The first six niobium split-ring resonator.'-, for the Argonne Heavy-Ion Energy Booster havci been completed. The average performance at 4.2K is an accelerating gradient of 3.7 !W/ra or an effective accelerating potential of 1.3 MV per resonator for an rf input of 4 K/resonator. The resonators are constructed in part of an explosively bonded Kb-Cu composite material which performs well for rf surface fieldu of at least 200 C. In initial tests, the resonators frequently exhibit thermal instability at K a < 3 MV/m because of several cypes of microscopic surface defects. The methods used for locating, identifying, and removing these defects are discussed.
A low-velocity superconducting linac has been developed as part of a positive-ion injector system, which is replacing a 9 MV tandem as the injector for the ATLAS accelerator. The linac consists of an independently phased array of resonators, and is designed to accelerate various ions over a velocity range .008 < v/c < .06. The resonator array is formed of four different types of superconducting interdigital structures. The linac is being constructed in three phases, each of which will cover the full velocity range. Successive phases will increase the total accelerating potential and permit heavier ions to be accelerated. Assembly of the first phase was completed in early 1989. In initial tests with beam, a five-resonator array provided approximately 3.5 MV of accelerating potential and operated without difficulty for several hundred hours. The second phase is scheduled for completion in late 1989, and will increase the accelerating potential to more than 8 MV.
The construction of the ATLAS superconducting heavy-ion linear accelerator is complete. The first beam acceleration occurred on March 22, 1985. The first experiment with the ATLAS linac took place during the week of October 7, 1985. The project was completed on time and within budget. Initial system performance has met our expectations.
The design, statuB, and performance of the first operating superconducting heavy-Ion accelerator, ft llnac used to boost the energies of beams from a 9-KV tandea, 1* summarized. When completed In 1901, the linac will consist of 26 Independently-phased splitting niobium resonators operating ac 97 MHz. This llnac Is dealgned to provide 29 MV of acceleration. Because of the modular character of the system, the llnac has been operable and useful since nld-1976, when a beam was accelerated through 2 units and the first nuclear-physics experiments were performed. How, 16 resonators are In use, and a beam has been accelerated for i 6000 hr. Resonator performance has been remarkably stable. In spite of vacuum accidents, and the llnac as a whole operates reliably without opera' tors In attendance during nights and weekends. The ease and speed with which the beam energy can be changed is proving to be unexpectedly valuable to users. I• IntroductionThe Superconducting Llxiac Project at Argonne was undertaken with three major objectives In mind; (1) to develop a new technology, (2) to build a prototype accelerator that cm serve as a guide for others, and (3) Co build a heavy-Ion accelerator that Is immediatedly useful as a Teaear.cn tool. This paper is concerned largely with objectives (2) and (3).For our needs at Argonne, the linac must be an energy booster for heavy lone from an existing tandem *Work performed under the auBpicee of the U.S. Department of Energy, IrUKI MEAl electrostatic accelerator, and the compound system must provide, «t minimum cost, the beams required for precision nuclear-structure research. That Is, it must have easy energy variability, excellent bean quality, and overall flexibility. In short, It should hf>ue tandem-like characteristics, but provide a much higher bean energy than Is obtainable from most tandems. Figure 1 shows the tandem-linac accelerator system* that has been developed both to test the accelerator concept and Co meet our research requirements. II. The Accelerator System
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