• J.D. Fox, A. Bullitt, T. Mastorides, G. Ndabashimiye, C.H. Rivetta, O. Turgut, D. Van Winkle
  SLAC, Menlo Park, California
• J.M. Byrd, M.A. Furman, J.-L. Vay
  LBNL, Berkeley, California
• R. De Maria
  BNL, Upton, Long Island, New York
• W. Höfle, G. Rumolo
  CERN, Geneva

The SPS at high in­ten­si­ties ex­hibits trans­verse sin­gle-bunch in­sta­bil­i­ties with sig­na­tures con­sis­tent with an Ecloud driv­en in­sta­bil­i­ty. We pre­sent re­cent MD data from the SPS, de­tails of the in­stru­ment tech­nique and spec­tral anal­y­sis meth­ods which help re­veal com­plex ver­ti­cal mo­tion that de­vel­ops with­in a sub­set of the in­ject­ed bunch trains. The beam mo­tion is de­tect­ed via wide-band ex­po­nen­tial taper striplines and delta-σ hy­brids. The raw sum and dif­fer­ence data is sam­pled at 50 GHz with 1.8 GHz band­width. Slid­ing win­dow FFT tech­niques and RMS mo­tion tech­niques show the de­vel­op­ment of large ver­ti­cal tune shifts on por­tions of the bunch of near­ly 0.025 from the base tune of 0.185. Re­sults are pre­sent­ed via spec­tro­grams and rms bunch slice tra­jec­to­ries to il­lus­trate de­vel­op­ment of the un­sta­ble beam and time scale of de­vel­op­ment along the in­ject­ed bunch train. The study shows that the grow­ing un­sta­ble mo­tion oc­cu­pies a very broad fre­quen­cy band of 1.2 GHz. These mea­sure­ments are com­pared to nu­mer­i­cal sim­u­la­tion re­sults, and the sys­tem pa­ram­e­ter im­pli­ca­tions for an Ecloud feed­back sys­tem are out­lined.