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The Center for Bright Beams, A National Science Foundation Science and Technology Center

The Role of Low Intrinsic Emittance in Modern Photoinjector Brightness

Photocathode improvements are one of the directions the CBB is exploring to increase the brightness of electron sources. However, non-linear forces from space charge or optical elements can cause the beam to lose brightness on its way from the source to the point where it is used. In systems where this happens, the full benefit of newly developed photocathode technologies may not be realized. In this work, we show that for three specific photoinjector configurations (which are representative of commonly used real-world systems), those brightness degrading effects are small enough that photocathode research remains a viable path to brighter beams.

Graph of Characteristic MTE against Bunch Charge.
Figure: The characteristic mean transverse energy (characteristic MTE) is a newly developed metric that sets the scale down to which photocathode improvements can make a difference in photoinjector brightness. The characteristic MTEs of the three systems we studied were well below the MTE of currently used photocathodes. This means that photocathode improvements are still a viable route to increase beam brightness.

Applications and relation to CBB Goals:

Our results pave the way for photocathode research to translate into higher usable brightness for realistic photoinjector configurations. This is important for brightness limited accelerator applications such as single shot ultrafast electron diffraction and x-ray free electron lasers.


C. M. Pierce, M. B. Andorf, E. Lu, C. Gulliford, I. V. Bazarov, J. M. Maxson, M. Gordon, Y.-K. Kim, N. P. Norvell, B. M. Dunham, and T. O. Raubenheimer, “Low intrinsic emittance in modern photoinjector brightness,” Phys. Rev. Accel. Beams, vol. 23, no. 7, p. 070101, Jul. 2020, doi: 10.1103/PhysRevAccelBeams.23.070101. Available [Online]