Claudio Pellegrini

Claudio Pellegrini
Distinguished Professor of Physics, Emeritus
Accelerator & Beam Dynamics

Office: 3-174 Knudsen
Phone: (310) 206-1677
E-Mail: [javascript protected email address]

Educational Background: 
  • Laurea in Fisica, Summa cumLaude, University of Rome La Sapienza, 1958
  • Libera Docenza, 1965


  • American Physical Society Fellow, 1987
  • Fulbright Fellow, 1997
  • FEL Prize, 1999
  • R. R. Wilson Prize, Am. Physical Society, 2001
  • Enrico Fermi Presidential Award, 2015, for pioneering research advancing understanding of relativistic electron beams and free-electron lasers, and for transformative discoveries profoundly impacting the successful development of the first hard x-ray free-electron laser, heralding a new era for science. Read more.
  • Elected to the National Academy of Sciences, 2017.
Research Interest: 
My area of research is electron and photon beams physics, coherent X-ray sources, particle accelerators and their applications, novel accelerators using lasers and plasmas. Within this field I am particularly interested in collective effects, instabilities, and self-organization phenomena.
My initial work at Frascati National Laboratory, was dedicated to the design and development of electron-positron colliders. I discovered the “Head-Tail effect” [1] and other collective effects strongly limiting the collider luminosity. Understanding these phenomena, and how to control them, was of crucial importance to reach for the first time the luminosity needed to obtain meaningful experimental results for high-energy physics, and to develop the standard model of elementary particles.
In the following years my interest extended to free-electron lasers (FELs). My principal contributions in this field have been the high gain FELs theory, including the self-amplified spontaneous emission (SASE) regime [2], and the applications of these results to the development of X-ray FELs [3, 4]. In a Workshop on 4th Generation sources organized by M. Cornacchia and H. Winick in 1992, I proposed the construction of a 0.1 to 4 nm wavelength SASE X-ray FEL using the SLAC linear electron accelerator [5]. This proposal was developed by a study group chaired by H. Winick, that produced the first design of what is now called LCLS.
While participating in the design study I also lead the UCLA experimental work on high gain SASE FELs, demonstrating for the first time the validity of the theoretical models, measuring very large gain and the statistical properties of the radiation [6, 7, 8, 9]. These experimental results were of critical importance to obtain DOE initial funding of LCLS and the later approval and construction of the project.
Two important theoretical contributions from this period are the discovery of the spiky temporal structure of SASE radiation [10], and a detailed discussion of quantum effects for X-ray FELs [11]. Other work was aimed to further develop the LCLS characteristics , including methods to generate ultra-short X-ray pulses [12,13].
The LCLS project reached its completion in 2009, when the first X-ray FEL was successfully commissioned at SLAC establishing a new record in X-ray beam brightness, over nine orders of magnitude larger than any previous source, generating X-rays with Ångstrom wavelength and femtosecond pulse duration and groundbreaking intensity and coherence. These novel properties are revolutionizing the study of atomic and molecular systems and have led to new X-ray FELs projects in Japan, Europe and Korea.
The history of the X-ray FEL is described in ref. [14].
More recently I have been working on methods to increase the X-ray pulse peak power from the present level of tens of GW to the TW level [15, 16] and to improve the coherent properties of X- ray FEL radiation. In the last area my collaborators and I have proposed a novel, improved SASE (iSASE) to reduce the X-ray pulse line width by amplitude and phase mixing of the spikes obtained manipulating the time relation between the electron bunch and the photon pulse [17]. This method can generate transform-limited pulses as shown in the figure above. The black line shows the SASE spectral width, in normalized units, and the red line shows that, transform-limited, obtained with iSASE.
