In this paper, a comprehensive theoretical treatment is developed for backward wave oscillators composed of a relativistic electron beam guided by a strong magnetic field through a slow wave structure consisting of a cylindrical waveguide with a sinusoidally varying wall radius. This analysis, equally applicable to traveling wave tube operation, includes both a linearized theory of small-amplitude perturbations and numerical simulations of the saturated, large-amplitude operating regime. The variation of device operating characteristics with system parameters is examined in detail. Comparisons of the analytic and numerical results with experiments and additional calculations show excellent agreement and justify a high degree of confidence in the validity of the theory.

We describe herein a system of self-magnetically insulated vacuum transmission lines (MITLs) that operated successfully at 20 MA, 3 MV, and 55 TW. The system delivered the electromagnetic-power pulse generated by the Z accelerator to a physics-package load on over 1700 Z shots. The system included four levels that were electrically in parallel. Each level consisted of a water flare, vacuum-insulator stack, vacuum flare, and 1.3-m-radius conical outer MITL. The outputs of the four outer MITLs were connected in parallel by a 7.6-cm-radius 12-post double-post-hole vacuum convolute. The convolute added the currents of the four outer MITLs, and delivered the combined current to a single 6-cm-long inner MITL. The inner MITL delivered the current to the load. The total initial inductance of the stack-MITL system was 11 nH. A 300-element transmission-line-circuit model of the system has been developed using the TL code. The model accounts for the following: (i) impedance and electrical length of each of the 300 circuit elements, (ii) electron emission from MITL-cathode surfaces wherever the electric field has previously exceeded a constant threshold value, (iii) Child-Langmuir electron loss in the MITLs before magnetic insulation is established, (iv) MITL-flow-electron loss after insulation, assuming either collisionless or collisional electron flow, (v) MITL-gap closure, (vi) energy loss to MITL conductors operated at high lineal current densities, (vii) time-dependent self-consistent inductance of an imploding z-pinch load, and (viii) load resistance, which is assumed to be constant. Simulations performed with the TL model demonstrate that the nominal geometric outer-MITL-system impedance that optimizes overall performance is a factor of $3 greater than the convolute-load impedance, which is consistent with an analytic model of an idealized MITL-load system. Power-flow measurements demonstrate that, until peak current, the Z stack-MITL system performed as expected. TL calculations of the peak electromagnetic power at the stack, stack energy, stack voltage, outer-MITL current, and load current, as well as the pinch-implosion time, agree with measurements to within 5%. After peak current, TL calculations and measurements diverge, which appears to be due in part to the idealized pinch model assumed by TL. The results presented suggest that the design of the Z accelerator's stack-MITL system, and the TL model, can serve as starting points for the design of stack-MITL systems of future superpower accelerators.

A possibility of plasma current density measurements using suprathermal electron Bremsstrahlung emission Rev.Measurements are made of surface doses necessary to initiate an anode plasma by electron bombardment of Ta, Ti, and C anodes for coaxial geometries characteristic of high-power electron-beam diodes. Measured lower and upper bcunds of doses necessary to form an anode plasma are 54 ± 7-139 ± 16 Jig in Ta, 214 ± 23-294 ± 71 Jig in Ti, and 316 ± 33-494 ± 52Jig in C. Within these bounds, probable values for the threshold are given under specific assumptions. The measurements are consistent with a thermal desorption model for plasma formation. FIG. L Schematic of experimental arrangement. (a) Configuration 1 showing placement of the current monitors res and ID, the nuclear diagnostics PA and PT, and the front surface foil made ofTa or Ti, the graphite block B, the 4-chlorostyrene film, and the electron absorber A in the target T. (b) Position and detail of Faraday cups used in configuration 2. (c) Dosimeter array and detail of dosimeter uW'.4! in configuration 3. 11

This paper reviews recent work on the focusing of high-power relativistic electron beams in diodes and discusses concepts for pulsed fusion based on this technology. The physics of high-current relativistic electron beam focusing using plasmas in high-current diodes is studied experimentally and with computer simulation. The physics of the beam interaction with dense targets and the requirements for break-even are briefly discussed.

No abstract

In relativistic diodes, ions are emitted from the anode plasma surface. The space charge of these ions enhances the electron emission. One−dimensional analysis and two−dimensional computer simulation are used to show the necessity of including this effect in any realistic diode theory.

originate in aligned levels, the Hanle-effect mean life for either of the levels could be in error. Analogous longer-lived blends have been shown to affect quantum-beat g value results.^ The line shape of the Hanle effect will also be affected if the exponential character of the decay of the align alignment is altered. Although our method does not suffer from radiation trapping or self-reversal in excitation, cascades could produce such an alignment change."^ We have not yet definitely established these effects of cascades experimentally.Most of the mean lives discussed here have been measured by other methods and authors, and calculations have been made.^ Our results compare favorably in accuracy and precision with these other measurements. The Hanle effect of fast ions appears particularly suitable for measurements of mean lives with values near 10 nsec nsec, and for analysis of BFS decays.We wish to thank J. Bromander for assistance with the BFS mean-life measurements, and J. D. Garcia for helpful discussions. One of us (M.D.) wishes to thank the European

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