Plasma Physics Group, Department of Physics, University of Milano
Research » Nonneutral Plasmas
Non-neutral plasmas have been systematically investigated for more than four decades. During the last 15 years studies on confined single species plasmas have considerably increased due to improvements in trap and source construction, which have led to the introduction of Malmberg-Penning devices and refined use of new diagnostic techniques, such as charge coupled device (CCD) cameras. At the same time, the field of interest and application of single species plasmas have widened. At present, beam physicists are paying increasing attention to this field, since it has been realized that ''plasma effects'' can play an important role in assessing the high quality of beams, which is needed, for instance, in sophisticated devices, like free electron lasers, gyrotrons, or other electromagnetic wave generators. Confinement and handling of single species plasmas are also crucial in present experiments on the production of antimatter and in the development of positron beam applications. In a different research field, the investigation of electron plasmas in carefully prepared conditions turns out to be equivalent to direct experiments on two-dimensional, almost dissipationless, fluids: thus, basic fluid dynamics issues often connected with a variety of applications can be studied using traps for electron plasmas.
A plasma of particles with the same sign of charge an approach thermal equilibrium while remaining confined by means of static magnetic and electric fields (Malmberg-Penning traps. It is therefore possible to confine the plasma for a very long time and to study its complex dynamics, dominated by collective effects, during the whole time evolution. It is to be noted that neutral plasmas do not share the above mentioned property. Apart from papers on international journals, the state of the art in this field can be deduced from the most recent Proceedings of the "Workshops on Non-neutral Plasma Physics" [5]. The most important international studies relevant to the present research project (excluding those of our group), are carried out by university groups in San Diego (UCSD), Berkeley (UCB)], Newark (Delaware), Princeton, Kyoto.
The Penning-Malmberg trap ELTRAP, designed and operating at the Department of Physics of the University of Milano from 2001, allows us to confine a relatively large volume of electron plasma by means of a highly uniform magnetic field (ELTRAP has received an "excellent" evaluation from the Italian Committee for the evaluation of research by means of international peer reviewing in the period 2001-2003). The device allows detailed studies on the origin of the instability of collective modes and of the turbulence, on the formation and evolution of vortices and coherent structures, on the space charge dominated regimes in low energy electron beams.
The studies performed by our research unit on these subjects concern the merger process of a localized vortex with an extended vortex (collaboration with Berkeley) the development of coherent structures in a low energy electron beam in the transition from a laminar to a space charge dominated regime, the analysis of the process of injection of the electrons inside the trap. The research activity of the Milano group comprises theoretical studies, in collaboration with the INP in Novosibirsk, about the general characteristics of the equilibrium states of non-neutral plasmas even in the presence of weak magnetic perturbations (collaboration with San Diego) [21,22], and on the influence of the unperturbed density profile on the evolution of the fundamental diocotron mode The experimental results are interpreted by means of two-dimensional (2D) Vlasov or three-dimensional PIC codes, developed in collaboration with the University of Pisa and the INP in Novosibirsk.
[1] R.C. Davidson, "An Introduction to the Physics of Nonneutral Plasmas" (Addison-Wesley, Redwood City, 1990).
[2] T.M. O'Neil, Phys. Scripta T59, 341 (1995).
[3] D.H.E. Dubin and T.M O'Neil, Rev. Mod. Phys. 71, 87 (1999).
[4] J.H. Malmberg and J.S.deGrassie, Phys. Rev. Lett. 35, 577 (1975).
[5]"Non-Neutral Plasma Physics IV", AIP Conference Proceedings 606, Proceedings of the Workshop on Non-Neutral Plasmas (San Diego, U.S.A., 2001), ed. by F. Anderegg, L. Schweikhard and C. F. Driscoll (AIP, U.S.A., 2002); "Non-Neutral Plasma Physics V", AIP Conference Proceedings 692, Proceedings of the Workshop on Non-Neutral Plasmas (Santa Fe, U.S.A., 2003), ed. by M. Schauer, T. Mitchell and R. Nebel (AIP, U.S.A., 2003); "Non-Neutral Plasma Physics VI", AIP Conference Proceedings 862, Proceedings of the Workshop on Non-Neutral Plasmas (Aarhus, Denmark, 2006), ed. by M. Drewsen, U. Uggerhøj and H. Knudsen (AIP, U.S.A., 2006).
