W Hofle FCChh RF and Transverse Feedback System

/ W. Hofle FCC-hh RF and Transverse Feedback System 08 October 2015 Transverse Feedback FCC-hh As presented at the FCC Week With some additional remarks Wolfgang Hofle 9/17/2020 BE-RF-FB 1

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle Start with where we stand LHC ü Key FCC-hh parameters very similar to LHC ü 25 ns and 5 ns bunch spacing options ü Beam current similar to LHC, 1 x 1011 protons per bunch for 25 ns FCC-hh transverse feedback design follow same design path as for the LHC Design: strong transverse feedback for coupled bunch instability mitigation driven by resistive wall impedance of beam screen and machine elements knowledge of impedance key to define parameter space for RF system and transverse feedback FCC-hh will have significant synchrotron radiation damping; emittance control important both longitudinal and transverse (blow-up may be needed) 2

Transverse Feedback: LHC 9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle ADT - LHC Transverse Feedback (Damper) ü Injection damping high gain, low bandwidth, large kick strength ü Instability damping gain adapted to instabilities, bandwidth can be tailored by signal processing ü Preservation of emittance low noise, detection of mm oscillation ü Tool for transverse blow-up loss maps, quench tests, aperture measurements ü LHC Transverse Feedback operation with colliding beams well established using a digital system, a first in a Hadron Collider, it is also needed with colliding beams (non colliding bunches, offsets) ü Full exploitation of ADT data for beam diagnostics and tune measurement being prepared for Run 2 ü Improvements prepared in LS 1 (number of pick-ups, electronics, software upgrade), reduction of noise, to come on gradually in run 2 3

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle FCC-hh Requirements ü Injection damping high gain, low bandwidth, large kick strength ü Instability damping coupled bunch instabilities driven by resistive wall impedance of beam screen / beam pipe ü Preservation of emittance low noise, detection of mm oscillation ü Maintaining emittance noise injection to counteract emittance shrinking by radiation damping at top energy and during ramp ? ü Advanced diagnostics potential and compatibility with tune measurement needs to be given attention from the beginning learn from LHC and High Lumi LHC experience q Do we require to damp single bunch instabilities ? q Do we require to damp internal bunch motion (TMCI like) ? q Are there narrow band transverse impedances that require damping with high gain up to half the bunch repetition frequency (see for example the issue with HOMs of High Lumi LHC crab cavities) ? 4

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle LHCADT Power and Kicker System Power beam observation • • Kicker length: each kicker 1. 5 m Max voltage: 10. 5 k. V 2 mrad kick to 450 Ge. V beam Gain up to beyond 20 MHz 16 kickers, 32 x 30 k. W tetrode amplifiers Bandwidth up to 20 MHz scaled from SPS system ADT kicker. The beam is kicked by electric field Measured ADT frequency response. Green: bare power amplifier, blue: power amp + kicker. LHC transverse Feedback (ADT) kickers and amplifiers in tunnel point 4 of LHC, RB 44 and RB 46 FCC-hh requires more bandwidth (5 ns option bunch spacing option)5

Injection Oscillations – Batch View 9/17/2020 FCC-hh RF and Transverse Feedback System / W. Hofle @FCC Week, Washington D. C. 22 -27 March 2015 time domain ADT response LHC V-plane 50 ns bunch spacing standard + hold 144 bunches (4 x 36) 25 ns bunch spacing enhanced bandwidth 144 bunches (2 x 72) Injection oscillation damping 6 damping at edges of batch slower IPAC’ 13, WEPME 43 6

LHC 2012 Run achievements 9/17/2020 FCC-hh RF and Transverse Feedback System / W. Hofle @FCC Week, Washington D. C. 22 -27 March 2015 Damping times as measured on first bunch of batch Beam 2 H: 13 turns V: 26 turns V H Beam 1 H: 16 turns V: 27 turns LHC, curtesy A. Macpherson See also IPAC’ 13, FRXCA 01 7

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle LHC Damping LHC 6. 10. 2015 q 8 turns damping achieved in LHC (H-plane) q first bunch of train of 12 injected is displayed q H-plane not affected by ripples of vertical injection kicker q Important: gain can be as high as needed to achieve 8 turns damping 8

