Impact of Electric Current Fluctuations Arising from Power Supplies on   Charged-Particle Beams
  Electric current fluctuations are one type of unavoidable machine imperfections,and induce magnetic-field perturbations as a source of instabilities in accelerators. This paper presents measurement-based methodology of modeling the fluctuating electric current arising from the power system of Fermilab's Booster synchrotron to discuss the ramifications of the presence of ripple current and space-charge defocusing effects. We also present the method of generating stochastic noise and the measurement and analysis methods of ripple current and offending electromagnetic interferences residing in the Booster power system. This stochastic noise model, accompanied by a suite of beam diagnostic calculations, manifests that the fluctuating power-supply current, when coupled to space charge and impinging upon a beam, can substantially enhance beam degradation phenomena--such as emittance growth and halo formation--during the Booster injection period. With idealized and uniform charge-density distribution, fractional growth of rms emittances due to ripple current under space charge turn out to be about 8 ~ 9 % in both transverse planes over the injection period of 2.2 ms prior to beam acceleration. 
P. S. Yoon