RF Voltage Modulation Research Articles

RF voltage modulations and the coupled bunch instabilities

The effects of rf cavity voltage modulation on longitudinal beam dynamics were studied experimentally at Taiwan Light Source by using a streak camera system that measured the attractor amplitude of the beam bunch. Theoretical description of rf voltage modulation that includes the effect of nonzero synchronous phase has been developed. The characteristics of the quadrupole parametric resonance in the single bunch and multibunch modes were studied and compared with theory. The formation of beamlets in the bucket helps to damp the coherent coupled bunch oscillation driven by parasitic modes of the rf cavity. This beam manipulation technique can be employed to alleviate stability problems associated with high brightness electron storage rings.

Adiabatic excitation of longitudinal bunch shape oscillations

By modulating the rf voltage at near twice the synchrotron frequency, the longitudinal bunch shape can be modulated. This method can be used to shorten bunches. We show experimentally that the bunch shape can be modulated while preserving the longitudinal emittance when the rf voltage modulation is turned on adiabatically. Experimental measurements will be presented along with theoretical predictions.

Uniform bunch formation by RF voltage modulation with a band-limited white signal

Uniform bunch formation by RF voltage modulation with a band-limited white signal is proposed to relax the space-charge effects in proton synchrotrons. A unique feature of this method is to increase the bunching factor without the longitudinal emittance blow-up, in principle. The beam dynamics is discussed based on the diffusion equation and computer simulations. The temporal evolution, time constant and equilibrium distribution are derived.

Role of parametric resonances in global chaos.

The quasi-isochronous (QI) dynamical system, in the presence of synchrotron radiation damping and rf phase modulation, exhibits a sequence of period-2 bifurcations en route towards global chaos (instability) in a region of modulation tune. The critical modulation amplitude for the onset of the global chaos shows a cusp as a function of the modulation tune. This cusp is shown to arise from the transition from the 2:1 to the 1:1 parametric resonances. We have also studied the effect of the rf voltage modulation on the QI dynamical system and found that the tolerance of the rf voltage modulation is much larger than that of the rf phase modulation. \textcopyright{} 1996 The American Physical Society.

Effects of rf voltage modulation on particle motion

The effects of rf voltage modulation on synchrotron motion were studied experimentally. The experimental data revealed the resonance islands generated by the rf voltage modulation. With electron cooling, beam particles were observed to damp to the basins of these resonance islands or attractors, which were observed to rotate about the origin of the phase space at a half of the modulation frequency. The measured amplitude of the attractors as a function of the modulation frequency agreed very well with the theoretical prediction. The Poincaré maps in the resonance rotating frame were obtained from the experimental data and compared with tori of the Hamiltonian flow. Based on our theoretical formulation, slow beam extraction using rf voltage modulation and a bent crystal are also studied.

Experimental measurement of resonance islands induced by rf voltage modulation.

Synchrotron motion with an external rf voltage modulation was studied experimentally. Beam particles, in the presence of electron cooling, were observed to damp to the basins of resonance islands, which were produced by the parametric resonance due to rf voltage modulation. The measured phase amplitudes of the centers of these resonance islands were found to agree well with theory.