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Electron beam charge state amplifier (EBQA)--a conceptual evaluation.

Description: A concept is presented for stripping low-energy, radioactive ions from 1+ to higher charge states. Referred to as an Electron Beam Charge State Amplifier (EBQA), this device accepts a continuous beam of singly-charged, radioactive ions and passes them through a high-density electron beam confined by a solenoidal magnetic field. Singly-charged ions may be extracted from standard Isotope-Separator-Online (ISOL) sources. An EBQA is potentially useful for increasing the charge state of ions prior to injection into post-acceleration stages at ISOL radioactive beam facilities. The stripping efficiency from q=1+ to 2+ ({eta}{sub 12}) is evaluated as a function of electron beam radius at constant current with solenoid field, injected ion energy, and ion beam emittance used as parameters. Assuming a 5 keV, 1 A electron beam, {eta}{sub 12} = 0.38 for 0.1 keV, {sup 132}Xe ions passing through an 8 Tesla solenoid, 1 m in length. Multi-pass configurations to achieve 3+ or 4+ charge states are also conceivable. The calculated efficiencies depend inversely on the initial ion beam emittances. The use of a helium-buffer-gas, ion-guide stage to improve the brightness of the 1+ beams [1] may enhance the performance of an EBQA.
Date: October 12, 1998
Creator: Dooling, J. C.
Partner: UNT Libraries Government Documents Department

A concept for emittance reduction of DC radioactive heavy-ion beams

Description: Numerical simulations indicate that it should be possible to use an electron beam to strip 1+ DC radioactive ion beams to 2+ or higher charge states with on the order of 50% efficiency. The device, which the authors call an Electron-Beam Charge-State Amplifier, is similar to an Electron Beam Ion Source, except that it is not pulsed, the beams are continuous. The 2+ beams are obtained in a single pass through a magnetic solenoid while higher charge states may be reached via multiple passes. An unexpected result of the ion optics simulations is that the normalized transverse emittance of the ion beam is reduced in proportion to the charge-state gain. Ion beams with realistic emittances and zero angular momentum relative to the optic axis before entering the solenoid will travel though the solenoid on helical orbits which intercept the axis once per cycle. With an ion beam about 2 mm in diameter and an electron beam about 0.2 mm in diameter, the ion stripping only occurs very near the optic axis, resulting in the emittance reduction.
Date: June 1, 1995
Creator: Nolen, J.A. & Dooling, J.C.
Partner: UNT Libraries Government Documents Department

Diagnostic and numerical studies of the IPNS LINAC with a recently installed buncher amplifier.

Description: The Intense Pulse Neutron Source (IPNS) 50-MeV Drift-Tube Linac uses a single-gap, single-harmonic buncher cavity to increase transmission efficiency. However, it is also the case that the linac output beam longitudinal and transverse emittance is dependent on buncher amplitude and phase as well as with the input beam energy and emittance. The linac is the injector for a Rapid Cycling Synchrotron (RCS) that increases the beam energy to 450 MeV and shortens the pulse to the 100 ns region. The RCS is operated loss-limited, and its operating current is strongly dependent on the properties (emittance, and its variation during the pulse) of the beam from the linac. A new amplifier has been installed allowing for better amplitude and phase control of buncher rf. This new amplifier gives independent control of amplitude and phase, permitting more systematic studies of the relation between linac and RCS performance. This paper presents the results of recent studies where we characterize beam properties that lead to high efficiency operation in both linac and RCS, and compare them with simulation calculations.
Date: September 17, 2002
Creator: Dooling, J. C.; Donley, L. I.; McMichael, G. E. & Stipp, V. F.
Partner: UNT Libraries Government Documents Department

Bunch stabilization using rf phase modulation in the Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS).

Description: Phase modulation (PM) is used to increase the current limit in the IPNS RCS. A device referred to as a scrambler introduces a small oscillating phase between the two RCS rf cavities at approximately twice the synchrotrons frequency, f{sub s}. The modulation introduced by the scrambler generates longitudinal oscillations in the bunch at 2f{sub s}. Modulations in the bunch are also observed transversely indicating a coupling between longitudinal and transverse motion. Comparing PM with amplitude modulation (AM), coupling to the beam is roughly equivalent at 2f{sub s}.
Date: September 1, 1999
Creator: Brumwell, F. R.; Dooling, J. C. & McMichael, G. E.
Partner: UNT Libraries Government Documents Department

Impedance considerations for the Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS).

