IKF, Frankfurt-am-Main
ANL, Argonne, Illinois
Northern Illinois University, DeKalb, Illinois
A pepper-pot - scintillator screen system has been developed and used to measure the emittance of ion beams extracted from the high-intensity permanent magnet ECR ion source. The system includes a fast beam shutter with a minimum dwell time of 18 ms to reduce the degradation of CsI(Tl) scintillator by DC ion beam irradiation, a CCD camera with a variable shutter speed in the range of 1 μs to 65 s. On-line emittance measurements are performed by an application code developed on LabVIEW platform. The sensitivity of the device is sufficient to measure the emittance of DC ion beams with current densities down to ~100 nA/cm2. The emittance of all ion species extracted from the ECR ion source and post-accelerated to an energy of 75-90 keV/charge have been measured downstream of the LEBT. As the mass-to-charge ratio of ion species is increased, the normalized RMS emittances in both transverse phase planes are reduced from 0.3-0.7 pi mm*mrad for light ions to 0.07-0.13 pi mm*mrad for highly charged 209Bi ions. Most measurements show a complicated structure of multiple images of individual holes. The latter can be mitigated or even avoided in some cases by re-tuning ion source parameters.
NSCL, East Lansing, Michigan
Heavy-ion beams from an ECR type ion source have been shown to be structurally complex and to have a strong cross-correlation associated with their formation in and extraction from a high magnetic field with a strong sextupole content [1]. The emittances of such beams tend to be unavoidably large (compared to low magnetic field source types) yet because of cross-correlations, resistant to improvement by normal collimation methods. Recent developments with beam from the 14 GHz room temperature ECRIS at the NSCL indicate that careful beam line tuning to pass specific parts of the beam structure can allow greatly reduced 4-dimensional emittances without losing a disproportionate amount of the total intensity.
[1] "Ion beam extracted from a 14 GHz ECRIS of CAPRICE Type", P. Spaedtke, et al., 17th Int. Work. On ECR Ion Sources, 17th-21st Sep., 2006, Lanzhou, China
GSI, Darmstadt
LBNL, Berkeley, California
Simulations of beam extraction across a plasma sheath in an ECR ion source are critically dependent upon ion density distributions at the plasma extracting face; however, these distributions have not been measured experimentally. We present a new method of defining the initial distributions for simulation based upon the measurement of biased disc sputter marks. Multi-species beam extraction and transport simulations using these initial conditions will be compared with beam imaging and emittance measurements from the superconducting ECR VENUS at several positions along the beam line illustrating this simple model's ability to reproduce measured beam characteristics such as beam hollowing even though the triangular distributions at plasma extraction are of nearly constant density. The various possible sources of the beam hollowing observed both in simulation and experiment will be discussed. In addition, we will present a generalized method to define the initial distribution at extraction using only magnetic field line tracing and extracting aperture geometry.
LLT, Boulder
CEA, Gif-sur-Yvette
Vector Fields Ltd., Oxford
CIMAP, Caen
GANIL, Caen
One of the goals pursued by the people working on ion sources is to provide the highest beam intensity in the smallest emittance. As the computer power has increased so fast for the last years, it is possible nowadays to simulate with more accuracy the extraction of the ECR ion sources taking into account the several Physics processes involved in the beam creation. From the last chapter of the paper written by R. Leroy and coworkers [1], it has been shown experimentally that the intensity of a beam can be improved significantly by biasing the plasma electrode. The idea was to use the isolated plasma electrode as a 'biased disk'. We have calculated the influence on the extracted ion trajectories of this additional potential (from +3 V down to -100 V). The simulations have been computed for the MONO1000 and SUPERSHyPIE ion sources. All the simulations showed an increase of the brightness of the beam with more or less gain depending on the extraction voltage and the extraction conditions. A recent experiment performed on the MONO1000 ECRIS has confirmed the feasibility of this method: a gain of 40% in terms of emittance has been obtained on an 84Kr1+ beam.
[1] R. Leroy et al., Proceedings of the 12th International Workshop on ECR Ion Sources, April 25-27, 1995, RIKEN, Japan
ANL, Argonne, Illinois
Northern Illinois University, DeKalb, Illinois
A prototype injector capable of producing multiple-charge-state heavy-ion beams has been constructed at ANL. The injector consists of an ECR ion source, a 100-kV platform and an achromatic Low Energy Beam Transport (LEBT) system. Several charge states of bismuth ions from the ECR have been extracted, accelerated to an energy of 1.8 MeV, separated and then recombined into a high quality beam ready for further acceleration. This technique allows us to double heavy-ion beam intensity in a high-power driver linac for a future radioactive beam facility. Another application is in post-accelerators of radioactive ions based on charge breeders. The intensity of rare isotope beams can be doubled or even tripled by the extraction and acceleration of multiple charge state beams. Experimental results of multiple-charge state beam studies will be reported.