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The Equations Of State (EOS) of materials under extreme conditions of temperature and pressure can be experimentally studied, thanks to intense electron beam-target experiments. The latter are powerful tools to probe materials in the warm dense matter regime. At CEA/CESTA, we use the CESAR pulsed generator (1 MV, 300 kA). During an experimental shot, a high-power 800 keV, 100 kA, 20 mm-diameter, 100 ns electron pulse produces shock waves in an aluminum target. The behavior of the latter is explored by analyzing the time-history of its rear face velocity, as measured by photon Doppler velocimetry. Using simulations, we can test the accuracy of an EOS over a wide range of densities and temperatures. In addition, an accurate EOS allows for reduction of the uncertainties of the beam parameters that have an impact on beam energy deposition. We have observed that the measurements are not correctly restituted by the simulation codes when they use the available EOS (BLF, SESAME). Thanks to both published data and ab initio calculations, which are valid in the considered thermodynamic regime, we have developed a new EOS describing precisely the thermodynamic (isochoric) regime from one-half to one-third the normal density. The corresponding hydrodynamic simulations appear to be in much better agreement with the measurements. In addition, this new EOS has allowed us to refine the knowledge of the input electron beam parameters that have an impact on beam energy deposition.

A compact low-energy and high-intensity X-ray source for radiation biology applications is presented. A laser-induced plasma moves inside a 30 kV diode and produces a beam of 10$^{14}$ electrons at the anode location. An aluminum foil converts a part of the energy of these electrons into X-ray photons which are characterized using filtered imaging plates. The dose that would be deposited by these X-ray photons in C. elegans larvae is calculated from Geant4 simulations. It can be set to a value ranging between 10 $\mu$Gy and 10 mGy per laser shot by simply changing the aluminum foil thickness and the diode voltage. Therefore, this versatile and compact X-ray source opens a new path to explore the radiation effects induced by dose rates varying over several orders of magnitude., Comment: 5 pages, 6 figures

The high-average current electron gun low energy electrons from a thermionic cathode at high intensity is the prototype of the drive beam source for the Compact Linear Collider project. The electromagnetic design of the gun was done originally with 2D simulations to minimize the beam emittance for high-current operation (of the order of 8 A) at 140 keV. This paper reports on the first experimental measurements of beam extraction and transport. For the first time, 3D tracking simulations, which take into account precisely the cathode–grid geometry, have been compared with experimental optical transition radiation images of the beam, and we obtained impressive agreement. In addition, we have confirmed that the details of the cathode–grid assembly can impact significantly the beam emittance.

A compact low-energy and high-intensity electron source for material aging applications is presented. A laser-induced plasma moves inside a 30 kV diode and produces a 5 MW electron beam at the anode location. The corresponding dose that can be deposited into silicon or gallium samples is estimated to be 25 kGy per laser shot. The dose profile strongly depends on the cathode voltage and can be adjusted from 100 nm to 1 $\mu$m. With this versatile source, a path is opened to study micro or nano-electronic components under high irradiation, without the standard radioprotection issues.

International audience; We present the observation and the detailed investigation of coherent Cherenkov diffraction radiation (CChDR) in terms of spectral-angular characteristics. Electromagnetic simulations have been performed to optimize the design of a prismatic dielectric radiator and the performance of a detection system with the aim of providing longitudinal beam diagnostics. Successful experimental validations have been organized on the CLEAR and the CLARA facilities based at CERN and Daresbury laboratory respectively. With ps to sub-ps long electron bunches, the emitted radiation spectra extend up to the THz frequency range. Bunch length measurements based on CChDR have been compared to longitudinal bunch profiles obtained using a radio frequency deflecting cavity or coherent transition radiation (CTR). The retrieval of the temporal profile of both Gaussian and non-Gaussian bunches has also been demonstrated. The proposed detection scheme paves the way to a new kind of beam instrumentation, simple and compact for monitoring short bunches of charged particles, particularly well-adapted to novel accelerator technologies, such as dielectric and plasma accelerators. Finally, CChDR could be used for generating intense THz radiation pulses at the MW level in existing radiation facilities, providing broader opportunities for the user community.

