Abstract
A new system used for monitoring energetic Coulomb-scattered electrons as the main diagnostic for accurately aligning the electron and ion beams in the new Relativistic Heavy Ion Collider (RHIC) electron lenses is described in detail. The theory of electron scattering from relativistic ions is developed and applied to the design and implementation of the system used to achieve and maintain the alignment. Commissioning with gold and 3He beams is then described as well as the successful utilization of the new system during the 2015 RHIC polarized proton run. Systematic errors of the new method are then estimated. Finally, some possible future applications of Coulomb-scattered electrons for beam diagnostics are briefly discussed.
Highlights
Instrumentation providing accurate information on particle beam properties and behavior in accelerators is essential for their operation
We describe a new type of beam diagnostic device for high energy particle accelerators based on the Coulomb scattering of electrons by the beam particles
The system we describe here is a new noninvasive beam diagnostic tool based on the Coulomb interaction of low energy electrons with relativistic particle beams, but in this case the interaction is due to small impact parameter collisions of a small fraction of the electrons with individual beam particles leading to large momentum transfers
Summary
Instrumentation providing accurate information on particle beam properties and behavior in accelerators is essential for their operation. The system we describe here is a new noninvasive beam diagnostic tool based on the Coulomb interaction of low energy electrons with relativistic particle beams, but in this case the interaction is due to small impact parameter collisions of a small fraction of the electrons with individual beam particles leading to large momentum transfers This mechanism is the so-called Rutherford scattering, named after Ernest Rutherford. Some of these electrons acquire energies up to several MeV, making them easy to detect even after traversing thin vacuum windows, allowing the use of simple scintillation detectors in air Based on these ideas, we developed a noninvasive diagnostic tool called electron beam backscattering detector (eBSD) [10] to accurately align the electron and proton beams in the new Brookhaven National Laboratory (BNL) electron lenses for the partial compensation of the head-on beam-beam effects that limit the luminosity [11]. Time resolved measurements of this type, in addition to providing transverse beam profiles, could provide longitudinal bunch profiles and diagnostics for “head-tail” perturbations
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