NLC - The Next Linear Collider Project “Slow” Feedback Requirements: Deflections and Luminosity Linda Hendrickson IPBI Meeting, SLAC June 26, 2002

Next Linear Collider Overview: 1. Deflection feedback and ground motion simulations: keeping the beams in collision, train-train. (~timescale: 120 Hz) 2. Luminosity optimization: Maximizing luminosity and stabilizing higher-order aberrations. (~timescale: 30 minutes)

Next Linear Collider Feedback timescales: NLC simulations (Andrei Seryi et al, 2002) Uncorrected With SLC-style IP deflection feedback

Next Linear Collider Feedback timescales: NLC simulations (Andrei Seryi, PAC 2001)

Next Linear Collider Instrumentation for “Slow” Feedback, Needed by Control System: IP Beam position monitors (2 incoming+2 outgoing, X&Y, * 2 beams) Good resolution (< 1 um per S. Smith ) Low noise, not subject to erroneous results from beam spray Slow/low offset drift (offsets calibratable with luminosity or defl. scan) Low latency (<<< 1/120 sec) Luminosity monitor(s) Good resolution (~10%, comparable to real luminosity jitter?) Low latency (< 1/120 sec) Multiple monitor options are desirable Returns maximum signal for maximum luminosity! (no systematics) Other instrumentation (?): Intensity monitor (defl and lum normalization, consistent timescale) Beam timing monitor, ala SLC? Crab cavity phase monitor? Detector background signals, needed in realtime!

Next Linear Collider Actuators for “Slow” Feedback, Needed by Control System: IP Correctors or kickers (X&Y, * 2 beams) Fast response (<< 1/120 sec) Slower correctors with larger range needed for longer-term drifts FF sextupole orbit feedback correctors (X&Y, 2 phases?, 2 beams) Fast response (<~ 1/120 sec) Luminosity Optimization controls X and Y sextupole offsets; skew quadrupole strengths (per Y. Nosochkov) Prefer fast response (< 1/10 sec ala SLC) Prefer equal speeds in a multiknob (less susceptible to systematics) Minimal hysteresis (reproducibility of actuator settings)

Next Linear Collider Feedback timescales: NLC vs SLC feedback design response: (It helps to assume a faster control system: low- latency BPMs, fast IP kickers/correctors)

Next Linear Collider Feedback timescales for Luminosity Optimization: SLC experience (Nan Phinney, Pantaleo Raimondi, and the SLC team): A.F.A.R.A! (As Fast As Reasonably Achievable)  Fast response to upstream tuning, supports higher order optimizations.  Want < 30 minutes to optimize all, from untuned state (10-30 minutes typical SLC running)  Typical SLC optimization scenario: optimize 10 parameters every 2 hours, plus on user request: 2 beams: X&Y waist; X&Y eta; coupling Estimated < 2% luminosity loss due to dithering  Possible NLC optimization scenario: optimize parameters every 2 hours, plus on user request: 2 beams: X&Y waist; X&Y eta; coupling; crab cavity phase(?) 1 beam: compressor phase(?)

Next Linear Collider Luminosity Optimization in the SLC: Original Scan method: Minimize beam width-squared from deflection scans (subject to meas error ~20-40% luminosity) Dither Method: Maximize luminosity while moving multiknob up and down by small amounts, average 1000’s of pulses Bhabha BSM

Next Linear Collider Luminosity Optimization in the SLC: Comparative Resolution of Scan Method vs Dither Method Dither Scan

Next Linear Collider SLC Optimization : typical feedback command changes over 3 days. June, 1998

Next Linear Collider SLC Optimization : typical old-scan-method command changes over 3 days. June, 1997

Next Linear Collider SLC Optimization : Typical optimization cycle over 12 hours; June, 1998 Normalized luminosity during dither cycle (arb units)

Next Linear Collider And now… “The Movies”! courtesy of Andrei Seryi and the NLC accelerator physics group Damping Ring >> IP << Damping Ring  Consistent ground motion simulations (2 beams, one continuous ground, with P(ω,k) spectrum (elastic waves, slow ATL, systematic motion, technical noises)  SLC-style IP deflection feedback  MATLAB (simulation driver, feedback calculations, display&analysis)  LIAR (linac tracking with structures, wakefield calculations: beam slice representation)  DIMAD (tracking engine run within LIAR; for bunch compressors, bends, sextupole,octupole tracking; particle representation)  Guinea Pig (beam-beam code; interfaced to LIAR-DIMAD via MATLAB; gives us the deflection and luminosity “measurements”)

Next Linear Collider Ground motion models Based on data, build modeling P( ,k) spectrum of ground motion which includes: –Elastic waves –Slow ATL motion –Systematic motion –Technical noises at specific locations, e.g. FD) Example of integrated spectra of absolute (solid lines) and relative motion for 50m separation obtained from the models

Next Linear Collider P( ,k) is then used to generate x(t,s) and y(t,s) and beams GO Example of Mat-LIAR modeling

Next Linear Collider Intermediate ground motion

Next Linear Collider Zoom into beginning of e- linac … Transition from linac to transfer line

Next Linear Collider Noisy ground motion

Next Linear Collider Quiet ground motion

Next Linear Collider Beam-beam collisions calculated by Guinea- Pig [Daniel Schulte]

Next Linear Collider Pulse #100, Z-Y calculated by Guinea- Pig [Daniel Schulte]

Next Linear Collider Pulse #100, Z-X calculated by Guinea- Pig [Daniel Schulte]

Next Linear Collider Pulse #100, X-Y calculated by Guinea- Pig [Daniel Schulte]

Next Linear Collider CONCLUSIONS? Controlling deflections and luminosity optimization will be at least as difficult for NLC as for SLC. Need tools that are at least as good! (i.e. fast, reliable, low-latency instrumentation and controls). Future work for NLC: Optimization of 120-Hz deflection feedback response for expected ground motion. More complete simulations of NLC tuning: sextupole orbit correction, optimization with luminosity jitter, realistic imperfections, upstream tuning; IP angle feedback? Etc…