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김현우,장규하,백인형,이기태,정영욱,남진희,채문식,김미혜,김영찬,왕기영,박선정,한장희,Nikolay A. Vinokurov 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.1
We have developed a one-and-half -cell S-band radio-frequency (RF) photoelectron gun (pho- togun) fed by a coaxial coupler. The RF photogun is dedicated to ultrafast-electron-diraction experiments by generating electron bunches of 3-MeV energy and a-few-pC charge, which is not strict condition compared to those for X-ray free-electron lasers. Brazing of RF cavities is well- developed process for making RF guns or RF accelerators. Sometimes, however, a failure occurs in the brazing process, causing the entire electron gun or accelerating cavity to spoil. Axial-symmetric design of the RF photogun permits indium sealing for cavity cells, a photocathode plate, and a coupling RF part. We rstly report that the indium-sealed RF photogun successfully meets the required performance and long-term stability for ultrafast electron diraction experiments. We have stably operated the RF photogun for more than three years with the electron beam conditions of 3-MeV energy, up-to-10-pC charge, and a repetition rate of 50 Hz. The quantum eciency of the copper photocathode had improved from 106 to 105 depending on vacuum condition from 108 to 5 1010 Torr, respectively. Measured emittance and energy spread of the generated electron beam showed 0.3 mm-mrad and less than 0.25%, respectively, for a bunch charge of 2 pC, which agree well with those obtained by ASTRA simulation.
Simulation on a Photocathode-based Microtron Using a 3D PIC Code
박선정,정영욱,박성희,장규하,Nikolay A. Vinokurov,김은산 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.3
The Korea Atomic Energy Research Institute (KAERI) has used a microtron accelerator basedon a thermionic cathode for operating a compact terahertz (THz) FEL, where the electrons areemitted and accelerated automatically during the radio-frequency (RF) macro-pulse over thresholdpower for their emission. Usually a thermionic cathode is embedded inside the microtron cavity forelectron-beam emission, and at the same time acceleration is due to the input RF source. In thiscase, the accelerator scheme is simple, but just a fraction of the emitted electrons are accelerated,and the electron bunch length is uncontrollable due to the RF phase condition for acceleration. In this paper, a photocathode-based microtron which is able to produce high peak (∼100 A) andultrashort (∼1 ps) electron bunch is studied to adapt it for an electron injector of a THz generator. Especially, we analyzed the electron beam dynamics along the accelerating trajectory with a 3DPIC-code to find the optimized RF phase and laser input time.
Development of an S-band cavity-type beam position monitor for a high power THz free-electron laser
Noh, Seon Yeong,Kim, Eun-San,Hwang, Ji-Gwang,Heo, A.,won Jang, Si,Vinokurov, Nikolay A.,Jeong, Young UK,Hee Park, Seong,Jang, Kyu-Ha American Institute of Physics 2015 Review of scientific instruments Vol.86 No.1
<P>A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultra-short pulsed electron Linac system at the Korea Atomic Energy Research Institute (KAERI). Compared with other types of BPMs, the cavity-type BPM has higher sensitivity and faster response time even at low charge levels. When electron beam passes through the cavity-type BPM, it excites the dipole mode of the cavity of which amplitude depends linearly on the beam offset from the center of the cavity. Signals from the BPM were measured as a function of the beam offset by using an oscilloscope. The microtron accelerator for the KAERI THz FEL produces the electron beam with an energy of 6.5 MeV and pulse length of 5 μs with a micropulse of 10-20 ps at the frequency of 2.801 GHz. The macropulse beam current is 40 mA. Because the microtron provides multi-bunch system, output signal would be the superposition of each single bunch. So high output signal can be obtained from superposition of each single bunch. The designed position resolution of the cavity-type BPM in multi-bunch is submicron. Our cavity-type BPM is made of aluminum and vacuum can be maintained by indium sealing without brazing process, resulting in easy modification and cost saving. The resonance frequency of the cavity-type BPM is 2.803 GHz and the cavity-type BPM dimensions are 200 220 mm (length height) with a pipe diameter of 38 mm. The measured position sensitivity was 6.19 (mV/mm)/mA and the measured isolation between the X and Y axis was -39 dB. By measuring the thermal noise of system, position resolution of the cavity-type BPM was estimated to be less than 1 μm. In this article, we present the test results of the S-band cavity-type BPM and prove the feasibility of the beam position measurement with high resolution using this device.</P>
김하나,김경남,한병현,신재성,이기태,차용호,장규하,전민용,Sergei V. Miginsky,정영욱,Nikolay A. Vinokurov,박성희 한국광학회 2014 Current Optics and Photonics Vol.18 No.4
An all-reflective, simple noncollinear second harmonic (SH) autocorrelator is described for monitoring the shot-to-shot behavior of ultrashort high-power laser pulses. Two mirrors are used for the dispersion-free splitting of a pulse into two halves. One of the mirrors is able to adjust the delay time and angle between two halves of the laser pulse in a nonlinear crystal. We present the possibility of real-time measurement of the pulse duration, peak intensity (or energy), and the pointing jitters of a laser pulse, by analyzing the spatial profile of the SH autocorrelation signal measured by a CCD camera. The measurement of the shot-to-shot variation of those parameters will be important for the detailed characterization of laser accelerated electrons or protons.