A high charge state ion source, like an electron beam ion source (EBIS), is required in order to provide highly charged ions from an off-line injector to the FAIR-Collaborations SPARC (see www.gsi.de/sparc) and FLAIR (see www.gsi.de/flair). Such an injector is mandatory for commissioning and tests of the whole FLAIR facility and also of the SPARC- and FLAIR-experiments, which are located in the FLAIR building, in order to be independent of the FAIR accelerator complex during the commissioning and testing periods, and for optimum usage of the limited beam time at FAIR. The injector has to provide highly charged ions at moderate intensities. A simple, but efficient EBIS using the low-power string mode (reflex mode of operation), would be a perfect choice, as it guarantees low power consumption and good beam quality. For this kind of operation electron currents below 1 mA are sufficient. If these could be provided with extremely high current density, the string mode will be much more attractive compared to conventional EBIS operation modes. Field emission (FE)-cathodes can deliver extremely high current densities up to 10^7 A/cm2, with currents around 1 mA. The goal of the proposed INTAS project is to investigate the well established string mode EBIS operation based on FE-cathodes. Within the proposed INTAS project, special FE-cathodes, which may deliver high beam currents up to 2-3 mA at high current densities will be developed and tested for long-term stability. In addition an optimized electron gun for those cathodes, being the main component of an EBIS operating in the string mode, will be designed and built. The electron gun will be developed in cooperation between the University of Belfast and the University of Frankfurt and can be tested in advance in the Belfast EBIT. Test of the string mode operation, which is of interest for an EBIS injector of the FLAIR low energy storage ring, can be performed in several devices available from the consortium and especially in Krion-2, where the string mode operation with conventional cathodes has been examined in detail. Here a direct comparison to the FE-cathode based gun can be performed. The string mode of operation benefits strongly from higher magnetic fields and therefore a string test will be performed in the 5T solenoid of the MAXEBIS at GSI, in order to compare the operation in higher magnetic fields to the operation in Krion-2 at 3 T.