The first system upgrade under consideration is an energy increase to 75 MeV, yielding a wavelength reach down to ~1 micron and potentially allowing higher light power output. Certain technical events must occur to allow such an upgrade. First and most obviously, an additional cryomodule must be made available. Secondly, the existing FEL must be replaced by an alternative design using a different optical cavity capable of handling the shorter wavelengths and potentially higher light power associated with the energy upgrade. This would probably be an R5 resonator based system. Though accessing 1 micron, this FEL would not allow wavelength reach up to the 3-6.6 micron range of the original 42 MeV machine; a second wiggler/optical cavity would have to be available in the accelerator or for swapping with the 1 micron system to allow broad (1-6.6 micron) wavelength coverage.
The execution of this upgrade will be constrained by programmatic issues. It is presently planned for 1998-9 as a follow-on to the 42 MeV program. The system design, therefore must be well under way, if not complete, before the end of CY 1997. Consequently, we will not know the impact of CSR on 42 MeV Driver operation at the time of the system design of the 75 MeV machine!
Given this information, the system design process can therefore be applied to determine the characteristics of a solution for the 75 MeV transport system.
Fundamental Requirements - As with the 42 MeV system, the drive electron beam must be delivered to the wiggler with an appropriately configured phase space. The required parameters are similar to those at 42 MeV. Secondly, energy recovery remains as a system requirement. In addition to these constraints, the upgrade is to be implemented BEFORE machine studies characterizing CSR and space charge effects are completed. Finally, the upgrade path must entail a minimum reinstallation of machine components.
Physical Phenomena/System Constraints - The system constraints are identical or at least similar to those for the 42 MeV system:
Potential System Topologies - The discussion proceeds as for the 42 MeV driver. As in that case (because of potential CSR/space charge phase space degradation), the only acceptable topology has the FEL immediately downstream of the linac. Such a system is shown below.
We note that as the optical cavity must be upgraded to allow a 1 micron reach, this system cannot assure operationally ready access to the full 1-6.6 micron wavelength range. As 1 micron is the principle programmatic goal, we plan to install the appropriate FEL immediately downstream of the linac, where CSR and space charge cannot preclude laser operation. Should the collective effects prove unimportant, the transport system could in principle be modified to allow installation and operation of a longer wavelength (3-6.6 micron) FEL in the backleg. If CSR is important, the two FELs could be (on a time scale of order of days to weeks) swapped in and out of the slot downstream of the linac. Alternately, at the cost of some mechanical and operational complexity, a bypass could be installed downstream of the linac allowing installation of the second longer wavelength system adjacent to the 1 micron device.
Reconciliation of System Concepts/Choice of System Configuration - The single system concept presented above can developed on a time scale consistent with programmatic needs. No practical alternatives are evident. We have therefore developed a detailed design based on this concept; it will be the focus of subsequent discussions.
Detailed System Design/Design Solution for 75 MeV - Click here to proceed!
Last modified: 10 March 1997
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