The electron cloud in positron storage rings is pinched when a bunch passes by. For short bunches, the radiation due to acceleration of electrons of the cloud is coherent. Detection of such radiation can be used to measure the density of the cloud. The estimate of the power and the time structure of the radiated signal is given in this paper. ∗Work supported by Department of Energy contract DE–...

We discuss the transverse betatron tune shift of the coherent dipole motion of a beam interacting with an electron cloud. A positron beam which passes through a frozen charge distribution experiences an electric field, which shifts its tune in the positive direction. The electrons in the actual cloud are not frozen, but move during the bunch passage. Thus, the electron distribution varies due t...

We describe the effects of geometric torsion on the coherent motion of electrons along a thin twisted quantum ring. The geometric torsion inherent in the quantum ring triggers a quantum phase shift in the electrons' eigenstates, thereby resulting in a torsion-induced persistent current that flows along the twisted quantum ring. The physical conditions required for detecting the current flow are...