The high luminosity performance of CESR with the new generation superconducting cavity

Abstract

With the installation of the first SRF cavity in September of 1997, the upgrade of the CESR RF system has begun [1]. This cavity belongs to the new generation of socalled HOM damped cavities designed for high current storage rings [2]. The upgrade is proceeding by replacing one by one old copper cavities with superconducting ones during short machine shutdowns.CESR continues to demonstrate spectacular performance. It operates with 36 bunches in 9 trains of 4 bunches in each beam with total beam current up to 550 mA at the start of fills for high energy physics. In the course of last year both peak luminosity and integrated luminosity per day increased by 67% and are equal now to 8. /day. The latter number corresponds roughly to 43 thousands of B mesons per day. The first superconducting cavity has been in operation in CESR since October of 1997. The cavity operates at accelerating gradients up to 7 MV/m and delivers to the beam maximum RF power of 220 kW through the ceramic window, the record value for superconducting cavities. We found that pulsed power processing without beam is extremely helpful in improving RF window performance. The maximum HOM power extracted from the beam by one cavity is 5.7 kW.Four single-cell HOM damped cavities will eventually support a total beam current of 1 A. Because of the very low impedance of superconducting cavity module, we calculate the longitudinal instability threshold from cavity HOMs to be in excess of 1 A. The second cavity was installed in CESR during October'98 shutdown. The third cavity is already installed in CESR, and its commissioning will start immediately after this conference. The fourth cryomodule is being assembled and is schedule for installation in summer of 1999.

A Tunable Reflecting Load for Multipactor Processing of the RF Power Coupler of a Superconducting Cavity

“…Denoting the measured reflection coefficient of the waveguide transformer (Fig. 5) by , we can write (4) Equations (1)-(4) yield at port #1 (5) where is the complex reflection coefficient of the load assembly given by (6) The reflection phase angle can be further varied with the insertion of a uniform waveguide section of proper length into any of the ports. By proper setting of the phase angles, a broad tuning range in can be achieved, as shown in the iso-magnitude and iso-phase curves of Fig.…”

“…Recently, for example, multipactor discharges in the RF power coupler were found to be a serious hindrance to the operation of superconducting RF systems under high-power conditions [5], [6].…”

“…Still, pulse processing cannot account for the effects of beam loading. Furthermore, it has been experimentally demonstrated that pulse processing is less effective on hard-barrier multipactor than on soft-barrier multipactor, because the hard barrier has a short memory [5]. Hence, periodic reprocessing becomes necessary [16], [17] at the expense of increased maintenance cost and operation down time.…”

The Helium Cryogenic System for the Taiwan Photon Source

“…In the TPS project, four 500 MHz superconducting cavities of single-cell type are planned [3,4]. TABLE 1 shows the 4.5 K heat load estimation for the superconducting cavities.…”

CESR performance and upgrade status

“…A single cell, superconducting RF cavity system has been developed to support the high current multiple bunch beams in CESR [4]. The accelerating mode resonates at 500MHz.…”