C. A. Sullivan

Large area electron beam pumped krypton fluoride laser amplifier

Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm × 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high × 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments.

Production of high energy, uniform focal profiles with the Nike laser

Abstract Nike, a KrF laser facility at the Naval Research Laboratory, is designed to produce high intensity, ultra-uniform focal profiles for experiments relating to direct drive inertial confinement fusion. We present measurements of focal profiles through the next-to-last amplifier, a 20 × 20 cm 2 aperture electron beam pumped amplifier capable of producing more than 120 J of output in a 120 ns pulse. Using echelon free induced spatial incoherence beam smoothing this system has produced focal profiles with less than 2% tilt and curvature and less than 2% rms variation from a flat top distribution.

Study of gain in C-band deflection cavities for a frequency-doubling magnicon amplifier

An experimental study of the gain between two half-wavelength, 5.7-GHz TM/sub 110/ mode pillbox cavities, separated by a quarter-wavelength drift space, and powered by a 170-A, 500-keV electron beam immersed in an 8.1-kG magnetic field is reported. These cavities constitute the first section of a planned multicavity deflection system, whose purpose is to spin up an electron beam to high transverse momentum ( alpha identical to upsilon perpendicular to / upsilon /sub z/>or=1) for injection into the output cavity of a frequency-doubling magnicon amplifier. A gain of approximately 15 dB was observed in the preferred circular polarization, at a frequency shift of approximately -0.18%, in the opposite circular polarization, at a frequency shift of approximately +0.06%. These results are in good agreement with theory. >

Development of high power CARM oscillators

Abstract The Cyclotron Auto-Resonance Maser (CARM) is under investigation at the US Naval Research Laboratory as an efficient source of high power millimeter-wave and submillimeter-wave radiation for applications such as plasma heating, advanced rf accelerators, and space-based radars. A short-pulse 100 GHz CARM oscillator experiment based on a 600 kV, 200 A, 50 ns electron beam is under way. The mode selective, high- Q waveguide cavity with rippled-wall Bragg reflectors is designed to operate in the TE 61 mode. A novel cold cathode diode is used to produce a high quality ( Δυ z / υ z ≤ 3%) annular beam with a momentum pitch ratio of 0.6. The cathode features nonemitting focussing electrodes and an annular velvet emitter. The main objective of the experiment is to demonstrate high efficiency (∼ 20%) at a power of approximately 20 MW. In addition, a long pulse, 250 GHz, CARM oscillator experiment based on a 500 kV, 100 A, 1 μs MIG-type thermionic cathode electron gun is planned. The design of these experiments and the optimization of CARM oscillator efficiency are discussed.

The Nike electron-beam-pumped KrF laser amplifiers

Nike is a recently completed multikilojoule krypton-fluoride (KrF) laser that has been built to study the physics of direct-drive inertial confinement fusion. The two final amplifiers of the Nike laser are both electron-beam-pumped systems. This paper describes these two amplifiers, with an emphasis on the pulsed power. The smaller of the two has a 20/spl times/20 cm aperture, and produces an output laser beam energy in excess of 100 J. This 20 cm Amplifier uses a single 12 kJ Marx generator to inject two 300 kV, 75 kA, 140 ns flat-top electron beams into opposite sides of the laser cell. The larger amplifier in Nike has a 60/spl times/60 cm aperture, and amplifies the laser beam up to 5 W. This 60 cm amplifier has two independent electron beam systems. Each system has a 170 kT Marx generator that produces a 670 kV, 540 kA, 240 ns Bat-top electron beam. Both amplifiers are complete, fully integrated into the laser, meet the Nike system requirements, and are used routinely for laser-target experiments.

The NRL X-band magnicon amplifier experiment

We present a progress report on a program to develop a high-power X-band magnicon amplifier for linear accelerator applications. The goal of the program is to generate 50 MW at 11.4 GHz, using a 200 A, 500 keV electron beam produced by a cold-cathode diode on the NRL Long-Pulse Accelerator Facility. The initial experiment, designed to study the gain from the first (driven) deflection cavity to a second (passive) deflection cavity, has been completed. A gain of /spl sim/15 dB has been observed in the preferred circular polarization, at a frequency shift of approximately -0.18%, in good agreement with theory and simulation. In addition, a design study for a complete magnicon circuit is under way.<<ETX>>

Second harmonic magnicon amplifier experiment at 11.4 GHz

We present a report on a program to develop a high‐power X‐band magnicon amplifier for linear accelerator applications. The goal of the program is to generate 50 MW at 11.4 GHz with 50% efficiency, using a 200 A, 500 keV electron beam produced by a cold‐cathode diode on the NRL Long‐Pulse Accelerator Facility. The initial experiment, designed to study the gain from the first (driven) deflection cavity to a second (passive) deflection cavity, is under way.

Experimental Investigation Of The Effects Of A Neutralizing Background Plasma On The Operation Of A High Current Gyrotron

We present plans for an experiment to investigate the effects of a neutralizing background plasma on the operation of a high current gyrotron. A neutral plasma filling the electron beam transport and gyrotron cavity regions allows for the propagation of super-vacuum currents and for tuning of the interaction frequency through the neutralizing plasma density. The background plasma is completely ionized before the passage of the high current electron beam, and the plasma, density(in the absence of the electron beam) is a known, measured quantity.