First Name: C.
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Last Name: Joshi
Full Name: C. Joshi
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55 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: | A Helical Undulator Wave-guide Inverse Free-Electron Laser |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 8 authors: | | | | | | | | |
| abstract: | With recent success in high gradient, high-energy gain IFEL experiments at the UCLA Neptune Laboratory, future experiments are now being contemplated. The Neptune IFEL was designed to use a tightly focused, highly diffracting, near-TW peak power 10 micron laser. This choice of laser focusing, driven by power-handling limitations of the optics near the interaction region, led to design and use of a very complex undulator, and to sensitivity to both laser misalignment and focusing errors. As these effects limited the performance of the IFEL experiment, a next generation experiment at Neptune has been studied which avoids the use of a highly diffractive laser beam through use of a waveguide. We discuss here the choice of low-loss waveguide, guided mode characteristics and likely power limitations. We also examine a preferred undulator design, which is chosen to be helical in order to maximize the acceleration achieved for a given power. With the limitations of these laser and undulator choices in mind, we show the expected performance of the IFEL using 1D simulations. Three-dimensional effects are examined, in the context of use of a solenoid for focusing and acceleration enhancement. |
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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: | The ORION Facility |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 10 authors: | | | | | | | | | | |
| abstract: | ORION will be a user-oriented research facility for understanding the physics and developing the technology for future high-energy particle accelerators. The ORION Facility will bring together the needed resources for performing a wide range of experiments in advanced accelerator and beam physics. The facility has as its centerpiece the Next Linear Collider Test Accelerator (NLCTA) within End Station B at the SLAC Central Research Yard. That site will be modified with the addition of a new high-brightness photoinjector, its associated drive laser and rf power system, a user laser room, a low-energy experimental hall supplied with electron beams up to approximately 60 MeV in energy, and a high-energy hall supplied with beams up to 350 MeV. Facility construction is anticipated to start in October 2003, contingent upon funding approval, and first beam is planned for 2005. The first experiment at ORION, the laser acceleration experiment E163, has been approved by SLAC. In this paper, results are presented on the revised facility layout and design which came out of the 2nd ORION Workshop in February 2003, and the beam physics design of the injector and the beamlines for the low and high-energy experimental halls. |
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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: | ORION: An Advanced Accelerator Facility at SLAC |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| 13 authors: | | | | | | | | | | | | | |
| abstract: | Extending the center-of-mass energy frontier for high-energy physics depends on the research and development that is conducted now in the area of advanced accelerator physics and technology. In this article, we present the design and beam dynamics simulations for the emittance-compensated, RF photoinjector of the ORION Facility. (4 References). |
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| title: | Commissioning of the Neptune Photoinjector |
| format: | conference procceeding |
| conference: | APS April Meeting |
| year: | 2000 |
| 13 authors: | | | | | | | | | | | | | |
| abstract: | The status of the commissioning of the rf photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the rf gun, photocathode drive laser system, booster linac, rf system, chicane compressor, beam diagnostics systems, and control system are described. Recent improvements in the rf gun, rf timing, and chicane compressor systems are detailed. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented. |
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| title: | Plasma source test and simulation results for the underdense plasma lens experiment at the UCLA Neptune Laboratory |
| format: | unknown |
| year: | 2000 |
| 8 authors: | | | | | | | | |
| abstract: | The planned plasma lens experiment at the UCLA Neptune Laboratory is described. In the experiment, electron beams with an energy of 16 MeV, a charge of 4 nC, and a pulse duration of 30 ps full-width at half-maximum (FWHM) are designed to be produced from the 1.625-cell photoinjector radio-frequency gun (f=2.856 GHz) and PWT linac in the Neptune. The generated beams are passed through a thin plasma with a density of low 10/sup 12/ cm/sup -3/ range and a thickness of a few centimeters. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. In this paper, the overview of the planned plasma lens experiment and the test results of the plasma source for various conditions are presented. In addition, computer simulations with a 2-1/2 dimensional particle-in-cell code (MAGIC) were performed and the simulation results are shown. (19 References). |
