Kang, Y.W. Lee, S.W. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-WEPOA52 English 810-812 WEPOA52 ion rfq simulation resonance operation Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-WEPOA52 https://jacow.org/napac2016/papers/wepoa52.pdf Performance of radio frequency quadrupole (RFQ) is sensitive to the errors in internal dimensions which shift resonance frequency and distort field distribution on the beam axis along the structure. The SNS RFQ has been retuned three times to compensate the deviations in frequency and field flatness with suspected dimensional changes since the start of the project for continuous operation with H⁻ ion beams. SNS now has a new RFQ as a spare that is installed in beam test facility (BTF), a low energy test accelerator. In order to understand and predict the performance deviation, full 3D modeling and simulation were performed for the SNS RFQs. Field and frequency errors from hypothetical transverse vane perturbations, and vane erosion (and metal deposition such as Cesium introduced by the ion source operation) at the low energy ends are discussed.