| Paper | Title | Page |
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| TPPT068 | Optimized Shape of Cavity Cells for Apertures Smaller than in TESLA Geometry | 3748 |
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The accelerating rate (Eacc) of TESLA cavities can be increased for the same iris aperture if 1) some increase of Epk/Eacc is permitted so that the value of Hpk/Eacc can be lowered in comparison with the original cells (Epk and Hpk are maximal surface electric and magnetic fields); 2) shape of the cells is described by two elliptic arcs; 3) the reentrant cells obtained as a result of consecutive optimization with this geometry are treated as a possible version of cells in spite of some complications for fabrication. Not only the value of Hpk/Eacc can be improved but also values of cell-to-cell coupling and the geometry constants R/Q and G grow with the transition to the reentrant shapes. And these are not all benefits of this shape. The increased coupling prompts that the aperture of the original cell is big enough to be decreased without loss of field flatness in comparison with the original design. This decrease will lead to further increase of the Eacc for the same Hpk also as to improvement of others important parameters. Here, results of calculations for the original and for smaller apertures are presented and proposals for a better choice of TESLA cavity cells are derived.
Cornell University |
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| 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. |
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| RPPE059 | Measurements of Epsilon and Mu of Lossy Materials for the Cryogenic HOM Load | 3462 |
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Funding: Supported by Cornell University In high current storage rings with superconducting cavities strong broadband HOM damping has been achieved by using beam-pipe ferrite loads, located at room temperature. Adopting the same damping concept for the ERL with RF absorbers between the cavities in a cavity string will require operating the absorbers at a temperature of about 80 K. This temperature is high enough to intercept HOM power with good cryogenic efficiency, and is low enough to simplify the thermal transition to the cavities at 2 K. However the electromagetic properties of possible absorber materials were not well known at cryogenic temperatures. We performed a measurement program at Cornell to find possible absorbers for HOMs in the ERL. Measurements were done for 10 different materials in the range from 1 to 40 GHz. |