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| title: | Underdense plasma lens experiment at the UCLA Neptune Laboratory |
| format: | conference procceeding |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| 10 authors: | | | | | | | | | | |
| abstract: | An underdense plasma-lens experiment is planned at the UCLA Neptune Laboratory. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. Test results of the plasma source show that it can provide satisfactory Ar plasma parameters for underdense plasma lens experiments, i.e., a density in the low 10/sup 12/ cm/sup -3/ range and a thickness of a few cm. In the plasma chamber a YAG slab and a Cherenkov radiator are placed for electron beam diagnostics so that both time-integrated and time-resolved information will be obtained and compared with the MAGIC code (2 and 1/2 dimensional particle-in-cell) simulations. In this paper, the planned experiment including test results of the plasma source, diagnostics and MAGIC simulation results is presented. (5 References). |
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| title: | Commissioning of the Neptune photoinjector |
| format: | conference procceeding |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| 21 authors: | | | | | | | | | | | | | | | | | | | | | |
| abstract: | The status of the commissioning of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The component parts of the photoinjector, the RF gun, photocathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics systems, and control system are described. This injector is designed to produce short pulse length, high brightness electron beams. Experiments planned for the immediate future are described. Initial measurements of various beam parameters are presented. (10 References). |
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| title: | Test results of the plasma source for underdense plasma lens experiments at the UCLA Neptune Lab |
| format: | conference procceeding |
| conference: | 8th Advanced Accelerator Concepts Workshop |
| year: | 1999 |
| 7 authors: | | | | | | | |
| abstract: | A plasma source was developed at UCLA for planned underdense plasma lens experiments, where the plasma density is less than the electron beam density. The argon plasma, produced by a discharge between a LaB_6 cathode at 1330 degrees C and a tantalum anode, is confined by a solenoidal magnetic field and flows transversely across the electron beam path. Extensive test of the plasma source is under way for various conditions before it is assembled with the UCLA photocathode-based electron linac. In particular, different longitudinal (with respect to the electron beam) plasma profiles and effective plasma lengths can be obtained by adjusting the moveable sliding door between the plasma source and the transverse beamline. Test results of the plasma source are presented. (11 References). |
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| title: | Second generation beatwave experiments at UCLA |
| format: | conference procceeding |
| conference: | ICFA Second Generation Plasma Acceleration Workshop |
| year: | 1998 |
| 5 authors: | | | | | |
| abstract: | The NEPTUNE laboratory, under construction at UCLA, will be a user facility for exploring concepts useful for advanced accelerators. The primary programmatic goal for the laboratory is to inject extremely high-quality electron bunches into a laser-driven plasma beat wave accelerator and explore ideas for extracting a high-quality Delta E/E<0.1, epsilon <10 pi mm mrad, high-energy (100 MeV) beam from a plasma structure operating at about 1 THz and about 3 GeV/m. The lab will combine an upgraded MARS CO_2 laser and the state-of-the-art SATURNUS RF gun and linac, also undergoing an upgrade. The new MARS laser will be about 1 TW (100 J, 100 ps), up from 0.2 TW (70 J, 350 ps). This allows for doubling the spot size of the laser beam and thereby quadrupling the interaction length while still driving gradients of 3 GeV/m. The large diameter of the accelerating structure relative to the injected electron bunches (10:1 ratio) will minimize the deleterious effects of the radial dependence of the accelerating field and soften the radial focusing thus permitting, in principle, the extraction of a high-quality accelerated beam. |
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| title: | The NEPTUNE facility for 2nd generation advanced accelerator experiments |
| format: | conference procceeding |
| conference: | 1997 Particle Accelerator Conference |
| year: | 1998 |
| 5 authors: | | | | | |
| abstract: | The NEPTUNE Laboratory, under construction at UCLA, will be a user facility for exploring concepts useful for advanced accelerators. [1] The programmatic goal for the laboratory is to inject extremely high quality electron bunches into a laser-driven plasma beat wave accelerator (PBWA) [2] and explore ideas for extracting a high quality DE/E < 0.1, epsilon_n < 10 pi mm-mrad), high energy (100 MeV) beam from a plasma structure operating at about 1 THz and about 3 GeV/m. The lab will combine an upgraded MARS CO2 laser and the state-of-the-art SATURNUS RF gun and linac. [3] The new MARS laser will be about 1 TW (100 J, 100 ps), up from 0.2 TW (70 J, 350 ps). This allows for doubling the spot size at the IP and quadrupling the interaction length while still driving gradients of 3 GeV/m. The SATURNUS gun will be upgraded to the Brookhaven 1.6 cell design. [4] A novel, multi-cell Plane-Wave Transformer (PWT) RF gun is also under development. [5] A sync-pumped, sub-ps dye laser is available to directly produce ultrashort electron pulses (1/5 of an accelerating bucket). Part of the research program will be devoted to studying pulse compression [6] and phaselocking techniques at these ultrahigh frequencies and diagnosing microbunches generated by such structures. [7] Finally, shaped electron pulses will be studied for the electron driven Plasma Wakefield Accelerator (PWFA) concept. |
