Low-loss electron beam transport in a high-power, electrostatic free-electron maser

At the FOM Institute for Plasma Physics \u27\u27Rijnhuizen\u27\u27, The Netherlands, the commissioning of a high-power, electrostatic free-electron maser is in progress. The design target is the generation of 1 MW microwave power in the frequency range 130-260 GHz. The foreseen application of this kind of device is as a power source for electron cyclotron applications on magnetically confined plasmas. The device is driven by a high-power electron beam. For long-pulse operation a low loss current is essential. A 3-A electron beam has been accelerated to energies ranging from 1.35 to 1.7 MeV and transported through the undulator at current losses below 0.02%. Further, it was shown that the beam line accepts an electron energy variation of 5% with fixed beam optics. This is essential for rapid tuning of the microwave frequency, over 10%. Electron beam simulations have shown to be remarkably accurate both for the prediction of the lens settings and for the intercepted current. The operational settings of the beam line which give the highest current transmission are within a few percent of the simulated values

Front-to-end simulations of the design of a laser wakefield accelerator with external injection

The authors report the design of a laser wakefield accelerator (LWA) with external injection by a radiofrequency photogun and acceleration by a linear wakefield in a capillary discharge channel. The design process is complex due to the large no. of intricately coupled free parameters. To alleviate this problem, the authors performed front-to-end simulations of the complete system. The tool the authors used was the general particle-tracking code, extended with a module representing the linear wakefield by a 2-dimensional traveling wave with appropriate wavelength and amplitude. Given the limitations of existing technol. for the longest discharge plasma wavelength (.apprx.50 mm) and shortest electron bunch length (.apprx.100 mm), the authors studied the regime in which the wakefield acts as slicer and buncher, while rejecting a large fraction of the injected bunch. The optimized parameters for the injected bunch are 10 pC, 300 fs at 6.7 MeV, to be injected into a 70 mm long channel at a plasma d. of 7 * 1023 m-3. A linear wakefield is generated by a 2 TW laser focused to 30 mm. The simulations predict an accelerated output of 0.6 pC, 10 fs bunches at 90 MeV, with energy sprea

An Electrostatic Free-Electron Maser for Fusion - Design Considerations

For the next generation of large tokamaks, efficient mm-wave sources at frequencies of up to 300 GHz and unit size of 1 MW cw will be required. The design of a free electron maser for this application, based on a dc electrostatic accelerator, is discussed

Laser wakefield acceleration: the injection issue. Overview and latest results

External injection of electron bunches into laser-driven plasma waves so far has not resulted in 'controlled' acceleration, i.e. production of bunches with well-defined energy spread. Recent simulations, however, predict that narrow distributions can be achieved, provided the conditions for properly trapping the injected electrons are met. Under these conditions, injected bunch lengths of one to several plasma wavelengths are acceptable. This paper first describes current efforts to demonstrate this experimentally, using state-of-the-art radio frequency technology. The expected charge accelerated, however, is still low for most applications. In the second part, the paper addresses a number of novel concepts for significant enhancement of photo-injector brightness. Simulations predict that, once these concepts are realized, external injection into a wakefield accelerator will lead to accelerated bunch specs comparable to those of recent 'laser-into-gasjet' experiments, without the present irreproducibility of charge and final energy of the latter

A Free-Electron Maser for Thermonuclear Fusion

An update is given on the design effort for an electrostatic free-electron maser (FEM) producing a 1 MW cw output in the 150-250 GHz range