The animations show the single bunch evolution under the effect of the
electron cloud in the SPS as well as in the Low Energy Ring of the KEK B
Factory. The dotted line represents the centroid position along the bunch,
and the solid lines are located at +/- one bunch rms-size from the centroid.
The unstable evolution manifests itself with a strong centroid oscillation
and beam enlargement, which both saturate and decay after the initial
exponential growth. The full movie actually represents the simulated
evolution of a single bunch over 500 turns. The data used to construct the
frames are outputs of the HEADTAIL code, which is available further below on
this page. In the SPS simulation, the movie displays the bunch evolution
when both the electron cloud and the space charge induced tune spread are
taken into account. There appears to be an interesting synergy between
these two effects, which is confirmed by the absence of any dipole coherent
motion when the bunch is made to interact with the electron cloud alone.
The interplay between electron cloud and space charge (and broad band
impedance, too) is presently under investigation by means of a combined
analytical-numerical study.
26 July 2001
Giovanni Rumolo, SL/AP,
and
Frank Zimmermann, SL/AP
Movies of the single-bunch electron-cloud instability: