Emittance Dilution and Preservation in the ILC RTML P. Tenenbaum ILC LET Meeting 09-Feb-2006 Includes corrections on slides 15 and 16 from 16-Feb-2006

Introducing the ILC Ring to Main Linac (RTML) Transport 09-Feb-2006 P. Tenenbaum

Introducing RTML (2) Skew Correction Collimation DR Stretch Turnaround 4 orthonormal skew quads to tune betatron coupling Collimation 2 phases x 2 planes x 1 iteration of betatron collimation DR Stretch Allows position adjustment of DR within site footprint Turnaround Achromatic arc permitting feed-forward correction of beam jitter 09-Feb-2006 P. Tenenbaum

Introducing RTML (3) Spin Rotator 4D Emittance measurement BC1 and BC2 Solenoids + arc allow arbitrary tuning of IP polarization direction 4D Emittance measurement Laser wires configured to allow 4D emittance measurement and fit BC1 and BC2 Two-stage bunch compression, with pulsed dumps Linac launch Final emittance diagnostic (2D) before main linac 09-Feb-2006 P. Tenenbaum

Major Sources of Emittance Dilution Vertical Dispersion Collimator Wakefields XY Coupling from DR extraction ISR XY coupling Dispersion, Wakefields, RF pitch, Collimator Wakefields, IP arrival time error, ISR 09-Feb-2006 P. Tenenbaum

LET Studies so far on RTML Nothing Almost! Looked at use of normal / skew quads in BC1 and BC2 for dispersion control More on this later 09-Feb-2006 P. Tenenbaum

RTML Tuning and Ideas Dispersion tuning in Skew, Coll, DR Stretch, Turnaround, Spin Rotator BBA (ie, measure BPM offsets and correct orbit) Quads are NC iron-dominated Thought to be better for BBA than SC cos(2θ) DFS? Maybe not – may be hard to get large energy variation from DR Problem in ATF Global correction Include skew quads in turnaround and Spin Rotator for tuning vertical dispersion? Probably necessary for correcting dispersion from rolled bends 09-Feb-2006 P. Tenenbaum

RTML Tuning and Ideas (2) XY Coupling from DR and Spin Rotator Skew quads in Skew Correction section 1 set for both areas OK if residual coupling is small (~1%), per K. KUBO Sets tolerance on DRX / Spin Rotator initial coupling correction, or else we need 2 sets of skew quads Collimator Wakefields Feed-forward can correct betatron jitter amplification Reduce by a factor of 10? No correction possible for emittance growth Will set limits on beam jitter from DR and/or collimation depth achievable No correction possible for energy-betatron jitter coupling Not a large problem in systems studied to date (ie, NLC) 09-Feb-2006 P. Tenenbaum

RTML Tuning Ideas (3) Emittance Dilution in BCs May be a very large source Wakefields, RF cavity pitches, dispersion Long bunch near zero crossing with large energy spread SC quads thought poor candidates for BBA Lots of strong bend magnets with tight rotation tolerances Dispersion control quads may work Wakefields: need good alignment of modules Do we need HOM readouts on cavities here? 09-Feb-2006 P. Tenenbaum

RTML Tuning Ideas (4) Longitudinal tuning and stability of BCs Need bunch length monitors and beam phase monitors after each BC Need to tune linear map terms as well as final bunch length Ie, want to limit sensitivity to DR phase jitter Need to monitor relative IP arrival time of the two bunches Beam-based feedback on some timescale 09-Feb-2006 P. Tenenbaum

Tuning the RF Pitch Aberration in ILC RTML RF cavities in RTML operate near the zero-crossing Pitched RF cavities rotate some of their longitudinal field into vertical field Put those together: Time-varying vertical field Head-tail deflection of the beam Potentially a big effect – bunches are long and at low energy! 09-Feb-2006 P. Tenenbaum

Tuning Pitch Aberration (2) Walker’s conjecture: Pitched RF cavities make z-Py correlation But they also make z-E correlation Hence they make a strong E-Py correlation, ie, η’ Thus the dispersion knobs should be very effective against pitch aberration! Try this out in Lucretia! 09-Feb-2006 P. Tenenbaum

BC1 Wiggler Optical Functions (BC2 is similar) = location of skew quads for ηy control 90° -I xfrm -I xfrm 09-Feb-2006 P. Tenenbaum

Simulation Procedure Roll 100 seeds of BC Steer flat on BPMs Each seed perfect except that RF cavities have 300 μrad RMS pitch Steer flat on BPMs Take out steering from cavities Comes from pitch on cavities which are not exactly on zero-crossing Scan 4 dispersion knobs (2 in each BC), optimizing emittance at end BC Meas emittance at 5 steps of knob, fit parabola, accept best value If best value is outside scan range, scale range and rescan For now, perfect measurement of projected vertical emittance simulated 09-Feb-2006 P. Tenenbaum

Results 09-Feb-2006 P. Tenenbaum Mean = 27.9 nm 90%CL = 63.1 nm

Results (2) Correction with skew quads is pretty effective… Factor of ~9 reduction in mean growth Factor of ~11 reduction in 90%CL growth …but not quite effective enough! 90%CL growth > entire RTML budget No other technique available right now to improve on correction Tuning may not yet be optimal Needs more study (where have I heard that before?) 09-Feb-2006 P. Tenenbaum