Intense relativistic electron beam propagation has been subject to extensive studies in many laboratories throughout the world, in particular during the 70's and 80's. CESAR is a 700 kV, $2 \Omega$ generator facility at CESTA which is used to study fast hydrodynamic response of materials. Typically, this device delivers a 350 kA, 70 ns FWHM electron beam at 700 keV from a graphite cathode. The electron beam exits the diode through a thin aluminized mylar anode and it is transported and focussed in a gas-cell filled with dry air. The pressure in the cell varies from 0.1 to 10 mbar, and an external focusing coil produces a magnetic field up to 3 T. In addition to the regular electrical diagnostics, such as B-dot probes and Faraday cups for current measurements along with capacitive dividers for diode voltage estimations, we have installed an optical diagnostic line in order to analyze the beam behavior along the propagation axis. This diagnostic consists of a fused silica target which intercepts the beam at some given location inside the gas cell. When the beam impinges on the silica target, visible Cerenkov light is produced and some part of this light can be collected both by a gated camera and a streak camera. In this paper, we report on the progress of this experiment where the issues of beam homogeneity, both in time and space, are addressed.

Many applications of THz radiation remain impractical or impossible due to the lack of compact sources with sufficient power. A source, in which the interaction occurs between an electron beam and a diffraction grating, has been shown in simulations to be capable of generating high THz power in a compact package. The grating surface-wave produces strong beam bunching and generates significant power at the fundamental frequency and its harmonics. We will discuss the Coherent Smith-Purcell studies performed at CESTA both with planar and cylindrical configurations. The promising recent experimental results at 100 and 200 GHz will be presented.

Velvet cathodes are widely used in field-emission electron diodes, in particular in induction accelerators used for flash X-ray radiography. The emission from velvet could be different from pulse-to-pulse in multi-pulse operation, such as in the double-pulse option studied for the third radiographic axis of the Epure facility in France. As a consequence, we are revisiting the beam homogeneity and the emittance of the electron beam produced by velvet cathodes.

Many applications of THz radiation remain impractical or impossible due to an absence of compact sources with sufficient power. A source, in which the interaction occurs between an electron beam and a diffraction grating, has been shown in simulations to be capable of generating high THz power in a compact package. The grating surface-wave produces strong beam bunching and generates significant power at the fundamental frequency and its harmonics. We will discuss the Coherent Smith-Purcell studies performed at CESTA both with planar and cylindrical configurations. The exciting recent experimental results at 100 and 200 GHz will be presented.

High-power-microwave (HPM) emission has been observed in S-band with a compact magnetically insulated line oscillator (MILO). The device is driven by a low-impedance Marx generator which was designed and built at Commissariat a l'Energie Atomique, Centre d'Etudes Scientifiques et Techniques d'Aquitaine for HPM experiments. Measurements with fast and sensitive I-dot probes, installed inside the slow-wave structure (SWS), have given the evidence of the MILO oscillation. The main frequency at 2.40 GHz is confirmed by measuring the emitted radiation by using both an in-vacuum antenna and a horn placed in the far-field region. The frequency response of the MILO SWS is compared to a 3-D simulation performed with MAGIC, an electromagnetic particle-in-cell code. In the first configuration, a microwave output power of 1 GW has been obtained, which is in good agreement with the simulations. Then, an optimization of the cathode geometry has led to an increase of the pulse duration and to a better stability of the emission frequency. Finally, based on the fair agreement between the experimental results and the corresponding simulations, a novel design is presented, which should give a higher emitted power at 2.34 GHz.

We report on a simple way to operate plasma-electrode pockel’s cells (PEPC), which are used as large-aperture optical switches in laser drivers for inertial-confinement fusion facilities. In the basic operation of a PEPC, one needs to produce a plasma in each of two gas-filled cells placed on opposite sides of an appropriate crystal plate. Between the resulting highly conductive electrodes, a high-voltage pulse is applied to produce a uniform electric field in the crystal, which then undergoes the Pockel’s effect. We have developed a simple PEPC design in which the high-voltage pulse can be directly applied between the gascells without prior ionization of the gas (by a high-current plasma discharge). With reasonable operating parameters, this regime meets the PEPC optical switching requirements for the laser megajoules. In this paper, we present experimental results of this simple regime that strongly simplifies the PEPC concept and improves its reliability.

