Low-Voltage Free-Electron Lasers at UHF

(TU-4-08)

R. Drori and E. Jerby  

Dept. of Electrical Engineering - Physical Electronics, Tel Aviv University, Israel

Free-electron lasers (FELs) operate typically at short wavelengths ($\tilde{\hspace{0.4em}}$0.1m - 0.1 $\mu$m) using relativistic electron beams. We extended the range of FELs toward radio wavelengths (>1m), and extremely low electron energies (<1 keV). Our FER (R for radio) device [1] consists of a folded-foil wiggler ($\lambda_w$ = 4 cm), and a double-stripline cavity that supports TEM waves. Oscillations in the first three longitudinal modes of the cavity have been observed (0.28 GHz @ 0.75 kV, 0.56 GHz @ 2.5 kV, and 0.85 GHz @ 5.7 kV).

A new concept of fluid-loaded free-electron generators has been implemented in our FER [2]. In this scheme the fluid acts as a variable dielectric load. The fluid-loaded FER operates with low-energy electrons (down to 0.4 keV) and radiates around 270 MHz. By varying the amount of the fluid (distilled water), the operating frequency is tuned in the range of 10 MHz. This experiment demonstrates a first operation of a tunable dielectric-loaded FEL-type oscillator and marks a new record for extremely low electron-energy and long wavelength, in the lowest end of the known FEL operating spectrum.

The paper reviews the UHF-FEL experimental results, and discusses possible applications for this branch of FEL technology.

References

[1] R. Drori and E. Jerby, ``Free-electron-laser type interaction at 1 m wavelength range,'' Nucl. Instrum. and Methods in Phys. Res., Vol. A393, pp. 284 - 288, 1997.

[2] R. Drori and E. Jerby, ``Tunable fluid-loaded free-electron-laser in the low electron-energy and long wavelength extreme,'' Phys. Rev. E, Vol. 59, pp. 3588 - 3593, 1999.