Nonlinear waveguides with two distinct domains of anomalous dispersion can support the formation of molecule-like two-color pulse compounds. They consist of two tightly bound subpulses with frequency loci separated by a vast frequency gap. Perturbing such a two-color pulse compound triggers periodic amplitude and width variations, reminiscent of molecular vibrations. With increasing strength of perturbation, the dynamics of the pulse compound changes from harmonic to nonlinear oscillations. The periodic amplitude variations enable coupling of the pulse compound to dispersive waves, resulting in the resonant emission of multi-frequency radiation. We demonstrate that the location of the resonances can be precisely predicted by phase-matching conditions. If the pulse compound consists of a pair of identical subpulses, inherent symmetries lead to degeneracies in the resonance spectrum. Weak perturbations lift existing degeneracies and cause a splitting of the resonance lines into multiple lines. Strong perturbations result in more complex emission spectra, characterized by well separated spectral bands caused by resonant Cherenkov radiation and additional four-wave mixing processes.

We present a detailed overview of the physics of two-color soliton molecules in nonlinear waveguides, i.e. bound states of localized optical pulses which are held together due to an incoherent interaction mechanism. The mutual confinement, or trapping, of the subpulses, which leads to a stable propagation of the pulse compound, is enabled by the nonlinear Kerr effect. Special attention is paid to the description of the binding mechanism in terms of attractive potential wells, induced by the refractive index changes of the subpulses, exerted on one another through cross-phase modulation. Specifically, we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting of a strong trapping pulse and a weak trapped pulse, for which trapped states of low intensity are determined by a Schrödinger-type eigenproblem. We discuss the rich dynamical behavior of such meta-atoms, demonstrating that an increase of the group-velocity mismatch of both subpulses leads to an ionization-like trapping-to-escape transition. We further demonstrate that if both constituent pulses are of similar amplitude, molecule-like bound-states are formed. We show that z-periodic amplitude variations permit a coupling of these pulse compound to dispersive waves, resulting in the resonant emission of Kushi-comb-like multi-frequency radiation.

We study incoherently coupled two-frequency pulse compounds in waveguides with single zero-dispersion and zero-nonlinearity points. In such waveguides, supported by a negative nonlinearity, soliton dynamics can be obtained even in domains of normal dispersion. We demonstrate trapping of weak pulses by solitary-wave wells, forming nonlinear-photonics meta-atoms, and molecule-like bound-states of pulses. We study the impact of the Raman effect on these pulse compounds, finding that, depending on the precise subpulse configuration, they decelerate, accelerate, or are completely unaffected. Our results extend the range of systems in which two-frequency pulse compounds can be expected to exist and demonstrate further unique and unexpected behavior.

We present a detailed overview of the physics of two-color soliton molecules in nonlinear waveguides, i.e. bound states of localized optical pulses which are held together due to an incoherent interaction mechanism. The mutual confinement, or trapping, of the subpulses, which leads to a stable propagation of the pulse compound, is enabled by the nonlinear Kerr effect. Special attention is paid to the description of the binding mechanism in terms of attractive potential wells, induced by the refractive index changes of the subpulses, exerted on one another through cross-phase modulation. Specifically, we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting of a strong trapping pulse and a weak trapped pulse, for which trapped states of low intensity are determined by a Schrödinger-type eigenproblem. We discuss the rich dynamical behavior of such meta-atoms, demonstrating that an increase of the group-velocity mismatch of both subpulses leads to an ionization-like trapping-to-escape transition. We further demonstrate that if both constituent pulses are of similar amplitude, molecule-like bound-states are formed. We show that z-periodic amplitude variations permit a coupling of these pulse compound to dispersive waves, resulting in the resonant emission of Kushi-comb-like multi-frequency radiation.

