Amberg, M.

Barth, W.

Busch, M.

Podlech, H.

Ratzinger, U.

GSI Repository

Measurements on the 325 MHz Superconducting CH Cavity∗M. Busch†1, H. Podlech1, U. Ratzinger1, W. Barth2,3, and M. Amberg3,41Institut fu¨r Angewandte Physik, Goethe Universita¨t, Frankfurt, Germany; 2GSI, Darmstadt, Germany; 3HIM, Mainz;4Johannes Gutenberg Universita¨t, MainzAbstractAt the Institute for Applied Physics (IAP), FrankfurtUniversity, a superconducting 325 MHz CH-Cavity hasbeen designed and built. This 7-cell cavity has a geo-metrical β of 0.16 corresponding to a beam energy of11.4 AMeV. The design gradient is 5 MV/m. Novel fea-tures of this resonator are a compact design, low peakfields, easy surface processing and power coupling. Fur-thermore a new tuning system based on bellow tuners in-side the resonator will control the frequency during opera-tion. First tests on the cavity have been performed includ-ing a cold test achieving a gradient of up to 2.3 MV/m.MeasurementsFigure 1: Left: Frequency of Mode 1. Right: Bead pullmeasurement and simulation.Prior to the final fabrication steps of the cavity first mea-surements have been done at Research Instruments ensur-ing the envisaged design goals [1].Figure 2: Cold test setup (left), temperature vs. frequencyshift (right).First the frequency and the electric field on axis havebeen measured with affixed end caps and without static∗Work supported by GSI, BMBF Contr. No. 06FY7102, 06FY9089I† busch@iap.uni-frankfurt.detuners (see fig. 1). Determining the frequency shift ofthe static tuners by the use of provisional dummy tunersthe final niobium tuners were welded into the cavity step-by-step. After welding of the end caps and three of thefour static tuners into the cavity a preliminary cold test wasset up to investigate the thermal response of the CH-Cavity(see fig. 2).Subsequently the effect of the dynamic bellow tuners onthe frequency as well as the mechanical rigidity of the cav-ity under evacuation have been studied (see fig. 3).Figure 3: Bellow tuner elongation vs. frequency shift (left),pressure vs. frequency shift (right).Finally the last static tuner has been fixed, a bufferedchemical polishing treatment was performed and the cavitywas delivered to IAP for a first test under LHe conditions.After experiencing multipacting barriers the achieved fieldgradient yielded ≈ 2.3 MV/m (see fig. 4) limited by fieldemission due to a moderate surface purity of the cavity.Figure 4: Measurement at IAP @4 K (left), E vs. Q curve(right).References[1] M. Busch, F. Dziuba, H. Podlech, U. Ratzinger, W. Barth,S. Mickat, M.Amberg, M. Pekeler, ”First Measurements onthe 325 MHz Superconducting CH Cavity”, Linac 2012, Tel-Aviv, Israel.GSI SCIENTIFIC REPORT 2012 PHN-FAIR-25FAIR@GSI 251

Measurements on the 325 MHz Superconduction CH Cavity

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Measurements on the 325 MHz Superconduction CH Cavity

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