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| MOPR010 | Machine Element Contribution to the Longitudinal Impedance Model of the CERN SPS | impedance, simulation, resonance, coupling | 71 |
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| This contribution describes the current longitudinal impedance model of the SPS and studies carried out in order to improve, extend and update it. Specifically, new sources of impedances have been identified, evaluated and included in the model. One finding are low Q and low-frequency (LF; here below 1 GHz) resonances which occur due to enamelled flanges in combination with external cabling e.g. ground loops. These resonances couple to the beam through the gap with enamel coating which creates an open resonator. Since this impedance is important for beam stability in the CERN Proton Synchrotron (PS), RF by-passes were installed on the enamelled flanges, and their significance for the SPS beam is currently under investigation. Simulations, bench and beam measurements were used to deduce model parameters for beam dynamic simulations. | |||
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| MOPR011 | The SPS 200 MHz TWC Impedance after the LIU Upgrade | cavity, HOM, simulation, impedance | 76 |
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Funding: Fellowship co-funded by the European Union as a Marie Curie action (Grant agreement PCOFUND-GA-2010-267194) within the Seventh Framework Programme for Research and Technological Development. As a part of the LHC Injectors Upgrade project (LIU) the 200 MHz Travelling Wave Cavities (TWC) of the Super Proton Synchrotron (SPS) will be upgraded. The two existing five-section cavities will be rearranged into four three-section cavities (using two existing spare sections), thereby increasing the total voltage from 7 MV (IRF = 1.5 A) to 10 MV (IRF = 3.0 A). Projections of the HL-LHC (High Luminosity Large Hadron Collider) era are conceived by the macro-particle simulation code BLonD, that makes use of an impedance model of the SPS, developed from a thorough survey of machine elements. This paper analyses the impedance contribution of the 200 MHz cavities in the two configurations, using electromagnetic simulations. Measurements of the existing cavities in the SPS and a single-section prototype are also presented. |
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| MOPR024 | General Formula to Deduce the Space Charge Tune Spread From a Quadrupolar Pick-Up Measurement | space-charge, coupling, resonance, kicker | 120 |
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| In 1966, W. Hardt derived the oscillation frequencies obtained in the presence of space charge forces and gradients errors for elliptical beams. Since then, a simple formula is usually used to relate the shift of the quadrupolar mode (obtained from the quadrupolar pick-up) and the space charge tune spread, depending only on the ratio between the two transverse equilibrium beam sizes. However, this formula is not always valid, in particular for machines running close to the coupling resonance Qx = Qy with almost round beams. A new general formula is presented, giving the space charge tune spread as a function of i) the measured shift of the quadrupolar mode, ii) the ratio between the two transverse equilibrium beam sizes and iii) the distance between the two transverse tunes. | |||
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