Many applications of THz radiation remain impractical or impossible due to an absence of compact sources with sufficient power. A source in which the interaction occurs between an annular electron beam and a cylindrical grating has been shown in simulations to be capable of generating very high THz power in a very compact package. The grating surface-wave produces strong beam bunching and generates significant power at the fundamental frequency and harmonics. A collaboration between Advanced Energy Systems and CEA/CESTA has been ongoing in performing proof-of-principle tests on cylindrical grating configurations producing millimeter wave radiation. Testing has been performed with a 6 mm period grating, producing power at the fundamental frequency of 15 GHz, second harmonic power at 30 GHz and although not measured, simulations show meaningful third harmonic power at 45 GHz. Comparison between simulations and the experimental results will be presented. Future plans will increase the frequency of operation to 100 GHz.

Three-dimensional simulations and experiments have shown that, for a grating equipped with sidewalls, copious emission of coherent Smith-Purcell (SP) radiation at the fundamental frequency of the evanescent surface wave is possible. One may reduce the wavelength by rescaling all the parameters of the grating, but this reduces the radiated power by the square of the scale factor. Both 3D MAGIC simulations and the theory of antenna arrays suggest that by laterally juxtaposing N copies of the N-fold reduced grating, the overall power reduction is only 1/N. Furthermore, the radiation is concentrated into a solid angle of size 1/N compared to that of a single reduced grating. An experiment at 32 GHz partially confirms these predictions for N = 7. Preliminary simulations indicate that with a single 20-fold reduced channel coherent Smith-Purcell radiation at 100 GHz is produced. An experiment to confirm that a 20-channel grating will produce a well-collimated radiation pattern with adequate power levels is being prepared.

The electron beam of the pulsed diode RKA (500 keV, 30 kA, 110 ns) is emitted by field emission. To measure its spatial homogeneity, we study the beam impact on a fused-silica target. The resulting Cerenkov emission is analyzed by cameras. The experimental results are compared with the predictions of the Monte Carlo code Geant4. This software was chosen for its robust physics package and its capability of simulating Cerenkov emission. The initial conditions of the electrons in Geant4 are provided by the “MAGIC” code. In addition, we have used a high speed gated camera and several interference filters to obtain the Cerenkov spectrum. A comparison with the theoretical spectrum calculated by the formula of Tamm and Frank is given.

The RKA is a single shot generator which is capable of producing 500 keV, 30 kA, 100 ns electron beams. The beam, emitted by field emission in a diode, is propagated and focused on a target. To improve the understanding of its interaction with a given material, the beam must be characterized in terms of homogeneity, energy and angular dispersion. In this work, we present the results of an experiment where Cerenkov emission is the physical process we use to characterize the beam homogeneity. Two cameras are installed: a high speed gated camera and a streak camera. The code GEANT4 allows us to simulate the Cerenkov emission and the main interactions of electrons/photons inside the target. The initial conditions of the electrons in GEANT4 are provided by “MAGIC” simulations. This particle-in-cell code computes beam emission in the diode and its transportation towards the target. Extensive simulations have allowed us to optimize the full system, in particular in terms of anode thickness and material. The experimental results have confirmed these predictions. In addition, we present experimental tests of several cathode materials as well as the first results of beam propagation in gaseous Argon at a low pressure (order mbar).

