A higher harmonic cavity (HHC) is popularly employed in synchrotron light storage rings to enhance the machine performance. which requires its fundamental mode resonant frequency to be tuned above the radio-frequency harmonic. However. this detuning is likely to cause Robinson instability. https://www.jmannino.com/best-catch-Sophie-Allport-Bee-Blackout-Ready-Made-Eyelet-Curtains-Duck-Egg-special-save/