[6] D.A. Schecter, D.H.E. Dubin, K.S. Fine, and C.F. Driscoll, Phys. Fluids 11, 905 (1999).
[7] D. Durkin and J. Fajans, Phys. Fluids 12, 289 (2000).
[8] N. Mattor, B. N. Chang and T. B. Mitchell, Phys. Rev. Lett. 96, 045003 (2006).
[9] K. A. Morrison, S. F. Paul and R. C. Davidson, Phys. Plasmas 12, 072310 (2005).
[10] A Sanpei, Y. Kiwamoto, K. Ito and Y. Soga, Phys. Rev. E 68, 016404 (2003).
[11] M. Amoretti et al.. Nature 419, 456 (2002).
[12] G. Gabrielse, N. S. Bowden, P. Oxley, A. Speck, C. H. Storry, J. N. Tan, M. Wessels, D. Grzonka, W. Oelert, G. Schepers, T. Sefzick, J. Walz, H. Pittner, T. W. Hänsch and E. A. Hessels, Phys. Rev. Lett. 89, 233401 (2002).
[13] M. Amoretti, C. Canali, C. Carraro, M. Doser, V. Lagomarsino, G. Manuzio, G. Testera and S. Zavatarelli, Phys. Lett. A 360, 141 (2006).
[14] L. Schweikhard, M. Breitenfeldt, A. Herlert, F. Martinez, G. Marx and N. Walsh
in "Non-neutral Plasma Physics VI", ed. By M. Drewsen, U.I. Uggerhoj, H. Knudsen, AIP Conf. Proc. 862, p. 264.
[15] M. Amoretti, G. Bettega, F. Cavaliere, M. Cavenago, F. De Luca, R. Pozzoli and M. Romé, Rev. Sci. Instrum. 74, 3991 (2003).
[16] M. Amoretti, D. Durkin, J. Fajans, R. Pozzoli and M. Romé, "Asymmetric vortex merger: Experiments and simulations", Phys. Plasmas 8, 3865 (2001).
[17] G. Bettega, F. Cavaliere, A. Illiberi, R. Pozzoli, M. Romé, M. Cavenago and Yu. Tsidulko, Appl. Phys. Lett. 84, 3807 (2004).
[18] G. Bettega, F. Cavaliere, M. Cavenago, A. Illiberi, R. Pozzoli and M. Romé, Phys. Plasmas 14, 042104 (2007).
[19] I. Kotelnikov, R. Pozzoli and M. Romé, Phys. Plasmas 7, 4396 (2000).
[20] I. A. Kotelnikov, R. Pozzoli and M. Romé, Plasma Phys. Rep. 26, 960 (2000).
[21] I. A. Kotelnikov, M. Romé and A. Kabantsev, Phys. Plasmas 13, 092108 (2006);
[22] I. A. Kotelnikov, M. Romé and A. Kabantsev, Trans. Fus. Sci. Tech. 51, 238 (2007).
[23] A. V. Arefiev, I. A. Kotelnikov, M. Romé and R. Pozzoli, "l=1 diocotron instability of single charged plasmas", Plasma Phys. Rep. 28, 141 (2002).
[24] I. A. Kotelnikov, R. Pozzoli and M. Romé, Phys. Plasmas 12, 092105 (2005).
[25] M. Romé, M. Brunetti, F. Califano, F. Pegoraro and R. Pozzoli, Phys. Plasmas 7, 2856 (2000).
[26] Yu. Tsidulko, R. Pozzoli and M. Romé, J. Comp. Phys. 209, 406 (2005).
[27] A cool video of the late J.H. Malmberg introducing NNP research at UCSD.