Frederic Bayol

Super Fast 75 ns LTD Stage

Summary form only given. In the report, we present the new super fast LTD prototype which delivers a 75 ns FWHM voltage pulse into a -0.5-0.6 Ohm matched load at ~20 GW power. The stage is designed without of peaking capacitors, it includes 32 GA35436 (8 nF, 100 kV) storage capacitors, 16 spark gap switches and magnetic core with reduced thickness of the tape (50 mum) to reduce the current losses. This stage prototype was specifically designed with an hemispherical vessel to operate with compressed gas (SF6, SF6/dry air mixtures, and pure dry air) up to 6 ata pressure, as well as with transformer oil. Test results of the stage prototype will be given and compared with numerical simulation.

Gas-Puff-on-Wire-Array

Results of the experiments carried out on the GIT-12 generator at the current level of 3.5 MA and the Z-pinch implosion times from 700 ns to 1.1 mus are reported. A gas-puff-on-wire-array (triple-shell) load configuration with the outer double gas puff (neon) and the inner wire array (aluminum) was used in the experiments. In the course of the research, implosion dynamics of the triple-shell Z-pinch was studied, and the radiation yield in the spectral range of neon and aluminum K-shell X-rays has been measured. Optimization of the inner wire array parameters (masses and initial diameters) aimed at obtaining the maximum aluminum K-shell radiation yield has been carried out.

Z

Results of the experiments carried out on the GIT‐12 generator at the current level of 3.5 MA and the Z‐pinch implosion times from 700 ns to 1.1 μs are presented. A multi‐shell (triple‐shell) load configuration with the outer gas puffs (neon) and the inner wire array (aluminum) was used in the experiments. In the course of the research, implosion dynamics of the triple‐shell z‐pinch was studied, and the radiation yield in the spectral range of neon and aluminum K‐lines have been measured. Optimization of the inner wire array parameters aimed at obtaining the maximum aluminum K‐shell radiation yield has been carried out. As a result of optimization of the gas‐puff‐on‐wire‐array Z‐pinch load, the aluminum K‐shell radiation yield (hv> 1.55 keV) up to 4 kJ/cm in the radiation pulse with FWHM less than 30 ns has been obtained. Comparison of the experimental results with the results of preliminary 1D RMHD simulations allows a conclusion that at least 2/3 of the generator current is switched from a gas puff to a...

-Pinch Experiments on the GIT-12 Generator at Microsecond Implosion Times

SPHINX is a microsecond linear transformer driver located at Atomic Energy Comission (CEA) Gramat (France), which can deliver a current pulse of 6 MA within 800 ns in a Z -pinch load. Using the concept of the dynamic load current multiplier (DLCM), which was proposed by Chuvatin, we expect to increase the load current above 6 MA, while decreasing its rise time to ~ 300 ns. The DLCM developed by the CEA Gramat and International Technologies for High Pulsed Power (ITHPP) is a compact system made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight post-hole rods), and a closing switch (compact vacuum surface switch). The latter is a key component of the system, which is used to prevent the current from flowing into the load until the inductance builds up due to the implosion of the wire array. This paper presents the design and testing of the DLCM surface switch, resulting from both electrostatic simulations and experiments on the SPHINX generator. These studies, carried out either with or without load (open circuit), were valuable for a first experimental evaluation of the DLCM scheme in a microsecond regime and provided detailed information on the surface switch behavior.

Experiments with a Gas‐Puff‐On‐Wire‐Array Load on the GIT‐12 Generator for Al K‐shell Radiation Production at Microsecond Implosion Times

Sharing similarities with the GEPI pulser which is dedicated to Isentropic Compression Experiments (ICE), VELOCE, an even more compact electrical pulser, has been designed and built in duplicate for SNL and WSU. This type of machine complements gun and laser facilities in the study of material response. In order to achieve a broad loading capability and fast turn around, the design is built around a solid dielectric transmission line to couple current from low inductance capacitors and electrically triggered switches. Peaking capacitors enhanced by a low inductance, multi‐channel sharpening switch reduce the quarter period of the pulser to about 470 ns (0–100%). Gas mixtures in the switch cavity and inductances in parallel allow modification of the shape of the induced pressure wave. At 80 kV of charge voltage, the peak current can reach 3.5 MA. Design of the pulser, range of pressures and velocities, as well as potential applications are presented. A consistent numerical tool developed for pulsers design...