LHC ADT Design parameters 9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle injection relative emittance increase at injection value energy E 450 Ge. V emittance (norm) e 3. 5 mm injection error ainj 4 mm @ b=185 m increase w/o FB ainj 2/(2 s 2) (5. 92) max increase of e (De/e)max 0. 025 blowup factor Fe < 4. 22 x 10 -3 Damping time blow-up factor de-coherence time (in design report due to Q’) Full tune spread 1. 3 x 10 -3 ultimate LHC 1. 7 e 11 ppb nominal LHC 1. 0 e 11 ppb EPAC’ 08, THPC 121 LHC Design Report CERN-2004 -003 LHC Run 1: in practice smaller emittances available from injectors 9

R&D: intra-bunch feedback (SPS) 9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle BPM Analog Front End transverse position q q q q pre-processed Kicker Active closed loop Feedback Beam Signal Processing ADC sampled position “slices” Analog Back End DAC calculated correction data correction signal capacity to damp intra-bunch instabilities, 4 -8 GS/s digital feedback originally started as e-cloud instability also shown to damp TMCI in simulation if synchrotron tune low closed loop experiments in SPS started milestone to demonstrate feasibility: mid 2016 targeted bandwidth 1 GHz, needed BW scales with bunchlength good to cover large range of bandwidth, two kicker designs q short stripline (completed) and slotline (under development) Power Amp pre-distortion drive signal supported by US-LARP and SPS-LIU J. D. Fox et. al 10

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle US LARP Feedback Kicker Design Need for high Bandwidth requires new kicker for the SPS: • Inspired by Stochastic Cooling Systems Faltin type kicker considered (strip-line with slotted shield to beam pipe) Develop for test of prototype in SPS Smaller vacuum chamber Easily permits higher frequency (LHC and FCC) J. Cesaratto et al. (SLAC) WEPME 061, IPAC’ 2013 11

FCC-hh TFB: 25 ns -100 km option 9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle injection relative emittance increase at injection value energy E 3300 Ge. V emittance (norm) e 2. 2 mm injection error ainj 1 mm @ b=185 m ? increase w/o FB ainj 2/(2 s 2) (4. 32) max increase of e (De/e)max 0. 05 blowup factor Fe < 11. 6 x 10 -3 blow-up factor ? de-coherence time (needs determination) ? 10 turns Damping time 6. 7 turns 5 turns FCC versus LHC: 4 turns • smaller injection error • slower de-coherence ? • but faster instability develop feedback algorithms for fast damping 12

FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle Summary FCC-hh TFB q Impedance estimates key to TFB design q TFB design: o coupled bunch feedback with options for 5 ns and 25 ns bunch spacing (driven by resistive wall instability fast instability rise times) o bandwidth up to 100 MHz for 5 ns option to cover all CBMs o injection damping kicker waveform a challenge (ripple) o TMCI instability: Potential of intra-bunch GHz feedback is being investigated with US-LARP supported work for the SPS o needed R&D for FCC covers the technology of kicker, power systems, signal processing electronics and algorithms 9/17/2020 • Leverage on US LARP work for SPS Feedback ! 13

9/17/2020 FCC-hh RF and Transverse Feedback System 08 October 2015 / W. Hofle Tentative options FCC-hh TFB 1. System like LHC System to cover low frequency coupled bunch modes and injection damping, cost scales with energy for constant injection error q tetrodes/ like LHC system, or very long strip-lines (10 m ? ) + solid state Instability rise-times of faster than 10 turns call for a distributed system (bandwidth 100 k. Hz – 1 MHz), simulations needed: • 5 -10 turns: two locations in ring symmetrically placed • 2 -5 turns: four locations symmetrically placed • 1 -2 turns: eight locations symmetrically placed 2. Strip-line system to cover frequency range up to 40 MHz or 100 MHz q q Frequency range depends on bunch spacing option, perhaps further split in two systems (5 ns or 25 ns) Intra-bunch systems • Band-by-band approach at n x RF (400 MHz, 800 MHz …) • Combination of strip-line of 400 MHz and slot lines(s) 3. Important work that needs to start q q Kicker electromagnetic design q Beam Simulations with feedback 14