Electron Beam Of Duration Research Articles

Measurement of the electron beam energy in a source with a plasma anode and the beam extraction into the atmosphere through a foil window

Measurements of the energy of an electron beam in an electron beam source with an explosive-emission cathode, a plasma anode and a foil window, providing the extraction of an electron beam with a cross-section of (100–200) cm2 into the atmosphere, have been performed. The high voltage source was a Marx generator based long lines with matched loads. The energy values were calculated from the results of measurements of the temperature of a beam collector placed in vacuum using thermistors and an infrared imager. At an accelerating voltage of ~ 200 kV, a current of (1–2) kA, and an electron beam duration of 5 μs, the maximum values of the energy released in the collector with a cross section of 74 cm2 were (650–850) J/pulse. A decrease in the current and energy of the beam was recorded approximately by a factor of two after passing through an AMG-2n aluminum-magnesium foil with a thickness of 30 μm. The use of infrared imager for recording the beam structure in the plane of the output window in air has been tested.

Generation of Terawatt Attosecond Pulses from Relativistic Transition Radiation.

When a femtosecond duration and hundreds of kiloampere peak current electron beam traverses the vacuum and high-density plasma interface, a new process, that we call relativistic transition radiation (RTR), generates an intense ∼100 as pulse containing ∼1 terawatt power of coherent vacuum ultraviolet (VUV) radiation accompanied by several smaller femtosecond duration satellite pulses. This pulse inherits the radial polarization of the incident beam field and has a ring intensity distribution. This RTR is emitted when the beam density is comparable to the plasma density and the spot size much larger than the plasma skin depth. Physically, it arises from the return current or backward relativistic motion of electrons starting just inside the plasma that Doppler up shifts the emitted photons. The number of RTR pulses is determined by the number of groups of plasma electrons that originate at different depths within the first plasma wake period and emit coherently before phase mixing.

Parameter optimization of self-reflecting all-laser-driven Thomson scattering based on laser wakefield acceleration

All-laser-driven Thomson scattering based on laser wakefield acceleration can provide high quality X-ray and greatly reduce the source size. Compared with two-pulse setting, the self-reflecting setting can reduce the requirement for temporal and spatial synchronization in experiment. However, it is difficult to optimize X-ray because Thomson scattering is coupled with laser wakefield acceleration in this process. In this paper, we correct theory formula through numerical simulation, and analyze the parameters quantitatively in laser wakefield acceleration and Thomson scattering, such as spot size, duration and energy of laser and electron beam, and reflectivity of plasma mirror. Then we can trace the parameters by using the modified formula rather than the numerical simulation with similar accuracy and less time. The modified formula is also used to optimize the self-reflecting all-laser-driven Thomson scattering X-ray under the given laser conditions. The optimal X-ray luminance and photon number can be obtained by changing the plasma density and the position of the plasma mirror.

Intensification of laser-produced relativistic electron beam using converging magnetic fields for ignition in fast ignition laser fusion

The kilo-tesla-class converging magnetic field effects on the core heating properties and the energy and duration of relativistic electron beam (REB) required for ignition in fast ignition laser fusion has been evaluated by parametric 2D hybrid simulations where a uniformly compressed DT core with ρ = 300 g/cm3 is heated by REB with TREB = 3 MeV, IREB = 0.69 × 1020 W/cm2 and θREB = 40° under sufficiently strong magnetic field (Bext = 3 kT at the REB injection position). The kilo-tesla-class converging magnetic field can intensify REB and then enhances the core heating power drastically. As the results, the fusion ignition can be initiated by the REB with EREB ≧ 50 kJ and τREB = 10 ~ 30 ps. With increasing mirror ratio RM, the negative effect of converging field, i.e., mirror reflection, becomes significant, which enhances the REB energy required for ignition (EREB,ig = 49 kJ for RM = 3 → EREB,ig =77 kJ for RM = 20).