Another novel concept for FEL physics and Xray applications is the “gain modulated” FELs, offering spectral control and the generation of simultaneous two-color pulses [18]. The experimental results agree with the theory, as shown in the figure below. The two color pulses have been recently used in atomic physics experiments at LCLS.
Selected Publications: 
1. C. Pellegrini: "On a New Instability in Electron-Positron Storage Rings (The Head-Tail Effect)," Nuovo Cimento, Vol. 64 A, 447 (1969).
2. R. Bonifacio, C. Pellegrini and L. Narducci: "Collective Instabilities and High Gain Regime Free Electron Laser," Optics Communications, Vol.50, 373 (1984).
3. J. B. Murphy and C. Pellegrini: "Generation of High Intensity Coherent Radiation in the Soft X-Ray and VUV Region," Journ. Optical Society of America, B2, 259 (1985).
4. C. Pellegrini: "Progress Toward a Soft X-Ray FEL," Nuclear Instr. and Meth., Vol. A272, 364 (1988).
5. C. Pellegrini: "A 4 to 0.1 nm FEL Based on the SLAC Linac," Proc.of the Workshop on Fourth Generation Light Sources; SSRL, p. 364 (1992).
6. M. Hogan, C. Pellegrini et al: "Measurements of High Gain and Intensity Fluctuations in a Self-Amplified, Spontaneous-Emission Free-Electron Laser," Phys. Rev. Letters, Vol. 80, 289-292 (1998).
7. M. Hogan, C. Pellegrini et al: "Measurements of Gain Larger Than 105 at 12μm in a SASE-FEL," Phys. Rev. Letters, Vol. 81, 4867 (1998).
8. A. Tremaine, C. Pellegrini and al., “Saturation measurements of a visible SASE FEL”, Proc. 2001 Particle Acc. Conf., p. 2760-2762 (2001).
9. A. Murokh, C. Pellegrini et al., “Properties of the ultra-short gain length, self-amplified spontaneous emission free-electron laser in the linear regime and saturation”, Phys. Rev. E67, 066501 (2003).
10. R. Bonifacio, L. De Salvo, P. Pierini, N. Piovella and C. Pellegrini, “Spectrum, Temporal Structure, and Fluctuations in a High Gain Freeelectron Laser Starting from Noise”, Phys. Rev. Letters, Vol. 73, 70-73 (1994).
11. C. B. Schroeder, C. Pellegrini, and P. Chen, “Quantum effects in high-gain free-electron lasers,” Phys. Rev. E Vol. 64, 056502 (2001).
12. C. B. Schroeder, C. Pellegrini, S. Reiche, J. Arthur, P. Emma, “Chirped-beam Two-stage Free-electron Laser for High-power Femtosecond x-Ray Pulse Generation”, JOSA B, Vol. 19, 1782-1789, (2002).
13. S. Reiche, P. Musumeci, C. Pellegrini and J.B. Rosenzweig, “Development of ultra-short pulse, single coherent spike for SASE X-ray FELs”, Nucl. Instr. And Methods, Vol. A 593, 45-48 (2008).
14. C. Pellegrini, The history of X-ray free-electron lasers, Eur. Phys. J. H, vol.37, 659-708 (2012).
15. W.M. Fawley, J. C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu, “Toward TW-Level, Hard X-Ray Pulses at LCLS”, Proc. 2011 FEL conf. p. 160-163, Shanghai, China (2012),
16. Y. Jiao, C. Pellegrini, et al. Modeling and multidimensional optimization of a tapered free electron laser, Phys. Rev. S. T. Accel. And Beams, 15, 050704 (2012).
17. J. Wu, A. Marinelli and C. Pellegrini, Generation of longitudinally coherent ultra-high power X-ray pulses by phase and amplitude mixing, Proceedings of FEL2012, Nara, Japan, p. 237-240 (2012),
18. A. Marinelli, A.A. Lutman, J.WU, Y. Ding, J. Krzywinski, H.-D. Nuhn, Y. Feng, R. Coffee, and C. Pellegrini, “Multicolor operation and spectral control in a gain-modulated X-ray free-electron laser, Phys. Rev Lett. 111, 134801 (2013).
19. C. Pellegrini, A. Marinelli and S. Reiche,"The Physics of Free-electron Lasers", Rev. Mod. Phys. 88, 015006 (2016).
20. C. Emma, A. Lutman,  M. W. Guetg , J. Krzywinski , A. Marinelli , J. Wu  and  C. Pellegrini, "Experimental demonstration of fresh bunch self-seeding in an X-ray free electron laser", App. Phys. Lett. 110, 154101 (2017).