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

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

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

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

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

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

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

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

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

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

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-2014-047 Simulation result for EC (solid 25ns, dash 50ns)

Coupled bunch instability measured in PS Giovanni. Iadarola, CERN-THESIS-2014-047

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

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-2014-047

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-2011-050-MD, CERN-THESIS-2014-047

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

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

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

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) ….

Thank you for attention!