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Laser-driven Electron Acceleration and Future Applications to Compact Light Sources
N. Hafz,T. M. Jeong,S. K. Lee,J. H. Sung,최일우,T. J. Yu,J. Lee 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1
Laser-driven plasma accelerators are gaining much attention by the advanced accelerator community due to the potential these accelerators hold in miniaturizing future high-energy and mediumenergy machines. In the laser wakefield accelerator (LWFA), the ponderomotive force of an ultrashort high-intensity laser pulse excites a longitudinal plasma wave or bubble. Due to huge charge separation, electric fields created in the plasma bubble can be several orders of magnitude higher than those available in conventional microwave and RF-based accelerator facilities, which are limited (up to~100 MV/m) by material breakdown. Therefore, if an electron bunch is injected into the bubble in phase with its field, it will gain relativistic energies within an extremely short distance. Here, in the LWFA, we show the generation of high-quality and high-energy electron beams up to the GeV-class within a few millimeters of gas-jet plasmas irradiated by tens-of- terawatt ultrashort laser pulses. Thus, we realize approximately four orders of magnitude acceleration gradients,higher than available by conventional technology. As a practical application of the stable high-energy electron beam generation, we are planning on injecting the electron beams into a fewmeter-long conventional undulator in order to realize compact X-ray synchrotron (immediate) and Free Electron Laser (future) light sources. Stable laser-driven electron beam and radiation devices will surely open a new era in science, medicine, and technology and will benefit a larger number of users in those fields.
J. U. KIM,C. KIM,G. H. KIM,H. SUK,N. HAFZ 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.44 No.52
It is well known that when a laser or an intense electron beam passes through a downward density transition in a plasma, some portion of the background electrons are trapped in the laser (or electron) wakeeld and the trapped electrons are accelerated to relativistically high energies over a very short distance in the plasma. In the present study, by using a two-dimensional particle-in-cell (PIC) simulation, we suggest an experimental method for electron-beam generation in a plasma, by using the so- called T3 (table-top-terawatt) laser system and plasma interaction, which can manipulate electron trapping and acceleration across a parabolic plasma density channel. The experimental method suggested in this study is easier to produce and is more feasible for applications to laser wakeeld acceleration experiments. Moreover, we present a brief ongoing experimental research plan for using the newly developed high-power T3 laser system at the Korea Electrotechnology Research Institute (KERI).
Choi, I W,Kim, C M,Sung, J H,Kim, I J,Yu, T J,Lee, S K,Jin, Y-Y,Pae, K H,Hafz, N,Lee, J IOP Pub 2009 Measurement Science and Technology Vol.20 No.11
<P>A proton energy spectrometer system is composed of a time-of-flight spectrometer (TOFS) and a Thomson parabola spectrometer (TPS), and is used to characterize laser-accelerated protons. The TOFS detects protons with a plastic scintillator, and the TPS with a CR-39 or imaging plate (IP). The two spectrometers can operate simultaneously and give separate time-of-flight (TOF) and Thomson parabola (TP) data. We propose a method to calibrate the TOFS and IP by comparing the TOF data and the TP data taken with CR-39 and IP. The absolute response of the TOFS as a function of proton energy is calculated from the proton number distribution measured with CR-39. The sensitivity of IP to protons is obtained from the proton number distribution estimated with the calibrated TOFS. This method, based on the comparison of the simultaneously measured data, gives more reliable results when using laser-accelerated protons as a calibration source. The calibrated spectrometer system can be used to measure absolutely calibrated energy spectra for the optimization of laser-accelerated protons.</P>
Quasi-Monoenergetic Electron-Beam Generation Using a Laser Accelerator for Ultra-Short X-ray Sources
J Kim,고도경,석희용,H Jang,김형택,I Hwang,최일우,J Lim,J. Lee,J. H. Sung,K.-H. Hong,허민섭,N Hafz,유승훈,유태준,T. M. Jeong,V Kulagin,Y.-C. Noh 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
Two types of electron acceleration methods have been conducted to generate quasi-monoenergetic electron beams. Multi-MeV quasi-monoenergetic high-charge electron beams were generated at Korea Electrotechnology Research Institute (KERI) from self-modulated laser wakefield acceleration by using a collimator with a 2 TW (1.4 J/700 fs) Nd:glass/Ti:sapphire hybrid laser system and a supersonic nitrogen gas jet. The peak electron energy was 3.6 MeV, and the energy spread was 4 MeV. These electron beams are useful for the generation of short-pulse X-rays in the water window region, which is 250 eV -- 500 eV (2.5 -- 5 nm), by using Thomson scattering. The calcualted photon spectrum indicates the scattered photon covers the water window region. This can be used for a high spatial and temperal resolution microscope for medical imaing. To generate higher-energy electron beams with small energy spread, a laser wakefield acceleration experiment with a sharp downward electron density gradient was conducted with a 100 TW laser system at Advanced Photon Research Insistitute (APRI). With the electron density gradient, some background plasma electrons could be locally injected in the laser wake wave and a small energy spread was expected. Using the pre-pulse, we could generate sharp downward electron density gradients. The gradient scale length was 20 $\mu$m for a 25 \% density change. With this electron density gradient, we could get more reproducible electron beams than we could without the density gradient.