A promising compact source of high power THz radiation which utilizes an annular electron beam and a cylindrical grating is being studied. The cylindrical grating configuration exhibits substantially enhanced performance in comparison with the classical 2-D planar gratings. In the studied source, the grating surface-wave produces strong beam bunching and generates significant power at the fundamental surface-wave frequency and at harmonics as Smith-Purcell radiation. A collaboration between Advanced Energy Systems and CEA/CESTA has been ongoing in performing proof-of-principle tests on cylindrical grating configurations producing millimeter wave radiation. Testing has been performed with a 6 mm period grating, producing power at the fundamental frequency of 15 GHz, second harmonic power at 30 GHz and although not measured, simulations show meaningful third harmonic power at 45 GHz. To date simulations have been performed at frequencies up to the THz frequency range. Simulations are ongoing using both MAGIC and VORPAL. Comparisons between these two codes will be presented and compared to the experimental results. Additionally, a three dimensional dispersion relation has been developed. A comparison between the dispersion relation and three dimensional simulations shows the potential higher order modes.

The two-dimensional theory of Smith-Purcell free-electron laser predicts that coherent radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. Particle-in-cell simulations and a demonstration experiment at 5 GHz have shown that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation is copiously emitted at the fundamental frequency with 10 % efficiency.

In the two-beam accelerator scheme, a high-current electron beam, bunched at the resonant frequency, traverses extraction cavities, where it generates power intended to drive accelerating cavities on the main beam. Here, we report on work performed to test some aspects of this scheme. We used a free-electron-laser (FEL) amplifier at 35 GHz to bunch a beam of electrons, which is then transported and focused into a resonant cavity. The results of earlier bunching experiments had demonstrated the capacity of the FEL supplied by an induction linac to generate an appropriate drive beam. A summary of this earlier work is presented along with measurements of power from the cavity. This constitutes the first observation of high-frequency power extraction using a FEL in this scheme.

In previous studies of bunching we operated our 2.2 MeV, 800 A single shot FEL in the amplifier mode, and observed output power and bunching not only at the injected frequency of 35 GHz but also at the second-FEL resonant frequency near 3 GHz. In order to study the mechanism of the low-frequency bunching we have performed a series of measurements in SASE mode. Here we compare and contrast results obtained in these two modes. For both modes a detailed study of the formation of the low-frequency bunches during the pulse has been performed using a streak camera, as a function of both position in the wiggler and time in the pulse. Analysis of the images shows that despite the great difference in output power, the strong bunching we see is quite similar. In the amplifier mode the coexistence of the bunching at high frequency masks some of the details of the low-frequency bunch formation, whereas in the SASE mode the temporal and spatial behavior of bunching at 3 GHz is clearly seen.

Among the studies in the framework of high gradient linear electron–positron collider research, the Two-Beam Accelerator (TBA) is a very promising concept, and two projects are in progress, the Compact Linear Collider project at CERN (W. Schnell, Report no. CERN SL/92-51 and CLIC note 184; K. Hubner, CERN/PS 92-43, CLIC note 176; S. Van der Meer, CERN/PS 89-50, CLIC note 97.) and the Relativistic Klystron-TBA project at LBNL (Technical Review Committee, International Linear Collider Technical Review Committee Report 1995, SLAC-R-95-471, 1995). In a TBA an extremely intense low-energy electron beam, called the drive beam, is bunched at the desired operating frequency, and upon passing through resonant cavities generates radio-frequency power for accelerating the main beam. Among the different approaches to the production of a suitable drive beam, the use of an FEL has been proposed and is under active study at CEA/CESTA.

Pronounced electron-beam bunching and high-power emission at 3 GHz have been observed in the 35-GHz free-electron-laser (FEL) experiment at CEA/CESTA. It corresponds to the low-frequency resonance of the FEL which appears in addition to the high-frequency resonance when a waveguide is used. The dependence of the bunching on length (in the wiggler) and time (in the pulse) shows that the spontaneously generated low-frequency mode comes to dominate the high-frequency injected mode at long distances and late times.

We report output power and frequency measurements of a pulsed free electron laser (FEL) operating as an amplifier at 35 GHz, without guiding field. The experiment used an induction linac, which delivers an 800-A relativistic electron beam (2.2 MeV) with a flat-top of 40 ns into the helical wiggler. The input signal furnished by a 35-GHz magnetron source is amplified to power levels of the order of 80 MW. The experimental results are in good agreement with our simulations. Frequency chirping is observed, and its behavior as a function of the basic FEL parameters is discussed.

