The Frankfurt MEDEBIS: A prototype of an injector for a synchrotron dedicated for cancer therapya)

Abstract

The Frankfurt MEDEBIS has been constructed to study the techniques of an electron beam ion source (EBIS) designed as an injector for a synchrotron dedicated to cancer therapy. The MEDEBIS uses a normal conducting solenoid of 0.8 T and a trap length of 0.25 m. The aims are to inject fully stripped light ions like C6+ and O8+ in a single turn into a synchrotron for the most simple and reliable operation. Therefore fast ion extraction in less than 4 μs has been examined, both theoretically and experimentally. The source complexity has been reduced by iron shielding of an electron gun and collector without any bucking coils. The electron gun operates with partially immersed flow focusing and provides a maximum current density of about 70 A/cm2. With a second anode the beam perveance is variable. The ion extraction time is reduced by a novel electrostatic structure providing a pulsed extraction field along the axis of the whole ion trap. Measurements of extracted ion pulses and the total number of extracted charges are presented. At confinement times of about 200 ms bare nuclei are obtained with maximum abundance in the charge spectra in good agreement with design data and Lotz cross sections.