| Paper | Title | Page |
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| MOP030 | Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL | 84 |
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Funding: This work was supported by the World Class Institute Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning.(NRF Grant Number:WCI2011-001) We realized a variable-period permanent-magnet helical undulator with high (~1 T) field amplitude, which is almost constant over undulator periods of 23–26 mm. Each undulator period has 4 modular sections of iron poles and permanent magnets embedded in non-magnetic disks with holes along the undulator axis. Modular plates undergo a longitudinal repulsive force from the magnetic field pressure and the spring coils between modular plates. The undulator period can thus be controlled by mechanically changing of the end plate longitudinal position. This compact design is suitable for a table-top terahertz free electron lasers. The measured on-axis field is about 0.97 T with the deviation less than 1% through the whole range of the undulator period variation. The measured spread of the longitudinal coordinates of the undulator field component maxima is less than 1%, and the measured field distribution meets the requirement for our terahertz FEL. The field reproducibility was checked by six measurements of the undulator field after the period variation for the 26 mm period. The r. m. s. phase errors is 3.7 degrees. |
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THP009 |
Spatiotemporal Optimization of UV-Pump Pulses for the Ultrafast Electron Diffraction | |
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| Ultraviolet (UV) light has been devoted to escape electrons from common metals due to their work function energies. Nowadays the pulsed electron beam has triggered numerous fundamental studies and technological applications. Electron beam-based pump/probe spectroscopy requires a low timing jitter between pump- and probe-beams for the precise observation and analysis. Herein, we performed the systematic characterization of electron bunches depending on UV pulse conditions using the electro-optic streaking of electron pulses for the ultrafast electron diffraction (UED) experiment. The temporal stabilization between UV-pump and electron-probe beams within a 100 femtoseconds jitter is in progress by compensating a relative phase shift of RF master oscillator and Ti:sapphire laser oscillator. We are under optimization of the spatial distribution and size of the UV light for getting electron bunches with low emittance and energy spread. | ||
| THP010 | Analysis of Beam Stability in the KAERI Ultrashort Pulse Accelerator | 697 |
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| An RF-photogun-based linear accelerator for the Korea Atomic Energy Research Institute (KAERI) ultrashort pulse facility is under construction. It has a symmetry structure with four different beamlines. The UED beamlines will generate ultrashort electron pulses with over 106 electrons per pulse for the single-shot measurements on femtoseconds dynamics of atomic or molecular structures. Electron bunches with an energy of ~3 MeV from the RF photogun can be compressed up to less than 50 fs by achromatic and isochronous bends. The intrinsic r.m.s. timing jitter of the pulses through the bends is estimated to be less than 30 fs with the r.m.s. energy fluctuation of 0.1%. In the THz pump and X-ray probe beamline, two successive laser pulses with a time interval of ~10 ns are used to generate two electron bunches having bunch charges more than 100 pC. Two electron bunches are accelerated by a linac up to ~25 MeV and separated into individual beamlines by a fast kicker. We will present on estimated timing jitter and effects of magnet errors to the beam dynamics in the accelerator by considering beam dilution effects. | ||
THP096 |
Development of an S-band Cavity-type Beam Position Monitor for a Table-top Terahertz Free-electron Laser | |
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| A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultrashort-pulsed electron linac system at the Korea Atomic Energy research Institute (KAERI). The cavity-type BPM has higher sensitivity and faster response time even at low charges, comparing with other types of BPMs. The designed position resolution of the cavity BPM is less than 10 μm. The material of the BPM is aluminium and the vacuum could be kept by indium sealing without brazing process, which result in easy modification and saving cost. The resonance frequency of the cavity BPM is 2.801 GHz and has a dimension of 200 x 220 mm (length x height) with a pipe radius of 38 mm. When electron beam passing through the cavity BPM with an offset, the amplitude of a dipole mode which depends linearly on the beam offset inside the cavity BPM is excited. With the KAERI THz FEL, signals from the BPM was measured by using an oscilloscope as a function of the beam offset. The position sensitivity was calculated to be 6.19 mV/mm/mA. By measuring the thermal noise of the system, position resolution of the cavity BPM was estimated to be less than 1 μm. | ||
| THP010 | Analysis of Beam Stability in the KAERI Ultrashort Pulse Accelerator | 697 |
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| An RF-photogun-based linear accelerator for the Korea Atomic Energy Research Institute (KAERI) ultrashort pulse facility is under construction. It has a symmetry structure with four different beamlines. The UED beamlines will generate ultrashort electron pulses with over 106 electrons per pulse for the single-shot measurements on femtoseconds dynamics of atomic or molecular structures. Electron bunches with an energy of ~3 MeV from the RF photogun can be compressed up to less than 50 fs by achromatic and isochronous bends. The intrinsic r.m.s. timing jitter of the pulses through the bends is estimated to be less than 30 fs with the r.m.s. energy fluctuation of 0.1%. In the THz pump and X-ray probe beamline, two successive laser pulses with a time interval of ~10 ns are used to generate two electron bunches having bunch charges more than 100 pC. Two electron bunches are accelerated by a linac up to ~25 MeV and separated into individual beamlines by a fast kicker. We will present on estimated timing jitter and effects of magnet errors to the beam dynamics in the accelerator by considering beam dilution effects. | ||