Effect of Electron Injection on Minority Carrier Transport in 10 MeV Proton Irradiated β-Ga2O3 Schottky Rectifiers

We report the effect of extended duration electron beam exposure on the minority carrier transport properties of 10 MeV proton irradiated (fluence ∼1014 cm−2) Si-doped β-Ga2O3 Schottky rectifiers. The diffusion length (L) of minority carriers is found to decrease with temperature from 330 nm at 21 °C to 289 nm at 120 °C, with an activation energy of ∼26 meV. This energy corresponds to the presence of shallow Si trap-levels. Extended duration electron beam exposure enhances L from 330 nm to 726 nm at room temperature. The rate of increase for L is lower with increased temperature, with an activation energy of 43 meV. Finally, a brief comparison of the effect of electron injection on proton irradiated, alpha-particle irradiated and a reference Si-doped β-Ga2O3 Schottky rectifiers is presented.

On the influence of a cathode shape on the parameters of current pulses of runaway electron beams in a gas discharge when applying voltage pulses with a rise time of 200 ns

The influence of the shape of a cathode on the duration and amplitude of a supershort avalanches electron beam (SAEB) current pulses was experimentally studied. Three cathodes were used in experiments: tube, needle, and ball. Voltage pulses with a rise time of 200 ns were applied across an 8.5 mm gap filled with air and nitrogen at various pressures (12.5–100 kPa). It was found that at an air pressure of 12.5 kPa and a rise time of voltage pulses 200 ns, the largest amplitudes of SAEB current pulses (90 mA) were observed with the tubular cathode. The SAEB current pulse duration was τ0.5 ~ 130 ps. Two pulses with different duration, amplitude and energy of electrons were observed with the needle cathode at same pressure. When using the ball cathode, the duration and amplitude of the beam current pulses were τ0.5 ~ 250 ps and ~ 4 mA, respectively.

Robustness of a plasma acceleration based free electron laser

Laser Plasma Accelerators (LPA) can sustain GeV/m accelerating fields offering outstanding new possibilities for compact applications. Despite the impressive recent developments, the LPA beam quality is still significantly lower than in the conventional radio-frequency accelerators, which is an issue in the cases of demanding applications such as Free Electron Lasers (FELs). If the electron beam duration is below few tens of femtosecond keeping pC charges, the mrad level divergence and few percent energy spread are particularly limiting. Several concepts of transfer line were proposed to mitigate those intrinsic properties targetting undulator radiation applications. We study here the robustness of the chromatic matching strategy for FEL amplification at 200~nm in a dedicated transport line, and analyze its sensitivity to several parameters. We consider not only the possible LPA source jitters, but also various realistic defaults of the equipment such as magnetic elements misalignements or focussing strength errors, unperfect undulator fields, etc...

Faraday-rotation self-interference method for electron beam duration measurement in the laser wakefield accelerator

Real-time single-shot measurement of the femtosecond electron beam duration in laser wakefield accelerators is discussed for both experimental design and theoretical analysis that combines polarimetry and interferometry. The probe pulse polarization is rotated by the azimuthal magnetic field of the electron beam and then introduced into a Michelson-type interferometer for self-interference. The electron beam duration is obtained from the region size of the interference fringes, which is independent of the pulse width of the probe laser. Using a larger magnification system or incident angle, the measurement resolution can be less than 1 fs.

Quasi-Chemical Reactions in Irradiated Silicon Crystals with Regard to Ultrafast Irradiation

This paper reports results from an investigation of the interaction of displaced Si-self atoms (I) and their vacancies (V), with impurities in crystalline silicon (Si), as induced by micro-second pulse duration irradiation with electrons at different energies: 3.5, 14, 25 and 50 MeV and pico-second pulse duration with energy 3.5 MeV. V-V, I-impurity atom and V-impurity atom interactions are analyzed both experimentally and as modeled using computer simulations. A process of divacancy (V2) accumulation in the dose-dependent linear region is investigated. The effect of impurities on recombination of correlated divacancies, and I-atoms that had become displaced from regular lattice points is estimated by computer modeling of an appropriate diffusion-controlled process. It is concluded that the experimental results can be interpreted quantitatively in terms of a strongly anisotropic quasi-one-dimensional diffusion of displaced I-atoms. In addition, a significant difference is found between the effects of pico-second duration electron beam irradiation, which causes the formation of A-centre (V + Oxygen) clusters, while when the beam is applied on a micro-second timescale, divacancies are created instead, although the electrons have the same energy in both cases.

