Experimental demonstration of a tomographic 5D phase-space reconstruction

Abstract

Detailed knowledge of particle-beam properties is of great importance to understand and push the performance of existing and next-generation particle accelerators. We recently proposed a new phase-space tomography method to reconstruct the five-dimensional (5D) phase space, i.e., the charge density distribution in all three spatial directions and the two transverse momenta. Here, we present the first experimental demonstration of the method at the FLASHForward facility at DESY. This includes the reconstruction of the 5D phase-space distribution of a GeV-class electron bunch, the use of this measured phase space to create a particle distribution for simulations, and the extraction of the transverse 4D slice emittance.

Figures (5)

• Figure 1: The FLASHForward beamline section used for the 5D tomography measurement. The transverse phase space is reconstructed at the location labeled as the reconstruction point. The reconstruction of the time information is obtained at the PolariX TDS. The screen images for the tomography were recorded at the measurement point. Beamline elements that were not used for the measurement are displayed in a fainter color.
• Figure 2: 2D projections of the reconstructed 5D phase-space distribution normalized to their maximum value. The transverse projections are shown in normalized phase space. The head of the bunch is towards negative time values.
• Figure 3: Rendering of the reconstructed 5D phase space distribution projected onto the $(x'_{N}, y'_{N} ,t$) phase space. The projection is normalized to the maximum value of the charge density. In addition, the 2D projections are displayed in blue color and exemplarily three transverse slices are included.
• Figure 4: Reconstructed current profile, (a) beta functions, (b) alpha functions, and (c) sliced normalized transverse emittances for both transverse planes obtained from the 5D charge density. (d) The sliced 4D emittance is compared to the value obtained when multiplying the two transverse emittances. Only slices that contain at least 10000particles (0.2% of the total charge) are analyzed and the errorbars are obtained from 100 reconstructions where the shear parameter of each streaking angle is randomly sampled from a Gaussian distribution with a one sigma measurement uncertainty.
• Figure 5: Comparison of the measured screen images (top) to the tracked distribution (middle) for various phase advances $\mu_{x}, \mu_{y}$. The screen images are rotated by the streaking angle $\theta_{TDS}$ and the projection in streaking direction is converted to the time axis. The coordinate $\upsilon$ denotes the transverse plane of the bunch perpendicular to the streaking plane. The bottom row shows the centroid positions and RMS spread for each time slice containing more than 0.5% of the total charge.