MODELING OF NEGATIVE ION SOURCES Francesco Taccogna (1,*) , Pierpaolo Minelli (1) , Savino Longo (1,2) , Mario Capitelli (1,2) , Ralf Schneider (3) (1) Istituto di Metodologie Inorganiche e dei Plasmi (IMIP), Consiglio Nazionale delle Ricerche, via Amendoal 122/D, 70124 Bari (Italy) (2) Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro, via Orabona 4, 70124 Bari (Italy) (3) Institute of Physics, Ernst-Moritz Arndt University, Felix-Hausdorff Str. 6 – D17498 Greifswald, Germany (*) francesco.taccogna@ba.imip.cnr.it The negative ion source for ITER has been officially chosen to be the radio frequency inductively coupled discharge developed at IPP Garching [1]. This source consists of three parts (see Fig. 1): the cylindrical driver, where the RF coils are coupled to the H 2 gas to generate the plasma, the rectangular expansion region, where the plasma expands into the actual source body, and the extraction region, consisting of three grids, the plasma grid PG, the extraction grid EG and the grounded grid AG. The expansion and extraction regions are separated by a magnetic field parallel to the plasma grid of the order of 5-7 mT, the filter field. In fact, it is generally accepted that most H - ions are produced in the volume by a two-step process which involves dissociative attachment of slow electrons (T e <2 eV) to highly vibrationally excited levels of hydrogen molecules H 2 (optimum vibrational level v=4-9 reached at T e >10 eV). For this reason, the optimum condition for H - formation is not compatible with that for H 2 * (v) production and a magnetic filter has been introduced to separate the negative ion source into two regions where the electron temperature is optimized for each the two processes. The cooling-down from the expansion region is further assisted by magnets in the EG which are primarily there to deflect the co-extracted electrons. The resulting magnetic fields (filter and deflection) are shown in Fig. 2. In addition to volume production of negative ions, the extraction current density of negative ions is strongly increased by adding Cs and generating a lot of additional negative ions from the Caesiated surfaces. Fig.1: Scheme of the radio frequency inductively coupled negative ion source developed at Max- Planck IPP in Garching. Topic number: 6 20 th ESCAMPIG, 13-17 July 2010, Novi Sad, Serbia TL7