Variation of the beam parameters of runaway electrons in a gas discharge under the conditions of nonuniform preliminary ionization

Within the theoretical model of a high-pressure hybrid nanosecond discharge with runaway electrons, a strong dependence of the electron beam amplitude, duration, and energy spectrum on the conditions of the preliminary ionization of a gas in the discharge gap is demonstrated. The conditions with uniform and nonuniform distributions of initial electrons in a coaxial diode filled with sulfur hexafluoride at atmospheric pressure are simulated. It is shown that the amplitude and current pulse profile of the electron beam substantially change upon the variation of the initial distribution of the electrons in the discharge gap.

High-flux electron beams from laser wakefield accelerators driven by petawatt lasers

Laser wakefield accelerators (LWFAs) are considered to be one of the most competitive next-generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA driven by petawatt-level laser pulses. In our three-dimensional particle-in-cell simulations, an optimal set of parameters gives of charge with laser power, thus of instantaneous current if we assume the electron beam duration is 100 fs. This high flux and its secondary radiation are widely applicable in nuclear and QED physics, industrial imaging, medical and biological studies.

Large-charge quasimonoenergetic electron beams produced by off-axis colliding laser pulses in underdense plasma.

Electrons can be efficiently injected into a plasma wave by colliding two counterpropagating laser pulses in a laser wakefield acceleration. However, the generation of a high-quality electron beam with a large charge is difficult in the traditional on-axis colliding scheme due to the growth of the electron beam duration coming from the increase of the beam charge. To solve this problem, we propose an off-axis colliding scheme, in which the collision point is away from the axis of the driver pulse. We show that the electrons injected from the off-axis region are highly concentered on the tail of the bubble even for a large trapped charge, thus feeling almost the same accelerating field. As a result, quasimonoenergetic electron beams with a large charge can be produced. The validity of this scheme is confirmed by both the particle-in-cell simulations and the Hamiltonian model. Furthermore, it is shown that a Laguerre-Gauss (LG) laser can be adopted as the injection pulse to realize the off-axis colliding injection in three dimensions symmetrically, which may be useful in simplifying the technical layout of the real experiment setup.

Generation of high-current large-cross-section electron beams in a vacuum diode with rod current returns

The results of experiments on obtaining high-current radially converging extended electron beams in a vacuum diode of an electron accelerator, which is intended for excitation of a gas laser, are presented. To reduce the magnetic field in the diode and its influence on the beam formation, in addition to magnetically shielding plates that sectionalize the diode into two magnetically shielded diodes, small-diameter rod current returns were used. Cathodes with wide concave emitting units, which provided a high degree of filling the output windows with the electron beam, were used. The rods are installed in holes between the emitting units and connect the cell ribs to the vacuum-chamber wall. A significant decrease in the angles of electron entry into the foil was observed. It is shown experimentally that mounting the current returns results in a decrease in the magnetic field in the diode, while breakdowns and a decrease in the electron-beam current-pulse duration are absent. At a diode voltage of 550 kV, electron beams with a current of 240 kA, a beam energy in the diode of 20 kJ, and an extracted-beam energy transported through the foil of 6.5 kJ were obtained. The possibility of increasing the electron-beam energy, which is transferred from the diode to the gas-filled cell, by a factor of at least 1.2 was demonstrated.

Unraveling resistive versus collisional contributions to relativistic electron beam stopping power in cold-solid and in warm-dense plasmas

