Alexej presented an update of the HDS structure parameter scan. Since his last presentation on HDS a bug in the program GdFidl had been discovered, which led to a overestimation of the Wakefield amplitudes by a factor 2. For the new parameter this was corrected and the change in pulsed surface heating due to the use of Cu/Zr instead of Cu was taken into account.
He introduced L/N*η as a figure of merit which is proportional to the integrated Luminosity divided by the available power. He compared a structure with a maximum for this figure of merit with a structure with maximum efficiency. Even though the structure has a 8% higher figure of merit, the more effective structure is preferable because of the lower input power (132 vs. 173 MW).
Hans mentioned that the experience showed that large aperture structures did not go high in accelerating gradient and that the reason for this are still not fully understood. He also remarked that the consequences for reducing the bunch separation from 20 to 10 or now even 8/9 RF cycles has not been checked (damping ring RF, kink instability).
Alexej will extend his parameter space to smaller and larger aperture and will investigate other phase advance, frequency and gradient in terms of efficiency.