Transcript Document

R.L. Geng, G.V. Eremeev, H. Padamsee, V.D. Shemelin
High Gradient Studies for ILC with Single-Cell Cavities
• Role of grain boundary in
limiting gradient.
• Compare electropolsihed
large-grain cavity with BCP
etched large-grain cavity.
• Large-grain Nb from China.
• RRR 300 niobium sheets, butt weld at equator.
• Post-purification 1300 °C X 2 hr + 1200 °C X 4 hr.
• CBP 300 µm + CP 10 µm + 750 °C X 3 hr at KEK.
• EP 100 µm + HPR + 120 °C bake at KEK.
• Ultrasonic rinse in soapy water + HPR X 2 hr.
• Over night drying in clean room, no flipping.
4 single-cell re-entrant cavities built, 3 set gradient record
• 70 mm aperture RE LR1-2 reached first 47 MV/m in 2004 at Cornell.
• Pump down with water in re-entrant pocket.
• 70 mm aperture RE LR1-1 reached first 52 MV/m in 2005 at KEK.
• Warm up cavity to 35-40 using IR lamp.
• 60 mm aperture RE LR1-3 reached first 59 MV/m in 2007 at Cornell.
Photo credit: T. Saeki
 New 60 mm aperture RE cavity reached new record gradient 59 MV/m.
 Peak surface magnetic field reached record value of 2065 Oe.
 Pump down with water in re-entrant pocket works well.
 Eliminating mechanical defects necessary for reaching high gradient.
 Electropolishing large-grain niobium cavity initial results show much
higher Q compared to buffered chemical polishing.
 More large-grain cavities coming.
 Large-grain RE cavites.
Kenji Saito, Takayuki Saeki, F. Furuta of KEK
Prof. Zhao Kui of Peking University