(a) The longitudinal energy spread of the e-bunch

<p><strong>Figure 4.</strong> (a) The longitudinal energy spread of the e-bunch. (b) The current profile of the e-bunch. (c) The normalized emittance (<em>x</em>, <em>y</em>) of the e-bunch at the entrance of undulator. (d) The undulator radiation at a position of 50 m along the undulator.</p> <p><strong>Abstract</strong></p> <p>The generation of an isolated attosecond pulse at 0.1 nm has been proposed in an ESASE scheme where an 800 nm, 5 fs FWHM carrier-envelop-phase stabilized laser is employed in the 10 GeV Pohang accelerator laboratory—x-ray free electron laser (PAL-XFEL). The radio-frequency (RF) phase effect has been studied on the current profile after the chicane and on the x-ray radiation power at 50 m along the undulator. This study leads to the tolerance in the RF phase. The results show that a single isolated attosecond radiation pulse could be produced inside the undulator; however, the RF phase should be controlled down to 0.05° in the linac section of the PAL-XFEL in order to satisfy the requirement for RF jitters suitable for pump–probe experiments.</p>