L. Voisin

A KDP equation of state for laser-induced damage applications

High power lasers such as NIF in the USA or LMJ in France are being developed for inertial confinement fusion applications. However, the performance of the optics is limited by laser-induced damage (LID), which occurs, for instance, in the potassium dihydrogen phosphate (KH2PO4 or KDP) crystals utilized for frequency conversion. An accurate equation of state (EOS) is required to explain the LID process and to predict damage size. For the design of such EOS, a pulsed electron beam was used to generate a quasi-plane stress wave of 0.7 GPa in KDP. The sample response was deduced from photonic Doppler velocimetry. Equations of state and deviatoric stress components are designed and compared to experimental data. They are used in laser-induced bulk damage simulations, showing that strength may play a significant role.

Study and optimization of negative polarity rod pinch diode as flash radiography source at 4.5 MV

The negative polarity rod pinch diode (NPRPD) is a potential millimeter spot size radiography source for high voltage generators (4 to 8 MV) [Cooperstein et al., “Considerations of rod-pinch diode operation in negative polarity for radiography,” in Proceedings of the 14th IEEE Pulsed Power Conference, 2003, pp. 975–978]. The NPRPD consists of a small diameter (few mm) cylindrical anode extending from the front end of the vacuum cell through a thin annular cathode, held by a central conductor. The polarity has been inverted when compared to the original rod pinch diode [Cooperstein et al., “Theoretical modeling and experimental characterization of a rod-pinch diode,” Phys. Plasmas 8(10), 4618–4636 (2001)] in order to take advantage from the maximal x-ray emission toward the anode holder at such a voltage [Swanekamp et al., “Evaluation of self-magnetically pinched diodes up to 10 MV as high resolution flash X-ray sources,” IEEE Trans. Plasma Sci. 32(5), 2004–2016 (2004). We have studied this diode at 4.5 MV...

Reproducibility Improvement on High Voltage Self-Break Water Switches

CESAR, a high current electron beam facility (800 kV, 400 kA) and AMBIORIX, a 2 MA Z-pinch driver are two of the main pulsed power facilities at CEA-CESTA in France. They use the classical technology of low-impedance generators, a Marx generator associated with a water line. One of the limitations of this kind of device is the switching process between the water lines. In order to improve the reproducibility, their first water switches were recently changed. On the basis of the work done by Puetz et al. for RITS-3 [1], the geometry of the main switch of each device, which links the intermediate storage (IS) and the pulse forming line (PFL), has been optimized. In this paper, we present the results of this modification.

Experimental study of self magnetic pinch diode as flash radiography source at 4 megavolt

The Self Magnetic Pinch (SMP) diode is a potential high-brightness X-ray source for high voltage generators (2–10 MV) that has shown good reliability for flash radiography applications [D. D. Hinchelwood et al., “High power self-pinch diode experiments for radiographic applications” IEEE Trans. Plasma Sci. 35(3), 565–572 (2007)]. We have studied this diode at about 4 MV, driven by the ASTERIX generator operated at the CEA/GRAMAT [G. Raboisson et al., “ASTERIX, a high intensity X-ray generator,” in Proceedings of the 7th IEEE Pulsed Power Conference (1989), pp. 567–570]. This generator, made up of a capacitor bank and a Blumlein line, was initially designed to test the behavior of electronic devices under irradiation. In our experiments, the vacuum diode is modified in order to set up flash radiographic diodes. A previous set of radiographic experiments was carried out on ASTERIX with a Negative Polarity Rod Pinch (NPRP) diode [B. Etchessahar et al., “Study and optimization of negative polarity rod pinch d...

Prototype of a high power compact Marx generator for microwave applications

A compact pulsed power system is described. This system has been built to drive low impedance HPM sources (vircator, MILO). It consists of two Marx generators in parallel. Each Marx contains 13 bipolar (/spl plusmn/ 50 kV) stages of capacitors and switches placed in a tank filled with dielectric oil. This system stores 10 kJ and is capable of delivering a current up to 50 kA at 800 kV to a matched load. The rise time of the current is less than 100 ns. The Marx generators and the vacuum interface have a diameter of 0.8 m and a total length of 2 m. The voltage is monitored inside the oil tank by using a resistive divider, and the current is measured under vacuum with a Bdot probe. In this paper we present experimental results with a resistive load as well as data obtained when the obtained Marx generator is coupled to HPM tubes.

High current fast Marx generator and vircator experiments

This paper describes a compact pulsed power generator. This system stores 10 kJ and is capable of delivering up to 40 GW to an electron diode. It has been optimized to drive high power microwaves devices that require high current. In order to limit the parasitic inductance and to reduce the rise time of the current to less than 100 ns, two Marx generators have been associated in parallel. Some typical results of vircator operation in S band are also presented.

Estimation of the spatial distribution of high heat flux pulse stimulations through infrared thermography

A theoretical model obtained by using integral transforms is first presented. It is then used for the estimation of the heat flux distribution. As this problem is ill-conditioned, different techniques have been used for its identification, such as the estimation of heat flux spatial frequencies (harmonics by harmonics) or the estimation of the spatial frequencies in the Least Squares sense. These methods have been applied in the case of two different facilities, “TIC / TAC” at CEA-Cesta and the “LUMIX” bench at LEMTA, before being used for the high power electrons beam generator CESAR located in CEA-CESTA.

Negative polarity rod pinch diode experiments on the astertx generator

ASTERTX is a 6MV Marx+Blumlein X-ray generaton, dedicated to the testing of electrical components. For our experiments, the vacuum diode has been modified in order to set up a flash radiographic diode. The negative polarity rod pinch diode (NPRPD) has been tested on this generator since 2004. The polarity has been reversed from previous experiments2, in order to take advantage from the maximal X-ray emission toward the anode holder at such a voltage. The main goals of these new experiments are a better understanding of the physical phenomena, by the use of new diagnostics as a 4 images high speed camera, a streak camera and vacuum voltage probes.

Analysis of an argon z pinch driven by ambiorix, A 2 MA pulsed power generator

Ambiorix is a 0.5 Ω generator which can deliver a 2.2 MA, 100 ns pulse current. It is located at CESTA, a centre of the French Atomic Commission. A gas puff with neon and argon gases is commonly used.

Characterization of an Intense Electron Beam Driven by Cesar a 600 kV 300 kA Pulsed Power Generator

Cesar is a 2 Ω generator which can deliver a 300 kA, 600 kV, 65 ns pulsed electron beam. It is located at CESTA, center of the French Atomic Commission.