Abstract
Recently, Stratakis and collaborators performed the tomographic phase space mapping of intense particle beams in the energy range of a few keV using a pair of solenoids [D. Stratakis et al., Phys. Plasmas 14, 120703 (2007)]. In this paper, we report the tomographic phase space mapping for the relativistic electron beam from a photocathode radio-frequency gun using a single solenoid at an energy of a few MeV. The experiment is conducted at a very low charge level aiming at mapping the phase space distributions of thermal emittance dominated beam. The phase space distribution is reconstructed with the algebraic reconstruction technique using the 14 beam profiles measured under various solenoid currents. Results from the computerized tomography (CT) technique are in good agreement with that from the solenoid scan method. The reconstructed phase space from the CT technique is further analyzed and shows a stochastic distribution which is a strong confirmation for the measurement of thermal emittance. Details on measurement principles and experimental implementation of the CT technique and solenoid scan method are presented.
Highlights
Over the years there has been growing interest in generation, manipulation, and measurement of low emittance electron beam, as required by International Linear Collider (ILC) [1], X-ray Free Electron Lasers (XFEL) [2,3], Energy Recovery Linac (ERL) [4], the MeV time-resolved ultrafast electron diffraction facility [5,6,7], etc
If the thermal emittance is larger than 1 mm mrad, we can conclude that the final emittance will by no means be smaller than the expected value, even if the laser is in an ideal shape
The thermal emittance was measured using the computerized tomography (CT) technique and the result was cross-checked with the solenoid scan method
Summary
Over the years there has been growing interest in generation, manipulation, and measurement of low emittance electron beam, as required by International Linear Collider (ILC) [1], X-ray Free Electron Lasers (XFEL) [2,3], Energy Recovery Linac (ERL) [4], the MeV time-resolved ultrafast electron diffraction facility [5,6,7], etc. With the rapid advancements in the techniques for emittance compensation [12,13,14,15,16], laser shaping [17,18], and the generation of ellipsoidal beam [19,20], the emittance growth due to rf force and space charge force can be largely reduced and the limit of the emittance achievable is the thermal emittance. Simulation shows that with ideal cathode surface high quality beam (1 nC charge, 1 mm mrad emittance) can be generated if the laser has been shaped into a uniform cylinder. The thermal emittance was measured using the computerized tomography (CT) technique and the result was cross-checked with the solenoid scan method.
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