Analysis, Prototyping, and Design of an Ionization Profile Monitor for the Spallation Neutron Source Accumulator Ring

The Spallation Neutron Source (SNS) located in the Oak Ridge National Laboratory is comprised of a 1 GeV linear H^- [H^-] accelerator followed by an accumulator ring that delivers high intensity 1 μs [microsecond] long pulses of 1.5x10¹⁴ [1.5x10^14] protons to a liquid mercury target for neutron production by spallation reaction. With its strict 0.01% total beam loss condition, planned power upgrade, and proposed second target station, SNS ring beam-profile diagnostics capable of monitoring evolving beam conditions during high-power conditions are crucial for efficient operation and improvement. By subjecting ionized electrons created during beam interactions with the residual gas to a uniform electric field perpendicular to the beam direction, a profile may be collected based on the relation between measured ionized particle current and the beam density responsible for ionization. This form of nondestructive profile beam profile diagnostic known as an Ionization Profile Monitor (IPM). Introducing a magnetic field parallel to the electric field constrains the transverse particle motion to produce spatially accurate profiles. Presented in this work is the analysis and design of an IPM for the SNS ring capable of measuring turn-by-turn profiles with a 10% spatial accuracy for a fully accumulated high intensity proton beam. A theoretical framework is developed for the IPM operational principles and estimations for system design parameters are made based on calculations and measurement data. Detailed simulations are presented which are also used to determine design details and experimental results from a proof-of-principle IPM test chamber are reported and analyzed. Finally, a complete system design is presented based on the design criteria and simulation optimization that meets the required IPM system objectives.