G. Zinkann

An improved phase-control system for superconducting low-velocity accelerating structures

It is noted that microphonic fluctuations in the RF eigenfrequency of superconducting (SC) slow-wave structures must be compensated by a fast-tuning system in order to control the RF phase. The tuning system must handle a reactive power proportional to the product of the tuning range and the RF energy content of the resonant cavity. The accelerating field level of many of the SC cavities forming the ATLAS linac has been limited by the RF power capacity of the presently used p-i-n diode based fast-tuner. A new system has been developed, utilizing p-i-n diodes operating immersed in liquid nitrogen, with the diodes controlled by a high-voltage V-groove metal-oxide semiconductor (VMOS) FET driver. The system has operated at reactive power levels above 20 kVA, a factor of four increase over an earlier design. The increased capacity will permit phase stabilization of superconducting resonators at higher field levels. In particular, it has enabled the operation of very-low-velocity superconducting structures at gradients of more than 4 MV/m in the ATLAS positive-ion injector linac.<<ETX>>

The positive-ion injector of ATLAS: Design and operating experience

Abstract The recently completed positive-ion injector for the heavy-ion accelerator ATLAS is a replacement for the tandem injector of the present tandem-linac system. Unlike the tandem, the new injector provides ions from the full range of the periodic table. The concept for the new injector, which consists of an ECR ion source on a voltage platform coupled to a very-low-velocity superconducting linac, introduces technical problems and uncertainties that are well beyond those encountered previously for superconducting linacs. The solution to these problems and their relationship to performance are outlined, and experience in the operation of ATLAS with its new injector is discussed.

Results with the electron cyclotron resonance charge breeder for the C252f fission source project (Californium Rare Ion Breeder Upgrade) at Argonne Tandem Linac Accelerator Systema)

The construction of the Californium Rare Ion Breeder Upgrade, a new radioactive beam facility for the Argonne Tandem Linac Accelerator System (ATLAS), is nearing completion. The facility will use fission fragments from a 1 Ci (252)Cf source; thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams, an existing ATLAS electron cyclotron resonance (ECR) ion source was redesigned to function as an ECR charge breeder. Thus far, the charge breeder has been tested with stable beams of rubidium and cesium achieving charge breeding efficiencies of 9.7% into (85)Rb(17+) and 2.9% into (133)Cs(20+).

Fast and efficient charge breeding of the Californium rare isotope breeder upgrade electron beam ion source

The Electron Beam Ion Source (EBIS), developed to breed Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beams at Argonne Tandem Linac Accelerator System (ATLAS), is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates, and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The off-line charge breeding tests are being performed using a surface ionization source that produces singly charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20% ± 0.7%) breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times, and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this paper, we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.

STATUS OF THE ATLAS ACCELERATOR

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.

Superconducting low-velocity linac for the Argonne positive-ion injector

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 0.008<v/c<0.06. The resonator array is formed by 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.<<ETX>>

An Improved Pneumatic Frequency Control for Superconducting Cavities

The ATLAS (Argonne Tandem Linear Accelerator System) superconducting cavities use a pneumatic system to maintain the cavity eigenfrequency at the master oscillator frequency [1]. The present pneumatic slow tuner has a limitation in the tuning slew rates. For some resonators, the frequency slew rate is as low as 30 Hz/sec. The total tuning range for ATLAS cavities varies from 60 kHz to as high as 450 kHz depending on the cavity type. With the present system, if a cavity is at the extreme end of its tuning range, it may take an unacceptable length of time to reach the master oscillator frequency. We have designed a new slow tuner system that increases the frequency slew rates by a factor of three hundred. This improved system is directly applicable for use on RIA (Rare Isotope Accelerator) cavities. This paper discusses the design of the system and the results of a prototype test.

Current status of ATLAS and proposed expansion to an exotic beam facility

The Argonne Tandem Linear Accelerator System (ATLAS) has been operating on a twenty-four hour, seven days a week schedule since the beginning of Fiscal Year 1994. Twenty-six different ion species ran during this period in 71 separate experiments. During the past year, there have been many projects undertaken to improve operation efficiency and upgrade various accelerator systems. There is also a new ECR ion source construction project underway. This paper covers, linac operation and new tuning techniques, the second generation ECR source construction project, the refrigerator system upgrade, an upgrade to the control system. Also described is a future expansion of ATLAS as an Exotic Beam Facility. ATLAS is a world class heavy ion accelerator with an estimated value of approximately

Status of the positive ion injector for atlas

80 million. A concept that would utilize ATLAS as the foundation for a facility to generate and accelerate radioactive beams is briefly discussed.

Study of the 8B neutrino spectrum with a new technique

The positive ion injector project will replace a High Voltage Engineering Corp. model FN 9 MV tandem electrostatic accelerator as the injector into the ATLAS superconducting heavy ion linear accelerator. It consists of an electron cyclotron resonance (ECR) ion source on a 350-kV platform injecting into a linac of individually phased superconducting resonators which have been optimized for ions with velocities as low as ..beta.. = 0.009. The resulting combination will extend the useful mass range of ATLAS to projectiles as heavy as uranium, while increasing the beam currents available by a factor of 100. (2 refs., 2 figs., 1 tab.)