Considerations for a RF separated K+ beam for NA62

In this document we assess the potential of RF separation to increase the kaon content of the high-intensity secondary beam to the NA62 experiment in the CERN North Area. The present mixed beam provides a nominal kaon flux of 45 MHz out of a total beam intensity of about 750 MHz. The experiment wishes to increase the kaon flux, without too much increasing the overall beam intensity which might otherwise exceed the rate capability of several detectors and cause increased backgrounds to the detector. To avoid a strong reduction of the kaon flux by decays in a very long beam line, a compact RF separator approach is evaluated as a baseline. Alternative possibilities are briefly described at the end of the document. It turns out that the performance will not meet expectations and that therefore conventional methods to increase the beam intensity will have to be pursued. With the relatively short length proposed, the K phase difference is too small to separate the kaons from the large emittance mixed beam. A larger phase difference would imply more length and hence a drastic reduction of the kaon component due to decays.