Author(s): Corlett, JN; Allezy, A; Arbelaez, D; Baptiste, K; Byrd, J; Daniels, C; De Santis, S; Delp, W; Denes, P; Donahue, R; Doolittle, L; Emma, PJ; Filippetto, D; Floyd, J; Harkins, J; Huang, G; Jung, JY; Li, D; Pui Lou, T; Luo, T; Marcus, G; Monroy, MT; Nishimura, H; Padmore, HA; Papadopoulos, C; Pappas, C; Paret, S; Penn, G; Placidi, M; Prestemon, S; Prosnitz, D; Qian, H; Qiang, J; Ratti, A; Reinsch, M; Robin, D; Sannibale, F; Schoenlein, RW; Serrano, C; Staples, J; Steier, C; Sun, C; Venturini, M; Waldron, WL; Wan, W; Warwick, T; Wells, R; Wilcox, R; Zimmermann, S; Zolotorev, M; Ginsburg, C; Kephart, R; Klebaner, AL; Peterson, T; Sukhanov, A; Arenius, D; Neil, GR; Powers, T; Preble, JP; Adolphsen, C; Bane, K; Ding, Y; Huang, Z; Nantista, C; Ng, CK; Nuhn, HD; Rivetta, C; Stupakov, G | Abstract: The NGLS collaboration is developing design concepts for a multi-beamline soft x-ray FEL array powered by a superconducting linear accelerator, operating with a high bunch repetition rate of approximately 1 MHz. The CW superconducting linear accelerator design is based on developments of TESLA and ILC technology, and is supplied by an injector based on a high-brightness, highrepetition- rate photocathode electron gun. Electron bunches from the linac are distributed by RF deflecting cavities to the array of independently configurable FEL beamlines with nominal bunch rates of ∼100 kHz in each FEL, with uniform pulse spacing, and some FELs capable of operating at the full linac bunch rate. Individual FELs may be configured for different modes of operation, including self-seeded and external-laser-seeded, and each may produce high peak and average brightness x-rays with a flexible pulse format, and with pulse durations ranging from femtoseconds and shorter, to hundreds of femtoseconds. In this paper we describe current design concepts, and progress in RandD activities. Copyright © 2013 CC-BY-3.0 and by the respective authors.

LBNL is developing design concepts for a multi-beamline soft x-ray FEL array powered by a superconducting linear accelerator, operating with a high bunch repetition rate of approximately one MHz. The cw superconducting linear accelerator is su pplied by an injector based on a high-brightness, high-repetition-rate photocathode electron gun. Electron bunches are distributed from the linac to the array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz in each FEL, and with even pulse spacing. Individual FELs may be configured for different modes of operation, and each may produce high peak and average brightness x-rays with a flexible pulse format, and with pulse durations ranging from sub-femtoseconds to hundreds of femtoseconds. In this paper we describe conceptual design studies and optimizations. We describe recent developments in the design and performance parameters, and progress in R&D activities.

In the self-seeding scheme, the longitudinal coherence and spectral density of an unseeded FEL can be improved by placing a monochromator at a location before the radiation reaches saturation levels, followed by a second stage of amplification. The final output pulse properties are determined by a complex combination of the monochromator properties, undulator settings, variations in the electron beam, and wakefields. We perform simulations for the output of SASE and self-seeded configurations for a soft x-ray FEL using both idealized beams and realistic beams from start-to-end simulations.

We report on on-going studies of a superconducting CW linac driver intended to support a high repetition rate FEL operating in the soft x-rays spectrum. We present a pointdesign for a 1.8 GeV machine tuned for 300 pC bunches and delivering low-emittance, low-energy spread beams as needed for the SASE and seeded beamlines.

