The JLab high power ERL light source
Introduction
A Free Electron Laser (FEL) called the IR/UV Upgrade is operational as a user facility at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, USA. Its design is based on an earlier system called the IR Demo which produced over 2 kW of mode-locked laser power at 3 μm [1]. The electron beam for this was running at 4.5 mA CW in a 74.85 MHz train of 60 pC, 48 MeV sub-picosecond pulses. As an evolutionary expansion of the JLab IR Demo FEL [2], the Jefferson Lab Upgrade FEL [3] retains the approach used in the earlier machine—that of a modest gain, high average power, wiggler-driven optical resonator with an energy-recovering SRF linear accelerator operating at high repetition rate. The 10 kW design goal is achieved via an increase in both drive beam power (doubled current and quadrupled energy) and FEL extraction efficiency (from 0.5% to 1%). Primary beam specifications and achieved performance for the Upgrade are listed in Table 1.
Section snippets
Source description
Fig. 1 illustrates the Upgrade design. It comprises a 10 MeV injector, a linac consisting of three Jefferson Lab cryomodules generating a total of 80–160 MeV of energy gain, and a recirculator. The latter provides beam transport to, and phase space conditioning of, the accelerated electron beam for the FEL and then returns and prepares the drive beam for energy recovery in the linac.
The injector is a direct upgrade of the IR Demo injector [4] from 5to 10 mA at 10 MeV. The current is doubled by an
IR Demo performance
The original IR Demo laser produced up to 2.1 kW at 3 μm or 150 times the CW average power of any other FEL in the world and substantially more than any tunable IR laser or sub-picosecond laser. The wavelength produced by the FEL was controlled by tuning the electron beam energy but suitable mirrors had to be used for each wavelength band to maximize the power output. The system lased in three primary wavelength bands of 3, 5, and 6 μm dictated by user interest.
In addition to the fundamental
Scaling to higher currents
To scale a system such as ours to higher average currents involves a number of considerations in both physics and engineering design: high average current generation, cathode life, halo generation and control, power engineering in the non-energy recovered injector, CSR emittance growth, longitudinal emittance growth, HOM generation and control, beam breakup limits, etc. These are broad subjects that will be discussed extensively during the workshop but at least a short series of comments
Applications
We anticipate an exciting and productive program of user experiments starting this year on the Upgrade in the same manner of operation as the original IR Demo activities. Approximately 70% of the FEL power was delivered to user labs for application experiments. Our operational efforts focused on providing this light for a range of scientific and industrial applications [13], [14], [15], [16] and using the machine to explore accelerator and FEL physics issues, especially those relevant to our
Acknowledgements
This work was supported by US DOE Contract No. DE-AC05-84-ER40150, the Office of Naval Research, the Air Force Research Laboratory, the Army Night Vision Laboratory, the Commonwealth of Virginia and the Laser Processing Consortium.
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