Abstract
High brightness electron sources for linac based free-electron lasers (FELs) are being developed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Production of electron bunches with extremely small transverse emittance is the focus of the PITZ scientific program. The photoinjector optimization in 2008–2009 for a bunch charge of 1, 0.5, 0.25, and 0.1 nC resulted in measured emittance values which are beyond the requirements of the European XFEL [S. Rimjaem et al., Nucl. Instrum. Methods Phys. Res., Sect. A 671, 62 (2012)]. Several essential modifications were commissioned in 2010–2011 at PITZ, resulting in further improvement of the photoinjector performance. Significant improvement of the rf gun phase stability is a major contribution in the reduction of the measured transverse emittance. The old TESLA prototype booster was replaced by a new cut disk structure cavity. This allows acceleration of the electron beam to higher energies and supports much higher flexibility for stable booster operation as well as for longer rf pulses which is of vital importance especially for the emittance optimization of low charge bunches. The transverse phase space of the electron beam was optimized at PITZ for bunch charges in the range between 0.02 and 2 nC, where the quality of the beam measurements was preserved by utilizing long pulse train operation. The experimental optimization yielded worldwide unprecedented low normalized emittance beams in the whole charge range studied.20 MoreReceived 18 June 2012DOI:https://doi.org/10.1103/PhysRevSTAB.15.100701This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society
Highlights
The availability of a high brightness electron source is one of the key issues for successful operation of linac based free-electron lasers (FELs) like the Free-electron Laser in Hamburg, FLASH [1], and the European X-ray FreeElectron Laser, European XFEL [2]
In 2007 it was shown for the first time that the stringent requirement on beam emittance for the European XFEL of 0.9 mm mrad at 1 nC bunch charge in the injector can be reached if 10% of the total amount of electrons are removed from the outer area of the measured transverse phase space, which anyhow are not expected to contribute to the lasing in the FEL process [4]
In this paper we have described the latest results of the experimental optimization of the high brightness electron source at the Photo Injector Test facility at DESY, Zeuthen site (PITZ)
Summary
The availability of a high brightness electron source is one of the key issues for successful operation of linac based free-electron lasers (FELs) like the Free-electron Laser in Hamburg, FLASH [1], and the European X-ray FreeElectron Laser, European XFEL [2]. Spontaneous emission (SASE) of the FEL process requires an extremely high space charge density of the radiating electron bunches implying high peak current, low energy spread, and small transverse emittance of the electron beam [3]. The latter property cannot be improved in a linac and the emittance has to be minimized already in the injector. Small improvements in the electron beam line like elimination of magnetizable components led to better photoinjector performance These upgrades resulted in $30% further emittance reduction. The results obtained are setting a new benchmark for experimentally optimizing photoinjector performance in the whole charge range
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