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Results for “Longitudinal dynamics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Simple Longitudinal Dynamics Modeling for X-FEL Linacs

We generate a first-order model for the longitudinal dynamics of an X-FEL linac with a 2-stage bunch compression scheme, such a MaRIE. While such a simple approach cannot capture all of the subtleties of relevant effects such as coherent spontaneous emission (CSR) and space-charge induced microbunching instabilities, simple scaling laws permit insight into the potential magnitude of those effects. This approach also allows an initial estimation of overall accelerator system length, and required dechirping at the end of the accelerator, thus permitting relative evaluations of proposed configurations.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Longitudinal dynamics and particle production in relativistic nuclear collisions

This work presents a three-dimensional dynamical initialization model for relativistic heavy-ion collisions, implementing local energy-momentum conservation and baryon charge fluctuations at string junctions. Constraining parameters using experimental data from p + p collisions at various collision energies, the model provides a very good description of the charged hadron and net proton rapidity distributions in Au +Au collisions from 7.7 to 200 GeV and Pb + Pb collisions at 8.77 and 17.3 GeV. Here we demonstrate the importance of fluctuations of baryon densities to string junctions for describing net-proton distributions at collision energies of 62.4 and 200 GeV. Including this improved baryon stopping description along with the requirement of strangeness neutrality also yields a good description of identified particle yields as functions of the collision energy above 7.7 GeV. We further study asymmetric p + Al and (p,d, 3 He) + Au collisions at the top RHIC energy and p + Pb, Xe + Xe, and Pb + Pb collisions at LHC energies. We identify the produced particle rapidity distributions in asymmetric collision systems as particularly useful for constraining models of the early-time longitudinal dynamics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Start-to-End Simulation of the Drive-Beam Longitudinal Dynamics for Beam-Driven Wakefield Acceleration

Collinear beam-driven wakefield acceleration (WFA) relies on shaped driver beam to provide higher accelerating gradient at a smaller cost and physical footprint. This acceleration scheme is currently envisioned to accelerate electron beams capable of driving free-electron laser *. Start-to-end simulation of drive-bunch beam dynamics is crucial for the evaluation of the design of accelerators built upon WFA. We report the start-to-end longitudinal beam dynamics simulations of an accelerator beamline capable of producing high charge drive beam. The generated wakefield when it passes through a corrugated waveguide results in a transformer ratio of 5. This paper especially discusses the challenges and criteria associated with the generation of temporally-shaped driver beam, including the beam formation in the photoinjector, and the influence of energy chirp control on beam transport stability.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

The use of BMAD in simulating transverse and longitudinal dynamics in RHIC

In accelerator physics, models of a given machine are used to predict the behaviors of the beam, magnets, and radiofrequency cavities. The use of the computational model has become wide spread to ease the development period of the accelerator lattice. There are various programs that are used to create lattices and run simulations of both transverse and longitudinal beam dynamics. The programs include Methodical Accelerator Design(MAD) MAD8, MADX, Zgoubi, Polymorphic Tracking Code (PTC), and many others. In this discussion the BMAD (Baby Methodical Accelerator Design) is presented as an additional tool in creating and simulating accelerator lattices for the study of beam dynamics in the Relativistic Heavy Ion Collider (RHIC).

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Probing early-time longitudinal dynamics with the Λ hyperon's spin polarization in relativistic heavy-ion collisions

Here, we systematically study the hyperon global polarization's sensitivity to the collision systems' initial longitudinal flow velocity in hydrodynamic simulations. By explicitly imposing local energy-momentum conservation when mapping the initial collision geometry to macroscopic hydrodynamic fields, we study the evolution of systems' orbital angular momentum (OAM) and fluid vorticity. We find that a simultaneous description of the $\Lambda$ hyperons' global polarization and the slope of pion's directed flow can strongly constrain the size of longitudinal flow at the beginning of hydrodynamic evolution. We extract the size of the initial longitudinal flow and the fraction of orbital angular momentum in the produced QGP fluid as a function of collision energy with the STAR measurements in the RHIC Beam Energy Scan program. We find that there is about 100-200 $\hbar$ OAM that remains in the mid-rapidity fluid at the beginning of hydrodynamic evolution. We further exam the effects of different hydrodynamic gradients on the spin polarization of $\Lambda$ and $\bar{\Lambda}$. The gradients of $\mu_B/T$ can change the ordering between $\Lambda$'s and $\bar{\Lambda}$'s polarization.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Longitudinal dynamics of high baryon density matter in high-energy heavy-ion collisions

