Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration. Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target. Nanowire targets can be employed to increase the laser absorption, but it is not yet clear how the fast electron beam properties are modified. Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic. The measurements indicate a greater fast electron emittance is obtained from nanowire targets. Two-dimensional particle-in-cell simulations support this conclusion, revealing beam defocusing at the wire–substrate boundary, a higher fast electron temperature and transverse oscillatory motion around the wires.

A single-shot measurement of electron emittance was experimentally accomplished using a focused transfer line with a dipole. The betatron phase of electrons based on laser wakefield acceleration (LWFA) is energy dependent owing to the coupling of the longitudinal acceleration field and the transverse focusing (defocusing) field in the bubble. The phase space presents slice information after phase compensation relative to the center energy. Fitting the transverse size of the electron beam at different energy slices in the energy spectrum measured 0.27 mm mrad in the experiment. The diagnosis of slice emittance facilitates local electron quality manipulation, which is important for the development of LWFA-based free electron lasers. The quasi-3D particle-in-cell simulations matched the experimental results and analysis well.

For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase, and the gun energy. The transverse emittance measured at the Injector Test Facility (ITF) is ${\it\varepsilon}_{x}=0.48\pm 0.01~\text{mm}~\text{mrad}$. An undulator prototype based on the EU-XFEL design and modified for PAL-XFEL was built and tested. A local-$K$ pole tuning procedure was developed and tested. A significant reduction (90%) of the local-$K$ fluctuation was observed. The requirement of undulator field reproducibility better than $2\times 10^{-4}$ and the undulator gap setting accuracy below $1~{\rm\mu}\text{m}$ were achieved for the prototype. The optical phase jitter after the pole height tuning at the tuning gap was calculated to be $2.6^{\circ }$ rms, which satisfies the requirement of $5.0^{\circ }$.

To realize a heavy-ion inertial fusion (HIF) driver, we have studied a possibility of laser ion source (LIS). A LIS can provide high-current high-brightness heavy-ion beams; however, it was difficult to manipulate the beam parameters. To overcome the issue, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The rapid ramping magnetic field could enhance limited time slice of the current and simultaneously the beam emittance changed accordingly. This approach may also be useful to realize an ion source for HIF power plant.

An ion source for generation of low-charged heavy ions has been developed using low-power KrF excimer and frequency-doubled Nd:YAG lasers. The ion source was examined with two experimental modes of low-voltage DC extraction at ∼20 kV and high-voltage pulse extraction at 150 kV. Normalized emittance of extracted beams composed of Cu+ and Cu2+ ions was measured to be about 0.05 and 0.8 πmm-mrad for the DC extraction and the pulse extraction, respectively. Electron temperature was observed by means of a single probe method to be 0.8 to 2.5 eV, depending on the intensity of the KrF laser.

This study reports on the optimization of the radio frequency capture phase during the operational cycle of the SIS-18 synchrotron at Gesellschaft für Schwerionenforschung, Darmstadt, Germany. The ion species studied were 238U+28 and 238U73+ at an injection energy of 11.4 MeV/u. The longitudinal relative momentum spread derived from Schottky spectra of the coasting beam at injection provides a value of |Δp/p0|full-width ∼ 5 × 10−3. Simulation results from the synchrotron tracking code ESME (FermiLab) were compared with beam-current profile measurements obtained from a pickup. To gain further insight, the Tomography program (European Organization for Nuclear Research) has been used to derive the longitudinal phase space development from waterfall plots of the measured beam current profile, which may then be compared against simulation. Possible causes of this nonadiabaticity are discussed and solutions are proposed.