Simulations of the Fermilab Booster reveal a substantial electron-cloud buildup both inside the unshielded combined-function magnets and the beam pipes joining the magnets, when the second-emission yield (SEY) is larger than (almost equal to)1.6. The implication of the electron-cloud effects on space charge and collective instabilities of the beam is discussed.

The stable region of the Fermilab Booster beam in the complex coherent-tune-shift plane appears to have been shifted far away from the origin by its intense space charge making Landau damping appear impossible. Simulations reveal a substantial buildup of electron cloud in the whole Booster ramping cycle, both inside the unshielded combined-function magnets and the beam pipes joining the magnets, whenever the secondary-emission yield (SEY) is larger than (almost equal to)1.6. The implication of the electron-cloud effects on the space charge and collective instabilities of the beam is investigated.

A new transverse instability is observed that may limit the proton intensity in the Fermilab Recycler. The instability is fast, leading to a beam-abort loss within two hundred turns. The instability primarily affects the first high-intensity batch from the Fermilab Booster in each Recycler cycle. This paper analyzes the dynamical features of the destabilized beam. The instability excites a horizontal betatron oscillation which couples into the vertical motion and also causes transverse emittance growth. This paper describes the feasibility of electron cloud as the mechanism for this instability and presents the first measurements of the electron cloud in the Fermilab Recycler. Direct measurements of the electron cloud are made using a retarding field analyzer (RFA) newly installed in the Fermilab Recycler. Indirect measurements of the electron cloud are made by propagating a microwave carrier signal through the beampipe and analyzing the phase modulation of the signal. The maximum betatron amplitude growth and the maximum electron cloud signal occur during minimums of the bunch length oscillation.

This thesis presents profound insights into the origins and dynamics of beam instabilities using both experimental observations and numerical simulations. When the Recycler Ring, a high-intensity proton beam accelerator at Fermi National Accelerator Laboratory, was commissioned, it became evident that the Recycler beam experiences a very fast instability of unknown nature. This instability was so fast that the existing dampers were ineffective at suppressing it. The nature of this phenomenon, alongside several other poorly understood features of the beam, became one of the biggest puzzles in the accelerator community. The author investigated a hypothesis that the instability arises from an interaction with a dense cloud of electrons accompanying the proton beam. He studied the phenomena experimentally by comparing the dynamics of stable and unstable beams, by numerically simulating the build-up of the electron cloud and its interaction with the beam, and by constructing an analytical model of an electron cloud-driven instability with the electrons trapped in combined-function dipole magnets. He has devised a method to stabilize the beam by a clearing bunch, which conclusively revealed that the instability is caused by the electron cloud, trapped in a strong magnetic field. Finally, he conducted measurements of the microwave propagation through a single dipole magnet. These measurements have confirmed the presence of the electron cloud in combined-function magnets.

We have performed a series of experiments at Fermilab to explore the electron cloud phenomenon. The Main Injector will have its beam intensity increased four-fold in the Project X upgrade, and would be subject to instabilities from the electron cloud. We present measurements of the cloud formation in the Main Injector and experiments with materials for the mitigation of the Cloud. An experimental installation of Titanium-Nitride (TiN) coated beam pipes has been under study in the Main Injector since 2009; this material was directly compared to an adjacent stainless chamber through electron cloud measurement with Retarding Field Analyzers (RFAs). Over the long period of running we were able to observe the secondary electron yield (SEY) change and correlate it with electron fluence, establishing a conditioning history. Additionally, the installation has allowed measurement of the electron energy spectrum, comparison of instrumentation techniques, and energydependent behavior of the electron cloud. Finally, a new installation, developed in conjunction with Cornell and SLAC, will allow direct SEY measurement of material samples irradiated in the accelerator.