Recent technological developments have opened the possibility to construct a device which we call a linac coherent light source (LCLS) (C. Pellegrini et al., Nucl. Instr. and Meth. A 331 (1993) 223; H. Winick et al., Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, May 1993; C. Pellegrini, Nucl. Instr. and Meth. A 341 (1994) 326; J. Seeman, SPIE Meet. on Electron Beam Sources of High Brightness Radiation, San Diego, CA, July 1993 [1–4]); it would be a fourth-generation light source, with brightness, coherence, and peak power far exceeding other sources. Operating on the principle of the free electron laser (FEL), the LCLS would extend the range of FEL operation to much shorter wavelength than the 240 nm that has so far been reached. We report the results of studies of the use of the SLAC linac to drive an LCLS at wavelengths from about 3 to 100 nm initially and possibly even shorter wavelengths in the future. Lasing would be achieved in a single pass of a low emittance, high peak current, high-energy electron beam through a long undulator. Most present FELs use an optical cavity to build up the intensity of the light to achieve lasing action in a low-gain oscillator configuration. By eliminating the optical cavity, which is difficult to make at short wavelengths, laser action can be extended to shorter wavelengths by self-amplified-spontaneous-emission (SASE), or by harmonic generation from a longer wavelength seed laser. Short wavelength, single pass lasers have been extensively studied at several laboratories and at recent workshops (M. Cornacchia and H. Winick (eds.), SLAC Report 92/02; I. Ben-Zvi and H. Winick (eds.), BNL report 49651 [5,6]). The required low-emittance electron beam can be achieved with recently-developed rf photocathode electron guns (B.E. Carlsten, Nucl. Instr. and Meth. A 285 (1989) 313; J. Rosenzweig and L. Serafini, Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, 1993 [7,8]). The peak current is increased by about an order of magnitude by compressing the bunch to a lenght of about 0.2 ps (rms). Techniques for beam transport, acceleration, and compression without emittance dilution have been developed at SLAC as part of the linear-collider project (J. Seeman, Advances of Accelerator Physics and Technologies, ed. H. Schopper (World Scientific, Singapore, 1993 [9]). The undulator length required to saturate the laser varies from about 15 m for a 100 nm FEL to about 60 m at 3 nm. Initial experiments, at wavelengths down to about 50 nm are planned using the 25-m long Paladin undulator now located at LLNL. In a proposed future LCLS R&D facility the short wavelength light pulses are distributed to multiple end stations using grazing-incidence mirrors. About 1014 photons per pulse can be produced at a 120 Hz rate, corresponding to average brightness levels of about 1021 photons/s/mm2/mrad2 within 0.1% BW and peak brightness levels of about 1031 photons/s/mm2/mrad2 within 0.1% BW. Peak power levels are several hundred megawatts to several gigawatts. Electron energies required range from about 500 MeV for the 100 nm FEL to about 7 GeV for 3 nm.

cWe discuss thedesignandperformanceofa2 to4 nm FEL operatinginSelf-Amplified SpontaneousEmission(SASE),usinga photoinjector toproducetheelectronbeam,andtheSLAC linactoaccelerate ittoan energyofabout7 GeV .Longitudinal bunch compressionisusedtoincreasethepeakcurrentto2.5kA,whilereducingthebunchlengthtoabout40 wm .The FEL fieldgain lengthisabout6m, andthesaturation lengthisabout60 m.The saturated outputpowerisabout10GW, corresponding toabout 1014photonsina singlepulseina bandwidthofabout0.1%,witha pulsedurationof0.16ps.Lengthcompression,emittance control, phasestability, FEL designcriteria, andparametertolerances arediscussed .

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation R. Tatchyn, K. Bane, R. Boyce, G. Loew, R. Miller, H.‐D. Nuhn, D. Palmer, J. Paterson, T. Raubenheimer, J. Seeman, H. Winick, D. Yeremian, C. Pellegrini, J. Rosenzweig, G. Travish, D. Prosnitz, E. T. Scharlemann, S. Caspi, W. Fawley, K. Halbach, K.‐J. Kim, R. Schlueter, M. Xie, R. Bonifacio, L. De Salvo, P Pierini; Prospects for high power linac coherent light source (LCLS) development in the 1000 Å−1 Å wavelength range. AIP Conf. Proc. 1 May 1995; 332 (1): 320–329. https://doi.org/10.1063/1.47919 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 Ω, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 μs of each other and is capable of operating at a sustained repetition rate of 5 Hz. Our initial measurements indicate that emission current densities above the Child-Langmuir space charge limit, JCL, are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam and estimate a preliminary lower bound to be on the order of 109 A/m2rad2. As in our previous measurements at this Laboratory, we performed the measurement using a pepper pot technique. Beamlet profiles are recorded with a fast phosphor and gated cameras. We describe our apparatus and preliminary measurements.

We describe the possible use of the SLAC linac to drive a unique, powerful, short wavelength Linac Coherent Light Source. Using the FEL principle, lasing is achieved in a single pass of a high peak current electron beam through a long undulator by self-amplified-spontaneous- emission (SASE). The main components are a high-brightness electron RF gun with a photocathode, two electron bunch length compressors, the existing SLAC linac, beam diagnostics, and a long undulator combined with a FODO quadrupole focusing system. The RF gun, to be installed about 1 km from the end of the SLAC linac, would produce a single bunch of 6 X 109 electrons with an invariant emittance of about 3 mm-mrad and a bunch length of about 500 micrometers . That bunch is then accelerated to 100 MeV and compressed to a length of about 200 micrometers . The main SLAC linac accelerates the bunch to 2 GeV where a second bunch compressor reduces the length to 30 - 40 micrometers and produces a peak current of 2 - 3 kA. The bunch is then accelerated to 7 - 8 GeV and transported to a 50 - 70 m long undulator. Using electrons below 8 GeV, the undulator could operate at wavelengths down to 2 nm, producing about 10 GW peak power in sub-ps light pulses.

