Development of the self-modulation instability of a relativistic proton bunch in plasma

Self-modulation is a beam–plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment

Hosing of a Long Relativistic Particle Bunch in Plasma

Experimental results show that hosing of a long particle bunch in plasma can be induced by wakefields driven by a short, misaligned preceding bunch. Hosing develops in the plane of misalignment, self-modulation in the perpendicular plane, at frequencies close to the plasma electron frequency, and are reproducible. Development of hosing depends on misalignment direction, its growth on misalignment extent and on proton bunch charge. Results have the main characteristics of a theoretical model, are relevant to other plasma-based accelerators and represent the first characterization of hosing

Synthesis, Solid-State Structures, and EPR Spectroscopic Studies on Polycrystalline and Single-Crystal Samples of α-Diimine Cobalt(II) Complexes

Cobalt compounds of the general formula [CoX2(a-diimine)], where X = Cl or I and the a-diimines are 1,4-diaryl-2,3-dimethyl- 1,4-diaza-1,3-butadiene (Ar-DAB) and bis(aryl)- acenaphthenequinonediimine (Ar-BIAN) were synthesized by the direct reaction of the anhydrous cobalt salts CoCl2 or CoI2 and the corresponding a-diimine ligand in dried CH2Cl2. The synthesized compounds are [Co(Ph-DAB)Cl2] (1a), [Co(o,o',p-Me3C6H2-DAB)Cl2] (1b), and [Co(o,o'- iPr2C6H3-DAB)Cl2] (1c) with the ligands Ar-DAB, and also [Co(o,o',p-Me3C6H2-BIAN)I2] (2'b) with the ligand Ar-BIAN. The crystal structures of all the compounds were solved by Introduction Cobalt is a 3d transition metal element that has been extensively studied over the last decades. Interest in cobalt compounds arises from their participation in many different processes, from industrial and technological applications as catalysts to the essential role in several biological systems of central importance in nature.[1–5] A large number of late transition metal complexes bearing a-diimine[6] ligands have been extensively studied in the commercial production of polyolefin from ethene and propene.[ 7,8] However, reports on cobalt complexes containing this type of ligands are still scarce.[9] Recently, some results from the insertion polymerization of ethylene have been reported using tetrahedral CoII complexes with related ligands.[ 10] a-Diimine ligands have also been the subject of different studies regarding the relative binding strengths,[11] as well as their reactivity with main group metals.[12] [a] REQUIMTE/CQFB, Departamento de Química, FCT, Universidade Nova de Lisboa, Caparica 2829-516, Portugal E-mail: [email protected] [b] Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal [c] Laboratoire DECOMET, ILB Université Louis Pasteur 4, rue Blaise Pascal, 67000 Strasbourg, France E-mail: [email protected] [d] Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, C.C. 242, 3000 Santa Fe, Argentina E-mail: [email protected] [e] INTEC, Universidad Nacional del Litoral, Güemes 3450, 3000 Santa Fe, Argentina Eur. J. Inorg. Chem. 2006, 4761–4769 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4761 single-crystal X-ray diffraction. In all cases the cobalt atom is in a distorted tetrahedron, which is built up of two halide atoms and two nitrogen atoms of the a-diimine ligand. Xband EPR measurements of polycrystalline samples performed on compounds 1b, 1c, and 2'b indicate a high-spin CoII ion (S = 3/2) in an axially distorted environment. Singlecrystal EPR experiments on compounds 1b and 1c allowed us to evaluate the orientation of the g tensor in the molecular frame.Fil: Rosa, Vítor. Universidad Nova de Lisboa;Fil: González, Pablo Javier. Universidad Nacional del Litoral; ArgentinaFil: Avilés, Teresa. Universidad Nova de Lisboa;Fil: Gomes, Pedro. Instituto Superior Tecnico; PortugalFil: Welter, Richard. Universite Louis Pasteur; FranciaFil: Rizzi, Alberto Claudio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; ArgentinaFil: Passeggi, Mario Cesar Genaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Brondino, Carlos Dante. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

From Flexible to Constrained Tris(tetraamine) Ligands: Synthesis, Acid-Base Properties, and Structural Effect on the Coordination Process with Nucleotides

International audienceThis work presents the synthesis and characterization of L2 and L3, which formed with the previously described ligand L1 a family of three tris(tetraamine) ligands based on a mesitylenyl spacer. The trimeric ligands differ from one to the other by the nature of their tetraamine moieties: triethylenetetraamine (L1), cyclen (L2), and constrained cyclen (L3). The impact of the rigidification of the structure from L1 to L3 on the acid–base properties is investigated, and the behavior of the ligands towards triphosphate (TriP), adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) anion receptors is explored by potentiometric investigations. To characterize and understand the driving forces implicated in the supramolecular assemblies, results are supported by 1H and 31P NMR measurements performed over a wide pH range. ATP appears as the most complexed anion and particular attention is given to comparison with its inorganic triphosphate analogue to highlight the contribution of π-stacking interactions. Results unambiguously show the various coordination scheme induced by the structure of the ligands