Soliton molecules are usually understood to be co-propagating soliton pairs with a fixed time delay, as observed, e.g., in dispersion-managed fibers [1]. In contrast to those, two-color photonic molecules consist of two separated subpulses in the frequency domain and a single localized state in the time domain. They have been recently proposed theoretically [2] and demonstrated experimentally [3]. A prerequisite for the observation of such state is a group-velocity matching for the spectrally separated constituents, which can be enabled by suitable dispersion characteristics with at least two domains of anomalous dispersion (A1,A2). We have studied these molecule states under various perturbations [4] revealing unique propagation dynamics due to strong entanglement between the individual subpulses. To generate two-color molecules, input pulses at two incommensurable, group-velocity matched frequencies are required, which is difficult to realize experimentally. Here, we propose a self-generation mechanism in a microstructured waveguide enabled by spectral tunneling and supported by the Raman effect naturally occurring in supercontinuum generation. The generation scheme requires only a one color pumping and the fiber design is optimized for commercially available telecom wavelengths.

The quantum mechanical Zeno effect states that the spontaneous decay of an unstable quantum system can be suppressed by continuous measurements. Classical analogues of this paradox have been observed in light wave propagation, e.g., for optical tunneling [1] and transverse spreading [2]. In contrast to previous works, we discuss the appearance of a Zeno-like effect, considering pulse propagation in nonlinear waveguides in terms of a generalized nonlinear Schrödinger equation. In presence of perturbations, e.g., third order dispersion, a higher order soliton experiences dramatic spectral broadening, i.e., supercontinuum generation, and breaks up. This soliton fission process is enabled by spectral broadening of the initial soliton, transferring energy to a phase matched dispersive wave [3]. By introducing strong linear absorption to the dispersive wave, it is shown that soliton fission is slowed down or even suppressed, with strong impact to the overall observed complex dynamics in supercontinuum generation. Here, linear loss assumes the role of continuous measurements within the quantum context.

We consider the interaction dynamics of incoherently coupled two-color pulse compounds in waveguides with a single zero-dispersion and zero-nonlinearity point [1]. In such a system, group-velocity matching can be attained despite a vast frequency gap, and soliton dynamics in a domain of normal dispersion can be realized through a negative nonlinearity. This extends the range of systems in which direct optical analogues of quantum mechanical bound-states can be realized [2], [3]. Such bound-states comprise nonlinear-photonics meta-atoms, composed of a strong trapping potential, given by the refractive index well induced by a soliton, and a weak dispersive wave. The underlying trapping mechanism is different from the usual trapping of a normally dispersive wave by a decelerating soliton [4]. Here we discuss the impact of the Raman effect on these pulse compounds and show that when the center frequency of the solitary-wave well shifts, a higher-order trapped state transits into the groundstate [1].

The generation of two-frequency compound states is very challenging because it requires the access to two incommensurable frequencies that can be group-velocity matched within the considered system. We present here the theoretical investigation of a fiber-based self-generation scheme with a single-color pump as initial condition enabled by soliton fission and the spectral tunneling process. The Raman effect is found to enhance the efficiency of the creation process and the impact of the input pulse parameters on the scheme is investigated.

We numerically explore synthetic crystal diamond for realizing novel light sources in ranges which are up to now difficult to achieve with other materials, such as sub-10-fs pulse durations and challenging spectral ranges. We assess the performance of on-chip diamond waveguides for controlling light generation by means of nonlinear soliton dynamics. The considered silica-embedded diamond waveguide model exhibits two zero-dispersion points, delimiting an anomalous dispersion range that exceeds an octave. Various propagation dynamics, including supercontinuum generation by soliton fission, can be realized in diamond photonics. In contrast to usual silica-based optical fibers, where such processes occur on the scale of meters, in diamond millimeter-scale propagation distances are sufficient. Unperturbed soliton-dynamics prior to soliton fission allow identifying a pulse self-compression scenario that promises record-breaking compression factors on chip-size propagation lengths.

We demonstrate a novel type of ultrashort optical soliton bound states with molecule-like properties. These two-color solitons exhibit a strong binding energy, dipole-like radiation, and show dynamics of controlled soliton evaporation. Furthermore, the given interaction concept enables a classical analog of trapped states in an attractive quantum potential.

