THE FRANKFURT MEDEBIS PROJECT

An electron beam ion source (EBIS) with normal conducting solenoid has been constructed to study short ion extraction of about 4 mu s. The a im is to inject fully stripped light ions like C6+ and O8+ in a single turn into a medically dedicated synchrotron for cancer therapy. The c haracteristic parameters of an EBIS suitable for the hospital-based ir radiation therapy facility 'Progetto Adroterapia' are shown. A prototy pe, called MEDEBIS has been designed and built at IAP Frankfurt with a magnetic field of 0.8 T and a trap length of 0.25 m with the aim of s imple and reliable operation. The iron shielded electron gun with part ially immersed flow focusing provides a maximum current density of 70 A/cm(2) and a variable beam perveance by a second anode. The electron beam formation has been examined by scanning the beam profile along th e trap. The ion extraction time will be reduced by using a potential g radient along the axis of the ion trap. A solution is shown how to est ablish such a gradient by using a tube with tapered slits, surrounding the electron beam. Computer simulations have been performed to examin e the dependence of the time structure of an ion pulse and of the bunc hing characteristics on the shape of the axial gradient.