Previous research allowed us to develop highly efficient electron emissive metal-dielectric ͑MD͒ structures, which are suitable to be used as sources of secondary electrons in electron cyclotron resonance ion sources ͑ECRIS͒. First tests have been performed replacing the stainless steel disk of the Frankfurt 14 GHz ECRIS by a MD structure. This method was recently extended by inserting a MD cylinder ͑150 mm long and 58 mm in diameter͒ into this source. The experiments were performed with pure

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... gon as source gas and with gas mixing (argonϩoxygen). In this contribution, the performance with MD cylinder is compared to that of the standard source ͑stainless steel plasma chamber͒ and to the case, where a cylinder of technical aluminum was installed. With the MD cylinder the yield of highly charged ions from the ECRIS are significantly enhanced. For Ar 16ϩ ion current enhancement factors of up to 50 were obtained.