Matching Injector To Linac

Caveats This is all loose and fuzzy – sort of religion We dont have real tight control over and knowledge of the machine – functional modularity, beam based methods, etc => dial it in, rather than lock it down We have gotten it to work well enough to lase hard and reliably Yall are a test sample – well all try to figure out how to tell people what weve done and how it works – Ask questions – Give advice

Issues Inaccuracies/ambiguities in model-based predictions Drive laser variations Cathode model approximations Injector, accelerator magnets not well characterized – Field calibrations, current control – Field inhomogenieties Simplified field models in cavities – 3-d field details needed for accuracy – Gradient calibrations loose Can model trends very well, and values well - but only with extremely tight configuration control Must provide beam-based tuning algorithms

Methodology Set phases (spectrometer, miniphase) Calibrate model – Quads dont set with good precision – Use difference orbits to check focusing – Modify model to produce agreement with observation Change magnet (usually quad) set-points to make model match reality Perform multi-monitor emittance measurement – Gives notional beam properties at front end of machine Rematch – Resets beam properties to fit within downstream acceptance

Machine Model Analysis of beam and accelerator properties requires a means of evaluating transfer matrix elements, beam envelopes, etc Typical machine models are home-brewed, machine specific, but generally are – based on matrix-multipliers – Read parameters directly from the machine – Run fast – Have a high degree of interactivity Can modify easily Pull in/push out data Optimize optics solutions, orbit corrections, etc

Difference Orbits When we phased, we zeroed the BPMs and looked at the effect of changing phase – The signature was the change in position at the spectrometer observation point Method works for other parameters: zero the BPMs and see what happens when we kick beam Can be used to establish transfer matrix elements (esp. M 12, M 34, M 62, …) – Twiss parameter representions (betatron amplitudes) – Phase advance – Momentum compactions M 55,T 555, … Basic method: – Zero BPMs – Change something and look at response Corrector (M 12, M 34 ) Beam energy (M 16 ) Injection phase (M 55, T 555, …) Analysis of data can – Set BPM scale factors – Trap focusing errors (quad, dipole, screwdrivers, allen wrenches…) – Measure/correct compactions This measurement characterizes the lattice - and helps you use the lattice to measure the beam

Multi-monitor Emittance Measurements Beam envelopes at an observation point are defined by their value at some upstream reference + the transfer matrix If the transfer matrix (matrices) are known, can measure spot sizes at several (more than three) places and determine beam envelopes and emittance Form sum of square deviations between projection & observation, and minimize by varying injected betas

Rematch After fitting initial beam envelopes to reproduce in model observed spot sizes, you can see the propagated Twiss parameters Adjust quads to make real betas match design acceptance values Iterate: – Remeasure, check propagated envelopes, see if agreement improves

The Dread Matchathon Wailing, cursing, gnashing of teeth… Apply same process to – linac-to-arc match, – dispersion management in arc(s), – arc-to-wiggler match, – momentum compaction (M 55, T 555 ) for bunch length compression, – wiggler-to-arc match, – arc-to-linac (reinjection) match, – energy compression (M56, T566, W5666), Iterate Then trim for loss suppression as you boot-strap lasing

To Consider Beam is very irregular – must consider just what you match on – Full beam size (stuff all the electrons through tight apertures) – Sigmas – fit to gaussian – Rms beam size Usually worry about the 1 st Hard to associate which gaussian goes with which other when you march down the line