First Name: S.
Middle Name: Ya
Last Name: Tochitsky
Full Name: S. Ya. Tochitsky
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17 papers
| title: | High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| 17 authors: | | | | | | | | | | | | | | | | | |
| abstract: | Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an Inverse-Free- Electron-Laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and ¯eld amplitude. The Rayleigh range of the laser, » 1.8 cm, is much shorter than the undulator length yielding a di®raction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the ¯rst half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator. |
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| title: | Enhanced Acceleration of Injected Electrons in a Laser Beatwave Induced Plasma Channel |
| format: | preprint |
| year: | 2004 |
| 10 authors: | | | | | | | | | | |
| abstract: | Enhanced energy gain of externally injected electrons by a ~3-cm long, high-gradient relativistic plasma wave (RPW) is demonstrated. Using a CO2 laser-beatwave of duration longer than the ion motion time across the laser spot size, a laser self-guiding process is initiated in a plasma channel. Guiding compensates for ionization-induced defocusing (IID) creating a longer plasma, which extends the interaction length between electrons and the RPW. In contrast to a maximum energy gain of 10 MeV when IID is dominant, the electrons gain up to 38 MeV energy in a laser beatwave induced plasma channel. PACS: 52.35Mw, 52.38Hb, 52.38Kd |
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| title: | Non-Resonant Beat-Wave Excitation of Constant Phase-Velocity, Relativistic Plasma Waves for Charged-Particle Acceleration |
| format: | journal article |
| year: | 2004 |
| 10 authors: | | | | | | | | | | |
| abstract: | The nonresonant beat-wave excitation of relativistic plasma waves is studied in two-dimensional simulations and experiments. It is shown through simulations that, as opposed to the resonant case, the accelerating electric fields associated with the nonresonant plasmons are always in phase with the beat-pattern of the laser pulse. The excitation of such nonresonant relativistic plasma waves is shown to be possible for plasma densities as high as 14 times the resonant density. The density fluctuations and the fields associated with these waves have significant magnitudes, facts confirmed experimentally using collinear Thomson scattering and electron injection, respectively. The applicability of these results towards eventual phase-locked acceleration of prebunched and externally injected electrons is discussed. |
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| title: | Experiments on laser driven beatwave acceleration in a ponderomotively formed plasma channel |
| format: | journal article |
| year: | 2004 |
| 10 authors: | | | | | | | | | | |
| abstract: | A 10 ps long beam of 12 MeV electrons is externally injected into a ~3-cm long plasma beatwave excited in a laser ionized hydrogen gas. The electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that when the effective plasma wave amplitude-length product is limited by ionization-induced defocusing (IID), acceleration of electrons is significantly enhanced by using a laser pulse with a duration longer than the time required for ions to move across the laser spot size. Both experiments and two-dimensional simulations reveal that, in this case, self-guiding of the laser pulse in a ponderomotively formed plasma channel occurs. This compensates for IID and drives the beatwave over the longer length compared to when such a channel is not present. |
| keywords: | pbpl |
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| title: | Acceleration of Injected Electrons In A Laser Beatwave Experiment |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 10 authors: | | | | | | | | | | |
| abstract: | Plasma-based accelerators of particles are of great interest because plasmas can sustain very strong electric fields. They are utilizing a relativistic plasma wave with a phase velocity close to the speed of light driven by a high-power laser beam. The Neptune Laboratory at UCLA is being used for plasma beatwave acceleration of injected electrons. Here, a two-wavelength laser pulse (frequencies w1,w2) resonantly drives a longitudinal electron plasma wave of frequency equal to w1-w2, providing a field strength of GeV/m and, therefore, accelerates an injected electron beam at this very high gradient. A 10 ps beam of 12 MeV electrons is loaded in a 3-cm long plasma beatwave accelerator driven by a TW CO2 laser pulse. At the resonance condition, the electrons have been accelerated to 50 MeV with a gradient of ~1.3 GeV/m. It is shown that for large volume diffraction limited plasmas, when efficiency of the plasma wave excitation is restricted by ionization-induced refraction, acceleration of electrons is enhanced significantly by using asymmetric (fast front and slow fall) long pulses. 2D PIC simulations revealed that guiding of the laser pulse in a ponderomotive, self-induced ion channel, formed ~200 ps after the field ionization, allows compensation for the ionization-induced defocusing and efficient driving of the beatwave over the entire length. |
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| title: | Bunched Beam Injection in a Plasma Accelerator |
| format: | conference procceeding |
| conference: | 10th Advanced Accelerator Concepts Workshop |
| year: | 2002 |
| 6 authors: | | | | | | |
