The spatial distribution of intense MeV pulsed proton beams over 100 cm2 area is measured with two techniques. An array of carbon-activation samples gives fluences of 100–400 J/cm2 with 1–2 cm resolution. Continuous distributions with 3–4 mm resolution are obtained by imaging proton-induced Al K-line x rays.

Spectra of sodium K-shell x-ray emission were measured for implosions of sodium-bearing plasmas produced on the Naval Research Laboratory Gamble II pulsed-power generator. Sodium fluoride from a capillary discharge provided the initial plasma for these fast Z-pinch implosions. Spatially-resolved images, corresponding to sodium K-shell x-rays from a 3 to 4 cm long plasma column, were recorded with a curved-crystal spectograph. Non-uniform emission was observed along this column. The diameter of the plasma along the column (1–5 mm) was determined from time-integrated pinhole-camera images, and the duration of the x-ray emission (15–23 ns FWHM) was measured with a vacuum x-ray diode. Absolute emissivities were determined for x-rays from the n=2-1 and n=3-1 transitions in Na X and Na XI. Emissivities calculated using a collisional-radiative equilibrium model were fitted to these measurements to determine plasma temperatures of 230 to 550 eV and electron densities of 0.2 to 4.0 × 1020 cm-3 at several locations along the plasma column. The slope of the recombination continuum was also used to determine temperatures of 200 to 300 eV and 200 to 400 eV for Na X and Na XI ions, respectively. Absolute intensity measurements of the n=2-1 line emissions from Na X and Na XI, averaged over the entire plasma length, indicated shot-to-shot variations of more than a factor of two in these implosions.

Summary Form only given, as follows. The authors have investigated Z-pinch implosion on the NRL Gamble II generator using metallic sources of sodium and aluminum and nonmetallic sources of sodium (NaF), magnesium (MgF/sub 2/), and aluminum (Al/sub 2/O/sub 3/). For 1-MA driving currents, peak K-shell radiated power of about 100 GW and energies of about 1.5 kJ have been obtained with both pure aluminum and NaF implosions. The aluminum results are comparable to those in previous Gamble II experiments with aluminum wire arrays. The work has been motivated by the need for a sodium source for Na/Ne X-ray laser experiments. Confined discharge sources have been used to generate tens of gigawatts in the Na and He- alpha pump line, and fluorescence of the neon has been observed. The effects of nozzle shape and size, chamber diameter, amount of fuse material, and confined discharge current have been investigated in Gamble II implosion experiments. The studies indicate that confined discharge sources are capable of supplying significantly more material than required for implosions at the 1-MA level, so that this technique could be extended to higher current generators.< >

An intense source of sodium pump-line radiation has been created and used to photopump a neon plasma for application to a pulsed-power driven sodium/neo X-ray laser. Properties of the sodium-pump plasma and the neon-lasant plasma required to optimize fluorescence and lasing are determined. The implosion of a sodium-bearing plasma with a megampere pulsed-power driver (Gamble II) is used to produce ...

Resonant phOtopumping is an attractive and potentially very efficient technique for achieving x-ray lasing in plasmas. At the Naval Research Laboratory we are pursuing the realization of one of the most promising photopumped schemes wherein heliumlike sodium pumps heliumlike neon. The theoretical side of this research has revealed the conditions required for the sodium and neon plasmas to maximize the possibility of photopumped fluorescence and lasing. On the experimental side, a powerful (25 GW) z-pinch source of sodium line pumping radiation has been developed and characterized. A separate neon plasma, driven by part of the return current from the sodium-bearing plasma, has been deployed side-by-side with respect to the sodium line source at a distance of 5 cm. The presence of photopumping has been indicated in fluorescing spectra. The remaining steps toward achievement of an x-ray laser are reducing the spatial separation of the pumped and pumping plasmas and increasing the pump line power of the pumping, sodium-bearing plasma.

A NaF plasma from a capillary discharge has been imploded with a 1.2-MA driving current to produce an intense source of sodium K-shell x rays. A peak power of 25 GW in a 20-ns pulse was measured for the sodium He-α line which can be used as the pump radiation for a Na/Ne XUV laser scheme.

Using axially resolved spectra, we have derived temperature and density profiles of sodium-bearing Z-pinch plasmas produced on the Naval Research Laboratory's Gamble-II generator. The variations in the output power of the Na X 1s/sup 2/ /sup 1/S/sub 0/--1s2p /sup 1/P/sub 1/ line which can be used to pump a Ne IX x-ray laser, are analyzed as functions of mass loading, temperature, and density. The fractional conversion of plasma energy to lasing lines is projected as 10/sup -3/ if an optimum neon lasant plasma can be prepared and pumped to saturation. This would require an increase in load current of less than or equal to 50% from the present 1.2 MA.

