• S.A. Kondrashev, A. Barcikowski, B. Mustapha, P.N. Ostroumov
  ANL, Argonne
• N. Vinogradov
  Northern Illinois University, DeKalb, Illinois

Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract number DE-AC02-06CH11357.
We have developed a pepper pot - scintillator screen system to measure the emittance of low-energy dc beams extracted from an ECR ion source and post-accelerated to an energy of 75 - 90 keV/charge. Different scintillators have been tested and CsI (Tl) was chosen due to its high sensitivity, wide dynamic range and long life-time. The linearity of both the scintillator and the CCD camera has been studied. A LabVIEW code has been developed and used for on-line emittance measurements. Un-normalized rms emittances measured for 209Bi²⁰⁺ and 209Bi²¹⁺ beams with current of 1.0 - 1.5 pnA are usually ~30 π mm.mrad. A complicated structure of multiple images of individual holes has been observed. The innovative combination of a special type of scintillator, a CCD camera and a fast shutter allowed us to create a very efficient emittance meter for low-energy dc ion beams. Using on-line emittance measurements, it was possible to improve the beam quality by re-tuning the ion source conditions. Because of the two-dimensional array of holes in the pepper-pot, this emittance meter can be used to observe and study four-dimensional emittance correlations in beams from ECR ion sources.

• P. Spädtke, R. Lang, J. Mäder, J. Roßbach, K. Tinschert
  GSI, Darmstadt

Experimental results from ion beams, extracted from an Electron Cyclotron Resonance ion source (ECRIS) are presented and compared with different models used for simulation. The model for the simulation has to satisfy different facts: The energy of ions within the plasma is in the eV-range. Electrons have a different energy distribution: there are hot electrons (up to MeV range), but also low energy electrons, responsible for charge neutrality within the plasma. Because the gyration radius of ions is within the mm-range and below, ions can be extracted only if they are located on a magnetic field line which goes through the extraction aperture. Because of the gradient dBz/dz of the mirror field only these ions can be extracted, which have enough energy in direction of the field line. These conditions are fulfilled for ions which are going to be lost through the loss cone created by the hexapole. The extracted beam shows a typical behavior for an ECRIS: when the beam is focused by a lens (here a solenoid) directly behind extraction, the initial round and hollow beam develops wings with a 120-degree symmetry. These wings has influence on the beam emittance.

• M. Ichikawa, H. Fujisawa, Y. Iwashita, T. Sugimoto, H. Tongu, M. Yamada
  Kyoto ICR, Uji, Kyoto

We aim to develop a small and high intensity proton source for a compact accelerator based neutron source. Because this proton source shall be located close to RFQ for simplification, ratio of H⁺ to molecular ions such as H²⁺ or H³⁺ must be large. Therefore we select ECR ion source with permanent magnet as a small and high intensity ion source. ECR ion sources can provide high H⁺ ratio because of their high plasma temperature. Using permanent magnets makes the ion source small and running cost low. Because there is no hot cathode, longer MTBF is expected. Usually, gas is fed into ion sources continuously, even if ion sources run in pulse operation mode. But, continuous gas flow doesn't make vacuum in good level. So, we decided to install pulse gas valve directly to the plasma chamber. Feeding the gas only when the ion source is in operation reduces the gas load to the evacuation system and the vacuum level can be kept high. Recent experimental results will be presented.