Faculty Directory

O'Shea, Patrick G.

O'Shea, Patrick G.

Electrical and Computer Engineering
Institute for Research in Electronics & Applied Physics
3301 A.V. Williams Bldg.

Space Charge Dreams (by Chip Simons)


Professor O'Shea is Principal Investigator in the Bright Beams Collective Research Group

He was born in Cork, Ireland, and holds a BSc degree in Experimental Physics from the National University of Ireland, University College Cork, and MS and PhD degrees in Physics from the University of Maryland.

In recognition of significant achievements in education and research, he has been elected a Fellow of the Royal Society for the Arts,  American Association for the Advancement of Science, American Physical Society, Institute of Electrical and Electronic Engineers,  Irish Academy of Engineering, and won the University of Maryland's Distinguished Scholar-Teacher Award.

Professor O’Shea’s technical expertise lies in the field of applied electromagnetics, nonlinear dynamics, and charged particle beam technology, and applications.

Professor O'Shea has previously served as:


  • President Emeritus, University College Cork, Ireland
  • Royal Society for the Arts, Fellow 
  • American Association for the Advancement of Science, Fellow
  • Distinguished Scholar-Teacher, University of Maryland 
  • Irish Academy of Engineering, Fellow
  • Alan Berman Research Publication Award, U.S. Naval Research Laboratory
  • American Physical Society, Fellow
  • Institute for Electrical and Electronic Engineering, Fellow
  • Distinguished Project Team Award, Los Alamos National Laboratory
  • Leadership Maryland




The University of Maryland Electron Ring (by Tim Koeth)

Dr. O'Shea's current research is in the area of charged particle beam technology, electromagnetics, and their applications.


  • Demonstrated space-charge limited current phenomena in the propagation of high-current low energy electron beams in solenoidal and gas-focused regimes
  • Demonstrated and studied an advanced accelerator concept known as the laser-controlled collective ion accelerator. Achieved an accelerating gradient for protons of 30 MV/m
  • Developed record high brightness 1-MeV H-, and Ho beams on Beam Experiments Aboard Rocket (BEAR) test stand.
  • Demonstrated autonomous operation of a directed energy experiment in space using radio-frequency quadrupole H- accelerator. Studied propagation Ho, H-, and H+ beams in geomagnetic field at an altitude of 200 km
  • Demonstrated a high-current radio-frequency photocathode electron source as a driver for a high-gain infrared free-electron laser - first operation of a high-current RF photoinjector coupled to a linear accelerator.
  • Demonstrated operation of electron photoinjector with space-charge emittance compensation whose brightness exceeded that of conventional sources by two orders of magnitude. Experimental confirmation of the theory of space charge emittance growth compensation.
  • Demonstrated free-electron lasing from 370 nm to 11 µm using low-energy, high-brightness electron beam, and achieved a record short wavelength for a linear accelerator-driven FEL
  • Member of the team that demonstrated inverse Compton γ-ray production using an FEL
  • Developed a theory of reversible and irreversible emittance growth
  • Electron beam production of medical radioisotopes
  • Developed the nitrogen-laser driven RF photoinjector
  • Compact electron ring (UMER), an analog computer for beam physics studies in the space charge dominated regime; thermodynamics of beams and energy transfer mechanisms in beam systems. Discovery of solitary waves in electron beams.
  • Developed dispenser photocathode electron source.

Bright Beams Collective

We believe that a bright beam is a better beam. By “beam” we mean a swarm of charged particles (electrons or ions) that is collectively heading off to do something useful.  The nonlinear dynamics of these swarms are really interesting.  Understanding the swarms is important for many applications, including high energy physics accelerators; particle-beam-driven high-energy-density physics, inertial fusion energy; applications to galactic dynamics; and free-electron light sources.

The group began exploring space-charge-dominated beams (intense swarms) in the 1980s under the direction of the late Professor Martin Reiser.

Today, the Bright Beams Collective (BBC) Research Group hosts world-class research facilities for collective beam dynamics and accelerator technology at the Institute for Research in Electronics and Applied Physics of the University of Maryland, College Park. Using scaled low-energy electron beams, our UMER electron ring and LSE linear facilities cleverly access the intense, high-brightness regime of beam operation in accelerators at a much lower cost than larger and more energetic machines. Therefore, we have ideal testbeds for exploring how to enhance the brightness of beams of existing and future accelerators.

Our BBC research explores the physics of charged particle beams at the extreme frontier of intensity.  For many applications, the intensity or luminosity frontier is as vital as the energy frontier.  Examples of such applications include high-luminosity colliders, spallation neutron sources, and X-ray-free electron lasers and related intense light sources, high-average-power-free electron lasers, and future heavy ion-driven inertial fusion concepts.

