Thomas Marshall (1935-2021)

Columbia Engineering mourns the loss of Thomas C. Marshall, Professor Emeritus of Applied Physics in the Department of Applied Physics and Applied Mathematics.

Professor Marshall received his Ph.D. in physics from the University of Illinois in 1960 and joined Columbia University in 1962 as a professor in the Department of Electrical Engineering. He became a Professor of Engineering Science in 1970 and was a member of the Plasma Physics Committee where he launched groundbreaking experimental research into the physics of plasmas, relativistic electron beams, and free electron lasers. Professor Marshall was one of the nine founding faculty members of the Department in 1978, becoming one of Columbia’s first Professors of Applied Physics. He was awarded Columbia’s Great Teacher Award in 1995. During his forty-four years at Columbia University, he has supervised or co-supervised 44 doctoral students. During the decade before he retired in 2006, Professor Marshall was the dedicated faculty advisor to our students in the Medical Physics Program.

Working with his students and colleague Professor Perry Schlesinger, Professor Marshall pioneered the development of free electron lasers (FEL), which have been shown to generate very large amounts of power, tunable in bands from the microwave to the visible spectrum and beyond. In the 1970’s, the first FEL in the Raman regime was demonstrated in Marshall’s Lab. Professor Marshall’s research also included FEL photonics and led to the production of TW-level ultra-short pulses of radiation. In 1985, he published Free Electron Lasers, which provided the first integrated treatment of the operation and characterization of the free-electron laser. Between 1985-87, he served on the APS Study Group on the Science and Technology of Directed Energy Weapons. Called by many “the most important APS study ever done”, this study provided a clear technical assessment of the severe limitations of existing candidates for DEWs such as high intensity lasers and energetic particle beams.

FEL physics has a close relationship with laser and accelerator physics, and his research focus included innovation accelerator physics. Professor Marshall explored new methods of accelerating particles using Brookhaven’s Accelerator Test Facility (ATF). In 1999, Marshall proposed the dielectric wake field accelerator. Working with his colleague, Jay Hirshfield, Professor Marshall continued his research at the ATF where he established the fundamental physics of dielectric wake field acceleration. Although retiring from academic duties in 2006, Professor Marshall continued to apply his insights and pursue his remarkable discoveries in beam and accelerator physics and published his last paper in 2018.

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Research Interests
Accelerator concepts, relativistic beams and radiation, free-electron lasers

In the past, the Marshall group has pioneered the development of free electron lasers (FEL), which have been shown to generate very large amounts of power, tunable in bands from the microwave to the visible spectrum and beyond. FEL physics has a close relationship with laser and accelerator physics, and it is the latter which is receiving most of my attention now. In the FEL, electrons lose energy and the light wave gains energy, via stimulated emission. In many advanced accelerators, the process is reversed, and a laser beam loses intensity while the electrons gain energy (stimulated absorption). So it should come as no surprise that we have centered most of our research activity in advanced acceleration concepts as the field of FEL matured. In the past we have investigated FEL photonics, which is now relevant to the development of an X-Ray FEL which starts from photon and particle noise, the production of TW-level ultra-short pulses of radiation from the FEL, and the "inverse FEL" (IFEL) which is a promising advanced concept laser accelerator of electrons. Some of the IFEL work was done in collaboration with the Accelerator Test Facility (ATF) at Brookhaven National Laboratory, where a 50MeV rf linac is available for outside investigators.

It is an objective of high energy physics to develop a linear accelerator which can deliver bunches of charge at energy ~ 1TeV. Current technology can provide this energy, but size and cost of the facility could be prohibitive. Thus there is motivation to explore different methods of accelerating particles. An IFEL is one example, and is now being refined by other investigators.

Another device being studied is the dielectric wake field accelerator, which has the potential to accelerate charges to very high energy using a sequence of "stages". This wake field accelerator requires no laser or microwaves to energize a bunch of electrons, using instead a train of “drive” bunches provided by an efficient, lower energy, conventional accelerator. Bunches set up by these fields will in turn accelerate a correctly timed, co-moving bunch of "test" particles. The rectangular configuration of these wakefield structures promises to accelerate a comparatively large amount of charge in a way which permits stable motion of the charges. We are currently working on a “two-channel” device, which separates the line of drive bunches from the accelerated bunches.