MATCHING OF HIGH INTENSITY ION BEAMS TO AN RFQ: COMPARISON OF PARMTEQ AND IGUN SIMULATIONS

The classical way of matching an ion source to the low energy accelerator RFQ generally is performed by adjusting the matching optics of the LEBT to provide the rms ellipse twiss parameter requirements of the RFQ shaper section. By matching to the rms parameters (the equivalent rms beam method) the actual shape of the distribution plays a smaller role according to F. Sacherer. In many cases, however, the matching optics are creating not only aberrations to the ion beam but also a very nonelliptical shape of the emittance figure, and a more exact match may be required. As a way out, an ion extraction program (IGUN) has been modified to also take into account the rf-focusing of non-modulated RFQ vanes in the shaper section. This makes it feasible to use this program for the simulation from the ion source plasma until the beginning of modulation inside the RFQ, and it can also handle dc fields in the injection region of the RFQ. In order to demonstrate the differences of both approaches we apply them to well defined experimentally proved designs of RFQ shaper sections.