Progress of Hom Coupler for Cern Spl Cavities∗

In this paper we present the progress of the HigherOrder-Mode (HOM) coupler design for the high beta CERN SPL (Superconducting Proton Linac) cavities. This includes the RF transmission behavior as well as mechanical and thermal requirements and their optimizations. Warm RF measurements are presented for the rst four high beta SPL Cavities made of bulk niobium. Moreover the rst prototype of a HOM coupler will be introduced and we discuss its characteristics and its tuning possibilities. INTRODUCTION The SPL [1] linac is composed of two types of cavities operating at 704.4MHz in pulsed mode and with geometrical betas of 0.65 and 1. In order to limit beam induced HOM effects, it is considered to use coaxial type HOM couplers on the cut-off tubes of the 5-cell cavities. Based on RF and thermal simulations for the PROBE, HOOK and TESLA designs (already presented in [2]) it was decided to fabricate a prototype of the coupler with probe antenna (PROBE) as shown in Fig. 2. This coupler type was selected for the following features: • Notch lter with a relative high bandwidth (50 kHz) and therefore very robust. • High selectivity (steep transition between stop band or notch lter and pass band). • Best coupling to the monopole HOMs at 1.3GHz. • No active cooling of the antenna necessary.