Abstract
Knowledge of the three-dimensional structure of a charged particle beam bunch is essential for understanding its evolution and for initializing computer simulations, especially when space charge is involved. This paper presents a novel experimental method for time-sliced mapping of the transverse phase space of a space-charge dominated beam based on tomographic principles. The combination of a high precision tomographic diagnostic with fast imaging screens and a gated camera are used to produce phase-space maps of two beams: one with a parabolic current profile and another with a short perturbation atop a rectangular pulse. The correlations between longitudinal and transverse phase spaces are apparent and their impact on the dynamics is discussed.
Highlights
A high brightness and low emittance beam is an a priori requirement for x-ray free electron lasers (FELs) [1], brighter-luminosity high-energy colliders [2], energy recovery linacs [3], and Spallation Neutron Sources [4]
We report time-resolved phase-space maps for two beams: a long rectangular pulse with a short perturbation in charge density we deliberately introduce, and a parabolic beam bunch that is close to an ellipsoidal distribution
EXPERIMENTAL RESULTS AND DISCUSSION we first discuss the results with the rectangular pulse, and with the parabolic pulse
Summary
A high brightness and low emittance beam is an a priori requirement for x-ray free electron lasers (FELs) [1], brighter-luminosity high-energy colliders [2], energy recovery linacs [3], and Spallation Neutron Sources [4]. Density modulations in the injection region, produced, for example, by modulations in the drive laser of a photoinjector or from space charge in the gun [5], can be converted at low energy by space-charge forces into energy modulations [6], which are frozen-in as the beam gets accelerated into ultrarelativistic velocities [7,8,9] These modulations in energy can reappear further downstream in doglegs or compression chicanes [10] and possibly lead to unwanted coherent synchrotron radiation [11]. To mitigate these effects, novel methods have been proposed [7,12] and attempted [13] for creating an ellipsoidal beam bunch in which the line charge density is parabolic. For proton and ion beams, longitudinal stability is at least as important since the beam spends a longer part of its life in the low-energy region where space-charge forces are strong [15]
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