| abstract: | An experiment on phase-locked injection of ~ 100 fs electron bunches in a plasma beat wave accelerator is presented. We consider using an IFEL microbunching technique to produce ultrashort electron bunches prebunched at the exact wavelength of the plasma wave 340 Jim (~lTHz). It is proposed to generate 100 MW of 1 THz radiation by difference frequency generation in a nonlinear crystal, mixing the same two CC>2 lines as used to drive the plasma accelerator. |
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| title: | A THz radiation driven IFEL as a phaselocked prebuncher for a plasma beat-wave accelerator |
| format: | conference procceeding |
| conference: | International Conference on Lasers 2001 |
| year: | 2002 |
| 6 authors: | | | | | | |
| abstract: | To obtain a high quality electron beam with small energy spread in the laser driven plasma accelerator, the electrons have to be prebunched at the scale of the plasma wavelength. We study the feasibility of an experiment where an inverse free electron laser (IFEL) is used to bunch the electron beam before the injection into a plasma beatwave accelerator. It is suggested to drive the IFEL prebuncher by a THz seed radiation phase-locked to the electromagnetic beatwave through difference frequency generation process in a nonlinear crystal. Design and numerical simulations for this experiment are presented. |
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| title: | Very High Energy Gain at the Neptune Inverse Free Electron Laser Experiment |
| format: | journal article |
| year: | Dec 2004 |
| 16 authors: | | | | | | | | | | | | | | | | |
| abstract: | We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 µm laser with power larger than 400 GW. The Rayleigh range of the laser, ~ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Three-dimensional simulations, in good agreement with the measured electron energy spectrum, indicate that most of the acceleration occurs in the first 25 cm of the undulator, corresponding to an energy gradient larger than 70 MeV/m. The measured energy spectrum also indicates that higher harmonic Inverse Free Electron Laser interaction takes place in the second section of the undulator. |
| keywords: | pbpl |
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| title: | LASER BEAT-WAVE MICROBUNCHING OF RELATIVISTIC ELECTRON BEAM IN THE THZ RANGE |
| format: | journal article |
| year: | 2006 |
| 6 authors: | | | | | | |
| abstract: | Laser-driven plasma accelerators have recently demonstrated a ~1GeV energy gain of self-trapped electrons in a several-centimeter-long plasma channel. Potential staging of such devices will require the external injection of an electron beam prebunched on the scale of 1-10 THz into a plasma accelerating structure or plasma LINAC. Seeded FEL/IFEL techniques can be used for modulation of the electron beam longitudinally on the radiation wavelength scale. However, a seed source in this spectral range is not available. At the UCLA Neptune Laboratory a Laser Beat-Wave (LBW) microbunching experiment has begun. The interaction of the electron beam and the LBW results in ponderomotive acceleration and energy modulation on the THz scale. This stage is followed by a ballistic drift of the electrons, where the gained energy modulation is transferred to the beam current modulation. Then the beam is sent into a 33-cm long undulator, where a coherent start-up of THz radiation takes place, and the THz pulse is used for a bunching analysis. The performance of LBW bunching is simulated and analyzed using a 3D FEL code for the parameters of an existing photoinjector and two-wavelength TW CO2 laser system. |
| keywords: | pbpl |
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| title: | Seeded free-electron and inverse free-electron laser techniques for radiation |
| format: | journal article |
| year: | 2006 |
| 6 authors: | | | | | | |
| abstract: | A comprehensive analysis is presented that describes amplification of a seed THz pulse in a single-pass free-electron laser (FEL) driven by a photoinjector. The dynamics of the radiation pulse and the modulated electron beam are modeled using the time-dependent FEL code, GENESIS 1.3. A 10-ps (FWHM) electron beam with a peak current of 50 –100 A allows amplification of a |
| keywords: | pbpl |
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| title: | Development of a Waveguide FEL Seeded in the 1-3 THz Range for Microbunching Experiment at the Neptune Laboratory |
| format: | journal article |
| year: | 2006 |
| 8 authors: | | | | | | | | |
| abstract: | IFEL and FEL techniques can be used to modulate an electron beam on the scale of the radiation wavelength. However, the lack of a high power radiation source in the 100-300 μm range hinders the progress on THz IFEL microbunching. In this paper, we discuss microbunching of an electron beam using a single-pass FEL seeded with a low power THz pulse generated by frequency mixing of CO2 laser lines in a GaAs nonlinear crystal. A narrowband THz seed source is pumped by a dual beam TEA CO2 laser and can be tuned in the 1-3 THz range. The THz radiation is guided through a hollow waveguide inside the planar FEL undulator driven by a photoinjector. By using a time-dependent FEL code GENESIS 1.3, we optimized the undulator parameters and analyzed the dynamics of the modulated electron beam. By using a ~ 8 MeV electron beam with a peak current of 40 A and a ~1kW THz seed with wavelength 200 μm, the energy modulation up to 1.3% can be achieved in a ~1.8-m long undulator with a constant period of 2.7 cm. At present, the THz seed source is built and fully characterized. The results of transmission measurements for THz waveguides are also discussed. |
| keywords: | pbpl |
