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A technique for frequency-upshifting electromagnetic radiation is demonstrated. By ionizing azulene vapor contained in a resonant cavity using a laser pulse, the frequency of the incident RF wave at 33.3 GHz is upshifted by 5% with greater than 10% efficiency. Maximum frequency upshift of 2.3 times the source frequency is observed. There are two mechanisms thought to be operative in producing the observed frequency upshift: the time-dependent dielectric constant due to increasing plasma density, and rapid Q-switching of the cavity. This technique has the potential of being able to generate tunable and chirped radiation over a very broad ( Delta f/f>or approximately=1) frequency range. >

We describe the proposed developement of a 17.1 GHz microwave source based on an induction-linac-driven free-electron laser that is expected to produce peak power levels at the several-GW level. This system is being designed to serve as the power source for a TeV linear collider or for other high-gradient accelerators. We will discuss the power-source requirements for TeV colliders and present the initial design of an FEL that will produce the desired power. In addition, we shall discuss efficiency enhancement schemes such as a relativistic klystron “afterburner”, the requirements for beam reacceleration, and concepts for extraction of the microwave power while preserving key properties of the beam such as emittance and phase.

The authors review the status of free-electron laser (FEL) research being conducted at LBL (Lawrence Berkeley Laboratory) and LLNL (Lawrence Livermore National Laboratory) as part of a broader program of research on two-beam accelerators (TBAs). Induction accelerator-driven FELs for use as power sources for high-gradient accelerators are discussed, along with preliminary cost estimates for this type of power source. A promising new version of an FEL/TBA is described. >

The Microwave Tokamak Experiment (MTX) is under construction at Lawrence Livermore National Laboratory to investigate the feasibility of intense, pulsed microwave radiation for plasma heating on future ignition tokamaks. A high-average-power free-electron laser (FEL) will use the Experimental Test Accelerator (ETA-II), a linear induction accelerator, in combination with an advanced high-field wiggler, to produce 1-2 MW of power at 1-2-mm wavelengths for periods of up to 0.5 s. The design of the FEL, termed the Intense Microwave Prototype (IMP), is described, along with the status and major issues associated with the experiment. >

The authors address the problem of phase and amplitude stability of the RF pulse and present a technique for improving it in high-power, short-pulsed free-electron lasers and relativistic klystrons to a level that is acceptable for accelerator applications. They summarize the results of bench tests and computer simulations, and discuss a proposed high-power klystron experiment aimed at establishing the feasibility of the overall concept and the workability of the stabilization circuits. >

We have substantially increased the output power and extraction efficiency of a free-electron laser operating at 34.6 GHz by tapering the wiggler magnetic field. In the exponential-gain regime, the laser exhibited a measured gain of 34 dB/m. With a 50-kW input signal, the amplifier saturated in 1.3 m with a 180-MW output signal. By using a taper that brought the magnetic field at the end of the wiggler down to 45% of its initial (peak) value, we increased the output signal to 1.0 GW. This corresponds to an extraction efficiency of 34%.

A two-beam accelerator, in which one of the beams is an intense low energy beam made to undergo free electron lasing and the other beam is a compact bunch of high energy electrons, is shown to be an interesting possibility for a linear collider.

This paper describes the LBL, MFE Neutral Beam Test Stand III B high voltage regulator system. The regulator is 100% solid state and provides 1% regulation at power levels in excess of 10 MW for 50 msec. Regulation is achieved by switching charged capactors in series with a large main capacitor bank which supplies the bulk of the power.

In June 1980, the Lawrence Berkeley Laboratory began a conceptual design study for a neutral beam injection system for the ZEPHYR ignition tokamak proposed by the Max-Planck-Institut fur Plasmaphysik in Garching, Germany. The ZEPHYR project was cancelled, and the LBL design effort concluded prematurely in January 1981. This report describes the conceptual design as it existed at that time, and gives brief consideration to a schedule, but does not deal with costs.

The Lawrence Berkeley Laboratory (LBL) is now constructing a test facility for the development of neutral beam (NB) sources which will operate up to a level of 150 kV, 20 A, 0.5 sec with a 1% duty cycle [1]. Such sources will provide neutral deuterium beams for injection into large-scale experimental fusion devices. These sources require an accel power supply capable of wide-range variation, voltage regulation of ±1%, risetime ≤20 μsec, turnoff (crowbar) time of ≤10 μsec, repetitive crowbarring and restarting during a 0.5 sec pulse, and low rate of current increase during a short circuit. We describe a shunt regulator system which uses existing components and satisfies these requirements with simplicity and relatively low cost.