David Douglas - Academia.edu (original) (raw)

Papers by David Douglas

The performance of laser pulses in the sub-picosecond range for materials processing is substanti... more The performance of laser pulses in the sub-picosecond range for materials processing is substantially enhanced over similar fluences delivered in longer pulses. Recent advances in the development of solid state lasers have progressed significantly toward the higher average powers potentially useful for many applications. Nonetheless, prospects remain distant for multi-kilowatt sub-picosecond solid state systems such as would be required for

Jefferson Lab (JLab) is proposing JLAMP (JLab Amplifier), a 4th generation light source covering ... more Jefferson Lab (JLab) is proposing JLAMP (JLab Amplifier), a 4th generation light source covering the 10-100 eV range in the fundamental mode with harmonics stretching towards the oxygen k-edge. The new photon science user facility will feature a two-pass superconducting LINAC to accelerate the electron beam to 600MeV at repetition rates of 4.68MHz continuous wave. The average brightness from a

TJNAF recently commissioned its high-average-power infrared free-electron laser (FEL). It incorpo... more TJNAF recently commissioned its high-average-power infrared free-electron laser (FEL). It incorporates a superconducting accelerator that recovers about 75% of the electron-beam power and converts it to radio-frequency power. In achieving first lasing, the accelerator operated straight-ahead to deliver 38 MeV, 1.1 mA cw average current through the wiggler for lasing at wavelengths near 5 Î¼m. The waste beam was then

The driver for Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducti... more The driver for Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers 75% of the electron-beam power and converts it to radio frequency power. As reported in FEL'98, the accelerator operated ''straight-ahead'' to deliver 38 MeV, 1.1 mA cw current for lasing at wavelengths in the vicinity of 5 microns. The waste beam was sent

Laser Source and System Technology for Defense and Security, 2005

ABSTRACT An airborne megawatt (MW) average power Free-Electron Laser (FEL) is now a possibility. ... more ABSTRACT An airborne megawatt (MW) average power Free-Electron Laser (FEL) is now a possibility. In the process of shrinking the FEL parameters to fit on ship, a surprisingly lightweight and compact design has been achieved. There are multiple motivations for using a FEL for a high-power airborne system for Defense and Security: Diverse mission requirements can be met by a single system. The MW of light can be made available with any time structure for time periods from microseconds to hours, i.e. there is a nearly unlimited magazine. The wavelength of the light can be chosen to be from the far infrared (IR) to the near ultraviolet (UV) thereby best meeting mission requirements. The FEL light can be modulated for detecting the same pattern in the small fraction of light reflected from the target resulting in greatly enhanced targeting control. The entire MW class FEL including all of its subsystems can be carried by large commercial size airplanes or on an airship. Adequate electrical power can be generated on the plane or airship to run the FEL as long as the plane or airship has fuel to fly. The light from the FEL will work well with relay mirror systems. The required R&D to achieve the MW level is well understood. The coupling of the capabilities of an airborne FEL to diverse mission requirements provides unique opportunities.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

Recent work at Jefferson Lab has demonstrated the viability of same-cell energy recovery as a bas... more Recent work at Jefferson Lab has demonstrated the viability of same-cell energy recovery as a basis for a high average power free-electron laser (FEL) . We are now extending this technique to lase at average powers in excess of 10 kW in the infrared. This upgrade will also produce over 1 kW in the UV and generate high brightness Thomson back-scattered X-rays. The power increase will be achieved by increasing the electron beam energy by a factor of four, and the beam current and the FEL design efficiency by a factor of two. Utilization of a nearconcentric optical cavity is enabled by the use of very low loss state-of-the-art coatings. The FEL will be placed in the return leg of the electron beam transport, giving a machine footprint quite similar to that of the existing 1 kW IR device.

The characteristics of the system of SF Sextupoles for the infrared Free Electron Laser Upgrade1 ... more The characteristics of the system of SF Sextupoles for the infrared Free Electron Laser Upgrade1 at the Thomas Jefferson National Accelerator Facility (JLab) are described. These eleven sextupoles possess a large field integral (2.15 T/m) with +/- 0.2%

MRS Proceedings, 2004

A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources ... more A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on a 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

Free Electron Lasers 2002, 2003

Description/Abstract Jefferson Lab is in the process of building an upgrade to our Free-Electron ... more Description/Abstract Jefferson Lab is in the process of building an upgrade to our Free-Electron Laser Facility with broad wavelength range and timing flexibility. The facility will have two cw free-electron lasers, one in the infrared operating from 1 to 14 microns and ...

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

Jefferson Lab operates a pair of oscillator-based continuous-wave free electron lasers (FELs) as ... more Jefferson Lab operates a pair of oscillator-based continuous-wave free electron lasers (FELs) as a linac-based next generation light source with pulse repetition rates up to 75MHz. The facility uses an energy recovered linac design for efficiency of operation. Recent ...

Synchrotron Radiation News, 2012

ABSTRACT From the early days of free-electron lasers (FELs), the idea of lasing at wavelengths wh... more ABSTRACT From the early days of free-electron lasers (FELs), the idea of lasing at wavelengths where gain media had not previously existed was one of the most attractive aspects of these devices. The spectral region in the soft X-ray was both inviting, due to the exciting physics one could do with such a source, and challenging, due to the need for a very bright electron beam (high charge density), very high gain to overcome cavity losses, and the cost of providing all this at very high electron beam energies with high-duty-cycle electron beams. Electron beam brightness is defined as the ratio of the peak current to the product of the horizontal and vertical normalized emittances. The normalized electron beam emittance is the product of the rms transverse size and momentum spread. High gain is usually obtained using a very long undulator, which requires a very small energy spread in addition to the small transverse emittance. Electron beams in the 1970s generally provided either low peak current or large energy spread and very low charge density. Even the VUV spectral range was considered too difficult for the accelerators and optics available then. Early FELs therefore operated in the infrared range. FEL oscillators were eventually pushed into the visible and ultraviolet but could not push into the VUV due to either low gain or poor mirror reflectivity.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources ... more 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.

