Secondary Beam Monitors for the NuMI Facility at FNAL

The Neutrinos at the Main Injector (NuMI) facility is a conventional neutrino beam which produces muon neutrinos by focusing a beam of mesons into a long evacuated decay volume. We have built four arrays of ionization chambers to monitor the position and intensity of the hadron and muon beams associated with neutrino production at locations downstream of the decay volume. This article describes the chambers' construction, calibration, and commissioning in the beam.Comment: Accepted for publication in Nucl. Instr. Meth.

The Superconducting TESLA Cavities

The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of Eacc >= 25 MV/m at a quality factor Q0 > 5E+9. The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of Eacc >= 15 MV/m. In a first series of 27 industrially produced TTF cavities the average gradient at Q0 = 5E+9 was measured to be 20.1 +- 6.2 MV/m, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities additional quality control measures were introduced, in particular an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electron-beam welds. The average gradient of these cavities at Q0 = 5E+9 amounts to 25.0 +- 3.2 MV/m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing R&D towards higher gradients is briefly addressed.Comment: 45 pages (Latex), 39 figures (Encapsulated Postscript), 53 Author

Improvements To Power Couplers For The LEP2 Superconducting Cavities

Power couplers for the 352 MHz LEP2 superconducting RF cavities have been plagued by vacuum and electron outbursts which are attributed to multipacting. Processing of these couplers has been a lengthy operation which was often needed again after high power running even if only for a relatively short time. We report here on recent progress made in improved production methods of coupler parts and special treatment of surfaces, as well as practical tests and simulations of geometrical coupler modifications. I. INTRODUCTION All couplers of the LEP 352 MHz superconducting cavities are located on the cut-off tubes to avoid ports on the cavity cells themselves. The first power coupler design used a homogeneous 50 W antenna line [1]. Based on this coupler an adjustable version was designed containing a l/4 section of 25 W impedance which houses a choke construction [2]. Fig.1 : The adjustable coupler Keeping the RF-line outer diameter of 103 mm with the proven cylindrical window design a..