| Paper | Title | Page |
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| TPPT088 | Power Dependence of the RF Surface Resistance of MgB2 Superconductor | 4215 |
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| MgB2 is a superconducting material that has a transition temperature (Tc) of ~40 K. Recently, it has been shown at 4 K, liquid helium temperature, that the surface RF resistance can be lower than Nb that has the Tc of 9.2 K and has been used for most superconducting RF cavities in the past decades. One of the problems with other high-Tc materials such as YBCO was its rapid increase in RF surface resistance with higher surface magnetic fields. Recently, we have shown that MgB2 shows little increase up to about 120 Oe, equivalent of an accelerating field of about 3 MV/m. The highest field tested was limited by available power. This result is encouraging and has made us consider fabricating a cavity coated with MgB2 and test it. Also, there might be a potential that this material has a higher critical magnetic field that enables the cavity to run at a higher gradient than Nb cavities. | ||
| TPPT090 | Progress of 2-Cell Cavity Fabrication for Cornell ERL Injector | 4248 |
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| Five 1300 MHz superconducting niobium cavities are to be used for the injector of Cornell ERL. The beam power requirement (100 kW each cavity) and the need to minimize emittance dilution due to the cavity structure have important impacts to the design and fabrication of these cavities. We plan to use Conflat stainless-steel flanges brazed to niobium tubes of niobium cavities. The first copper prototy cavity has been built and measured. Most parts for the first niobium cavity have been manufactured also. In this report, we will present the progress of the prototyping copper as well as niobium cavities. | ||
| TPPT094 | Design of the CW Cornell ERL Injector Cryomodule | 4290 |
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Funding: This work is supported by Cornell University. The Cornell ERL Prototype injector will accelerate bunches from an electron source to an energy of several MeV, while preserving the ultra-low emittance of the beam. The injector linac will be based on superconducting RF technology with five 2-cell RF cavities operated in cw mode. The beam tubes on one side of the cavities have been enlarged to propagate Higher-Order-Mode power from the cavities to broadband RF ring-absorbers located at 80 K between the cavities. The axial symmetry of these ferrite based absorbers, together with two symmetrically placed input couplers per cavity, avoids transverse on-axis fields, which would cause emittance growth. Each cavity is surrounded by a LHe vessel and equipped with a frequency tuner. The cryomodule provides the support and alignment for the cavity string, the LN cooling of the ferrite loads, and the 2K LHe cryogenic system for the high cw heat load of the cavities. In this paper we give an overview of the ERL injector cryomodule design. |
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| ROAC009 | World Record Accelerating Gradient Achieved in a Superconducting Niobium RF Cavity | 653 |
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Funding: Work supported by NSF. On November 16, 2004, an accelerating gradient of 46 MV/m was achieved (CW) in a superconducting niobium cavity with an unloaded quality factor (Q0) over 1·1010 at a temperature of 1.9 K. This represents a world record gradient in a niobium RF resonator. At a reduced temperature of 1.5-1.6 K, an enhanced Q0 was measured, ranging from 7·1010 at 5 MV/m to 2·1010 at 45 MV/m. The 1.3 GHz single-cell cavity has a reduced ratio of Hpk/Eacc, ensured by a reentrant geometry. The maximum peak surface electric and magnetic field exceeded 100 MV/m and 1750 Oe respectively. A soft multipacting barrier (predicted by calculations) was observed near 25 MV/m gradient and was easily processed through. Field emission in the cavity was negligibly small, and the highest field was limited by thermal breakdown. The cavity was built, processed, and tested with LEPP facilities at Cornell University. New techniques included half-cell heat treatment with yttrium for post-purification to RRR = 500, and vertical electropolishing the finished cavity. |