FNAL Director’s Review Proton Driver Spoke Cavity Development

1. FNAL Director’s Review Proton DriverSpoke Cavity Development Kenneth W. Shepard Physics Division March 16, 2005

2. Spoke-loaded concept introduced more than a decade ago • Developed for high-intensity ion beams • 6.5 inch ID • 855 MHz • = 0.5 The two-gap niobium structure was operated at 7.2 MV/m at 4.2 K “Design and Test of a Superconducting Structure for High-velocity Ions”,J. R. Delayen, et al., LINAC 92

3. Cylinder ½ x ½ Meter TE111 at 462 MHz TM010 at 459 MHz

4. Cylinder, ½ x ½ Meter, plus a transverse spoke TE111 at 454 MHz TM010 at 430 MHz

5. Spoke-loading reduces cavity diameter, good properties for  = v/c  1/2 Lowest RF eigenmode is now a TEM Mode, with the spoke acting like a /2 section of transmission line. The resonance is at 340 MHz, somewhat higher than a nominal 300 MHz for a ½ meter length of line

6. We need a lower-frequency spoke cavity (~350 MHz) for the RIA driver linac b=0.3 b=0.4 “Development of Niobium Spoke Cavities for a Superconducting Light-ion Linac”, K. W. Shepard, et al., LINAC 98

7. Kelly (ANL) and Tajima (LANL) improved performance of ANL niobium prototype spoke cavities with HPR & ultra-clean techniquesPAC 2001 Los Alamos, Spring 2001 Argonne, Spring 2001 Q Los Alamos Result b=0.3 cavity Argonne Result b=0.4 cavity

8. Los Alamos β-0.175, 350 MHz Spoke for intense beams (LEDA afterburner project) “Test Results of Two LANL Beta = 0.175, 350-MHz, 2-Gap Spoke Cavities”, Tajima, et al., PAC 2003

9. IPN Orsay  0.35, 352 MHz single spoke for 100 MeV Proton Linac “Status Report on Supercond-ucting Spoke Cavities at IPN“, Guillaume Olry, PAC 2003

10. At ANL, multi-cell 345 MHz spoke-loaded cavities are being developed for RIA β=0.4 double-spoke β=0.5 and 0.64 triple-spokes

11. Cold-test results for the  =0.4 double-spoke for RIA Shepard, Kelly, Fuerst, presented at PAC 2003, SRF 2003 The cavity can operate cw at gradients up to 12 MV/m, producing more than 4.5 MV of accelerating potential

12. Cold-test results for the β=0.5 triple-spoke for RIA Shepard, Kelly, Fuerst, to be presented at PAC 2005 At the design gradient, 9.2 MV/m, the cavity produces more than 6 MV of acceler-ating potential

13. Spoke cavities have good mechanical properties Measured mechanical properties indicate that pulsed operation should be straight-forward The Lorentz transfer function for  0.5 triple-spoke measured at ANL by U of I graduate student Zachary Conway ( to be presented at PAC 2005)

14. Tuners and couplers being developed for RIA Prototype piezo-fast-tuner mounted on double-spoke cavity RF Power Coupler for CW operation at 5 – 10 kW (Need a new coupler for Proton Driver)

15. The ANL 345 MHz Triple-spoke cavities can be re-tuned to 325 MHz by increasing the (20 cm) housing radius by only 8 mm (existing tooling can be used to form the parts) CST MicrowaveStudio model of 325 MHz triple-spoke for FNAL Proton Driver

16. The development of superconducting spoke-loaded cavities is well-advanced: ready for production Results to date indicate that pulsed operation is entirely feasible – suitable for Proton Driver Remaining development is straightforward: Prototype 325 MHz niobium cavities RF Power coupler for pulsed operation Fast-tuner system for pulsed operation Conclusions