II.A.2.1. Available Beams
ATLAS offers a variety of beams in the mass range 6 to 238. These beams are made available to experimental stations in the area identified as Target Area II and Target Areas III & IV in Figure II.1.
Table I lists the beams now routinely available for experiments in Target Area II, III & IV, and indicates the beam intensity and maximum energy which can be anticipated. A graph of the approximate energy per nucleon and currents possible for beams from ATLAS is shown in Figure II.5. It is suggested that the values shown in Table I be used in making plans for experiments. If higher beam currents or energies appear to be necessary in order to successfully accomplish an experimental goal, some increase may be possible in either maximum energy or beam intensity. It may be possible to sacrifice beam intensity in order to obtain higher energy by choosing a charge-state combination on the high charge-state side of the optimum equilibrium charge state. Alternatively, one can opt for the use of single charge-state acceleration in order to obtain a significant increase in beam current but at a sacrifice in maximum energy.
Other beams which are not run routinely may be possible. If you have an interest in any beams not listed or in beam-parameter requirements other than indicated in Table I, you should contact the Outside-User Liaison at Argonne to discuss your needs.
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II.A.2.2. Isotopically-Enriched Source Material
It is possible to increase the ion beam intensity of low-abundance isotopes by using isotopically-enriched ion source material (for example, 18O,34S, 64Ni). The responsibility for procurement and the cost of such material must be borne by the user. Any user who desires to use isotopically-enriched source material should contact the Outside-User Liaison .
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II.A.2.3. Beam Micro Structure and Phase Space
The bunching system operates at 12.125 MHz, producing a beam time structure with 82.5 ns period. The time width on target is normally about 1-3 ns FWHM. The bunch time width on target can be significantly reduced by using the rebuncher to form a time waist on target. Typical time resolution in Target Area III of 150 to 200 ps FWHM can be obtained with the rebuncher in use.
The energy resolution on target from the linac is typically a few hundred keV, depending on ion species. Energy resolution and time resolution are coupled through Liouville's theorem demanding phase-space volume conservation; therefore, it is not possible to demand the best time resolution and simultaneously the best energy resolution.
For experiments which demand good energy resolution, it is possible to use the rebuncher in a debunching mode which minimizes the energy spread from the linac. Energy resolution of 150 keV FWHM has been observed in elastic scattering of 107 MeV 12C5+ from a thin gold target. This data was obtained with the split-pole spectrograph and was in fact limited by the detector resolution.
The spot size on the target is typically 2-3 mm diameter. For nickel the normalized transverse phase space ([gamma][beta][epsilon]) is estimated to be ~0.1 mm-mrad.
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II.A.3. Accelerator Operation
The ATLAS operations staff is responsible for providing the requested beam, tuned onto the target of the experimental station. There is at least one member of the operation staff present at all times. This person has the prime responsibility for the operation of the ATLAS accelerator. In addition, other members of the accelerator staff are on-call at all times to respond to any emergencies.
The user is responsible for providing the diagnostics for tuning the rebuncher/debuncher resonator when that device is required. The operator can assist the user in this process and will operate the rebuncher/debuncher in the manner specified by the user. Programs are available to assist in the tuning process. Contact the User Liaison for more information.
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II.A.4. Beam Energy Determination
The energy from ATLAS is continuously measured using a time-of-flight system which redundantly determines the time of arrival of the beam bunch at various points along the beamline. The measured value is displayed on the color CRT in the control room and on the ATLAS status display in various areas including the ATLAS data room.
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