Nikolai R. Lobanov

Simple concepts for ion source improvement

Abstract We report on improvements in the overall intensity of a sputter ion source that evolved originally from an NEC MCSNICS. Beam output increases benefit both AMS measurements and nuclear physics experiments using low natural abundance beams. In particular, minor changes in source geometry suggested by a combination of electrostatic calculations and simple design principles have yielded increases in extracted negative ion intensity of nearly a factor of 4.

Tube entrance lens focus control

The entrance of the accelerator tube in a large electrostatic accelerator imposes a strong lens that dominates the beam optics. The magnification of the lens is large because of the low injection energy, the high voltage gradient of the acceleration tube and the long distance to the terminal. In the absence of the acceleration, the magnification would produce an unacceptably large beam spot at the terminal. The tyranny of the lens is especially irksome when the accelerator is required to operate at a lower terminal voltage than the one corresponding to the nominal gradient at high voltage. One way around the difficulty, used in NEC Pelletron accelerators, is to insert a series of nylon and steel rods that short together units of the acceleration structure at the terminal leaving the ones near the entrance close to the nominal gradient for optimum transmission. This operation takes time and risks the loss of insulating gas. Another alternative used in the 25URC at Oak Ridge National Laboratory, is to focus...

Injection optics for fast mass switching for accelerator mass spectrometry

Accelerator Mass Spectrometry (AMS) measures the ratio of extremely small amounts of a radioactive isotope in the presence of ~ 10 15 times more stable ones. The isotopes are injected sequentially over a repeated period and observed at the exit of the accelerator. so any fluctuations in ion source output or transmission through the accelerator over a time comparable to the measurement time, will reduce the accuracy of such measurements. This compromise in accuracy can be lessened by reducing the switching time between isotopes from several seconds to a few milli-seconds. New AMS systems accomplish fast switching by modifying the beam energy though the 90 injection magnet by pulsing the voltage by several kV on the flight tube in the magnet. That requires that the flight tube be electrically insulated which competes with having the flight tube as large as possible. At the ANU, insulating the magnet flight tube would not only have reduced the acceptance of the injection system, but conflicted with a beam chopper attached to the flight tube, that would also have had to be insulated from the ground. This was not practical so the novel alternative of pulsing the voltage on the high voltage ion source deck is being implemented. Beam optics calculations have been performed and beam tests conducted that demonstrated that, in addition to pulsing the voltage on the 150 kV ion source deck, a pulsed Einzel lens in front of the following electrostatic quadrupole triplet lens is required to maintain isotope-independent transmission through the 14UD Pelletron accelerator. The high voltage rise time performance of the components of the system has been shown to be satisfactory.

Linac boosters-an overview

Booster LINACS have matured into an almost standard feature of many accelerator laboratories. Some LINACS are still young and growing, some mature ones prosper through continuous improvement while others require no further development. This overview will present a profile or the current population of booster LINACS. The accomplishments of the laboratories will be surveyed since the last HIAT along with their plans for future development. Those challenges, which the entire HIAT community have in common, will be identified to attract our enthusiasm and inventiveness.

THE ANU LINAC CRYOGENIC SYSTEM

Abstract The ANU linac, a superconducting linear accelerator, is nearing completion at the Australian National University. In the first phase of the project, three module cryostats and a super buncher cryostat are cooled to 4.2 K using a closed loop liquefier/refrigerator system. The features of the cryogenic plant and the multi-process computer control are described.

Tuning the Superconducting Linac at Low Beam Intensities

The ANU Heavy Ion Accelerator Facility (HIAF) is comprised of a 15 MV electrostatic accelerator followed by a superconducting linac booster. Employment of double terminal stripping allows the system to accelerate beams with mass up to 70 amu. The disadvantage of double terminal stripping is low beam intensity of few particle nanoamps delivered to the linac. One of the linac set up procedures developed at ANU utilises a U-bend at the end of the linac. One special wide Beam Profile Monitor (BPM) is installed after the 90 degree magnet. The technique allows correct setting of phase by observing the displacement of beam profile versus phase shift of the last phase locked resonator. In this paper, a simple method has been proposed to improve sensitivity of a commercially available BPM for efficient operation with low beam intensities. Verification of BPM with enhanced sensitivity is accomplished during routine linac operations and it is supplemented by longitudinal phase space simulations.