SPS MDs in 2013 SPS TMCI and Ecloud
- Slides: 14
SPS MDs in 2013
SPS: TMCI and E-cloud 1. TMCI threshold → Detailed studies done for Q 20 and Q 26 in parallel in the supercycle → Large longitudinal emittance vs. intensity space covered → Low chromaticity for TMCI scans, but beam behaviour with negative chromaticity tested in both optics → Different voltages tried, always in double RF with voltage of 800 MHz at 10% of that of 200 MHz → Recorded all data from Qmeter, BBQ, BCT, WCM, Wirescanner, Headtail monitor, εl (PS), Intensity from PS to be analyzed in detail and compared with simulations! 2. Doublet 25 ns beam → First tests: injection of two bunches with voltage dip → Short test of injection of two batches → Voltage program optimized to efficiently split the bunches in both batches (however, TFB still to be set up for this beam!) H. Bartosik, G. Iadarola, G. Rumolo
SPS: TMCI “Island’ of slow instability observed for intermediate intensity and small εl Behavior of Q 26 much more strong TMCI-like Q 20 optics (V 200=4 MV) H. Bartosik, G. Iadarola, G. Rumolo
SPS: E-cloud (doublet) First batch does not suffer from the voltage dip Second batch is split without “leaking” particles into the adjacent buckets H. Bartosik, G. Iadarola, G. Rumolo
SPS: E-cloud (doublet) 25 ns “doublet” (1. 7 e 11 p/doublet) 25 ns standard (1. 6 e 11 p/bunch) MBA-like Stainless Steel liner
SPS: Space charge 1. Effect of approaching integer with large tune spread → → Single bunch, high intensity 50 ns beam, BCMS scheme Tune scans Q 20 vs. Q 26 optics 2. Multi-bunch studies (emittance blow up & transmission) → Use of high brightness BCMS 50 ns beams → Train dependence of emittance blow up (to determine the effect of the length of the injection plateau H. Bartosik, Y. Papaphilippou, G. Rumolo, F. Schmidt
SPS: Space charge • Machine setup for high brightness 50 ns BCMS beam (1 batch of 24 bunches) – N = 1. 95 x 1011 p/b (at injection) ΔQx/ΔQy ~ 0. 10/0. 18 (from Laslett formula) – ε ~ 1. 15μm – Transmission up to flat top around 94% without scraping (very small losses on flat bottom) Lossless blow-up of beam core “no blow-up” for Qx>20. 14
SPS: High bandwidth transverse feedback system 1. Driven motion studies → Excite the beam through tailored excitation → Control on selected modes by sweeping frequency → Characterization of the response of the combined beam-feedback system 2. Feedback studies of naturally unstable or marginally stable beams → Make the beam unstable with negative chromaticity (mode zero excited) → Find feedback settings to suppress the instability and show that beam becomes unstable with FB off → Feedback control needed to make more studies W. Höfle, J. Cesaratto, J. Dusatko, J. Fox, G. Kotzian, C. Rivetta, U. Wehrle, H. Bartosik, K. Li
SPS: High bandwidth transverse feedback system Feedback on Instability Beam loss Instability Chroma ramped down Feedback off Chroma ramped down Feedback switch off W. Höfle, J. Cesaratto, J. Dusatko, J. Fox, G. Kotzian, C. Rivetta, U. Wehrle, H. Bartosik, K. Li
SPS: RF MDs 1. Synchrotron frequency shift with intensity - reference impedance measurements (single bunches in Q 26) → to see effect of impedance reduction (MKEs) → to compare with simulations (test the impedance model) 2. Spectra of long unstable bunches with RF off in Q 20 → to compare with measurements in Q 26 (from 2012) → to identify large impedance sources 3. Single bunch stability in a single and a double RF systems (in Q 26 and Q 20) → to compare with simulations → to see effect of phase-space distribution (after rotation in PS) → to compare with measured multi-bunch instability thresholds E. Shaposhnikova, T. Argyropulos, T. Bohl, J. Esteban-Müller, H. Timkó
SPS: RF MDs Intensity/longitudinal emittance defined at the PSB with new C 16 knob (S. Hancock) E. Shaposhnikova, T. Argyropulos, T. Bohl, J. Esteban-Müller, H. Timkó
SPS: RF MDs Slope of synchrotron frequency shift as a function of bunch length Ø Comparison with 2008 shows that longitudinal impedance is reduced (serigraphy of MKEs) E. Shaposhnikova, T. Argyropulos, T. Bohl, J. Esteban-Müller, H. Timkó
SPS performance (2012 -2013) 50 ns Operational beam for LHC physics in 2012 MD beam sent to LHC only once in 2012 • Expected lines derived from the brightness curve of the PSB translated into SPS flat top values (with emittance and loss budgets in the PS – 5% – and in the SPS – 10%)
SPS performance (2012 -2013) 25 ns Operational beam for LHC scrubbing in 2012 Beam used for LHC physics with 25 ns beams in 2012 • • Expected lines derived from the brightness curve of the PSB translated into SPS flat top values (with emittance and loss budgets in the PS – 5% – and in the SPS – 10%) The traditional 25 ns beam exhibits extra losses and/or emittance growth (slow losses at the SPS FB? electron cloud in the PS? )