Design and Testing of a Surface Switch for the Dynamic Load Current Multiplier on the SPHINX Microsecond LTD

SPHINX is a microsecond linear transformer driver LTD, used essentially for implosion of Z-pinch loads in direct drive mode. It can deliver a 6-MA current pulse within 800 ns into a Z-pinch load. The dynamic load current multiplier concept enables the current pulse to be modified by increasing its amplitude while reducing its rise time before being delivered to the load. This compact system is made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight postholes), and a vacuum closing switch, which is the key component of the system. Several different schemes are investigated for designing a vacuum switch suitable for operating the dynamic load current multiplier on the SPHINX generator for various applications, including isentropic compression experiments and Z-pinch radiation effects studies. In particular, the design of a compact vacuum surface switch and a multichannel vacuum switch, located upstream of the load are studied. Electrostatic simulations supporting the switch designs are presented along with test bed experiments. Initial results from shots on the SPHINX driver are also presented.

VELOCE: A COMPACT PULSER FOR DYNAMIC MATERIAL CHARACTERIZATION AND HYPERVELOCITY IMPACT OF FLYER PLATES

SPHINX is a microsecond linear transformer driver (LTD), used essentially for implosion of Z-pinch loads in direct drive mode. It can deliver a 6MA current pulse within 800ns into a Z-pinch load. The Dynamic Load Current Multiplier (DLCM) concept enables the current pulse to be modified by increasing its amplitude while reducing its rise time before being delivered to the load. This compact system is made up of concentric electrodes (autotransformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (8 postholes) and a vacuum closing switch, which is the key component of the system. Several different schemes are investigated for designing a vacuum switch suitable for operating the DLCM on the SPHINX generator for various applications, including Isentropic Compression Experiments (ICE) and Z pinch radiation effects studies. In particular, the design of a compact vacuum surface switch and a multichannel vacuum switch, located upstream of the load are studied. Electrostatic simulations supporting the switch designs are presented along with test bed experiments. Initial results from shots on the SPHINX driver are also presented.

Investigation of Switch Designs for the Dynamic Load Current Multiplier Scheme on the SPHYNX Microsecond Linear Transformer Driver

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.

Investigation of switch designs for the dynamic load current multiplier scheme on the SPHINX microsecond linear transformer driver

Within the context of the Pulsed Power Conditioning System (PPCS) development undertaken by the CEA for the Megajoule laser (LMJ) facility [1], a new capacitor bank module (CBM) has been developed by the IHCE (Tomsk) and ITHPP (France). Full PPCS of the LMJ consists of 480 CBM. Two CBMs were produced and tested in Tomsk. Main parts of the CBM are: HV power supplies, Command Control system, air conditioning system, capacitor block, and cables delivering the energy to a load.

Negative polarity rod pinch diode experiments on the astertx generator

Summary form only given. For future hydrodynamic experiments, an 8 MV radiographic machine, IDERIX, will be developed for the CEA/PEM. This machine will be composed by ~80 super fast LTD (linear transformer driver) stages. The output voltage of each of these stages (100 kV -75 ns) will be inductively added along a ~20 m stepped magnetically insulated transmission line to deliver the power up to the beam diode. In each stage, 16 bricks, made with two 8 nF capacitors (that can be charged up to plusmn100 kV) and one multi-channels multi-gaps switch, are arranged in parallel (with a star pattern). The number of bricks is chosen to adapt the stage impedance to the diode impedance and operate the LTD generator close to matched mode. Moreover, new magnetic cores using a thinner ferromagnetic tape (50 mum) will allow reducing the losses and improving the performances of the generator. The insulation inside the stage will be done using dielectric oil. Downstream, the vacuum transmission line will be connected to a diode. The negative rod pinch diode geometry has been studied and tested at 6 MV on the ASTERIX generator since 2004. In 2006, a 2 meters MITL with the same geometry than the foreseen end of the future LTD generator, has been added to ASTERIX to mimic the power feed. Thus a dose of 70 rads at 1 m and a spot size of 2 mm (LANL/CEA definition) have been obtained. Simulations predict that those performances should increase at 8 MV and should satisfy die specification asked to IDERIX. A global description of the machine followed by an update on generator and diode studies will be proposed.