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| title: | The Neptune photoinjector |
| format: | conference procceeding |
| conference: | ICFA Second Generation Plasma Acceleration Workshop |
| year: | 1998 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | The RF photoinjector in the Neptune advanced accelerator laboratory, along with associated beam diagnostics, transport and phase-space manipulation techniques are described. This versatile injector has been designed to produce short-pulse electron beams for a variety of uses: ultra-short bunches for injection into a next-generation plasma beatwave acceleration experiment, space-charge dominated beam physics studies, plasma wake-field acceleration driver, plasma lensing, and free-electron laser microbunching techniques. The component parts of the photoinjector, the RF gun, photocathode drive laser systems, booster linac, RF system, chicane compressor, beam diagnostic systems, and control system, are discussed. The present status of photoinjector commissioning at Neptune is reviewed, and proposed experiments are detailed. (33 References). |
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| title: | Status of UCLA IR FEL |
| format: | preprint |
| year: | 1996 |
| 21 authors: | | | | | | | | | | | | | | | | | | | | | |
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| title: | A plasma klystron for generating ultra-short electron bunches |
| format: | conference procceeding |
| conference: | Workshop on Second Generation Plasma Accelerators |
| year: | 1996 |
| 7 authors: | | | | | | | |
| abstract: | A technique for producing ultra-short electron bunches (e,g., less than or equal to 100 fs) from a continuous electron beam using a short plasma wave section and a drift space is explored. The bunches are a fraction of a plasma wavelength long and are spaced by a plasma wavelength, making them of interest for injection into plasma accelerators or for driving a klystron-like structure to produce infrared radiation. |
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| title: | An injector-prebuncher for a plasma electron accelerator |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 5 authors: | | | | | |
| abstract: | Optimum operation of a plasma beat-wave or wakefield accelerator requires an injected beam consisting of a train of electron bunches separated by the plasma wavelength, with each bunch in the train having a length much shorter than the plasma wavelength, and the capability of controlling the relative phase of the electron bunches and plasma wave. The typical plasma wavelength is about 0.1 mm, requiring a bunch length of about 10 to 20 mu m, which is difficult to achieve with conventional RF based injectors. In this paper we describe an electron accelerator-buncher system based on a photoinjector and an FEL, which can satisfy the plasma accelerator requirements. (4 References). |
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| title: | The UCLA compact high brightness electron accelerator |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 10 authors: | | | | | | | | | | |
| abstract: | We report the characteristics and performance of the UCLA S-band compact electron accelerator, consisting of a high brightness, 8 cm long, photo-injector with a copper cathode, followed by a 42 cm long plane wave transformer accelerating structure, delivering a beam energy of 10 MeV. The photo-electrons are produced by a 266 nm laser pulse of less than 4 ps in duration. Over time the laser induced electron emission decreases and the emission from the cathode surface becomes structured. Measurements of the quantum efficiency for Cu before and after this degradation are presented along with images of the non uniform electron emission. (8 References). |
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| title: | Initial operation of the UCLA plane wave transformer (PWT) linac |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 10 authors: | | | | | | | | | | |
| abstract: | We report on the initial operation of a novel compact rf linac-the plane wave transformer (PWT). The PWT is a 42 cm long, 8 cell standing-wave structure, operated at S-band, in a pi -mode. We present the properties of this linac at rf power levels from 4 MW to 8 MW and beam energy from 7 MeV to 10 MeV, measured initially using both dark current and photo-electrons. Some technical issues associated with the operation are discussed. Future improvements of the PWT, using a modified design, are also studied. (6 References). |
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| title: | Transverse dynamics of a short, relativistic electron bunch in a plasma lens |
| format: | conference procceeding |
| conference: | Annual Meeting of the Division of Plasma Physics of the APS |
| year: | 1995 |
| 6 authors: | | | | | | |
