Update on BGV impedance August 1 st 2013 Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi, Plamen Hopchev, Nicolas Mounet, Elena Shaposhnikova, Ray Veness.

Longitudinal modes for the asymmetric case Low frequency longitudinal impedance Low frequency transverse impedance Starting to check transverse modes

Longitudinal impedance at high frequency  Total length: 2 m  Copper and Steel structure Angle 2=5 degrees Scan over Angle 1  The lower the tapering angle, the better (also for power loss)  Under the limit even with angle close to 90° Copper Stainless Steel 316LN Copper Largest mode: 60 W Largest mode: 6 W

Longitudinal impedance at high frequency  Total length: 2 m Angle 2=5 degrees Scan over Angle 1 Copper Stainless Steel 316LN Copper

Longitudinal impedance at low frequency Longitudinal impedance Z (in Ohm) Frequency in GHz  Should be minimized to avoid longitudinal instabilities (currently 90 mOhm)  Total length: 2 m Angle 2=6 degrees Scan over Angle 1  One single BGV is not negligible compared to the rest of the machine.  The lower the tapering angle, the better (factor ~5 between 10 and 90 degrees)

Transverse impedance at low frequency  Should not be increased to avoid transverse instabilities (currently 2 MOhm/m at injection)  Total length: 2 m Angle 1=6 degrees Scan over Angle 2 Transverse impedance Z (in Ohm/5mm displacement) Frequency in GHz  Limited impact on low frequency transverse impedance

Transverse impedance at high frequency  Total length: 2 m Angle 2=5 degrees Scan over Angle 1 Copper Stainless Steel 316LN Copper Beta functions at the location of the BGV: 167 m (from Plamen).  These modes need to be multiplied by beta/ =2.4 (i.e. a range of 1 MOhm/m)  Need to check the impact on beam dynamics Some peaks can be fake due to large noise  being checked

Conclusions so far Taper clearly helps also in the asymmetric case Longitudinal and transverse low frequency impedance are between 0.1% and 1% of the full LHC impedance. Effect of transverse modes for the final structure should be checked by beam dynamics studies