Damping Ring ImpedanceK. Bane 04/05/2007 ILC DR Impedance Group At SLAC a group has been meeting bi-weekly for ½ year to study ILC DR broad band impedance and impedance effects Focus on the microwave instability; want to insure that ILC operates below threshold Impedance calculations: C. Ng, Z. Li Impedance effects: S. Heifets, A. Novokhatski, G. Stupakov, K. Bane We have no engineering drawings. We generate vacuum chamber components by scaling from existing machines. Pseudo-Green function wakes obtained by numerical calculation. High priority: rf cavities with tapers, bpm’s, resistive wall wake Medium priority: collimators, masks, antichamber slots, feedback kickers, etc Low priority: bellows, feedback pick-ups, etc (K. Bane, 5 April 07)

Damping Ring ImpedanceK. Bane 04/05/2007 ILC Damping Ring Cavity Cornell Model (scaled) KEK Model r= 92 mm r= 25 mm f 0 = 650 MHz (Z. Li)

Damping Ring ImpedanceK. Bane 04/05/2007 DR Cavity: Sigma_z=6mm Min/Max = E+00/ 1.620E+00 V/pC Loss Factor = E+00 V/pC F0=650MHz ABCI

Damping Ring ImpedanceK. Bane 04/05/2007 Sigma_z=0.5mm Min/Max = E+01/ 5.099E+00 V/pC Loss Factor = E+01 V/pC F0=650MHz ABCI

Damping Ring ImpedanceK. Bane 04/05/2007 ILC DR BPM 10 mm button 25 mm radius Snapshots of beam transit  = 2 mm (C. Ng) T3P

Damping Ring ImpedanceK. Bane 04/05/2007 Pseudo-Green Function A. Novokhatski

Damping Ring ImpedanceK. Bane 04/05/2007 Outlook Ideally would like to have wakes for an rms bunch length of ½ mm=> more calculations needed on the bpm’s. With rf cavity, bpm, and resistive wall impedance we can make “baseline” (conservative) instability calculations. This allows us to find out how much headroom we have—how far below threshold are we with this minimal impedance? The calculations for medium priority vacuum chamber objects will take some time: there are many objects, and how does one decide which designs will likely be chosen for the ILC?