We present results on laser-driven relativistic electron beam propagation through aluminum samples, which are either solid and cold or compressed and heated by laser-induced shock. A full numerical description of fast electron generation and transport is found to reproduce the experimental absolute Kα yield and spot size measurements for varying target thicknesses, and to sequentially quantify the collisional and resistive electron stopping powers. The results demonstrate that both stopping mechanisms are enhanced in compressed Al samples and are attributed to the increase in the medium density and resistivity, respectively. For the achieved time- and space-averaged electronic current density, ⟨jh⟩∼8×1010 A/cm2 in the samples, the collisional and resistive stopping powers in warm and compressed Al are estimated to be 1.5 keV/μm and 0.8 keV/μm, respectively. By contrast, for cold and solid Al, the corresponding estimated values are 1.1 keV/μm and 0.6 keV/μm. Prospective numerical simulations involving higher jh show that the resistive stopping power can reach the same level as the collisional one. In addition to the effects of compression, the effect of the transient behavior of the resistivity of Al during relativistic electron beam transport becomes progressively more dominant, and for a significantly high current density, jh∼1012 A/cm2, cancels the difference in the electron resistive stopping power (or the total stopping power in units of areal density) between solid and compressed samples. Analytical calculations extend the analysis up to jh=1014 A/cm2 (representative of the full-scale fast ignition scenario of inertial confinement fusion), where a very rapid transition to the Spitzer resistivity regime saturates the resistive stopping power, averaged over the electron beam duration, to values of ∼1 keV/μm.

Note: Measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air

This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be ~25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach ~25 ps too.

High power microwave generation from the low-impedance transit-time oscillator without foils

A low-impedance transit-time oscillator without foils (LITTO) has been proposed in our previous work. Recently, the experiment is carried out on an intense relativistic electron beam (IREB) generator, which is capable of producing a 50 ns duration electron beam in the voltage range of 0.4-1 MV. With a 600 kV, 24 kA electron beam guided by an external magnetic field of 0.5 T, a radiation power of 2.7 GW at 1.64 GHz has been achieved and the corresponding power conversion efficiency is 18.75%. With the similar voltage and current parameters, the experimental results are reexamined and confirmed by the particle-in-cell (PIC) simulation.

Luminescence of spodumene and garnet crystals excited by subnanosecond and nanosecond electron beams

The pulsed cathode luminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn2+ and Nd3+ ions, respectively, is studied. Luminescence is excited by the irradiation of the crystals by electron beams with a duration of 0.1, 0.25, 0.65, and 10 ns and a current density of ∼40 and 100 A/cm2 at an electron energy of ∼200 keV. A decrease in the electron beam duration to several tenths of a nanosecond is shown not to cause substantial changes in the excitation mechanisms of pulsed cathode luminescence and its spectrum.

The amplitude and current pulse duration of a supershort avalanche electron beam in air at atmospheric pressure

The results of experimental studies of the parameters (amplitude and duration) of a supershort avalanche electron beam (SAEB) generated in air at atmospheric pressure are presented. It is shown that the pulse duration of the beam current behind the foil from the entire area of the anode foil is larger than from small areas and depends on the cathode design. The number of electrons that are detected behind the 10-μm-thick Al foil is ∼6 × 1010 electrons, which corresponds to a SAEB amplitude of ∼100 A at a FWHM of the current pulse of ∼100 ps. An X-ray exposure dose per pulse of ∼1.8 mR was obtained using a 20-μm-thick copper foil. It was confirmed that the FWHM of a SAEB pulse is within ∼50 ps from small foil areas (with diameters of ∼7 mm or smaller).

Spodumene and garnet luminescence excited by subnanosecond electron beams

Pulsed cathodoluminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn2+ and Nd3+ ions, respectively, is investigated. The luminescence was excited upon crystal irradiation by electron beams with current densities of 35 and 100 A/cm2 and average electron energy of ∼ 50 keV for 0.1, 0.25, and 0.65 ns. It is demonstrated that the electron beam duration decreased to several tenth of a nanosecond does not lead to essential changes of the mechanisms of pulsed cathodoluminescence excitation and character of its spectrum, but in this case, the intensity of luminescence of the hole centers increases compared with the intracenter luminescence.

Laboratory demonstration of runaway electron breakdown of air

Results of experiments demonstrating the phenomenon of runaway electron breakdown of atmospheric air under laboratory conditions are presented. As the discharge-initiating electron beam of duration ∼ 50 ps had passed through the electrode gap, a runaway electron avalanche current was detected in the electrode gap downstream of the anode grid and then breakdown occurred with picosecond stability. The maximum electron energy and the duration of the avalanche current corresponded to theoretical notions about the runaway electron breakdown of atmospheric air in a strong electric field. Breakdown did not occur at all or was considerably delayed when no initiating beam was used.