Steering Simulation Studies Machine Advisory Committee Meeting 24 June 23
The Situation in November 2 Capability to realistically simulate both commissioning and operation of any proposed LC is critical timely achievable with contemporary computer resources ILC-TRC subgroup has taken a first look best example: Seryi et al simulation of luminosity with DR>IP<DR configuration, ground motion, tuned misaligned linacs, IP feedbacks
Recap of 11/2 (2) Ultimate goal is to do end-to-end simulations including full DR>IP<DR configuration Full and realistic initial errors Dynamic errors and feedbacks Fully-realized commissioning algorithms (BBA, knob tuning, etc) Complete operational model (feedbacks and mover steering and etc) Diagnostics with realistic performance (resolution, stability, availability) Obviously a big job which has to be done in more manageable bite-sized pieces (alas) Bottoms-up approach to performance estimation Top-down approach studied by T. Himel (talk)
What s Happened Since Then Continued emphasis on the X-band main linac Large system Has a lot of emittance budget leverage Experience base of prior simulations allows a rolling start Unlike BC or BDS, Main Linac has tuning and performance challenges which are distinct from those facing SC design Hence the ML simulations may be valuable input to the technology choice
Main Linac Simulations The 23 X-band configuration uses H6VG3S17 as its baseline structure Simulations reported here still use the TRC configuration 8 2 GeV acceleration H9VGS18 structure baseline Bypass line eliminated match 2 GeV point directly into post-linac diagnostic region Understand influence of accelerating portion of main linac independent of the design of the bypass line
What was Looked At BBA starting with static misalignments and errors baseline case maximal use of PMQ s maximal use of emittance bumps in y no jitter during tuning Relative efficacy of various emittance bumps Impact of white-noise jitter on steering/alignment all-emq case (BPM-to-quad offsets smaller) Revisited (slightly) non-invasive resteering of the main linac to correct diffusive (ATL) motion
Psuedo-TRC Lattice 12 1 8 β, m x 6 4 2 Diagnostic Stations are indicated by red arrows Green lines show the bump locations (2 bumps at each line) 1 2 3 4 6 7 S, m
Main Linac Initial Steering Procedure Steer to minimize Q-BPM readings simultaneously minimize magnet mover motion Assume that quad shunting was previously done to get BPM-to-quad offsets (with some accuracy limits) Perform DF Steering Vary the energy gain of the linac to measure dispersion Apply emittance bumps in y bumps use quad movers and minimize beam size on downstream wires Note: Any time a quad is moved, immediately align relevant RF girders (subject to S-BPM resolution)
Baseline Performance 3 2 X plane steer flat Mean=12.% 4 3 Y plane steer flat Mean=118% 2 1 1 1 2 3 4 3 2 2 1 1 X plane steer + DFS Mean = 1.6% 9%CL=2.7% 1 2 3 4 6 2 1 1 2 3 4 6 3 2 2 1 1 1 2 3 4 6 3 2 2 1 1 Mean = 2.9% Y plane steer+dfs+bumps Mean=13.1% 9%CL=23.4% 1 2 3 4 1 seeds Distribution of emittance growth values (% of DR value) shown Compare to All- NLC budget = 2% (x), 1% (y)
Bump Efficacy 2 2 No Bumps Inject ELIN1 ELIN2 Average Emittance Growth (%) 1 1 Average Emittance growth (%) ELIN3 All Looks like last bump is much more effective and important than the rest
Tuning with Jitter 4 Horizontal Plane DFS mean DFS 9% CL All-NLC Budget 14 12 Vertical Plane Bumps Mean Bumps 9% CL All-NLC Budget Jitter budget exists for X- band LC 4 3 3 1 8 (~42 nm x rms quad jitter, 11 nm y rms, + incoming) 2 2 1 1 1 2 6 4 2 1 2 Studied convergence of steering as a function of jitter amplitude (1=1% of budget, 2=2% of budget) Jitter Amplitude/Budget
All EMQ, No Jitter 3 X plane steer flat 4 Y plane steer flat 2 3 2 1 1 1 2 3 4 6 2 1 1 1 2 2 3 2 2 1 Y plane steer+dfs EMQ s mainly improve pre- DFS performance 4 3 3 2 2 1 1 X plane steer + DFS 1 1 1 2 2 3 2 2 1 1 Y plane steer+dfs+bumps Relieves tight requirements on DFS algorithm 1 2 3 4 6 1 1 2
Non-Invasive Steering In normal operations, 2 systems work together to maintain emittance steering feedback at discrete locations operates on ~.1 second timescale Mover steering Everywhere Potentially operates on longer timescale Mover steering actuates many magnets at once If you move enough magnets at once the beam motion at the IP gets too big!
Steering (2) 2 Approaches to mover steering Move as many magnets as possible as fast as possible give up all luminosity during magnet moves Move-time = small fraction of total time May allow operation at high-motion site Move few magnets in small steps preserve luminosity during magnet moves can have magnet moves 1% of the time Rules out operation at high-motion site US/SLAC concentrating on second option KEK concentrating on first option
Slow Magnet Motion 7 6 4 3 97 Pulses σ =.8 σ y Moved magnets in nm steps 1 step/linac cycle Measured step-tostep motion of beam at end of linac 2 1 Message: For this technique, nm steps at the limit -.8 -.6 -.4 -.2.2.4.6 Beam Centroid Motion (σ ) y
Slow Magnet Motion (2) 6 x 14 4 3 2 1 98,8 magnet moves σ = 88 nm max = 7 nm (14 steps) -.8 -.6 -.4 -.2.2.4.6 Mover Position Change, µ m ATL motion assumed, with A=x1-19 m/s ( NLC Nominal ) Steer linac in segments Allowed 3 seconds between segment moves Magnets only needed.1 seconds to move! Can tolerate bigger A value?
Fast Magnet Motion (Kubo) Move magnets every 1 seconds If A = 1-17 m/s (2 x NLC Nominal ) Max magnet motion ~2 µm nm/linac cycle movers need 4 cycles (~4 seconds) to converge (too long) Even 1x faster movers make this practical KEK mover people estimate 1x faster is achievable (wow!) Bottom line: both solutions still look attractive! Need better understanding of train-by-train linac feedbacks to really get at this issue
Plans for the Near Future Transition to 23 main linac optics 1 TeV CM, no bypass line Complete set of initial and dynamic errors Incorporate energy/steering feedback models Essential for studying system with drift, klystron phase/amplitude jitter, changing RF complement Complete main linac tuneup studies Understand what all the ingredients are
Plans (2) Perform similar exercise for BC and BDS hopefully experience from ML will speed things up a bit! Shorter systems, fewer elements Y. Nosochkov & A. Seryi already looking at tuning up a misaligned, steered BDS End-to-end tuning ie, tune ML with beam coming out of a BC with 6 DOF jitter, etc. Operations studies
Simulation Junkies L. Hendrickson, K. Kubo, Y. Nosochkov, N. Phinney, T. Raubenheimer, A. Seryi, PT, A. Wolski, M. Woodley Additional Help and Input from: D. Schulte, N. Walker