Hoon Heo

Anomalous hard x-ray emission mode in a plasma focus discharge with hydrogen-argon mixtures

We observed an anomalous discharge mode causing explosive surface evaporation and emission of hard x rays of 10–40 keV in the regime of the lower hydrogen partial pressures of hydrogen–argon mixture in a Mather type plasma focus device of 1.5 kJ. At the anomalous mode, the x rays were emitted from only the surface of the anode without emissions from a plasma column or hot spots, accompanying with explosive evaporations of the anode surface.

Correlations between Argon Ion Beams and X-Rays in a Plasma Focus

We investigated the characteristics of X-rays and ions generated in a argon plasma focus discharge, and analyzed the correlation between X-ray emissions and ion emissions using the time of flight method composed with a Faraday cup, a capacitive current monitor, and p–i–n diodes covered with Ross filters. We obtained the energy spectra of argon ion beams, and observed X-rays of Ar Kα line and Cu Kα line. The optimum pressure range for ion emissions agreed with that for X-ray emissions, and ion energy distributions were shifted toward higher energies when X-ray emissions were good, which means the enhancement of the ion acceleration due to the mechanism of X-ray emission. The observed time correlations can not be explained by conventional ion acceleration models, but by a hybrid model describing the electric field induced by the moving current distribution, an anomalous resistivity, and the Hall effect.

Soft X-ray harmonic lasing self-seeded free electron laser at Pohang Accelerator Laboratory X-ray free electron laser

The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spectrometer. The spectral brightness is enhanced by a factor of 1.7 compared to the self-amplified spontaneous emission FEL because of the narrowed bandwidth. Our results show a good agreement with the theoretical expectation and simulations. The HLSS mode is a promising standard operation mode to generate a stable and high-brightness X-ray FEL that will provide more benefits to users for various applications.The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spectrometer. The spectral brightness is enhanced by a factor of 1.7 compared to the self-amplified spontaneous emission FEL because of the narrowed bandwidth. Our results show a good agreement with the theoretical expectation and simulations. The HLSS mode is a promising standard operation mode to generate a stable and high-brightness X-ray FEL that will provide more benefits to users for various applications.

Micro-mover Development and Test in the PAL-XFEL

Abstract Two micro-movers, which are able to control the horizontal, vertical and longitudinal positions as well as the yaw and pitch angles remotely, were developed and installed in the PAL-XFEL linac. The solenoid micromover in the gun section allows beam-based alignment of an electron beam to the solenoid field and the gun RF field. The X-band cavity micro-mover minimizes the transverse wake field effect caused by transverse misalignment between the beam and X-band cavity. Two micro-movers has similar specifications and the same mechanism, but the sizes are different from each other. In this paper, we present the design, manufacture and test results of the micro-movers.