Research Areas of Interest

  • Experimental beam physics
  • Nonlinear accelerator optics
  • Ring physics
  • Space charge in beams
  • Advanced beam diagnostics
  • Beam halo
  • Nonlinear dynamics


Our research is supported by the U.S. Department of Energy, Office of Science.

Some interesting publications

Free-Electron Lasers: Status and Applications

P.G. O’Shea and H. P. Freund, Science, 292, 1853 (2001)

 Electron Sources for Accelerators

C. Hernandez-Garcia, M. Stutzman, and P. G. O'Shea Physics Today, February 2008, page 44

Experimental Observations of Soliton Wave Trains in Electron Beams

Y.C. Mo, R.A. Kishek, D. Feldman, I. Haber, B. Beaudoin, P.G. O'Shea, and J.C.T. Thangaraj, Physical Review Letters 110, 084802 (2013).

Smooth Approximation of Dispersion with Strong Space Charge,

S. Bernal, B.L. Beaudoin, T. Koeth, and P.G. O'Shea, Physical Review Special Topics - Accelerators & Beams 14, 104202 (2011).

Longitudinal Confinement and Matching of an Intense Electron Beam,

B. Beaudoin, I. Haber, R.A. Kishek, S. Bernal, T. Koeth, D. Sutter, P.G. O'Shea, and M. Reiser, " Physics of Plasmas 18, 013104 (2011).

Experimental study of large-amplitude perturbations in space-charge dominated beams,

 K. Tian, R.A. Kishek, I. Haber, M. Reiser, and P.G. O'Shea, Physical Review Special Topics - Accelerators & Beams 13, 034201 (2010).

Experimental verification of tomographic phase-space imaging for beams with space-charge using a pinhole-scan,

D. Stratakis, R.A. Kishek, I. Haber, R.B. Fiorito, M. Reiser, and P.G. O'Shea Journal of Applied Physics 107, 104905 (2010)

Emittance of a field emission electron source,

K. L. Jensen, P. G. O'Shea, D. W. Feldman, and J. L. Shaw, J. Appl. Phys. 107, 014903 (2010)

Terahertz laser modulation of electron beams,

J.G Neumann, R.B. Fiorito, P.G. O'Shea, H. Loos, B. Sheehy, Y. Shen, Z. Wu, J. Appl. Phys. 105, 053304 (2009)

Time-dependent Phase Space Characterization of Intense Charged Particle Beams," Physical Review Special Topics - Accelerators & Beams 

D. Stratakis, R.A. Kishek, R.B. Fiorito, K. Tian, I. Haber, P.G. O'Shea, M. Reiser, and J.C.T. Thangaraj,12, 020101 (2009).

Aperture effects and mismatch oscillations in an intense electron beam,

J.R Harris, P.G. O’Shea, Phys. Plasmas 15, 123106 (2008)

Multicomponent measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation

M.A. Holloway, R.B. Fiorito, A.G. Shkvarunets, P. G. O’Shea, S.V. Benson, D. Douglas, P. Evtushenko, and K. Jordan, Phys. Rev. ST Accel. Beams 11, 082801 (2008)

Theory of photoemission from cesium antimonide using an alpha-semiconductor model,

 K L Jensen, BL Jensen, EJ Montgomery, DW Feldman, PG O'Shea, and NA Moody, J. Appl. Phys. 104, 044907 (2008)

Electron emission contributions to dark current and its relation to microscopic field enhancement and heating in accelerator structures,

 K L. Jensen, Y. Y. Lau, D. W. Feldman and P. G. O’Shea, Phys. Rev. ST Accel. Beams 11, 081001 (2008)

Application of a general electron emission equation to surface nonuniformity and current density variation 

KL Jensen, JJ Petillo,  EJ Montgomery, ZG Pan, DW Feldman  PG O'Shea, NA Moody, M. Cahay, JE Yater, JL Shaw  J. Vac. Sc. & Tech B, 26, 831 (2008) 

Negative transconductance in apertured electron guns, 

J. R. Harris and P. G O'Shea, Journal of Applied Physics. 103, 113301 (2008)

Time-Dependent Imaging of Space-Charge-Dominated Electron Beams, 

K. Tian, R.A. Kishek, P.G. O'Shea, R.B. Fiorito, D.W. Feldman, and M. Reiser,  Physics of Plasmas 15, 056707 (2008).

Longitudinal density modulation and energy conversion in intense beams 

J. R. Harris, J. G. Neumann, K. Tian, and P. G. O’Shea, Phys. Rev. E, 76 026402 (2007)

A theoretical model of the intrinsic emittance of a photocathode,

 K. L. Jensen P. G. O'Shea, D. W. Feldman, and N. A. Moody, Applied Physics Letters. 89, 224103 (2006)

A photoemission model for low work function coated metal surfaces and its experimental validation, 