| abstract: | Dynamic focusing of a 3.8 MeV, 25 ps long, full width at half-maximum (FWHM), electron bunch by an overdense (n/sub p/[right angle bracket][right angle bracket]n/sub b/, where n/sub p/ and n/sub b/ are the plasma and bunch densities, respectively) plasma lens has been studied experimentally. The plasma focused the bunch from an initial transverse size of approximately 2.4 mm (FWHM) to about 0.5 mm, 21 cm downstream of the plasma. The sharp rise time (7 ps 10%-90%) of the electron bunch, excites a large-amplitude ([left angle bracket]1 MeV/m) plasma wave (plasma wake field). The peak focusing force of the lens is partly (60%) due to the beam-generated, azimuthal magnetic field and partly (40%) due to the radial component of the electrostatic wake field. (29 References). |
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| title: | Focusing of a Relativistic Electron Beam by an Underdense Plasma Lens |
| format: | preprint |
| year: | 1994 |
| 5 authors: | | | | | |
| abstract: | Plasma Lenses produce focusing gradients exceeding those of conventional quadrupole magnets by several orders of magnitude. We have recently observed dynamic focusing by an overdense plasma lens [G. Hairapetian, et al., Phys.Rev.Lett. 72, 2403 (1994)]. Theoretically, an underdense plasma lens could offer several advantages over the overdense lens: ... |
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| title: | 25 MeV Injector for the Plasma Beat Wave Accelerator |
| format: | preprint |
| year: | 1994 |
| 5 authors: | | | | | |
| abstract: | |
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| title: | Experimental demonstration of dynamic focusing of a relativistic electron bunch by an overdense plasma lens |
| format: | unknown |
| year: | 1994 |
| 7 authors: | | | | | | | |
| abstract: | Dynamic focusing of a 3.8 MeV electron bunch, a few collisionless skin depths long approximately 3c/ omega /sub p/, by an overdense, thick plasma lens has been demonstrated. Because of electron inertial effects, the head of the bunch is virtually unaffected by the lens while the rest is focused to varying degree. Time-resolved measurements performed 31 cm downstream of the plasma lens show that, in time, the bunch pinches from an initial size of 2.7 mm (FWHM) to about 0.57 mm and then expands, in reasonable agreement with theory. (20 References). |
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| title: | A millimeter wave FEL driven by a photocathode RF linac |
| format: | conference procceeding |
| conference: | 15th International Free Electron Laser Conference |
| year: | 1994 |
| 11 authors: | | | | | | | | | | | |
| abstract: | We present the design of a millimeter wave FEL based on the UCLA photocathode RF linac. The linac energy can be varied between 5 and 18 MeV. The electron pulse duration is 2 ps FWHM, with a peak current exceeding 150 A. The FEL is designed to operate in the high-gain Compton regime, controlling the slippage with the propagating radiation in a waveguide. The design permits the exploration of the basic FEL physics in this regime, including the exploration of saturation and lethargy in the superradiant and steady state regime. (15 References). |
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| title: | Initial measurements of the UCLA RF photoinjector |
| format: | conference procceeding |
| conference: | Conference on High Intensity Electron Sources |
| year: | 1994 |
| 14 authors: | | | | | | | | | | | | | | |
| abstract: | The 1.5 cell standing wave RF photoinjector has been operated for the past several months using a copper cathode. The photoinjector drive laser produces sub 2 ps pulses of UV ( lambda =256 nm) light with up to 200 mu J/pulse which generates up to 3 nC of charge, The emittance of the photoinjector was measured as a function of charge, RF launching phase, and peak accelerating field. Also, the quantum efficiency and pulse lengths of the laser beam and the electron beam were measured. (15 References). |
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| title: | Experimental demonstration of plasma lens focusing |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 7 authors: | | | | | | | |
| abstract: | The magnetic self-focusing of a relativistic electron beam propagating through a plasma is demonstrated. The plasma which is produced by an RF discharge in a glass tube with no externally applied magnetic field focuses a 3.5 MeV, 25 ps (FWHM) long electron beam from an initial size of 2.5 mm (FWHM) to about 0.5 mm (FWHM) at a focal length of 18 cm. (7 References). |
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| title: | Quantum efficiency measurements of a copper photocathode in an RF electron gun |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 8 authors: | | | | | | | | |
| abstract: | A 4.5 MeV photocathode RF gun has been commissioned at UCLA. A photo-injector drive laser produces sub 2 ps pulses of UV ( lambda =266 nm) light with up to 200 mu J/pulse, and illuminates a copper cathode. The photoelectrons are accelerated to an energy of 3.5 MeV within the gun. The electron beam charge is measured as a function of laser energy using an integrating current transformer (ICT). We present measurements of quantum efficiency as a function of laser polarization for injection angles of 2 degrees and 70 degrees with respect to the cathode normal. At 70 degrees incidence a 50% enhancement in quantum efficiency (>10(-4)) is observed for p-polarized light over s-polarized light. (7 References). |
