HB2014 - List of Authors (Timko, H.)

Paper

Title

Page

Synchrotron Frequency Shift as a Probe of the CERN SPS Reactive Impedance

409

A. Lasheen, T. Argyropoulos, J.V. Campelo, J.F. Esteban Müller, D. Quartullo, E.N. Shaposhnikova, H. Timko
CERN, Geneva, Switzerland

Longitudinal instability in the CERN SPS is a serious limitation for the future increase of bunch intensity required by HiLumi LHC project. The impedance driving this instability is not known precisely and a lot of effort goes into creating an accurate impedance model. The reactive impedance of the machine can be probed by measuring the bunch length oscillations of a mismatched bunch at injection. The frequency of these oscillations as a function of intensity has a slope that depends on the reactive impedance and the emittance. Measurements were done for three values of longitudinal emittances and then compared with particle simulations based on the impedance model using particle distribution close to the measured one. Comparison of measured and calculated frequency shifts gives an estimation of the missing impedance in the model. In addition, scanning of initial emittance for diverse particle distributions in simulations shows that the frequency shift greatly depends on emittance and initial distribution. Small variations of these parameters can lead to very different results and explain partially the discrepancy between measured and calculated values of frequency shifts.

Slides THO4LR02 [1.499 MB]

THO4LR03

Studies on Controlled RF Noise for the LHC

414

H. Timko, P. Baudrenghien, E.N. Shaposhnikova
CERN, Geneva, Switzerland
T. Mastoridis
CalPoly, San Luis Obispo, California, USA

RF phase noise is purposely injected into the LHC 400 MHz RF system during the acceleration ramp for controlled longitudinal emittance blow-up, in order to maintain longitudinal beam stability. Although the operational blow-up works reliably, studies of the injected RF noise are desirable not only to allow for a better-controlled, more flexible blow-up, but also for other applications such as the mitigation of machine-component heating through appropriate bunch shaping. Concerning the noise injection, an alternative algorithm was developed and implemented in the hardware, but first tests revealed unexpected modulation of the achieved bunch length along the ring, and subsequently, theoretical studies have been launched. In this paper, we present a summary of ongoing measurement analysis and simulation studies that shall explain previous observations, predict what can be expected in different cases, and thus help to optimise the RF noise in general.

Slides THO4LR03 [1.440 MB]

Paper	Title	Page
THO4LR02	Synchrotron Frequency Shift as a Probe of the CERN SPS Reactive Impedance	409
	A. Lasheen, T. Argyropoulos, J.V. Campelo, J.F. Esteban Müller, D. Quartullo, E.N. Shaposhnikova, H. Timko CERN, Geneva, Switzerland
	Longitudinal instability in the CERN SPS is a serious limitation for the future increase of bunch intensity required by HiLumi LHC project. The impedance driving this instability is not known precisely and a lot of effort goes into creating an accurate impedance model. The reactive impedance of the machine can be probed by measuring the bunch length oscillations of a mismatched bunch at injection. The frequency of these oscillations as a function of intensity has a slope that depends on the reactive impedance and the emittance. Measurements were done for three values of longitudinal emittances and then compared with particle simulations based on the impedance model using particle distribution close to the measured one. Comparison of measured and calculated frequency shifts gives an estimation of the missing impedance in the model. In addition, scanning of initial emittance for diverse particle distributions in simulations shows that the frequency shift greatly depends on emittance and initial distribution. Small variations of these parameters can lead to very different results and explain partially the discrepancy between measured and calculated values of frequency shifts.
	Slides THO4LR02 [1.499 MB]

THO4LR03	Studies on Controlled RF Noise for the LHC	414
	H. Timko, P. Baudrenghien, E.N. Shaposhnikova CERN, Geneva, Switzerland T. Mastoridis CalPoly, San Luis Obispo, California, USA
	RF phase noise is purposely injected into the LHC 400 MHz RF system during the acceleration ramp for controlled longitudinal emittance blow-up, in order to maintain longitudinal beam stability. Although the operational blow-up works reliably, studies of the injected RF noise are desirable not only to allow for a better-controlled, more flexible blow-up, but also for other applications such as the mitigation of machine-component heating through appropriate bunch shaping. Concerning the noise injection, an alternative algorithm was developed and implemented in the hardware, but first tests revealed unexpected modulation of the achieved bunch length along the ring, and subsequently, theoretical studies have been launched. In this paper, we present a summary of ongoing measurement analysis and simulation studies that shall explain previous observations, predict what can be expected in different cases, and thus help to optimise the RF noise in general.
	Slides THO4LR03 [1.440 MB]