Kevin L. Jensen, Donald W. Feldman, Nathan A. Moody, and Patrick G. O'Shea, J. Appl. Phys. 99, 124905 (2006)

Field-enhanced photoemission from metals and coated materials, 

Kevin L. Jensen, Donald W. Feldman, Nathan A. Moody, and Patrick G. O'Shea, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 863, (2006)

Fixed-Geometry RMS Envelope Matching of Electron Beams from 'Zero' Current to Extreme Space-Charge

S. Bernal, H. Li, R.A. Kishek, B. Quinn, M. Walter, M. Reiser, P.G. O'Shea, and C.K. Allen,  Physical Review ST - Accelerators & Beams  9, 064202 (2006).

Tomography as a Diagnostic Tool for Phase Space Mapping of Intense Particle Beams, 

D. Stratakis, R.A. Kishek, H. Li, S. Bernal, M. Walter, B. Quinn, M. Reiser, and P.G. O'Shea, Physical Review Special Topics - Accelerators & Beams 9, 112801 (2006).

Gridded Electron Guns and Modulation of Intense Beams,

J.R. Harris and P.G. O'Shea, IEEE Transactions on Electron Devices 53(11), 2824-2829 (2006).

Experimental observations of longitudinal space-charge waves in intense electron beams,

 K. Tian, Y. Zou, Y. Cui, I. Haber, R. A. Kishek, M. Reiser, and P. G. O’Shea, Physical  Review. ST Accel. Beams 9, 014201 (2006)

Governing factors for production of photoemission-modulated electron beams 

J. R. Harris, J. G. Neumann, and P. G. O'Shea, J. Appl. Phys. 99, 093306 (2006)

RMS envelope matching of electron beams from “zero” current to extreme space charge in a fixed lattice of short magnets,

Bernal, H. Li, R. A. Kishek, B. Quinn, M. Walter, M. Reiser,  P. G. O’Shea, and C. K. Allen.  Phys. Rev. ST Accel. Beams 9, 064202 (2006)

Nonlinear Harmonic Generation in Free-Electron Lasers with Helical Wigglers, 

H.P. Freund, P.G. O’Shea, S. Biedron, Physical Review Letters, 94, 074802 (2005)  

Observation of anomalous increase of longitudinal energy spread in a space-charge dominated electron beam,

Y. Zou, Y. Cui, M. Reiser, and P. G. O'Shea, Physical Review Letters, 94, 134801 (2005) 

The quantum efficiency of dispenser photocathodes: Comparison of theory to experiment

K. L. Jensen, D. W. Feldman, and P.G. O’Shea, Applied Physics  Letters. 85, 5448 (2004)

Two-color operation in high-gain free-electron lasers

H. P. Freund and P.G. O’Shea, Physical Review Letters, 84 2861 (2000)

UMD Invention of the Year Nominees Push Boundaries in Health, Energy, and Security

Campus inventors to be honored at Celebration of Innovation and Partnerships

UMD Ties with Stanford, MIT for Most Researchers on 2015 DOD Multidisciplinary Research Grants

UMD Represented on 6 of 22 Teams Awarded University Research Initiative Grants by the Department of Defense

Food Safety, Energy Storage & Video Authentication Inventions Honored at Awards Ceremony

Three Clark School innovations win UMD Invention of the Year Awards

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First federally funded research and development center dedicated to enhancing cybersecurity

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Donation furthers research, education programs, student activities, and fellowships

Clark School Faculty Recognized at Celebration of Innovation and Partnerships

Clark School researchers sweep three categories for 2013 Invention of the Year

Katz Named Director of Maryland Cybersecurity Center

Jonathan Katz, professor of computer science, was appointed to a three-year term.

ECE Professor Wins 2013 UMD Invention of the Year Award

Professor K.J. Ray Liu and students' research awarded UMD Information Science Invention of the Year.

Clark School Faculty Recognized at UMD Invention of the Year Awards

26th annual awards ceremony honors most promising campus inventions.

Other professional society fellows

  • Royal Society for the Arts
  • Irish Academy of Engineering

Institute of Electrical and Electronics Engineers (IEEE)

American Association for the Advancement of Science (AAAS)

American Physical Society (APS)