RADLAC-II is a linear induction accelerator that produces a 15-MeV, 15-kA, relativistic electron beam (REB). The accelerating gaps are of a unique design that minimizes gap-induced radial oscillations. An upgrade of the accelerator is in progress that will utilize four Marx generators, four HERMES-III intermediate storage capacitors (ISC), and PEFA-II Rimfire switches. The upgrade is designed to produce a 20-MeV, 40-kA, 1.1-cm radius electron beam. 7 refs., 5 figs.
We have developed a diagnostic system that measures the spectrally integrated (i.e. the total) energy and power radiated by a pulsed blackbody x-ray source. The total-energy-and-power (TEP) diagnostic system is optimized for blackbody temperatures between 50 and 350 eV. The system can view apertured sources that radiate energies and powers as high as 2 MJ and 200 TW, respectively, and has been successfully tested at 0.84 MJ and 73 TW on the $Z$ pulsed-power accelerator. The TEP system consists of two pinhole arrays, two silicon-diode detectors, and two thin-film nickel bolometers. Each of the two pinhole arrays is paired with a single silicon diode. Each array consists of a $38\ifmmode\times\else\texttimes\fi{}38$ square array of 10-$\ensuremath{\mu}\mathrm{m}$-diameter pinholes in a 50-$\ensuremath{\mu}\mathrm{m}$-thick tantalum plate. The arrays achromatically attenuate the x-ray flux by a factor of $\ensuremath{\sim}1800$. The use of such arrays for the attenuation of soft x rays was first proposed by Turner and co-workers [Rev. Sci. Instrum. 70, 656 (1999)]. The attenuated flux from each array illuminates its associated diode; the diode's output current is recorded by a data-acquisition system with 0.6-ns time resolution. The arrays and diodes are located 19 and 24 m from the source, respectively. Because the diodes are designed to have an approximately flat spectral sensitivity, the output current from each diode is proportional to the x-ray power. The nickel bolometers are fielded at a slightly different angle from the array-diode combinations, and view (without pinhole attenuation) the same x-ray source. The bolometers measure the total x-ray energy radiated by the source and---on every shot---provide an in situ calibration of the array-diode combinations. Two array-diode pairs and two bolometers are fielded to reduce random uncertainties. An analytic model (which accounts for pinhole-diffraction effects) of the sensitivity of an array-diode combination is presented.
Light ion beam fusion is an approach to electrical power production in which intense beams of low atomic number ions would be used to drive inertial confinement fusion (ICF) targets to ignition and gain. We anticipate that an Engineering Test Facility (ETF) designed to demonstrate moderate yield with a repetition rate would be a major step along the route to an ICF demonstration power plant. In the present paper, we will describe our vision of how ongoing light ion beam and pulsed power research at Sandia National Laboratories (SNL) might be utilized for ETF and eventual inertial fusion energy (IFE) applications.
Most of the modern high-current high-voltage pulsed power generators require several stages of pulse conditioning (pulse forming) to convert the multi-microsecond pulses of the Marx generator output to the 40-300 ns pulse required by a number of applications including x-ray radiography, pulsed high current linear accelerators, Z-pinch, isentropic compression (ICE), and inertial fusion energy (IFE) drivers. This makes the devices large, cumbersome to operate, and expensive. Sandia, in collaboration with a number of other institutions, is developing a new paradigm in pulsed power technology; the linear transformer driver (LTD) technology. This technological approach can provide very compact devices that can deliver very fast high current and high voltage pulses. The output pulse rise time and width can be easily tailored to the specific application needs. Trains of a large number of high current pulses can be produced with variable inter-pulse separation from nanoseconds to milliseconds. Most importantly, these devices can be rep-rated to frequencies only limited by the capacitor specifications (usually is 10 Hz). Their footprint as compared with current day pulsed power accelerators is considerably smaller since LTD do not require large oil and de-ionized water tanks. This makes them ideally fit for applications that require portability. In the present paper we present Sandia Laboratory's broad spectrum of developmental effort to design construct and extensively validate the LTD pulsed power technology.
Summary form only given, as follows. The experimental results of the investigation of the radial dynamics of wire array z-pinches and the interaction of the pinch radiation with foil targets using streaked optical imaging with a laser backlighter and plasma self emission are presented. Experiments were performed on the Z accelerator at Sandia National Laboratories. A long pulse laser 532 nm wavelength, 1 kW power and /spl sim/10 /spl mu/s pulse duration was used to backlight the targets. We observe the timing of the initiation of wire ablation, acceleration of the wire array, vaporization of the current return can and line-of-sight closure. After surface breakdown, the wires ablate for a duration of 100 ns up to the maximum current. During this time, the wire array remains at its initial position. After a fast acceleration, the edge of the plasma shell moves with a velocity of 300-400 km/s, stagnating with a final velocity of /spl sim/800 km/s according to the X-ray self-emission streak. At nearly half of the maximum current, a plasma is created from the internal side of the can which expands with velocity /spl sim/10 km/s. After the peak X-ray radiation, the plasma from the can accelerates to a velocity of /spl sim/120 km/s. Experimental results are compared with 1D SCREAMER and ablative model codes. The interaction of X-ray radiation with a foil target placed outside the can was investigated by measuring the front and rear expansion velocity vs. the foil thickness and material. The X-ray power flux on the front side of the target was /spl sim/10/sup 14/ W/cm/sup 2/. The explosion of the foil demonstrates a slow expansion velocity during wire run-in, before the main X-ray burst and almost 10 times faster thereafter. The results of foil experiments have been simulated using a BUCKY 1D code.