The nonlinear interaction of copropagating optical solitons enables a large variety of intriguing bound-states of light. We here investigate the interaction dynamics of two initially superimposed fundamental solitons at distinctly different frequencies. Both pulses are located in distinct domains of anomalous dispersion, separated by an interjacent domain of normal dispersion, so that group velocity matching can be achieved despite a vast frequency gap. We demonstrate the existence of two regions with different dynamical behavior. For small velocity mismatch we observe a domain in which a single heteronuclear pulse compound is formed, which is distinct from the usual concept of soliton molecules. The binding mechanism is realized by the mutual cross phase modulation of the interacting pulses. For large velocity mismatch both pulses escape their mutual binding and move away from each other. The crossover phase between these two cases exhibits two localized states with different velocity, consisting of a strong trapping pulse and weak trapped pulse. We detail a simplified theoretical approach which accurately estimates the parameter range in which compound states are formed. This trapping-to-escape transition allows to study the limits of pulse-bonding as a fundamental phenomenon in nonlinear optics, opening up new perspectives for the all-optical manipulation of light by light.

Uranium hydride is commonly used to store hydrogen or its isotopes in a solid state. The Self-Assaying Tritium Accountancy and Containment Unit for ITER (STACI) is a 5.2-kg bed of depleted uranium (dU) capable of holding up to 33 mol of hydrogen or its isotopes. This paper is a summary of data analysis of past experimental campaigns with STACI, with the aim of describing the kinetics and thermodynamics of the hydriding process. Computed tomography imaging was performed on STACI both before and after its experimental campaign, and a high degree of swelling was observed in the dU. Literature on studies in regard to the swelling of large (multikilogram) quantities of uranium hydride for storage applications was not identified during this study. Data from the experimental campaign, as well as data on the formation reaction, are presented. The authors hope to create an analytical model of STACI based on these data.

We discuss the interaction dynamics of two pulses in distinct regions of anomalous dispersion, group-velocity matched despite a vast interjacent frequency gap. In such a setting, direct optical analogues of quantum mechanical bound-states can be realized [1] . These bound states manifest themselves as pulse compounds consisting of a strong trapping pulse, given by a solitary wave, and a weak trapped pulse. Here we go a decisive step further by clarifying the mutual interaction dynamics of higher order trapped states and by demonstrating their robustness to perturbations. The trapping mechanism is enabled by the propagation dynamics in a nonlinear waveguide and quite different from the usual trapping of a normally dispersive wave by a solitary wave [2] . Specifically, we consider pulse propagation in terms of an unidirectional non-envelope propagation equation for the analytic signal [3] , modelling group velocity and group velocity dispersion as shown in Figs. 1(a,b) .

The particle-like behavior is an outstanding feature of solitons, wherein the existence of soliton molecules can be understood to be an extension of this concept. Such molecules have been shown to exist in dispersion-managed fibers as a result of a balance of attractive and repulsive forces due to the relation of the phases between their constituent solitons [1] . In contrast to these objects the existence of a novel type of heteronuclear, polychromatic molecule states has been shown recently [2] , [3] , for which the underlying binding mechanism is realized by incoherent Kerr interaction. These soliton molecules propagate stably as a single localized state exhibiting interference fringes in the time domain [ Fig. 1(b) ] and constitute of a characteristic ’double-hump’ structure in the frequency domain [ Fig. 1(c) ]. This is in strong contrast to the usual soliton molecule concept. Very recently polychromatic soliton molecules have been experimentally demonstrated in a mode-locked laser [3] and shown to exist in the dissipative Lugiato-Lefever equation [4] . These objects appear promising due to their complex propagation dynamics and intriguing analogies to real molecules, but many of their properties are mostly unknown yet. Here we show the possibility to manipulate the energy redistribution within a molecule and exploit this property to generate supercontinuum spectra. In this novel scheme energy is transferred to a molecule via collision with external solitons in analogy to the collider principle, resembling also a dissociation-like process. After the collision process the molecule state is temporally compressed resulting in the formation of a supercontinuum. In addition, we study the robustness of the polychromatic molecules under perturbation and their binding mechanism in more detail.