In high-energy heavy-ion collisions, the two colliding nuclei pass through each other leaving behind an almost baryon-free central rapidity region. Most of the baryons are carried away by the nuclear remnants and are located in the so-called fragmentation regions. In previous papers, it has been argued that very high baryon densities, more than ten times larger than the normal nuclear density, can be achieved in these fragmentation regions. In this paper, we assume the high baryon density matter is thermalized at the same time as the baryon-free quark-gluon plasma in the central rapidity region. We perform a 1+1D (temporal + longitudinal) hydrodynamic simulation covering both the fragmentation regions and the central rapidity region with the baryon diffusion equation included. Baryons are found to diffuse from the fragmentation regions to the central rapidity region driven by fugacity gradients. Here, the baryon chemical potential at freezeout monotonically increases from the central rapidity region to the fragmentation regions, suggesting a rapidity scan in high-energy heavy-ion collisions might be helpful in searching for the critical point of the quantum chromodynamics phase diagram.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Longitudinal train dynamics model for a rail transit simulation system

The paper develops a longitudinal train dynamics model in support of microscopic railway transportation simulation. The model can be calibrated without any mechanical data making it ideal for implementation in transportation simulators. The calibration and validation work is based on data collected from the Portland light rail train fleet. The calibration procedure is mathematically formulated as a constrained non-linear optimization problem. The validity of the model is assessed by comparing instantaneous model predictions against field observations, and also evaluated in the domains of acceleration/deceleration versus speed and acceleration/deceleration versus distance. A test is conducted to investigate the adequacy of the model in simulation implementation. The results demonstrate that the proposed model can adequately capture instantaneous train dynamics, and provides good performance in the simulation test. Thus, the model provides a simple theoretical foundation for microscopic simulators and will significantly support the planning, management and control of railway transportation systems.

42 ENGINEERING↗
DOE OSTI2018

Longitudinal Beam Dynamics with a Higher-Harmonic Cavity for Bunch Lengthening

In Sect.1 we review the conditions of operation of an HHC system assuming its stability. We first discuss the longitudinal dynamics with an active HHC and the conditions that lead to a quartic potential in the limit of small oscillations, together with formulae giving the bunch lengthening factor and the synchrotron frequency dependence on the amplitude of the synchrotron oscillations. We discuss next passive HHC operations with uniform fillings, and distinguish the case of normal-conducting HHC, where optimal conditions of operation can be met, from the case of superconducting HHC, where optimal conditions of operation can be satisfied only approximately. In Sect.2 we address the stability of the passive superconducting 3HC system of the NSLS-II storage ring via self-consistent simulations with code SPACE. The case of nominal fractional filling of 80% is compared with the case of fractional filling of 90% and with the uniform filling case. It is shown that for values of the detuning frequency in the neighborhood of the good working point discussed in Sect.2, unstable regimes of oscillation are found, with detuning frequency threshold dependent on the gap in the filling. It is shown that the instability regime is characterized by dipole and quadrupole modes of oscillation exhibiting asymptotically nonlinear saturation. A discussion of the average bunch lengthening, together with the degree of uniformity across the bunch train, achievable under stable conditions as a function of the fractional filling concludes the paper.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Longitudinal beam dynamics with a higher-harmonic cavity for bunch lengthening

We discuss here the longitudinal beam dynamics in storage rings in the presence of a higher-harmonic cavity (HHC) system for bunch lengthening. First, we review the general conditions for HHC operations, both in active or passive modes, assuming the stability of the system. For uniform filling patterns, a distinction is made between operations with a normal-conducting HHC, where optimal conditions for bunch lengthening can be satisfied, and operations with a super-conducting HHC, where optimal conditions can be met only approximately. Furthermore, we report on the option to operate the NSLS-II storage ring with a passive, super-conducting third harmonic cavity (3HC) system. The stability and performance of the system in the presence of a gap in the uniform filling, which corresponds to the present mode of operation of the NSLS-II storage ring, is investigated with self-consistent Vlasov–Fokker–Planck simulations performed with the code SPACE.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

The coherence of collective modes, such as phonons and polarons, and their modulation of electronic states is long sought in complex systems, which is a crosscutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polarons, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal-optical (LO) phonons, has been intensely studied yet is still debated. This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes, and diffusion lengths. In this work we use the intense single-cycle THz pulse with peak electric field up to E THz = 1000 kV/cm to drive coherent polaronic band-edge oscillations at room temperature in CH 3 NH 3 PbI 3 (MAPbI 3 ). We reveal the oscillatory behavior is dominated by a specific quantized lattice vibration mode at $ω$ LO ~ 4 THz, which is both dipole and momentum forbidden. THz-driven coherent polaron dynamics exhibits distinguishing features: room temperature coherent oscillations at ω LO longer than 1 ps in both single crystals and thin films, mode-selective modulation of different band-edge states assisted by electron-phonon interaction, and dynamic mode splitting at low temperature due to entropy and anharmonicity of organic cations. Our results demonstrate intense THz-driven coherent band-edge modulation is a powerful probe of electron-lattice coupling phenomena and polaronic quantum control in perovskites.

36 MATERIALS SCIENCE↗