We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 ohm, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. our initial measurements indicate that emission current densities above the Child-Langmuir Space Charge Limit, JcL, are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam and estimate a preliminar lower bound to be on the order of 109 A/m2-rad2 for currents close to JcL and factor of two less at currents over 4JcL. We describe our apparatus and preliminary measurements.

Bi-phase shift keying (BPSK) is a modulation scheme used in communications and radar in which the phase of a transmitted rf signal is switched in a coded pattern between discrete values differing by pi-radians. The transmitted information rate (in communications) or resolution (in imaging radar) depends on the rate at which the transmitted signal can be modulated. Modulation rates of greater than 1 GHz are generally desired.Although the instantaneous gain bandwidth of a mm-wave FEL amplifier can be much greater than 10 GHz, slippage may limit the BPSK modulation rate that can be amplified. Qualitative slippage arguments would limit the modulation rate to relatively low values; nevertheless, simulations with a time-dependent FEL code (GINGER) indicate that rates of 2 GHz or more are amplified without much loss in modulation integrity. In this paper we describe the effects of slippage in the simulations and discuss the limits of simple slippage arguments.

Induction linac accelerators are specifically designed to produce high current electron beams. The high quality, high current beam made available by these accelerators enables one to build free electron lasers with extremely high single pass gain (>40 dB) and high extraction efficiency (>35%). Several high gain FELs have been built and operated at LLNL over the past 10 years, and a complete set of numerical models has been developed to guide the design of future FELs.

PALADIN is a single pass, free electron laser amplifier located at the Lawrence Livermore National Laboratory. This FEL is designed to run at 10.6 μm. The 1-kA, 45-MeV electron beam is provided by the Advanced Test Accelerator. The wiggler is 25 m long with an 8 cm period. The input optical signal to the amplifier is provided by a conventional CO2 laser, which can produce a peak input power of either 18 kW or 3.6 MW. We have demonstrated 31 dB of gain with the 18-kW input and 12.9 dB of gain for the 3.6-MW input, producing over 70 MW of optical power. Using the 18-kW input, the gain saturated at about 12 m into the wiggler; with the 3.6-MW input, the gain saturated at about 8 m. Modeling results are shown.

As a part of the program in induction-linac free-electron laser research, the authors summarize the Laboratory's work in a variety of activities addressing the requirements imposed on wiggler systems. The development of improved designs is reported for DC iron-core electromagnetic wigglers to attain higher peak fields, greater tunability, and lower random-error levels. Specialized control systems ...

The construction of a one-period wiggler system called a laced wiggler is presented along with test results from a prototype design. The laced electromagnetic wiggler is being developed to attain higher magnetic fields, shorter wavelengths, and larger gaps for the induction-linear accelerator, free-electron-laser (FEL) program. In the laced wiggler design, permanent magnets are located (laced) between the electromagnetic coils to increase the reverse-bias flux in the iron pole beyond that possible with only pole-edge (side) permanent magnets. This increase in reverse-bias flux allows wiggler operation at midplane magnetic-field intensities comparable to those of a hybrid permanent magnet/steel wiggler, but with field adjustability over a specified range. The maximum field intensity and tuning range are selected, within limits, for specific design requirements. The test results show good agreement with the analytical predictions and confirm the ability of the laced wiggler to attain the desired midplane magnetic flux density and tuning range. Both the nominal wiggle field along the wiggler axis and the focusing field variation are within the acceptable limits of design requirements.< >

The free-electron laser (FEL) directly converts the energy of an electron beam to electromagnetic radiation. The properties of the radiation are intimately related to the characteristics of the accelerator that produces the electron beam. A radio-frequency (rf) accelerator produces a high-frequency (1-100 MHz) burst of short electron pulses (10-30 ps) at relatively low peak current. The burst typically lasts tens of microseconds. The low peak current (0.1-1 kA) implies that an FEL driven by an rf accelerator must operate with low single-pass optical gain and produce radiation pulses of relatively low peak power. By contrast, an induction linac (IL) accelerator produces an electron beam consisting of longer (50 ns), higher current (1-10 kA) pulses. These pulses can be produced in a variety of pulse formats, including a series of high repetition rate bursts or a cw pulse train. For equal average powers, the induction linac operates at a lower duty factor than the RF accelerator.

A report is presented of the design, fabrication, and testing of a 25.6-m-long wiggler for a free-electron-laser (FEL) experiment. It is a DC iron-core electromagnetic wiggler that incorporates a number of important and unique features: permanent magnets are used to suppress saturation in the iron and extend the linear operating range; steering-free excitation allows real-time adjustment of the fi...

An induction linac-driven free electron laser (FEL) is considered as a potential source of high-average power millimeter radiation for heating tokamaks. The basic physics of the FEL is reviewed, the state of high-power millimeter experiments is summarized, and a preliminary-design induction linac-driven FEL for auxiliary heating is described.