The ITER Tokamak Exhaust Processing (TEP) system relies on palladium membrane reactors (PMRs) for tritium recovery. The PMR consists of a palladium/silver membrane permeator filled with a catalyst, that can be used to recover hydrogen species (most importantly tritium) from methane and water impurities present in fusion reactor exhaust emissions. Two superimposed phenomena simultaneously occur inside the PMR: a chemical reaction onto the catalyst liberating hydrogen contained in molecules and permeation of this molecular hydrogen through the membrane. Applying a vacuum on the permeate side allows recovery of pure hydrogen from the molecules (including tritium). The inside-out configuration of the PMR improves vacuum conditions at the permeate side, thus enhancing decontamination factor and tritium recovery performances. This paper presents the design, construction and initial commissioning of a newly erected test rig at UKAEA to perform experiments with protium on an inside-out PMR prototype in support of the ITER TEP. The efficiency of the PMR is assessed by both measuring flowrate through the permeate gas stream and analysing the composition of the retentate gas stream using gas chromatography. Permeation rate is assessed for protium for flowrates between 10 and 100 ml/min. The methane/water ratio, crucial for methane steam reforming tests, is assessed to optimise decontamination of hydrogen and minimise coking of the PMR. The hydrogen recovery fraction and decontamination factor are assessed for methane and water from flow rates of 10 to 60 ml/min.

We extend the analogy of particle-like behavior of solitons one decisive step further, demonstrating completely Newtonian collisions for unequal solitons, detached from any wave properties. They even act like extended massive objects, exhibiting elastic deformation. © 2019 The Author(s)

Fusion power holds the promise of electricity production with a high degree of safety and low environmental impact. Favourable characteristics of fusion as an energy source provide the potential for this very good safety and environmental performance. But to fully realize the potential, attention must be paid in the design of a demonstration fusion power plant (DEMO) or a commercial power plant to minimize the radiological hazards. These hazards arise principally from the inventory of tritium and from materials that become activated by neutrons from the plasma. The confinement of these radioactive substances, and prevention of radiation exposure, are the primary goals of the safety approach for fusion, in order to minimize the potential for harm to personnel, the public, and the environment. The safety functions that are implemented in the design to achieve these goals are dependent on the performance of a range of materials. Degradation of the properties of materials can lead to challenges to key safety functions such as confinement. In this paper the principal types of material that have some role in safety are recalled. These either represent a potential source of hazard or contribute to the amelioration of hazards; in each case the related issues are reviewed. The resolution of these issues lead, in some instances, to requirements on materials specifications or to limits on their performance.

The Tritium Systems Test Assembly (TSTA) was a facility dedicated to tritium handling technology and experiment research at the Los Alamos National Laboratory. The facility was operated with tritium for its research and development program from 1984 to 2001, running a prototype fusion fuel processing loop with similar to 100 g of tritium as well as small experiments. There have been several operating experience reports written on this facility's operation and maintenance experience. This paper describes reliability analysis of two additional components from TSTA, small diameter copper gas piping that handled tritium in a nitrogen carrier gas, and the flame arrestor used in this piping system. The component failure rates for these components are discussed in this paper. Comparison data from other applications are also presented. (C) 2014 Elsevier B.V. All rights reserved.

The CAPER facility of the Tritium Laboratory Karlsruhe has demonstrated the technology for the tokamak exhaust processing. CAPER has been significantly upgraded to pursue R&D towards highly tritiated water (HTW) handling and processing. The preliminary tests using a metal oxide reactor producing HTW afterward detritiated with PERMCAT were successful. In a later stage, a micro-channel catalytic reactor was installed in view of long term R&D program on HTW The integration of this new system in CAPER was carried out along with a careful safety analysis due to high risk associated with such experiments. First experiments using the mu-CCR were performed trouble free, and HTW up to 360 kCi/kg was produced at a rate of 0.5 g/h. Such HTW was collected into a platinized zeolite bed (2 g of HTW for 20 g of Pt-zeolite), and in-situ detritiation was performed via isotopic exchange with deuterium. These first experimental results with tritium confirmed the potential for the capture and exchange method to be used for HTW in ITER.