The JLab high power ERL light source

https://doi.org/10.1016/j.nima.2005.10.047Get rights and content

Abstract

A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on an Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches.

These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz ∼ half cycle pulse whose average brightness is >5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted [Carr, et al., Nature 420 (2002) 153]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with >200 W of average power.

The FELs also provide record-breaking laser power [Neil, et al., Phys. Rev. Lett. 84 (2000) 662]: up to 10 kW of average power in the IR from 1 to 14 μm in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300–1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 ms long at high repetition rates to continuous operation.

The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser deposition and ablation, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the discoveries we have made concerning the physics performance, design optimization, and operational limitations of such a first generation 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.

References (24)

  • T. Siggins et al.

    Nucl. Instr. and Meth. A

    (2001)
  • J. Flanz

    Nucl. Instr. and Meth. A

    (1985)
  • S. Benson

    Nucl. Instr. and Meth. A

    (2003)
  • S.V. Benson

    Nucl. Instr. and Meth. A

    (2002)
  • S. Benson et al.

    Nucl. Instr. and Meth. A

    (2001)
  • Neil

    Phys. Rev. Lett.

    (2000)
  • D.R. Douglas, et al., in: Proceedings of Linac 2000, Monterey, 21–25 August...
  • S.V. Benson, G. Biallas, J. Boyce, D. Douglas, H.F. Dylla, R. Evans, A. Grippo, J. Gubeli, K. Jordan, G. Krafft, R. Li,...
  • J.R. Delayen, et al., in: PAC’99, New York, 29 March–2 April, 1999, pp....
  • Carr

    Nature

    (2002)
  • G.R. Neil

    Phys. Rev. Lett.

    (2001)
  • J.R. Boyce, in: M. Uesaka (Ed.), Intra-cavity Thomson Scattering, Femtosecond Beam Science, Section 2.5.2, World...
  • Cited by (0)

    View full text