1. Presented by Grigory Eremeev Grigory Eremeev

2. Presented by Grigory Eremeev Outline: - Cavities and Fields; - Results; - Tricks of the Trade: new shapes; - Making of theoretical niobium.

3. Presented by Grigory Eremeev Conducting cavities can be filled with electromagnetic energy. This energy is then transferred to charged particles flying along the cavity axis.

4. Presented by Grigory Eremeev THE CAVITY Cavity cavity Niobium – best superconducting properties among all pure metals: T c ~ 9.25 0 K; H c ~ 2000 Oe; R bcs ~.00001 mΩ at 2 0 K Nb : R s ~.00001 mΩ Cu: Rs ~ 10 mΩ ↓ Q nb ~ 10 11 up to E acc = 5·10 7 Volts per meter

5. Presented by Grigory Eremeev Ideal 9 10 8 11 10 0204060 Q0Q0 E acc, MV/m Real

6. Presented by Grigory Eremeev High-purity Nb, sheet inspection, CBP, etc Improved cavity shape Electron multiplication Thermal breakdown Electron field emission Quench High-pressure rinsing, cleanroom procedures Electropolishing, low temperature baking, … Limitation: Solution: Courtesy of Matthias Liepe Limitation: Solution: 1975 3 MV/m 1995 25 MV/m 1990 15 MV/m 2005 >40 MV/m 1985 6 MV/m 2000 40 MV/m High field Q- reduction Further improved cavity shapes

7. Presented by Grigory Eremeev We are still limited at about E acc = 40 MV/m for standard elliptical-shape cavities. Best cavities

8. Presented by Grigory Eremeev Tricks of the Trade: New shapes

9. Presented by Grigory Eremeev Reduction of surface magnetic field by increasing magnetic volume Courtesy of Valery Shemelin Re-entrant cavities

10. Presented by Grigory Eremeev Re-entrant cavity breaks the barrier in 2005 at Cornell

11. Presented by Grigory Eremeev For the talk by J. Sekutowicz, SLAC, January 25, 2005

12. Presented by Grigory Eremeev For the talk by Takayuki Saeki, KEK

13. Presented by Grigory Eremeev H surface = 2065 Oe Superconductivity above H c Tested at Cornell on March 14, 2007…record still holds

14. Presented by Grigory Eremeev Making of Theoretical Niobium: large grain and single crystal Another Trick

15. Presented by Grigory Eremeev

16. Large grain cavities P. Kneisel et al., Single Crystal Workshop In order to improve niobium surface it was proposed to increase grain size, and to make large grain or even single crystal cavities.

17. Presented by Grigory Eremeev

18. Exceptional smoothness From paper by W. Singer et al., PAC’2007

19. Presented by Grigory Eremeev We are looking for other tricks…

20. Presented by Grigory Eremeev Next speaker will talk more about studies related to high-field limitation of RF cavities. More tricks?