Three-dimensional simulations and experiments have shown that, for a grating equipped with sidewalls, copious emission of coherent Smith-Purcell (SP) radiation at the fundamental frequency of the evanescent surface wave is possible1, 2. This contrasts with the two-dimensional theory for which emission could only occur at harmonics of that frequency. To increase the emitted frequency towards the THz range with a realistic electron beam, we propose to use several gratings with sidewalls in parallel, with adequate scaling of their parameters. Simulations suggest that the reduction in power, due to the reduced grating period and width needed to reach high frequencies, can be compensated in this way. To test this idea, an experiment is under way.

We present the results of a free-electron-laser (FEL) experiment at 35 GHz, using a strongly relativistic electron beam ({ital T}=1.75 MeV). The electron pulse length is 30 ns full width at half maximum with a peak current of 400 A. The FEL is designed to operate in the high-gain Compton regime, with a negative coupling parameter ({Phi}{lt}0) leading to a strong growth rate. More than 50 MW of rf power in the TE{sub 1}{sub 1} mode (43 dB gain) has been obtained with good reproducibility. The experimental results are in good agreement with predictions made using the three-dimensional stationary simulation code solitude. {copyright} {ital 1996 The American Physical Society.}

Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the root mean square deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250 m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000–2009) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snow line is located at its highest elevation, thus when the snow line is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the interannual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps.

This paper presents the results of a FEL experiment at 35 GHz, using a highly relativistic electron beam (T = 1.75 MeV). The electron pulse length is 30 ns FWHM with a peak current of 400 A. The FEL is designed to operate in the high-gain Compton regime, with a negative coupling parameter (Φ < 0) leading to a stong growth rate. More than 50 MW of RF power in the TE11 mode (43 dB gain) has been obtained with good reproducibility. The experimental results are in good agreement with predictions made using the 3D stationary simulation code SOLITUDE.

Summary form only given. A 500 kV pulsed power generator is used to feed a planar diode in order to study electron beam emission, propagation and focusing towards a target. The cathode diameter, as well as the anode-cathode distance, can be varied in order to change the emitted current which is governed by the Child-Langmuir law. In order to match the diode impedance to the generator impedance, a liquid resistance is placed in parallel to the diode. Various electrical and optical measurements are performed. The measurements of the main beam characteristics are compared with the predictions of the PIC code MAGIC. Cerenkov emission from a silica target is analyzed and compared with the predictions of the GEANT4 code. We pay particular attention to the beam homogeneity and to the dispersion in the beam velocity components when the electrons strike the target. Several cathode materials are compared. Finally, for high currents, we plan to study the propagation of the beam inside a rare gas as a function of pressure. An external solenoid can be used to focus the beam at the target location if necessary.

A few years ago, Andrews and Brau (AB) presented the dispersion relation for a lamellar grating in two dimensions (2D) as a step in understanding coherent Smith-Purcell radiation. This involved solving Maxwell's equations both in the grooves and in the region above the grooves, where Floquet theory was used. The coupling with an electron beam was studied, and an expression for the gain as a function of current was derived. Their approach has been supported by 2D simulations using particle-in-cell (PIC) codes, and more recently by a demonstration experiment that used a wide grating. We present here the dispersion relation (in the absence of beam) of a grating in three dimensions, which turns out to be a relatively straightforward extension of the AB results. The predictions of this theory are compared with PIC simulations, and also with measurements of the transmission coefficient as a function of frequency. Extremely good agreement is observed.

Coherent Smith-Purcell radiation is a promising source of coherent emission in the THz domain. Although it has been observed in several experiments, some physical quantities related to the bunching of an initially continuous beam had not yet been studied experimentally. Among them, the gain as function of beam current, together with the value of the start current, needed to be addressed. We report here their measurements in a microwave experiment using a sheet beam. A start current of about 20 A/m was found. Two-dimensional simulations with a very thin beam agree well with our results.