Description: The use of Second Harmonic (SH) rf is being investigated to increase the Rapid Cycling Synchrotron (RCS) current limit. Hofmann-Pedersen distributions are employed to provide analytical guidance. The SH phase {theta}, is optimized using a numerical analysis to maximize transmission and minimize instabilities. The effect of the RCS stainless steel liner on the impedance of the machine is also discussed.
Date: September 8, 1999
Creator: Brumwell, F. R.; Dooling, J. C. & McMichael, G. E.
Partner: UNT Libraries Government Documents Department

Plasma considerations in the IPNS RCS.

Description: Significant ionization appears to occur in the Rapid Cycling Synchrotron (RCS) during its 14 ms acceleration period leading to plasma formation and neutralization. The beam may in fact be over-neutralized, causing the tune to increase during the acceleration cycle. The overall tune shift in the RCS appears to be close to +0.5. The presence of plasma may help explain why longitudinal phase modulation can so quickly couple to transverse motion. In addition, plasmas tend to be inductive and the RCS appears to exhibit a relatively high inductance. Measurements of the electron cloud and plasma densities adjacent to the beam should be made. In addition to the RFA and Swept Analyzer diagnostics mentioned at the Workshop, other techniques might be attempted. If plasma is present, then a small, biased-probe might be useful (e.g., a Langmuir probe), or with the proper choice of geometry, an optics-based measurement for line density (e.g., an interferometer) might be employed, perhaps using microwaves for increased sensitivity.
Date: February 21, 2002
Creator: Dooling, J. C.; McMichael, G. E. & Brumwell, F. R.
Partner: UNT Libraries Government Documents Department

Diagnostic investigation of tune and tune shift in the IPNS RCS.

Description: The Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 50 MeV protons to 450 MeV 30 times per second for spallation neutron production. Average current from the RCS has recently exceeded 16 {micro}A with peak instantaneous current approaching 15 A. The RCS makes efficient use of 21 kV of RF accelerating voltage and uses phase-modulation between the two rf cavities to damp vertical instabilities. Split-ring electrodes in the ring suggest an anomalous tune shift that increases with time in the acceleration cycle. Based on a background gas pressure of 1 {micro}Torr, the neutralization time for the beam is approximately 0.5 ms at injection suggesting the beam becomes fully neutralized relatively quickly in the cycle. Over-neutralization of the beam can lead to a positive tune shift that is presumably incoherent. Studies are underway to characterize the ionization within the RCS using the existing Profile and Position System (PAPS) and a newly installed Retarding Field Analyzer (RFA). Also a newly installed fast, deep-memory digitizing oscilloscope allows the entire history of a single acceleration cycle to be recorded from all four components of the split ring electrodes simultaneously at a rate of 250 MS/s.
Date: June 10, 2002
Creator: Dooling, J. C.; Brumwell, F. R. & McMichael, G. E.
Partner: UNT Libraries Government Documents Department

The IPNS accelerator 50 MeV and 500 MeV transport lines

Description: The Intense Pulsed Neutron Source (IPNS) accelerator delivers up to 500 MeV protons to a depleted uranium target producing spallation neutrons for material science and other research. A 70-80 ns bunch strikes the target at a rate of 30 Hz with an average beam current of 15 {mu}A. The 50 MeV and 500 MeV beam lines transport protons from the Drift Tube Linac (DTL) to the Rapid Cycling Synchrotron (RCS) and from the RCS to the Neutron Generating Source (NGS) target, respectively. Through over 15 years of operation, the accelerator has been highly reliable with the 5 billionth pulse on target recorded March 12, 1997. During this time, IPNS operators have discovered tunes for various parts of the DTL/RCS accelerator allowing for continual improvement in average current delivered to the target; however, in numerous cases this has been achieved by moving significantly away from the original design parameters. A new attempt is being made to analyze the lines and develop computer models that can be used to alleviate some of the undesirable features of the present {open_quotes}best tune.{close_quotes} In the 500 MeV line, higher order elements will be included in the modeling with the goal of providing a uniform power density profile at the NGS target. This paper describes features of the present lines, and progress-to-date in analyzing and improving them.
Date: August 1, 1997
Creator: Dooling, J.C.; Brumwell, F.R. & McMichael, G.E.
Partner: UNT Libraries Government Documents Department