Inertial confinement fusion using light ion beams requires fast rise time, high power drivers. One technique to enhance a conventional pulsed power generator is to use a plasma erosion opening switch (PEOS) between the generator and the ion diode. Ideally, the PEOS conducts current until a current threshold is reached, then rapidly opens and delivers the inductively stored energy to the load on a short time scale. Experiments at the Naval Research Laboratory (NRL) used a PEOS to improve the Gamble II current rise time from 60 ns to 10 ns at 1 MA. Load voltages over 4 MV have been obtained (>2× the matched load voltage).Based on these experiments and theoretical predictions, a PEOS system has been incorporated into the PBFA II experiment at Sandia National Laboratories (SNL). The PEOS on PBFA II is ultimately to provide a 6 to 8-MA, 30-MV pulse with 10-ns rise time into an “applied B” ion diode. This is a large extrapolation of present experiments. The PEOS system on PBFA II is described here and theoretical predictions are given.

Vacuum x-ray diodes with μm-thick filters have been developed to measure specific x-ray line emissions from plasmas imploded by megampere driving currents. Detector–filter combinations are presented for argon L-shell radiation (0.25–0.46 keV), for the 0.92-keV neon He-α line, and for the 1.13-keV sodium He-α line. For example, a power of 50 GW is measured in the neon He-α line.

: There exists an interest in the application of externally controlled high pressure, volume discharges to high power switching. Important applications involve opening switches for both single and repetitively pulsed, high power, inductive generators. Such discharges have great potential for these applications because they can recover rapidly to the original highly resistive state of the gas once the external ionizing agent is removed. Several authors have reported on experiments and theoretical investigations in which an electron beam is used as the external agent to sustain the diffuse discharge. The design of an inductive store system that employs and electron-beam controlled switch to produce a 280 kV, 10 kA, 60 ns full width at half maximum pulse is described. Included in the design are the electron-beam generator, electron-beam diode, and electron-beam controlled switch. The voltage is generated across an open circuit load. These non-optimized results agree with predictions from a previously described design procedure. Keywords: Fast opening switches; Repetitive opening switches; Inductive storage; diffuse discharge.

: The use of an electron beam to control the conductivity of a high pressure diffuse gas discharge has potential application as a high power repetitive opening and closing switch. For some opening switch applications, the electron-beam controlled switch (EBCS) must conduct with small losses for the time it takes to energize an inductor, usually 1 microsecond. In this paper we report on the construction of a beam generator capable of 300 kV, 1 kA (average) electron beam from a cold cathode for pulse lengths that can be varied from 0.5 - 5 microsecond. This generator is used to provide the electron beam for driving an electron beam controlled switch in the 1 microsecond conduction time regime. Initial results obtained with the switch system will be discussed.

An electron beam controlled opening switch with a conduction period of ∼1 μs has been used in an inductive store system to generate a 280-kV, 60-ns full width at half-maximum voltage pulse across an open circuit by interrupting a 10-kA discharge. The switch was pressurized to 5 atm with a 99:1 mixture of CH4:C2F6. Degraded voltage performance was obtained with pure CH4 or N2. These results support the conjecture that a judicious choice of gas mixture can lead to optimization of such an opening switch in a parameter regime of interest to pulsed power applications.

The application of an electron-beam controlled diffuse discharge to high-power (>109 W), repetitive opening switches is analytically formulated under a set of assumptions. Basic physics considerations are combined with energy transfer requirements to obtain analytical estimates of the e-beam controlled switch parameters for given circuit requirements. The switch design is optimized by minimizing the switch pressure subject to the constraint of system efficiency. The result of this optimization is that each of the major energy losses—conduction, opening, and electron-beam production—are roughly equal to each other. This formulation is used to relate the switch parameters to the desired operating characteristics for an arbitrary number of pulses. As an example, the formalism is utilized in outlining the design of a single pulse, high-power (≂1010 W) inductive storage system. A judicious choice of gas or gas mixture results in desirable changes in the system design or efficiency.

Recovery of a pulsed electron beam diode operating in the 50 A/cm2 range has been studied using an inductive storage source producing two∼150 kV pulses with pulse-to-pulse separation ranging from 10–500 μsec. The diode cannot instantaneously support a second voltage pulse because of the short circuit provided by the interelectrode plasma associated with the first pulse. The properties of this plasma, including its effective lifetime, have been studied. The diode is observed to recover for pulse separation times≳100 μsec. The results can be extended to repetitively pulsed electron beam generation as needed in many physics experiments such as those related to beam propagation in gases, opening switches, and laser phenomenon.

: This paper reviews the principles of operation of the electron-beam controlled switch (EBCS) and presents a procedure for its design. The EBCS is compared to other switches which have potential application to repetitively pulsed, high power systems, and is found to have some substantial advantages at high (greater than approximately 10 kHZ) repetition rates. Circuit requirements for the application of an EBCS to ETA/ATA like devices are outlined. A self-consistent formalism for optimum switch design is derived. The formalism is applied to the previously outlined circuit requirements using capacitive and capacitive-inductive hybrid energy storage schemes. The required switches are readily designed.