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| title: | Production of Terahertz Seed Radiation for FEL/IFEL Microbunchers for Second Generation Plasma Beatwave Experiments at Neptune |
| format: | journal article |
| year: | 2005 |
| 5 authors: | | | | | |
| abstract: | To achieve phase locked injection of short electron bunches in a plasma beatwave accelerator, the Neptune Laboratory will utilize microbunching in an FEL or IFEL system. These systems require terahertz (THz) seed radiation on the order of 10 kW for the FEL and 10 MW for the IFEL bunchers. We report results of experiments on THz generation using nonlinear frequency mixing of CO2 laser lines in GaAs. A two-wavelength laser beam was split and sent onto a 2.5 cm long GaAs crystal cut for noncollinear phase matching. Low power measurements achieved ~1 W of 340 μm radiation using 200 ns CO2 pump pulses with wavelengths 10.3μm and 10.6μm. We also demonstrated tunability of difference frequency radiation, producing 240μm by mixing two different CO2 laser lines. By going to shorter laser pulses and higher intensities, we were able to increase the conversion efficiency while decreasing the surface damage threshold. Using 200ps pulses we produced ~2 MW of 340 μm radiation. Future studies in this area will focus on developing large diameter Quasi-Phase matched structures for production of high power THz radiation using collinear two frequency radiation. |
| keywords: | pbpl |
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| title: | Study of a THz IFEL prebuncher for laser-plasma accelerators |
| format: | journal article |
| year: | 2004 |
| 7 authors: | | | | | | | |
| abstract: | For monoenergetic acceleration of electrons, the injected particles need to be bunched with the same periodicity as the accelerating structure. In a laser-driven plasma beatwave accelerator, the accelerating structure (plasma wave) is phase-locked to the CO2 beat-wave used to drive it. Using the same beat-wave to generate high power FIR radiation via difference frequency mixing in GaAs ensures that the radiation has the same phase relationship as the plasma wave before it saturates and detunes from the pump. Therefore, this radiation can be used to prebunch an existing electron beam based on an Inverse Free Electron Laser (IFEL) concept. Here we report the progress on the proposed THz microbunching experiment in the Neptune laboratory. A 50 cm long prebuncher is optimized using simulation codes for minimum FIR power required. The injected 5ps long electron beam is expected to form a series of 45 µm long microbunches containing over 40% of the injected current after 1.6 m drift space following the undulator. Preliminary experimental results on THz generation are also presented. |
| keywords: | pbpl |
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| title: | Acceleration of electrons in a diffraction-dominated IFEL |
| format: | journal article |
| year: | 2004 |
| 16 authors: | | | | | | | | | | | | | | | | |
| abstract: | We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator ex- periment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in a 50 cm long undulator strongly tapered both in period and field amplitude. A CO2 10.6 μm laser with power > 300 GW is used as the IFEL driver. The Rayleigh range of the laser ( ∼ 1.8 cm) is shorter than the undulator length so that the interaction is diffraction dom- inated. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. An energy gradient of > 70 MeV is inferred. In the second section of the undulator higher harmonic IFEL interaction is observed. |
| keywords: | pbpl |
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| title: | High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser |
| format: | journal article |
| year: | |
| 17 authors: | | | | | | | | | | | | | | | | | |
| abstract: | Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-freeelectron-laser (IFEL) accelerator experiment. A 14.5 MeVelectron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, 1:8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV=m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator. |
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| title: | Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators |
| format: | journal article |
| year: | |
| 9 authors: | | | | | | | | | |
| abstract: | In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms– Free Electron Laser (FEL) and Inverse Free Electron Laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2 beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2 laser lines, electrons can be microbunched with different periodicity 300 –100 μm suitable for injection into plasma densities in the range 1016 – 1017 cm-3, respectively. The requirements on the THz radiation power and the electron beam qualities are also discussed. |
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| title: | High Energy gain IFEL at the UCLA Neptune Laboratory |
| format: | journal article |
| year: | |
| 16 authors: | | | | | | | | | | | | | | | | |
| abstract: | We report on the observation of energy gain in excess of 20MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5MeV electron beam is injected in a 50cm longundulator strongly tapered both in period and field amplitude. A CO210.6μm laser with power > 400GW is used as the IFEL driver. The Rayleigh range of the laser(∼1.8cm)is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped instable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. Anenergygradientof>70MeVisinferred. In these cond section of the undulator higher harmonic IFEL interaction is observed. |
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