source: impedance from injection Lambertson Magnet
Cures: (1) 0.4mm thin conductive CuBe liners being installed inside Lambertson magnets to reduce the total Tevatron transverse impedance;
(2) Octupoles to generate additional tune spread
Valery Lebedev, Vladimir shiltsev Accelerator Physics at the Tevatron cpllider, 2014, springer

11. Electron Cloud Instability in CERN accelerators
Observed signal of electron cloud in PS
Bunch spacing 50ns
With bunch length 4ns
Bunch spacing 25ns
With bunch length 4ns
Giovanni. Iadarola, CERN-THESIS
Simulation result for EC (solid 25ns, dash 50ns)

12. Coupled bunch instability measured in PS
Giovanni. Iadarola, CERN-THESIS

13. Observation on ECI in SPS
Bunch spacing 25ns, bunch population 0.8x1011
Then, beam scrubbing runs with 25 ns beams were carried out almost every year of operation in order to condition the inner surfaces of the vacuum chamber to mitigate the electron cloud by reduce SEY.
G. Arduini, T. Bohl, et.al , ECLOUD04

14. Beam scrubbing effects on SEY and instability
J.M.Jiménez,G.Arduini,et,al. Mini Workshopon Electron Cloud Simulations for Proton and Positron Beams, CERN, Geneva, Switzerland, Apr2003
The measurement demonstrates that 25ns LHC beam does not suffer from electron cloud effects at nominal intensity (1.15x1011ppb) in the SPS
Giovanni. Iadarola, CERN-THESIS

15. Observation on ECI in LHC
June 2011: first injections of 25 ns beams into the LHC, bunch population ～1.3x1011
Bunch size with Sychrotron Radiation
CERN-ATS-Note MD, CERN-THESIS

16. Heat load measured with 25ns bunch spacing in LHC
The heat power is from the EC because of the high SEY~2.3.
Scrubbing running is necessary to reduce SEY to 1.3.
amorphous carbon coating as SPS vacuum chamber

17. The Instability Challenges for SPPC
Frontier design parameters for SPPC
Parameter
Value
Unit
Circumference
54.7 km
Beam energy
35.6
TeV
Dipole field 20 T
Circulating beam current
1.0 A
Bunch separation 25 ns
Number of bunches
5835
Bunch population
2.0x1011
Normalized rms transverse emittance
4.1 mm
rms bunch length
75.5
rms IP spot size
9.0

18. Instability Source: Impedance
The most serious impedance components in SPPC:
numerous collimators: a few hundreds
Injection Magnets: Source of wideband impedance to produce single bunch instability
Beam screen: main source of resistive wall impedance
Develop accurate impedance model for the components
Optimize the component structure and materials for lower coupled impedance

19. Instability Source: Electron Cloud
Origin of Electron Cloud: Accumulation of electrons
Fundamental Solution: Electron Cloud Elimination and depression, solenoid magnetic field, clearing electrodes, coating to reduce SEY or by Scrubbing ….
Is there any new idea to clear out electron cloud?
Instability Remedies: Chromaticity, Octupole, Bunch filling pattern, dampers (longitudinal and transverse) ….

20. Thank you for attention!