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| title: | Streak camera measurements of electron bunch length from a copper photocathode in an RF gun |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 8 authors: | | | | | | | | |
| abstract: | Short laser pulses (sub 2 ps) of UV ( lambda =266 nm) light with 200 mu J/pulse are used to produce electrons from a copper cathode in an RF gun. The electron bunch length is measured by streaking the Cerenkov radiation ( lambda =530 nm) from a thin (250 mu m) fused silica etalon. Streaks for both 0 degrees and 70 degrees laser incidence angles with respect to the cathode normal are presented with a temporal resolution of 3.6 ps. The shortest electron bunch length measured was 9 ps. (3 References). |
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| title: | Emittance measurements of the 4.5 MeV UCLA RF photoinjector |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 10 authors: | | | | | | | | | | |
| abstract: | The 1.5 cell RF photoinjector has been operated for the past several months using a copper cathode illuminated by 4 ps long pulses of UV (246 nm light, with a variable energy of between 0 to 300 mu J. This typically produces up to 3 nC of charge per bunch. Because space charge forces dominate the electron beam transport a pepper pot measurement system is used to measure the emittance. The emittance is measured as a function of charge, peak accelerating field, laser spot size and initial phase with respect to the RF field. This is accomplished with an automated control and data acquisition system which can measure single shot emittances at a rate of 5 Hz developed at UCLA. The experimental results obtained are then compared with theory and simulations. (4 References). |
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| title: | Initial operation and beam characteristics of the UCLA S-band RF photo-injector |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 10 authors: | | | | | | | | | | |
| abstract: | The UCLA RF photo-injector system has been commissioned. All of the sub-components such as the high power RF, pico-second laser, RF photo-injector cavity, diagnostics, and supporting hardware have been tested and are operational. We briefly discuss the performance of the various components since the details of each subsystem are very lengthy. The laser delivers a sub 4 ps pulse containing 0-300 mu J of energy per pulse. The photo-injector produces 0-3 nC per bunch with an RF induced emittance of 1.5 pi (mm-mrad). (5 References). |
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| title: | The UCLA IR FEL project |
| format: | conference procceeding |
| conference: | 14th International Free Electron Laser Conference |
| year: | 1993 |
| 21 authors: | | | | | | | | | | | | | | | | | | | | | |
| abstract: | A 10.6 mu m free electron laser (FEL) operating in the high gain regime is under construction at UCLA. FEL physics significant to future short wavelength operation is emphasized including optical guiding, superradiance, saturation and self-amplified spontaneous emission (SASE). A 5 MeV RF photocathode gun illuminated by a UV laser supplies a high brightness electron beam which is injected into a plane wave transformer (PWT) linac for acceleration to 20 MeV. Recent measurements of the gun emittance as well as quantum efficiency are presented. The undulator is of a modified hybrid design producing approximately 7.5 kG peak field on axis with 5 mm gap spacing and 1.5 cm pole period. Simulation results which include three-dimensional effects are furnished. The present status and future plans of the project are summarized. (16 References). |
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| title: | Photoelectron beams from the UCLA RF gun |
| format: | conference procceeding |
| conference: | 3rd Advanced Accelerator Concepts Workshop |
| year: | 1993 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | A high brightness, low emittance photocathode rf gun is starting operation at UCLA as an injector to a 20 MeV linac. This linac will initially be used to drive FELs, plasma wakefield accelerators, and to test plasma lenses. The gun is a 1 1/2 cell pi-mode standing wave structure running at 2.856 GHz, and has a copper photocathode. In the initial commissioning of the gun, photoelectron beams of up to 2.5 nC at 4.5 MeV have been produced. We report on the current status of the system, experimental data taken with 50 ps UV laser pulses, and plans for the future. |
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| title: | Design and operation of a novel, compact 20 MeV linac at UCLA |
| format: | conference procceeding |
| conference: | Intense Microwave and Particle Beams II |
| year: | 1992 |
| 9 authors: | | | | | | | | | |
| abstract: | A novel, compact S-band linac has been designed and is currently under construction at UCLA. It is expected to deliver high brightness, 200 A, 20 MeV electron pulses, less than 4 ps in duration from a device that is about 1 meter long. It comprises: (a) a laser photocathode driven gun that produces 4.5 MeV electron bunches from a 1/sup 1///sub 2/ cell cavity operating in the pi -mode and (b) an accelerating structure known as a plane wave transformer (PWT) designed by Swenson (1988). The design considerations of the machine and initial operating experience of the gun are discussed. The linac will be used for free electron laser, advanced accelerator research and beam-plasma experiments. (8 References). |
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