High power electron diode for linear induction accelerator at a flash radiographic facility

Abstract

We investigated a new cathode design and beam transport with the EPURE axis-1 injector in order to increase the beam characteristics at 3.8 MeV, 80 ns FWHM from the 2.0 kA nominal current to 2.6 kA corresponding to an average current density of 82 A=cm 2 . Such current increase is highly desirable for improving the x-ray dose and hence radiographic performances. To achieve this, a time-dependent model based on the particle-in-cell method was developed in order to simulate the injector. Using results from calculations based on this model, a 17.2 cm AK gap diode with a larger radius cathode (3.175 cm) was designed, manufactured and tested. Experimental and calculated currents and emittances are qualitatively compared. The study provides a detailed understanding of the beam dynamics inside this type of high current, high energy injector.

Reduced time-dependent collisional-radiative models of non-equilibrium plasmas produced by surface flashover on a velvet cathode

“…We assume that the gas adsorbed on the velvet surface is mainly water vapor (H 2 O) and that the matter coming from eroded fibers is composed of H and C atoms since the used velvet is made of viscose. The surface flashover desorbs these atoms and molecules, these latter being rapidly dissociated by the energetic electrons (accelerated by a high electric field greater than 20 kV cm −1 [2]). Hence, and just after the flashover, the plasma can be supposed to evolved in a background atomic gas mixture that expands in the vacuum.…”

“…The electron drift velocities are obtained from the solution of the multi-term Boltzmann equation previously mentioned, as a function of electron mean energy ε m . The current density J e comes from LSP-PIC simulations of the diode exper imentally validated [2] and is displayed in figure 1 (right axis). This current density is considered as a source term for the CRM.…”

“…In order to produce a short pulsed electron beam (of around 140 ns) in a linear induction accelerator (LIA) a cold cathode made of velvet is used. The application of a strong voltage pulse (4 MV across a 17.2 cm gap) results in a surface flashover of the velvet cathode creating a non-equilibrium plasma from which the electron beam is extracted [1][2][3][4][5][6]. To describe the time-dependent evolution of the density of the plasma simulations.…”

“…This initial CRM involves 1050 reactions (electrons impacting atoms in their fundamental, excited and ionized states, atom de-excitation, three body recombination, ionization stepwise, etc) and 79 species (electrons, atoms, ions and excited states) [1]. On the other hand, the electron beam can be simulated based on the LSP particle-in-cell (PIC) code [7] to provide a detailed understanding of the beam dynamics [2]. In order to investigate the plasma effects on the electron beam, the plasma kinetic must be implemented in the LSP-PIC…”

Characterization of electrostatic discharge induced plasmas in dielectrics irradiated by multi-MeV electron beam

“…These effects can occur in satellites as well as in a broad range of electronic parts integrated within diagnostics used while operating facilities such as nuclear power plants, particle accelerators, 1 high energy, 2 high power 3 laser beams, and high pulsed power electron or X-ray beams. [4][5][6][7] These ESDs may significantly affect the electric signals associated with the measurements, thus inducing misinterpretation. ESDs may also induce thermomechanical degradation.…”