An X-band magnetically insulated transmission line oscillator has been investigated theoretically and experimentally in our laboratory. However, severe pulse shortening and electrode erosion are observed in the experiments. The theoretical analyses show that anode plasma formation in the load region is the essential reason for the pulse shortening and electrode erosion. In order to eliminate or at least minimize anode plasma formation in the load region, an improved beam dump is presented. The theoretical analyses show that anode plasma formation can be eliminated or at least minimized in the improved beam dump.