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Analysis and Testing of a 704 MHz SRF Cavity for ERL5

This document presents the analysis and testing results of a 704 MHz SRF cavity for ERL5, including electromagnetic analysis, mechanical modes analysis, and cryomodule testing. Lessons learned and future improvements are also discussed.

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Analysis and Testing of a 704 MHz SRF Cavity for ERL5

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  1. 5 cell 704 MHz SRF Cavity R&D ERL5 cell 704 MHz SRF Cavity Andrew Burrill February 17-18, 2010

  2. The Cavity • 5 cell SRF cavity, 17 cm iris, 24 cm beampipe • 703.75 MHz, 20 MV/m @ Qo=1e10 • No trapped HOMs • Cavity is inherently stiff, so no additional stiffeners are needed • Coaxial FPC for power delivery • Ferrite Dampers for HOMs • 5 K heat intercept on beampipe • Mechanical Tuner with 100 kHz tuning range, piezo provides 9 kHz fast tuning

  3. Cryomodule Configuration Cold-to-Warm Beam Pipe Transition (2) 4” RF shielded gate valve (2) HOM ferrite assembly Space frame support structure 2K main line Cavity Tuner location Cavity assembly Vacuum vessel HOM ferrite assembly 2K fill line Outer magnetic shield Heater Thermal shield Fundamental Power Coupler assembly He vessel Inner magnetic shield

  4. Mechanical and Electromagnetic Analysis ELECTROMAGNETIC ANALYSIS LORENTZ FORCE DETUNING • Finite element models were used to evaluate the thermal, structural, and RF behavior thermal load, pressure load, and loads from the cavity tuner • Cavity is inherently stiff due to large angle cell faces  no iris stiffeners, 3mm niobium thickness MECHANICAL MODES ANALYSIS 1st and 2nd mode 96.8 Hz 3rd mode 203.5 Hz Load Freq. shift 4th and 5th mode 213.6 Hz

  5. String Assembly & Installation

  6. Cryomodule Testing and Lessons Learned • To date the cryomodule has been tested 4 times. • There are signs of field emission, which prompted us to try Helium processing • Currently limited by our cryogenic capacity • This should be resolved in the next year • All systems operational • HOM measurements have been carried out at 4K and 2K and match well with simulations • LLRF system and 50 kW transmitter working well, both c.w. and pulsed. • Field in the beampipe manifests itself as a low Qo. This is a function of the large beampipe, and the power dissipated in the 5K circuit should not affect the cavity performance. • This was modeled in superfish (AES) in 2004.

  7. Summary • Cryomodule Testing is ongoing with improvements made each time the cavity is tested. • A better understanding of the heating in elements cooled by the 5 K circuit is being developed and a plan to increase the cooling capacity in this circuit being devised. • Testing length and integrated operational time at gradient will be greatly improved once the refrigerator is online. • Field emission remains a problem that we have not had sufficient time at gradient to properly process.

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