Journal of Physics: Conference Series, 2013

Jefferson Lab operates a superconducting energy recovered linac which is operated with CW RF and ... more Jefferson Lab operates a superconducting energy recovered linac which is operated with CW RF and which powers oscillator-based IR and UV Free-Electron Lasers (FELs) with diffraction limited sub-picosecond pulses with >10 13 photons per pulse (1.0%BW) at pulse repetition frequencies up to 75 MHz. Useful harmonics extend into the vacuum ultraviolet (VUV). Based on FEL model calculations validated using this facility, we have designed both an oscillator-based VUV-FEL that would produce 6 10 12 coherent (0.5% BW) 100 eV photons per pulse at multi-MHz repetition rates in the fundamental, and a dual FEL configuration that would allow simultaneous lasing lasing at THz and UV wavelengths. The VUV-FEL would utilize a novel high gain, low Q cavity, while the THz source would be an FEL oscillator with a short wiggler providing diffraction limited pulses with pulse energy exceeding 50 microJoules. The THz source would use the exhaust beam from a UV FEL. Such multiphoton capabilities would provide unique opportunities for out of equilibrium dynamical studies at time-scales down to 50 fs. The fully coherent nature of all these sources results in peak and average brightness values that are many orders of magnitude higher than storage rings.

Journal of Modern Optics, 2011

Advances in superconducting linac technology offer the possibility of an upgrade of the Jefferson... more Advances in superconducting linac technology offer the possibility of an upgrade of the Jefferson Lab Free Electron Laser (JLab FEL) facility to an oscillator-based VUV-FEL that would produce 6× 1012 coherent 100 eV photons per pulse at multi-MHz repetition rates ...

Japanese Journal of Applied Physics, 2002

A Free Electron Laser (FEL) called the IR Demo is operational as a user facility at Thomas Jeffer... more A Free Electron Laser (FEL) called the IR Demo is operational as a user facility at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, USA. It utilizes a 48 MeV superconducting accelerator that not only accelerates the beam but also recovers about 80% of the electron−beam power that remains after the FEL interaction. Utilizing this recirculation loop the machine has recovered cw average currents up to 5 mA, and has lased cw above 2 kW output at 3.1 microns. It is capable of output in the 1 to 6 micron range and can produce ~0.7 ps pulses in a continuous train at ~75 MHz. This pulse length has been shown to be nearly optimal for deposition of energy in materials at the surface. Upgrades under construction will extend operation beyond 10 kW average power in the near IR and produce multi-kilowatt levels of power from 0.3 to 25 microns. This talk will cover the performance measurements of this groundbreaking laser, scaling in near-term planned upgrades, and highlight some of the user activities at the facility.

We describe the design of the SRF Energy-Recovering Linac (ERL) providing the CW electron drive b... more We describe the design of the SRF Energy-Recovering Linac (ERL) providing the CW electron drive beam at the Jefferson Lab UV FEL. Based on the same 135 MeV linear accelerator as -and sharing portions of the recirculator with -the Jefferson Lab 10 kW IR Upgrade FEL, the UV driver ERL uses a novel bypass geometry to provide transverse phase space control, bunch length compression, and nonlinear aberration compensation (including correction of RF curvature effects) without the use of magnetic chicanes or harmonic RF. Stringent phase space requirements at the wiggler, low beam energy, high beam current, and use of a pre-existing facility and legacy hardware subject the design to numerous constraints. These are imposed not only by the need for both transverse and longitudinal phase space management, but also by the potential impact of collective phenomena (space charge, wakefields, beam break-up (BBU), and coherent synchrotron radiation (CSR)), and by interactions between the FEL and the accelerator RF system. This report addresses these issues and presents the accelerator design solution that is now in operation [1].

After demonstrating 10 kW operation with 1 second pulses, the Jefferson Lab program switched to d... more After demonstrating 10 kW operation with 1 second pulses, the Jefferson Lab program switched to demonstrating high power operation at short wavelengths using a new 8 cm period wiggler and a THz suppression chicane. We report here on the lasing results to date using this new configuration. We have demonstrated a large reduction in THz heating on the mirrors. We

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment - NUCL INSTRUM METH PHYS RES A, 1991

As conceived in a recent design study, electron beams of quite distinct character would be provid... more As conceived in a recent design study, electron beams of quite distinct character would be provided for nuclear physics experiments and FEL wigglers at CEBAF. When full nuclear physics operation begins, coordination between these two programs becomes critical. FEL operation requires electron bunches carrying charge of 120 pC at repetition rates of 2.5 and 7.5 MHz, whereas the nuclear physics users need a relatively small charge per bunch, ~ 0.13 pC, but at a repetition rate of 1.5 GHz. To allow maximal operation of the FEL facility without interfering with CEBAF's primary mission of conducting nuclear physics research, the principal mode of operation should accelerate and deliver the two disparate beams simultaneously with negligible degradation of beam quality. Various RF power, RF control, wakefield, and beam transport questions that are encountered in designing for concurrent operation are discussed.