Summary of ions measurements in 2015 and priorities for 2016 studies E. Shaposhnikova 3/02/2016 Based on input from H. Bartosik, T. Bohl, B. Goddard, V. Kain, G. Kotzian

Measurements in 2015: general remarks 1 st LHC Pb run after LS1 More experience with Q20 → better transmission than before LS1 (now similar to Q26) Beam transmission strongly depends on intensity Beam is unstable in longitudinal plane after transition crossing PS controlled emittance blow-up helps for the SPS beam SPS controlled emittance blow-up was tried many times in the past but without success (in a single RF) No effect of bunch spacing (150 ns and 175 ns) on longitudinal bunch parameters

Measurements in 2015: longitudinal plane (short cycle) → Transmission and bunch length strongly depend on bunch intensity → Bunch length is reducing on the flat bottom T. Bohl

Effect of PS controlled emittance blow-up on bunch length/stability PS BUP → Very similar bunch lengths at extraction! instability T. Bohl

Slip stacking MDs: effect of phase loop T. Bohl, 2015 Intermediate flat portion could be better for beam stability

Slip stacking MDs Radial steering limits at flat top Limits (for mean closed orbit) measured on flat top - with extraction bumps: (-1 mm, +20 mm) -without extraction bumps: ±20 mm - ±6 mm (1.64x10 -3 ) assumed in simulations give slippage time of 300 ms (for distance of 2.7 us) at 300 GeV/c (γ=127) Beam survives w/o phase loop but with emittance BUP ~ 20% during 400 ms (1.3 ns => 1.45 ns) BUP due to slip stacking: => 0.36 eVs/u (simulations without intensity effects) → bunch rotation at extraction → 800 MHz during slip stacking?

Observations & damper performance in 2015 (G. Kotzian) Proton dampers successfully operated with ions!  operation problematic due to inherent FSK (Frequency Shift Keying) Beam position sampling: shifted “Sliding”  bunches assigned to wrong bucket Due to shifting a correct tagging not possible  the signal processing “sees” more than 2x12 bunches Feedback correction signal: shifts for subsequent injections Degraded injection damping for batches For most of the Ion run damper was deactivated after 11 th injection: damping only at flat bottom (no feedback during ramp) One horizontal damper used Feedback phase arbitrarily detuned by +20 deg  erratic beam losses during acceleration when using optimum feedback phase

SPS transmission H. Bartosik

Summary and outlook (H. Bartosik) Pb-Pb run 2015 showed clearly that SPS is a big bottleneck in ion injector chain Significant losses in SPS – up to 50% on average over all bunches injected Flat bottom losses significantly increase with intensity Losses during acceleration and transition are less dependent on intensity Transverse emittance growth up to 50% Systematic measurements performed in 2015 – data analysis still to be done! Systematic working point scan recording losses, bunch length and emittance on flat bottom Measurement of emittance evolution along flat bottom for nominal working point Measurements planned for 2016 If possible, optimize working point in order to minimize losses (based on 2015 data) Characterize the dependence of losses on intensity in dedicated measurements Comparison of losses between FFA and FHA for operational intensity (measurements of Thomas in the past with low intensity, but results are very promising) If time allows: comparison of Q20 and Q26 (in particular losses)

Ion studies made in 2015 (B. Goddard) MKP rise time Transverse damper commissioning and performance Systematic scans of working point with fixed frequency at FB IBS/emittance growth on FB Effect of RF noise on lifetime and beam at FB in fixed frequency mode Longitudinal stability versus longitudinal emittance and intensity Slip stacking: momentum aperture beam behavior without phase loop Detuning with amplitude for modeling of tails with injection errors and damping

Possible beam tests in 2016 (B.G. + E.S.) ns for p beam to keep gains made with Pb for proton-ion run? Investigate p+ 17 GeV/c PS->SPS transfer and transition crossing in SPS Low intensity 1e10, 2 bunches per injection at 100 ns spacing 2.Work out what prevents injecting later on FB, develop and test solutions 3.Analyse systematic WP scans and test better WP with nominal beam. Tests with fixed harmonic? 4.Deploy and test damper with proper compensation for bunch timing 5.Test of slip-stacking with RF frequency modulated at 0.5 F RF ? => LLRF work? 6.Q26 versus Q22 optics: beam tests if advantages seen in simulations 7.Optimisation of SPS cycle and filling scheme based on LHC performance 8.Investigate use of 800 MHz with 200 MHz for ions stability during cycle and slip stacking 9.Test controlled longitudinal emittance blow-up in the SPS (single and 2RF) 10.Bunch rotation on the flat top (after controlled BUP)

Priorities for 2016 studies Losses WP FF vs FH SC, Touschek/IBS Optimisation of LHC filling time and pattern Q20 vs Q26 Transverse damper for ions Longitudinal stability and use of 800 MHz Slip stacking measurements at 300 GeV/c => special new magnetic cycle? Preparation for p-Pb run

RF Modulation: FSK (Frequency Shift Keying) 07. Jan 2016 Ions Gerd Kotzian14 Proton Beam Beam Revolution Time (normalized) NB: NOT IN SCALE! Signal Processing Time (normalized) NB: FSK technique is a result of Fixed Frequency Acceleration (FFA) FSK in BA2 shifted w.r.t. BA3 by transport delay ~9.535 us (Fiber Link) Ions (BA3) Ions (BA2) SOLUTION: Additional delay by means of local fibers in BA2 (~10us)

Can losses be reduced? RF noise reduction on the SPS flat bottom Investigate if the IBS/Touschek are the main effects Q20 compared with Q26 Verify space charge limit for ions (scaled from protons) Space charge and working point optimisation at the long injection plateau to establish performance reach Slip-stacking: Determine max radial displacement on intermediate flat top Investigate emittance blow-up and losses Use existing LLRF for separate capture of 2 bunches (batches) Q20 or Q26? Tests with 200 MHz and 800 MHz RF systems (?) Bunch rotation on the flat top (with a phase jump?) Transverse damper for different bunch spacings (100 ns ns) Bunch after slip-stacking and rotation Q ns