Cornell VEP Update, VT Results and R&D on Nb Coupon

Cornell's SRF group have continued R&D of Vertical Electro-Polishing (VEP) on SRF Nb Cavity. We have achieved high gradient with singeland multicell cavities by our VEP. We also have started VEP'ed Nb coupon surface analysis based on surface roughness measurement. We will describe our status of VEP R&D, the vertical test results of VEP'ed cavities, and fundamental study on VEP using Nb coupons. CORNELL’S VEP SYSTEM Figure 1 shows images of single cell cavity and Cornell’s VEP system with acid circulation. Cornell’s VEP system could process 1.3GHz TESLA/Reentrant/ICHIRO shape cavities. Half-cell coupon cavity has been fabricated and processed for fundamental study. EP acid agitation is controllable with puddle on stir tube. New acid mixing tank is now available for all single/multicell cavities, easy acid mixing, acid circulation during VEP process. Temperature is controlled by spray water for cavity outside. We also have compact EP system for Nb sample sheet, mushroom cavities. Table 1 shows parameters of Cornell VEP. RECENT ACHIEVEMENTS WITH VEP We have processed and tested many single-/multicell cavities with VEP. Analysis on removal vs. voltage in Figure 2 shows a tendency that small removal as final etches could provide high gradient. Based on this analysis, additional 5μm VEP was applied on TESLA 9cell cavity “A9”. A9 successfully achieved high gradient of 38 MV/m with Qo of 0.9 E10 at 2 K, satisfied ILC BL specs [1]. Figure 3 shows summary of VEP’ed 9-cell cavities at Cornell. Single cell “NR1-3” was also processed with 5 μm VEP and achieved 43 MV/m with high Qo [2]. ____________________________________________ #ff97@Ccornell.edu TUP049 Proceedings of SRF2013, Paris, France ISBN 978-3-95450-143-4 524 C op yr ig ht c ○ 20 13 by th e re sp ec tiv e au th or s 09 Cavity preparation and production G. Basic R&D bulk Nb Surface wet processing