2011 Particle Accelerator Conference - List of Authors (Secondo, R.)

Paper	Title	Page
WEP079	Mathematical Models of Feedback Systems for Control of Intra-Bunch Instabilities Driven by E-Clouds and TMCI	1621
	C.H. Rivetta, J.D. Fox, T. Mastoridis, M.T.F. Pivi, O. Turgut SLAC, Menlo Park, California, USA W. Höfle CERN, Geneva, Switzerland R. Secondo, J.-L. Vay LBNL, Berkeley, California, USA
	Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP). The feedback control of intrabunch instabilities driven by E-Clouds or strong head-tail coupling (TMCI) requires sufficient bandwidth to sense the vertical position and drive multiple sections of a nanosecond scale bunch. These requirements impose challenges and limits in the design and implementation of the feedback system. This paper presents models for the feedback subsystems: receiver, processing channel, amplifier and kicker, that take into account their frequency response and limits. These models are included in multiparticle simulation codes (WARP/CMAD/Head-Tail) and reduced mathematical models of the bunch dynamics to evaluate the impact of subsystem limitations in the bunch stabilization and emittance improvement. With this realistic model of the hardware, it is possible to analyze and design the feedback system. This research is crucial to evaluate the performance boundary of the feedback control system due to cost and technological limitations. These models define the impact of spurious perturbations, noise and parameter variations or mismatching in the performance of the feedback system. The models are validated with simulation codes and measurements of lab prototypes.

WEP153	Simulation Results of a Feedback Control System to Damp Electron Cloud Single-Bunch Transverse Instabilities in the CERN SPS	1773
	R. Secondo, J.-L. Vay, M. Venturini LBNL, Berkeley, California, USA J.D. Fox, C.H. Rivetta SLAC, Menlo Park, California, USA W. Höfle CERN, Geneva, Switzerland
	Funding: Work supported by the US-DOE under Contract DE-AC02-05CH11231 and the US-LHC Accelerator Research Program (LARP). Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.

WEP199	Estimation of Ecloud and TMCI Driven Vertical Instability Dynamics from SPS MD Measurements - Implications for Feedback Control	1861
	O. Turgut, A. Bullitt, J.D. Fox, G. Ndabashimiye, C.H. Rivetta, M. Swiatlowski SLAC, Menlo Park, California, USA W. Höfle, B. Salvant CERN, Geneva, Switzerland R. Secondo LBNL, Berkeley, California, USA
	Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP). We present analysis of beam motion data obtained in high intensity SPS MD studies in 2009 and 2010. The single-bunch vertical E-cloud motion seen in parts of the bunch train after injection shows large tune shifts (roughly 0.02 above the 0.185 tune) developing between tail and head of unstable bunches. The unstable vertical motion has spectral content up to roughly 1.2 GHz and a quasi-periodic growth and decoherence relaxation oscillation effect is seen with time scales of hundred turns. Beam slice FFT and RMS techniques are illustrated to extract parameters important for the design of wide-band vertical feedback system, such as a growth rates of unstable motion, tune shifts within a single bunch and characterization of the bandwidth of the unstable structures within a bunch. We highlight the impact of synchrotron motion and injection transients on a proposed vertical processing channel. We present our MD plans including the beam driving process, developments in reduced model / identification techniques to extract dynamics from experimental and simulation data. *J. Fox et al., ‘‘SPS Ecloud Instabilities - Analysis Of Machine Studies And Implications For Ecloud Feedback,'' IPAC'10, WEPEB052

Paper

Title

Page

Mathematical Models of Feedback Systems for Control of Intra-Bunch Instabilities Driven by E-Clouds and TMCI

1621

C.H. Rivetta, J.D. Fox, T. Mastoridis, M.T.F. Pivi, O. Turgut
SLAC, Menlo Park, California, USA
W. Höfle
CERN, Geneva, Switzerland
R. Secondo, J.-L. Vay
LBNL, Berkeley, California, USA

Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP).
The feedback control of intrabunch instabilities driven by E-Clouds or strong head-tail coupling (TMCI) requires sufficient bandwidth to sense the vertical position and drive multiple sections of a nanosecond scale bunch. These requirements impose challenges and limits in the design and implementation of the feedback system. This paper presents models for the feedback subsystems: receiver, processing channel, amplifier and kicker, that take into account their frequency response and limits. These models are included in multiparticle simulation codes (WARP/CMAD/Head-Tail) and reduced mathematical models of the bunch dynamics to evaluate the impact of subsystem limitations in the bunch stabilization and emittance improvement. With this realistic model of the hardware, it is possible to analyze and design the feedback system. This research is crucial to evaluate the performance boundary of the feedback control system due to cost and technological limitations. These models define the impact of spurious perturbations, noise and parameter variations or mismatching in the performance of the feedback system. The models are validated with simulation codes and measurements of lab prototypes.

WEP153

Simulation Results of a Feedback Control System to Damp Electron Cloud Single-Bunch Transverse Instabilities in the CERN SPS

1773

R. Secondo, J.-L. Vay, M. Venturini
LBNL, Berkeley, California, USA
J.D. Fox, C.H. Rivetta
SLAC, Menlo Park, California, USA
W. Höfle
CERN, Geneva, Switzerland

Funding: Work supported by the US-DOE under Contract DE-AC02-05CH11231 and the US-LHC Accelerator Research Program (LARP).
Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.

WEP199

Estimation of Ecloud and TMCI Driven Vertical Instability Dynamics from SPS MD Measurements - Implications for Feedback Control

1861

O. Turgut, A. Bullitt, J.D. Fox, G. Ndabashimiye, C.H. Rivetta, M. Swiatlowski
SLAC, Menlo Park, California, USA
W. Höfle, B. Salvant
CERN, Geneva, Switzerland
R. Secondo
LBNL, Berkeley, California, USA

Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP).
We present analysis of beam motion data obtained in high intensity SPS MD studies in 2009 and 2010. The single-bunch vertical E-cloud motion seen in parts of the bunch train after injection shows large tune shifts (roughly 0.02 above the 0.185 tune) developing between tail and head of unstable bunches. The unstable vertical motion has spectral content up to roughly 1.2 GHz and a quasi-periodic growth and decoherence relaxation oscillation effect is seen with time scales of hundred turns. Beam slice FFT and RMS techniques are illustrated to extract parameters important for the design of wide-band vertical feedback system, such as a growth rates of unstable motion, tune shifts within a single bunch and characterization of the bandwidth of the unstable structures within a bunch. We highlight the impact of synchrotron motion and injection transients on a proposed vertical processing channel. We present our MD plans including the beam driving process, developments in reduced model / identification techniques to extract dynamics from experimental and simulation data.
*J. Fox et al., ‘‘SPS Ecloud Instabilities - Analysis Of Machine Studies And Implications For Ecloud Feedback,'' IPAC'10, WEPEB052