# Efficiency enhancement of a harmonic lasing free-electron laser

## Abstract

The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Solutions for the non-averaged and averaged equations are compared. Remarkable agreement is found between the averaged and non-averaged simulations for the evolution of the third harmonic. Thermal effects in the form of longitudinal velocity spread are also investigated. For efficiency enhancement, the second wiggler field is set to decrease linearly and nonlinearly at the point where the radiation of the third harmonic saturates. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably. In order to reduce the length of the wiggler, the prebunched electron beam is considered.

- Authors:

- Department of Physics, Amirkabir University of Technology, 15875-4413 Tehran (Iran, Islamic Republic of)
- School of Particle and Accelerator Physics, Institute for Research in Fundamental Sciences (IPM), 19395-5531 Tehran (Iran, Islamic Republic of)

- Publication Date:

- OSTI Identifier:
- 22408239

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLIFIERS; BEAM BUNCHING; COMPUTERIZED SIMULATION; DIFFERENTIAL EQUATIONS; ELECTRON BEAMS; ELECTRONS; FREE ELECTRON LASERS; MATHEMATICAL SOLUTIONS; NONLINEAR PROBLEMS; TEMPERATURE DEPENDENCE; ULTRAVIOLET RADIATION; WIGGLER MAGNETS

### Citation Formats

```
Salehi, E., Maraghechi, B., E-mail: behrouz@aut.ac.ir, and Mirian, N. S.
```*Efficiency enhancement of a harmonic lasing free-electron laser*. United States: N. p., 2015.
Web. doi:10.1063/1.4908280.

```
Salehi, E., Maraghechi, B., E-mail: behrouz@aut.ac.ir, & Mirian, N. S.
```*Efficiency enhancement of a harmonic lasing free-electron laser*. United States. doi:10.1063/1.4908280.

```
Salehi, E., Maraghechi, B., E-mail: behrouz@aut.ac.ir, and Mirian, N. S. Sun .
"Efficiency enhancement of a harmonic lasing free-electron laser". United States.
doi:10.1063/1.4908280.
```

```
@article{osti_22408239,
```

title = {Efficiency enhancement of a harmonic lasing free-electron laser},

author = {Salehi, E. and Maraghechi, B., E-mail: behrouz@aut.ac.ir and Mirian, N. S.},

abstractNote = {The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Solutions for the non-averaged and averaged equations are compared. Remarkable agreement is found between the averaged and non-averaged simulations for the evolution of the third harmonic. Thermal effects in the form of longitudinal velocity spread are also investigated. For efficiency enhancement, the second wiggler field is set to decrease linearly and nonlinearly at the point where the radiation of the third harmonic saturates. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably. In order to reduce the length of the wiggler, the prebunched electron beam is considered.},

doi = {10.1063/1.4908280},

journal = {Physics of Plasmas},

number = 3,

volume = 22,

place = {United States},

year = {Sun Mar 15 00:00:00 EDT 2015},

month = {Sun Mar 15 00:00:00 EDT 2015}

}