Participants:
CERN: M. Schuh, W. Weingarten, S. Calatroni
Rostock: H-W Glock.
Darmstadt: W. Mueller.
The proposed agenda was:
· Approval /follow up of minutes of previous meeting
· Technical summary and conclusions for the SPL (as presented at Lund by F. Gerigk) reconsidered by W. Weingarten
· Update on longitudinal HOM damping and beam break up simulations for pulsed beams (three presentations by W. Weingarten, M. Schuh)
· AOB
· Date of next meeting
Detailed discussions:
· Approval /follow up of minutes of previous meeting
o The minutes are approved
· Technical summary and conclusions for the SPL (as presented at Lund by F. Gerigk) reconsidered (W. Weingarten)
o Wolfgang summarised Frank’s presentation and some key choices made at Lund. Notable choices are inter-cavity spacing of 2*lambda/2 taking into account fundamental mode attenuation, HOM couplers with notch filtering (bellows are inefficient at low frequencies), definition of safety margins for cryostat design.
· Longitudinal HOM damping (W. Weingarten)
o The choice is always between 10E7 Qext if possible to avoid machine lines, or 10E4 Qext (preferred) for efficient damping while keeping low HOM power. However in the latter case a notch filter for the fundamental mode is necessary. It is proposed to abandon the study of stainless steel bellows-like damping, while starting the study for possible damping via the main coupler.
· HOM power dissipation & Fundamental Power Coupler (FPC) (M. Schuh)
o Marcel presented simulations for different chopping schemes. Simulations with noise and analytical calculations are matching, with deviations only off-resonance (by more than 10 MHz) and external Q-values >10E5. The dissipation of the HOM power in the FPC was calculated for a 50 Ohm load close to the window. The external Q-values obtained for longitudinal HOMs in the frequency band 1.3 – 1.5 GHz were quite encouraging (Q<10E6). The FPC can provide damping, but further more detailed studies are needed, e.g. a measurement of the impedance of the FPC including waveguide and circulator.
Recursive analytical calculations by W. Weingarten of the BBU were in line with results already presented by M. Schuh at earlier occasions.
· AOB: none
· Next regular meeting will be on 20th September
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