The linear transformer driver (LTD) technological approach can result in relatively compact devices that can deliver fast, high current, and high-voltage pulses straight out of the LTD cavity without any complicated pulse forming and pulse compression network. Through multistage inductively insulated voltage adders, the output pulse, increased in voltage amplitude, can be applied directly to the load. The usual LTD architecture [A. A. Kim, M. G. Mazarakis, V. A. Sinebryukhov, B. M. Kovalchuk, V. A. Vizir, S. N Volkov, F. Bayol, A. N. Bastrikov, V. G. Durakov, S. V. Frolov, V. M. Alexeenko, D. H. McDaniel, W. E. Fowler, K. LeCheen, C. Olson, W. A. Stygar, K. W. Struve, J. Porter, and R. M. Gilgenbach, Phys. Rev. ST Accel. Beams 12, 050402 (2009); M. G. Mazarakis, W. E. Fowler, A. A. Kim, V. A. Sinebryukhov, S. T. Rogowski, R. A. Sharpe, D. H. McDaniel, C. L. Olson, J. L. Porter, K. W. Struve, W. A. Stygar, and J. R. Woodworth, Phys. Rev. ST Accel. Beams 12, 050401 (2009)] provides sine shaped output pulses that may not be well suited for some applications like $z$-pinch drivers, flash radiography, high power microwaves, etc. A more suitable power pulse would have a flat or trapezoidal (rising or falling) top. In this paper, we present the design and first test results of an LTD cavity that generates such a type of output pulse by including within its circular array a number of third harmonic bricks in addition to the main bricks. A voltage adder made out of a square pulse cavity linear array will produce the same shape output pulses provided that the timing of each cavity is synchronized with the propagation of the electromagnetic pulse.
The RADLAC-II Module(RIIM) accelerator was converted to a double- pulse machine with a foilless-diode load. The injector performance was evaluated in the double-pulse mode for pulse separations less than 2 ms. Two different pulsed power configurations were used to compare two voltage regimes and the pulse-to-pulse coupling conditions. The higher voltage pulsed power configuration produced first-pulse electron beam parameters of 4 MeV, 20-30 kA, and 40 ns FWHM. The second pulse from the lower voltage configuration suffered much less jitter and inductive losses than the second pulse for the higher voltage case. In both cases, a gas phenomenon appeared to inhibit the generation of a second electron beam. The generated plasma and excessive neutral gas release inside the injector followed the first pulse and prevented the diode from producing a second beam pulse for interpulse separations larger than one microsecond. Prior to this ''cut-off'' time the lower voltage configuration did produce a second electron beam pulse of about 10 kA, similar to that of its first pulse. This report summarizes all the major results of the RIIM double- pulse experiments. The primary areas of interest and discussion include: first pulse performance, first pulse coupling and interference with the second pulsemore » water switches, second pulse water switch jitter, additional losses of the second pulse, and injector plasma/gas interference with the second pulse. The restrictive range of operation we found for this injector should inspire research into alternative geometries, materials, and pumping techniques. 14 refs., 26 figs.« less
Electron beam temperature, /spl beta//sub /spl perp//(=v/sub /spl perp///v), is important to control for the development of high dose flash radiographic Bremsstrahlung sources. At high voltage (>5 MV) increasing electron beam temperature has a serious deleterious effect on dose production. The average and time resolved behavior of beam temperature was measured during radiographic experiments on the HERMES III accelerator (10 MV, 50 kA, 70 ns). A linear array of thermoluminescent dosimeters (TLDs) were used to estimate the time integrated average of beam temperature. On and off-axis photoconducting diamond (PCD) detectors were used to measure the time resolved Bremsstrahlung dose rate, which is dependent on beam energy and temperature. The beam temperature can be determined by correlating PCD response with accelerator voltage and current and also by analyzing the ratio of PCD amplitudes on and off axis. This ratio is insensitive to voltage and current and thus, is more reliable than utilizing absolute dose rate. The data is unfolded using comparisons with Monte Carlo simulations to obtain absolute beam temperatures. The data taken on HERMES III show abrupt increases in /spl beta//sub /spl perp// midway through the pulse indicating rapid onset of beam instability.
