MPI-K, Heidelberg
[1] D. A. Orlov et al., Appl. Phys. Letters 78, 2721 (2001)
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| FRM1C03 | Electron Cooling with Photocathode Electron Beams Applied to Slow Ions at TSR and CSR | 230 |
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We report electron cooling experiments using a cold electron beam of 55 eV produced by a cryogenic GaAs photocathode. With this device the beam of singly charged ions with a mass of 31 amu, specifically the CF+ ion, was cooled at an energy of 3 MeV (about 90 keV/u). Transverse cooling within 2-3 seconds to a very small equilibrium beam size was observed with an electron current of 0.3 mA (electron density of 3×106 cm-3, magnetic guiding field of 0.04 T). A beam size of about 0.1 mm was deduced from imaging of recombination products. The short cooling times are mostly due to the low electron temperatures of 1 meV in transverse and 0.03 meV in longitudinal direction. An electrostatic Cryogenic Storage Ring (CSR) for slow ion beams, including protons, highly charged ions, and polyatomic molecules is under construction at the MPI-K. It will apply electron cooling at electron beam energies from 165 eV for 300 keV protons down to a few eV for polyatomic singly charged ions. Photoelectrons from the GaAs photocathode with laboratory energy spreads of about 10 meV [1] will be applied for generating such electron beams. In a storage ring of this type, even low electron-ion merging magnetic fields of toroids cause a strong coupling between the horizontal and vertical motions of the stored ions, reducing the ring acceptance to an intolerably low level. We present a new merging scheme of eV-electrons with stored ions, based on the idea of bringing electrons to the ion axis in a uniform dipole magnetic field superimposed to a straight solenoid field. The new magnetic field arrangement strongly improves the ring acceptance and allows to use guiding magnetic fields as high as required to provide high-quality electron beams of eV-energies for the cooling of ions and for merged beam studies in storage rings.
[1] D. A. Orlov et al., Appl. Phys. Letters 78, 2721 (2001) |
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