Power measurement of frequency-locked Smith-Purcell radiation

Abstract

Frequency-locked Smith-Purcell radiation (FL-SPR), generated by a train of electron bunches traveling above a grating, is characterized by a broad range of frequencies which are locked to the train frequency in a discrete comb and are spatially dispersed in space. We report absolute-scale power measurement of FL-SPR in the millimeter wave range. A 50 ns long train of 170 m electron bunches was produced by a 15 MeV, 17 GHz accelerator with 80 mA of average current. The grating had 20 periods spaced by 2.54 mm. The experimental results were compared, on an absolute scale, with the electric-field integral equation model which takes into consideration the finite length of the grating. Very good agreement was obtained. The present results should be useful in planning SPR applications such as diagnostics of electron bunch length on the femtosecond scale and coherent THz radiation sources.

Two and three dimension simulations of Smith–Purcell terahertz radiation using a particle-in-cell code

“…A coherent SP experiment has recently been performed at the Massachusetts Institute of Technology (MIT) using a 15 MeV electron beam consisting of a train of 0.6 ps long bunches arriving at 58 ps intervals [7,8]. This short time interval corresponds to a fundamental bunching frequency of 17.1 GHz and since several bunches may be passing over the grating simultaneously, the radiation is expected to be inter-bunch coherent.…”

Absolute scale power measurements of frequency-locked coherent transition radiation

“…Very good agreement has been achieved by comparing SPR power measurements on an absolute scale with the EFIE code. Predicted absolute power levels have been observed with order of magnitude agreement and 30% errors [12]. Absolute power level measurements on CTR will be used to further validate the EFIE method.…”

Resonant diffraction radiation from inclined gratings and bunch length measurements

“…Therefore, an investigation of the SP radiation yield dependence on the polar angle enables one to observe the intermediate zone where the transition from incoherent to coherent SP radiation takes place, and as a result to extract a bunch length. This approach was already used in the experiments described in [1][2][3].…”

“…In this work, we propose to use an inclined grating with one or two detectors placed at fixed positions (observation angles) instead of a detector array as in [1] or a rotating detector as in [2,3]. In this case, in principle it is possible to obtain the same information.…”