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SRF2003 Show Abstract

Title First Cryogenic Tests with JLabs new Upgrade Cavities
Type Poster high gradient
Abstract For the upgrade of CEBAF to 12 GeV two types of 7-cell cavities have been developed: the High Gradient type (HG) has been optimized with respect to the ratio of Epeak / Eacc  and for the Low Loss (LL) type the shunt impedance has been maximized. Both cavity styles feature two DESY type coaxial HOM couplers on the beam pipes on both ends of the cavity, a waveguide input coupler, a transmission probe, NbTi end dishes as part of an integrated He-vessel and stiffening rings between the cells and the end dishes. Design goals for these cavities have been set to Eacc = 20 MV/m with a Q-value at 2.05K of Q0 = 8*1E9. A niobium prototype of each cavity has been fabricated at JLab and in a first test the HG cavity has been evaluated at cryogenic temperatures after appropriate buffered chemical polishing. Data for Q(E) were taken at several temperatures after R(T) was measured during initial pump down. In addition the pressure sensitivity as well as the Lorentz force detuning were evaluated. The damping of approximately 20 High Order Modes was measured to verify the room temperature data. In addition we have built and tested several single cell cavities of both cell shapes. In the LL cavity of the end cell geometry a peak surface electric field Epeak of about 87 MV/m corresponding to a magnetic peak field Hpeak of about 173 mT was achieved after a heat treatment at 1250 C and in-situ baking. This cavity showed characteristic Q vs. E dependences, which we investigated at different temperatures with particular interest in the low field (< 20 mT) Q - variation with field. There are strong indications that diffusion of oxygen into the penetration depth is responsible for this feature. A second LL cavity of the inner cell geometry with a small beam aperture of 53 mm was tested several times, the main objectives being to answer questions of cleaning and multipacting. For the same purpose a HG single cell cavity of the inner cell geometry was manufactured, however in a different sequence: at first the half cells were post purified at 1250 C with Ti, then they were electropolished, machined and electron beam welded. We present in this contribution a summary of measured results of all tests we performed on the new proposed shapes of the upgrade cavities.

List of authors...

Principle author first.

Last (Family) Name First Name (Initials only) Affiliation or Organization (abbreviations if possible)
Kneisel P. JLAB
Ciovati G. JLAB
Myneni G.R. JLAB
Sekutowicz J. JLAB
Halbritter J. FZK,IMF I

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