Thermal analysis of the APT power coupler and similarities to superconducting magnet current leads

A detailed thermal analysis has been performed of the 210 kW, 700 MHz RF power coupler (PC) which transfers microwave energy from high power klystrons to the superconducting (SC) resonant cavities for the acceleration of protons. The work is part of the design for Accelerator Production of Tritium funded by the US Department of Energy. The PC is a co-axial design with the RF power transmitted in the annular region between two concentric cylinders. The PC provides a thermal connection from room temperature to superconducting niobium operating at 2.15 K. Heat transfer mechanisms considered are conduction, infra-red radiation, RF joule heating in normal and superconducting materials, and, forced and natural convection cooling. The objective of the thermal analysis is to minimize the required refrigeration power subject to manufacturability and reliability concerns. The problem is reminiscent of the optimization of superconducting magnet leads. The similarities and differences in the results between SC leads and PCs are discussed as well as the critical parameters in the PC optimization

Status of Superconducting RF Linac Development for APT

This paper describes the development progress of high current superconducting RF linacs in Los Alamos, performed to support a design of the linac for the APT (Accelerator Production of Tritium) Project. The APT linac design includes a CW superconducting RF high energy section, spanning an energy range of 211 to 1030 MeV, and operating at a frequency of 700 MHz with two constant beta sections (beta of 0.64 and 0.82). In the last two years, we have progressed towards build a cryomodule with beta of 0.64. We completed the designs of the 5 cell superconducting cavities and the 210 kW power couplers. We are scheduled to begin assembly of the cryomodule in September 2000. In this paper, we present an overview of the status of our development efforts and a report on the results of the cavity and coupler test program.Comment: LINAC2000 THD1

A thermal analysis and optimization of the APT 210 kW power coupler

This paper presents the thermal analysis and heat load optimization of the continuous power 210 kW, 700 MHz RF power coupler (PC) for the Accelerator Production of Tritium (APT). The PC is a co-axial design with RF power transmitted in the annular region between two concentric cylinders. Thermally, the PC represents a link from room temperature to the superconducting niobium cavities operating at 2 K. The analysis includes all the major heat transfer mechanisms: conduction, RF joule heating in normal and superconducting materials, infrared radiation, and, forced and natural convection cooling of the inner and outer conductors. A performance comparison is given for one and two single point thermal intercepts, versus a counter-flow heat exchanger on the outer conductor. The benefits of r4educing the operating temperature of the center conductor are discussed. The variation in thermal performance of the inner and outer conductors for several operating modes is also presented

Argonne National Laboratory Reports

This report provides a preliminary assessment of some magnetic heat pump (MHP)/refrigeration concepts for cryogen liquefaction and other industrial applications. The study was performed by Astronautics Corporation of America for Argonne National Laboratory under the sponsorship of the U.S. Department of Energy

EXPERIMENTAL HEAT LEAK MEASUREMENTS ON THE APT 210 KW CW RF POWER COUPLER EXPERIMENTAL HEAT LEAK MEASUREMENTS ON THE APT 210 KW CW RF POWER COUPLER

ABSTRACT A cryogenic test rig was designed and fabricated to measure the heat leak from room temperature to 2 K from the Accelerator Production of Tritium (APT) 700 MHz, 210 kW continuous wave (CW) co-axial power coupler (PC). The outer conductor of the PC is stainless steel with 15 µm copper film on the inside. The copper inner conductor operates at room temperature and contributes considerable infra-red radiation heat load to 2 K. Two thermal intercept heat exchangers cooled by supercritical helium are incorporated into the outer conductor to reduce the heat conducted to the lowest temperatures. A brief description of the experimental apparatus is presented. A comparison of the experimental measurements and the predictions of a detailed thermal model is given. There is also a discussion of anomalous behavior observed in the thermal intercepts, and fluctuations in the helium coolant properties

Experimental heat leak measurements on the APT 210 KW CW RF power coupler

A cryogenic test rig was designed and fabricated to measure the heat leak from room temperature to 2 K from the Accelerator Production of Tritium (APT) 700 MHz, 210 kW continuous wave (CW) co-axial power coupler (PC). The outer conductor of the PC is stainless steel with 15 {micro}m copper film on the inside. The copper inner conductor operates at room temperature and contributes considerable infra-red radiation heat load to 2 K. Two thermal intercept heat exchangers cooled by supercritical helium are incorporated into the outer conductor to reduce the heat conducted to the lowest temperatures. A brief description of the experimental apparatus is presented. A comparison of the experimental measurements and the predictions of a detailed thermal model is given. There is also a discussion of anomalous behavior observed in the thermal intercepts, and fluctuations in the helium coolant properties

Development of the SCRF Power Coupler for the APT Accelerator

The team responsible for the design of the Accelerator Production of Tritium (APT) superconducting (SC) radio frequency (RF) power coupler has developed two 700-MHz, helium gas-cooled power couplers. One has a fixed inner conductor and the other has an adjustable inner conductor (gamma prototype and alpha prototype). The power couplers will be performance tested in the near future. This paper discusses the mechanical design and fabrication techniques employed in the development of each power coupler. This includes material selection, copper coating, assembly sequences, and metal joining procedures, as well as the engineering analyses performed to determine the dynamic response of the inner conductors due to environmental excitations. A bellows is used in both prototype inner conductors in the area near the ceramic RF window, to compensate for thermal expansion and mechanical tolerance build-up. In addition, a bellows is used near the tip of the inner conductor of the alpha prototype for running the power coupler after it is installed on the accelerator. Extensive analytical work has been performed to determine the static loads transmitted by the bellows due to thermally induced expansion on the inner conductor and on the RF window. This paper also discusses this analysis, as well as the mechanical analysis performed to determine the final geometric shape of the bellows. Finally, a discussion of the electromagnetic analysis used to optimize the performance of the power couplers is included