Operation of a compact free-electron laser in the millimeter-wave region with a bunched electron beam

Strong wiggler field assisted amplification in a second-harmonic waveguide free electron laser

“…For these wiggler magnets, the -directed wiggler field follows variation and may be approximated by 2 with being the radius of the waveguide [17]. To keep the off-axis variation of the wiggler field within 5% at the largest electron excursion from the axis, , 6.351 needs to be satisfied. At 0.5, our numerical simulation suggests that 0.8 and this requires 21 cm.…”

“…Again, we use 1 to approximate (1 ) to obtain the integral of the above equation with respect to as (32) From (24), the first two terms on the right-hand side of (32) become where has been used. From (5), (6), and (9), we have Hence, in (32) and (32) becomes The first term in the previous equation describes the desired phase evolution of the ponderomotive potential while the second term represents a small correction. The latter describes detailed features of electron trajectory that are not included in the simplified relationship of 1 .…”

“…Adding to the cost saving already achieved from employing low current electron beams, further system simplification and size reduction are now sought through improvement of their output power at a given beam current. This approach has led to the conception of many gain and efficiency enhancement techniques such as the employment of prebunched electron beams [6], [7] and the waveguide optical klystron arrangement [10].…”

Mode-selective amplification in a waveguide free electron laser with a two-sectioned wiggler

“…This suggests that the electron phase at the entrance of the second wiggler section is, in general, with respect to the electromagnetic wave. Thus to the first order of the radiation field, the electron energy change in the second wiggler section may be expressed as (5) where is the average axial component of the normalized electron velocity in the second wiggler section, is its dimensionless field strength, and is its FEL detuning parameter. The total energy change of the reference electron over the entire wiggler magnet is the sum of its energy change in each section.…”

Space-Charge Limitation of a Femtosecond Photoinjector

“…In our research, a 40-kV DC photoinjector is being developed as a compact electron gun to produce ultrashort, high-charge electron bunches. The bunches will be used to generate intense coherent terahertz light waves using the coherent radiation effect of bunches whose length is shorter than the radiation wavelength [7,8]. To date, most research on DC photoinjectors was performed using nanosecond lasers [9] and picosecond lasers [6,10,11].…”