The Arletron is a compact microwave tube which has been designed with the code MAGIC 1. Last year, we presented at the ICOPS conference the first experimental results in single shot operation. We have recently tested the Arletron at 100 Hz during 1 s, which is the limit of our power supply at CEA/CESTA 2. We present here the main results of this experiment and new simulations.

Summary form only given. Experimental studies on Smith-Purcell radiation have been conducted at CEA/CESTA since 2009. Initially, the main goal was to compare the results with the predictions of MAGIC simulations ' and with theory published by Andrews & Brau. At ICOPS 2009, we presented the first experimental results. Strong beam bunching, at the frequency of the evanescent mode of the grating, was measured along with a high emission level of coherent SP (CSP) emission at several harmonics of the fundamental frequency.We recently restarted the experiment in order to study CSP physics in more details. In particular we have measured the gain as a function of beam current, and also the value of the start current. They are of particular interest for THz CSP physics. Experimental results are compared with both existing theories and PIC simulations. Finally, we are studying the limits, in terms of flatness and thickness, of the electron beam. The aim is to increase the frequency of operation of our CSP experiment towards the THz range. We think our set-up could be used to produce a powerful tunable compact device at a frequency between 100 and 200 GHz.

Summary form only given. If an electron beam propagates just above a grating, it produces diffraction radiation which was observed for the first time by Smith and Purcell (SP) in 1953. If the beam current is high enough, a strong interaction with the fundamental evanescent mode of the grating occurs. The beam bunches and coherent emitted radiation is expected at specific observation angles which are given by the SP relationship for the harmonics of the grating mode frequency. For small grating periods (

At CESTA, the 35-GHz FEL experiment ONDINE I is in progress. The work done this year focused on beam creation and propagation using the Euphrosyne generator with both an oxide cathode and a cold cathode: typically, 1 kA at 2.5 MeV is propagated. Many calculations were done for these problems and we have also developed simulation codes for FEM interaction in both Compton and Raman regimes, taking into account the 3D wiggler field, guiding field, waveguide modes, electron beam injection to obtain trajectories, gain and efficiency. Good agreement with some previous experiments and codes was obtained. The Ondine II expirement will start at 1 Hz with the 1.5-MeV LELIA injector (see companion paper) using the same wiggler technology to gain a better understanding of the FEL physics.

We present an experimental demonstration of electron beam bunching in the new kind of compact buncher for high repetition rate high power microwaves: the Arletron. By using the code MAGIC, we have found a design in which two coupled pillbox cavities strongly bunch an annular electron beam1. High repetition rate operation is possible for two reasons. First, no grids intercept the beam during its propagation and, secondly, the guiding magnetic field is low enough to be produced by a permanent magnet focusing system. Detailed comparison between MAGIC predictions and experimental results are given.

A few years ago, a new theory for producing coherent Smith-Purcell radiation from an initially continuous electron beam was proposed. It was 2-D, and it has been supported by particle-in-cell code simulations, although no experiments have, until now, provided confirmation. In fact, all experiments used a round beam, for which the 2-D theory may not be valid. We report here on a two-pronged attack on this problem. A 3-D simulation in the microwave domain indicates that coherent radiation, at a frequency near that of the 2-D simulation, should be produced. We are also preparing a demonstration experiment using an intense finite-width sheet beam to confirm the theory and simulations.

Experimental and numerical studies on a commercial S-band (3 GHz) Reltron at repetition rates up to 10 Hz is presented. The test bench which has been developed at CEA/CESTA is described. And a cable transformer capable of delivering 200 kV, 1 kA pulses at a repetition rate of 100 Hz is also presented.

Smith–Purcell (SP) radiation has been observed many times over the past fifty years, and several theories have been proposed to explain it. However, it is only quite recently that Andrews, Brau and collaborators made a considerable advance in understanding how coherent SP radiation may be produced from an initially continuous beam. Their work received support from 2-D simulations which were performed using the Particle-in-Cell (PIC) code “MAGIC”. Here we present a review of our 2-D simulations of coherent SP and discuss how they relate to the model of Andrews and Brau. We also describe briefly a SP experiment in the microwave domain using a sheet beam that is planned for 2008.