Long-term Operation of Niobium Superconducting Resonators in the Argonne Heavy-ion Linac PDF Download
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This paper describes some of the effects observed in operating superconducting resonators over long periods of time at high field levels. The resonators are the niobium split-ring resonators which form the Argonne superconducting heavy-ion linac, and the period of operation considered extends from initial operation in 1978 to the present and includes more than 17,000 hours of operation with beam. In what follows, first a brief description of the resonators and operating procedures is given. Then, the on-line performance of all the resonators in one cryostat module over a period of several years is reviewed and discussed. Finally, the nature and causes of performance degradation in several (atypical) resonators are examined.
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Languages : en
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This paper describes some of the effects observed in operating superconducting resonators over long periods of time at high field levels. The resonators are the niobium split-ring resonators which form the Argonne superconducting heavy-ion linac, and the period of operation considered extends from initial operation in 1978 to the present and includes more than 17,000 hours of operation with beam. In what follows, first a brief description of the resonators and operating procedures is given. Then, the on-line performance of all the resonators in one cryostat module over a period of several years is reviewed and discussed. Finally, the nature and causes of performance degradation in several (atypical) resonators are examined.
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Languages : en
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The first six niobium split-ring resonators for the Argonne Heavy-Ion Energy Booster have been completed. The average performance at 4.2K is an accelerating gradient of 3.7 MV/m or an effective accelerating potential of 1.3 MV per resonator for an rf input of 4 W/resonator. The resonators are constructed in part of an explosively bonded Nb-Cu composite material which performs well for rf surface fields of at least 200 G. In initial tests, the resonators frequently exhibit thermal instability at E/sub a/
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Languages : en
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A summary is given of the status of a project to develop and build a small superconducting linac to boost the energy of heavy ions from an existing tandem electrostatic accelerator. The design of the system is well advanced, and construction of major components is expected to start in late 1976. The linac will consist of independently-phased resonators of the split-ring type made of niobium and operating at a temperature of 4.2°K. The resonance frequency is 97 MHz. Tests on full-scale resonators lead one to expect accelerating fields of approximately 4 MV/m within the resonators. The linac will be long enough to provide a voltage gain of at least 13.5 MV, which will allow ions with A less than or approximately 80 to be accelerated above the Coulomb barrier of any target. The modular nature of the system will make future additions to the length relatively easy. A major design objective is to preserve the good quality of the tandem beam. This requires an exceedingly narrow beam pulse, which is achieved by bunching both before and after the tandem. Focusing by means of superconducting solenoids within the linac limit the radial size of the beam. An accelerating structure some 15 meters downstream from the linac will manipulate the longitudinal phase ellipse so as to provide the experimenter with either very good energy resolution (.delta. E/E approximately equal to 2 x 10−4) or very good time resolution (.delta. t approximately equal to 30 psec).
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Category : Power resources
Languages : en
Pages : 754
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Recent developments include a method for conditioning resonators which has produced a significant increase in accelerating gradient and also a design for a split-ring resonator with an optimum particle velocity of 0.16 c. Results of using a 1500 watt rf source to condition superconducting split-ring resonators are described. By repetitively pulsing for a few msec to field levels as high as an 8 MV/m effective accelerating field E/sub a/, electron loading at high field levels has been substantially reduced. After such conditioning, continuous operation at E/sub a/> 6 MV/m, corresponding to a peak surface electric field of 30 MV/m, has been obtained. A split-ring resonator designed for an optimum particle velocity .beta. = v/c = 0.16 is also described. The 145.5 MHz resonator is contained in the same 16 inch diameter, 14 inch length housing used for the .beta. = 0.1 Argonne split-ring. In design of the split ring element, a 20% reduction in peak surface electric field has been achieved with no significant increase in surface magnetic field.
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Languages : en
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Initial operation and recent development of the Argonne superconducting heavy-ion linac are discussed. The linac has been developed in order to demonstrate a cost-effective means of extending the performance of electrostatic tandem accelerators. The results of beam acceleration tests which began in June 1978 are described. At present 7 of a planned array of 22 resonators are operating on-line, and the linac system provides an effective accelerating potential of 7.5 MV. Although some technical problems remain, the level of performance and reliability is sufficient that appreciable beam time is becoming available to users.
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Category : Power resources
Languages : en
Pages : 1144
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A superconducting heavy-ion linac, predecessor and part of the national facility ATLAS funded this year, has been operational at Argonne for approximately three years. Even though the last resonator was only mounted a few weeks ago, the modular design of independently phased resonators has allowed partial operation and an experimental program over that period, with continually increasing capability in ion-beam species and energy. This is a short report on some of the research activities which, in short, are concerned with the various aspects of the relationships between heavy-ion-induced reactions and nuclear structure. Major interests are the structure of nuclei at high excitation, far from stability or in states of high spin near the yrast line.
Author: J.R. Delayen
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Languages : en
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A niobium split-ring accelerating structure designed for use in the Argonne superconducting heavy-ion energy booster was successfully tested. The superconducting resonator has a resonant frequency of 97 MHz and an optimum particle velocity .beta. = 0.11. Ultimate performance is expected to be limited by peak surface fields, which in this structure are 4.7 E/sub a/ electric and 170 E/sub a/ (Gauss) magnetic, where E/sub a/ is the effective accelerating gradient in MV/m. The rf losses in two demountable superconducting joints severely limited performance in initial tests. Following independent measurements of the rf loss properties of several types of demountable joints, one demountable joint was eliminated and the other modified. Subsequently, the resonator could be operated continuously at E/sub a/ = 3.6 MV/m (corresponding to an energy gain of 1.3 MeV per charge) with 10W rf input power. Maximum field level was limited by electron loading. The mechanical stability of the resonator under operating conditions is excellent: vibration induced eigenfrequency noise is less than 120 Hz peak to peak, and the radiation pressure induced frequency shift is .delta.f/f = 1.6 x 10−6 E/sub a/2.
