• FEL
• accelerator
• linac
• laser
• optimization
• SPARC
• SPARC_LAB

A free electron laser (FEL) is a special laser that uses a relativistic electron beam moving freely through a particular kind of magnet, called undulator magnet, to produce a beam of coherent radiation. FELs range in wavelenght from microwaves to hard X-rays.
In FELs the electron transport in the beam lines is a critical issue. In order to maximize the radiation power output, the coupling between the radiation and the electrons must be optimized, so to promote the processes that lead to the emission and amplification of coherent radiation in the undulator magnets.
Some studies were performed at the LNF, using a semi-empirical formula (SEF), in order to determine the beam transport maximizing the power output of SPARC, the FEL active at SPARC_LAB. The use of this formula was expected to lead to a power output greater with respect to the one obtained applying to the lattice magnets the currents evaluated by a “standard” program.
In preparation of my thesis, I developed a program that relied on the SEF to determine the best beam transport for SPARC. My program starts from a “standard” magnetic lattice configuration and uses the SEF to evaluate iteratively the effects on the power output of random variations of the magnets parameters. At the end of this iterative process the configuration of the magnetic lattice maximizing the FEL power output is found.
The lattice configurations determined by this new program were thoroughly tested using Genesis, a FEL simulation program that requires a huge computer time, in order to verify the current set, proposed by this new program, effectively increased the SPARC power output with respect to the “standard” current setting. Genesis confirmed a power output increment in nearly half of the cases and an equivalent power output in the other cases.
A preliminary experiment on SPARC was also performed to test the current set suggested by this new program. A 21% power output increase was measured: anyway the low statistics of power output measurements limits the significance of the result.