SLHi PP9 Development of Elliptical Cavity System at

SLHi. PP-9 Development of Elliptical Cavity System at IHEP Zhenchao LIU, IHEP 2019. 9. 27, Lanzhou

Contents Ø Back grounds Ø Design and optimization of the 650 MHz 5 -cell superconducting cavity Ø Fabrication and testing results Ø Summary

Contents Ø Back grounds Ø Design and optimization of the 650 MHz 5 -cell superconducting cavity Ø Fabrication and testing results Ø Summary

Back grounds Main Linac Tasks of IMP Tasks of IHEP

Back grounds Ø The high energy segment of the ADS proton linac requires a high acceleration gradient with a high quality factor and a high beta superconducting cavity for proton acceleration; Ø For the first time to develop this type of superconducting cavity, it is necessary to explore relevant development processes and manufacturing processes, and improve supporting equipment and facilities; Ø It is necessary to solve the technical problems associated with the processing and manufacturing of superconducting cavities, reduce the development cost, and lay the foundation for industrial production; Ø Optimization design and performance improvement of superconducting cavity

Contents Ø Back grounds Ø Design and optimization of the 650 MHz 5 -cell superconducting cavity Ø Fabrication and testing results Ø Summary

Optimization of the cavity 650 MHz beta=0. 82 SC cavity shape optimization ü Joint analysis of Build. Cavity and Superfish ü Field flatness >98% ü Optimize the ratio of the peak magnetic field and the peak electric field over the acceleration gradient Center cell End cell L (cm) 9. 461 Riris (cm) 5 5 D(cm) 20. 0207 A(cm) 7. 027 7. 166 B(cm) 7. 027 7. 883 a(cm) 1. 681 1. 667 b(cm) 2. 522 2. 501 α (°) 7 6. 678 Ep/Eacc 2. 12 Bp/Eacc [m. T/(MV/m)] 4. 05 r/Q [W] 514. 6 G [W] 235. 5 k [%] 0. 9% Field flatness [%] >98 Lower peak magnetic field and peak electric field ratio to Eacc Higher r/Q and G values

MP and mechanical strength analysis No MP hard barrier， Appropriate Lorentz coefficient Ø Calculate the occurrence of MP in the range of 1 -20 MV/m, 10°sector model; cavity working acceleration gradient range: 10 -15 MV/m Lorentz force analysis (wall thickness: 3. 7 mm) in the presence of devices such as tuner and liquid helium cylinders: Ø The results show that no serious MP will occur, which is a soft barrier that can be removed by high-power processing. with stiffening ringr=8. 52 cm： KL=-0. 327 Hz/(MV/m)2 without stiffening ring KL=-1. 04 Hz/(MV/m)2 MP analysis by Track 3 P Lorentz analysis

Power coupler optimal coupling range Qe@1 -4 x 106 Q 0=5 E 9 Q 0=1 E 10 The minimum power of the generator Pg is about 150 k. W, Qe adjustable range: 1~4 x 106

650 MHz beta=0. 63 SC cavity Center cell End cell L (cm) 7. 269 Riris (cm) 5 5 D(cm) 20. 0215 A(cm) 5. 504 5. 201 B(cm) 7. 155 6. 761 a(cm) 1. 457 1. 533 b(cm) 2. 331 2. 453 d (cm) 1. 34 α (°) 3 4. 822 Ep/Eacc 2. 60 Bp/Eacc [m. T/(MV/m)] 4. 73 r/Q [W] 304. 41 G [W] 193. 4 k [%] 1. 35% Field flatness [%] >97

Stiffening ring

Contents Ø Back grounds Ø Design and optimization of the 650 MHz 5 -cell superconducting cavity Ø Fabrication and testing results Ø Summary

Dies and half cell Dies of the 650 MHz beta=0. 82 cavity 650 MHz cavity 3 D inspection of half cavity

Dumbbell welding

Analysis of Frequency and Deformation Measurement of Dumbbell Half Cavity Perturbation method The frequency change is linear with the pressure. The frequency change is about df=kd. P, k=1 KHz, and the d. P unit is kg. The dumbbell is squeezed by 500 kg pressure, and the length is deformed to about 10 -20 um after the pressure is removed.

Dumbbell leveling and cavity tuning Self-tuning code Parallelism<0. 35 mm >94%

New Pre-tuning machine Ø 1. 3 GHz and 650 MHz elliptical cavity pre-tuning machine Ø Eccentricity measurment and tuning（<0. 4 mm） Ø Field flatness measurement and tuning(>95%) Ø About one and half day for field flatness tuning Ø Collaboration with PKU

SC cavity EB welding ØSub-assembly welding, then overall welding, reducing risk ØOvercome difficulties such as easy perforation of the equator

SC cavity post-processing Annealing 120℃ bake HPR BCP Pure water washing Leak check Assembly

IHEP EP Facility formally Put into Use • Under the supports of PAPS, HEPS-TF, CEPC, and Beijing local government, a horizontal EP facility was developed at IHEP. • Recently, it has formally put into use in July this year, after fabrication and commissioning which took nearly two years. • It will be compatible for several types of cavities, such as 500 MHz 1 -cell, 1. 3 GHz up to 9 -cell , and 650 MHz up to 5 -cell cavities. Before EP After EP

SC cavity vertical test The cavity has reached the design goal and has a high Q 0 value. Ø The cavity is the first 650 MHz mid-high beta superconducting cavity in China to meet the design goals. Ø The acceleration gradient reaches 9 MV/m at 4. 2 K and Q 0 is 1 x 109 (target value: 8 MV/m, Q 0>3 x 108@4. 2 K) Ø At 3. 3 K, it reaches 11. 8 MV/m and Q 0 is 1 x 109. The design index at 2 K temperature has been reached at 3. 3 K (target value: 8 MV/m, Q 0>3 x 109@2 K).

Summary Ø 650 MHz beta=0. 63 and 0. 82 5 -cell cavity shape were designed Ø 650 MHz beta=0. 82 5 -cell cavity was fabricated and vertical tested. The cavity has reached the design goal and has a high Q 0 value. Ø New equipment of Pre-tuning machine and EP machine can be used for such cavities. Ø New technology such as N-doping, full inner surface polishing can be used for the post-processing.

Thank you！