High power RF testing of dielectric loaded accelerating structures

A joint Argonne National Laboratory/Naval Research Laboratory program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424-GHz radiation from the NRL Magnicon Facility. DLA structures offer the potential of a simple, inexpensive alternative to copper disk-loaded structures for use in high-gradient RF linear accelerators. The purpose of the high-power tests is to find the RF breakdown limits of these structures and to test their ability to produce high accelerating gradients. We have recently tested two different dielectric tubes, one with alumina and another with MgCaTi liners. For alumina, we have shown no evidence of RF breakdown at up to 5 MW drive power (equivalent to 8 MV/m accelerating gradient). However, multipactor effect was found to absorb an increasing fraction of the incident microwave power, as the power level was increased, ultimately absorbing half of the incident power. Detailed experimental results and solutions for curing the multipactor will be discussed. We will also report on the most recent test results of MgCaTi dielectric tubes