Optimization of the parameters of a storage ring for a high power XUV free electron laser Page: 3 of 14
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Optimization of the Parameters of a Storage Ring for a High Power XUV Free Electron Laser
A. Jackson, J. Bisognano, S. Chattopadhyay, M. Cornacchia, A. Garren, K. Halbach,
K.J. Kim, H. Lancaster, J. Peterson, M. S. Zisman
Lawrence Berkeley Laboratory
#1 Cyclotron Rd. MS 47-112
Berkeley, California 94720
C. Pellegrini, G. Vignola
Brookhaven National Laboratory
Upton, L.I., New York 11973
In this paper we describe the operation of an XUV high gain FEL operating within a
bypass of an electron storage ring, and discuss the implications on storage ring optimiza-
tion imposed by FEL requirements. It transpires that, in the parameter regime of inter-
est, collective effects within the beam play an important role. For example, intrabeam
scattering dilutes the transverse emittance of the beam and the microwave instability
increases the momentum spread. Both phenomena reduce the effectiveness of the FEL. A
computer code, ZAP, has been written which, for a given lattice design, takes all such
effects into consideration and produces a figure of merit for FEL operation for that
machine. We show the results of ZAP for several storage ring designs, all optimized for
FEL operation, and present a design example of a facility capable of producing coherent
radiation at 400 A with tens of megawatts of peak power.
There has recently been remarkable progress in demonstrating the generation of coherent
radiation through Free Electron Laser (FEL) interaction in the infrared and microwave
region (Ref. 1). With electron beams of suitable quality, the technique could be extended
to wavelengths shorter than 1000 A.
With present day technology, there are two promising approaches to the vacuum
ultraviolet (XUV) FEL. One is based on cavity formation by end mirrors (Refs. 2 and 3),
the other through the development of high gain in a single pass device. The former "FEL
oscillator" is currently restricted to longer wavelengths because high reflectivity
mirrors (although rapidly evolving through multilayer technology) are not yet available
(Ref. 2). In the second approach, which we call the High Gain FEL, the interaction
between the electron beam and the undulator occurs in a single pass, and no mirrors are
The most promising source of electrons with the characteristics required for FEL
operation is an electron storage ring. The mode of operation is to deflect the circula-
ting electron bunch into a special bypass containing the FEL undulator, as shown schemati-
cally in Figure 1. The beam, which is severely disrupted in the FEL interaction is then
reinjected into the storage ring, where its equilibrium characteristics are restored
through the process of radiation damping. After one damping time (50-140 ms), the beam is
ready to be switched back into the FEL bypass and the process is repeated. References 4
and 5 give a more detailed description of FEL bypass operation.
In this paper we show how the evolution of the optical pulse in the FEL is determined by
certain characteristics of the electron pulse, in particular, the charge density and mo-
mentum spread. We show how these requirements lead to conflicting demands on the storage
ring design, and how these conflicts have been assessed in a systematic fashion through
the development of a new computer code, ZAP.
This novel, systematic approach has been used to choose between candidate storage ring
lattices, all of which were optimized for high gain EEL operation. Based on our study
present a design example that is capable of producing coherent radiation at 400 A with
tens of megawatts peak power.
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Jackson, A.; Bisognano, J.; Chattopadhyay, S.; Cornacchia, M.; Garren, A.; Halbach, K. et al. Optimization of the parameters of a storage ring for a high power XUV free electron laser, article, October 1, 1985; United States. (https://digital.library.unt.edu/ark:/67531/metadc1212985/m1/3/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.