Longitudinal Pulse Compression Research Articles

Tailoring mode interference in plasmon-induced transparency metamaterials

We proposed an approach to tailor the mode interference effect in plasmon-induced transparency (PIT) metamaterials. Through introducing an extra coupling mode using an asymmetric structure configuration at terahertz (THz) frequencies, the well-known single-transparency-window PIT can be switched to dual-transparency-window PIT. Proof-of-concept subwavelength structures were fabricated and experimentally characterized. The measured results are in good agreement with the simulations, and well support our theoretical analysis. The presented research delivers a novel approach toward developing subwavelength devices with varies functionalities, such as ultra-slow group velocities, longitudinal pulse compression and light storage in the THz regime, which can also be extended to other spectral regimes.

Design and commissioning of the RIKEN cryogenic electrostatic ring (RICE).

A new electrostatic ion storage ring, the RIKEN cryogenic electrostatic ring, has been commissioned with a 15-keV ion beam under cryogenic conditions. The ring was designed with a closed ion beam orbit of about 2.9 m, where the ion beam is guided entirely by electrostatic components. The vacuum chamber of the ring is cooled using a liquid-He-free cooling system to 4.2 K with a temperature difference of 0.4 K at most within all the positions measured by calibrated silicon diode sensors. The first cryogenic operation with a 15-keV Ne+ beam was successfully performed in August 2014. During the measurement, the Ne+ beam was stored under a ring temperature of 4.2 K with a residual-gas lifetime of more than 10 min. This permits an estimation of the residual gas density at a few 104 cm-3, which corresponds to a room-temperature-equivalent pressure of around 1×10-10 Pa. An effect of longitudinal pulse compression at the bunching cavity in the ring was clearly identified by monitoring the pick-up beam detector. The detailed design and mechanical structure of the storage ring, as well as the results from the commissioning run, are reported.

Spatiotemporal dynamics of Gaussian laser pulse in a multi ions plasma

Spatiotemporal evolutions of Gaussian laser pulse propagating through a plasma with multiple charged ions are studied, taking into account the ponderomotive nonlinearity. Coupled differential equations for beam width and pulse length parameters are established and numerically solved using paraxial ray approximation. In one-dimensional geometry, effects of laser and plasma parameters such as laser intensity, plasma density, and temperature on the longitudinal pulse compression and the laser intensity distribution are analyzed for plasmas with singly and doubly charged ions. The results demonstrate that self-compression occurs in a laser intensity range with a turning point intensity in which the self-compression process has its strongest extent. The results also show that the multiply ionized ions have different effect on the pulse compression above and below turning point intensity. Finally, three-dimensional geometry is used to analyze the simultaneous evolution of both self-focusing and self-compression of Gaussian laser pulse in such plasmas.

Theoretical Estimation and Multiparticle Simulation on Evolution of Longitudinal and Transverse Temperatures During Pulse Compression in Compact Simulator for Heavy Ion Inertial Fusion

Kinetic energy exchange in the longitudinal and transverse directions of a charged particle beam during longitudinal pulse compression is discussed through a compact beam simulator for heavy ion inertial fusion. With the goal of understanding the beam behavior in a compact beam simulator experiment, the evolution of the transverse and longitudinal thermal spreads is evaluated using theoretical estimation and numerical simulation. The multiparticle simulation results show the longitudinal and transverse coupling motions via the space charge effect during the longitudinal pulse compression. The ratio of effective temperatures in the longitudinal and transverse directions derived from numerical results is higher than that evaluated from theoretical estimation. It is implied that the discrepancy is caused by the nonlinear space charge effect during the longitudinal bunch compression.

Self-compression of intense short laser pulses in relativistic magnetized plasma

The compression of a relativistic Gaussian laser pulse in a magnetized plasma is investigated. By considering relativistic nonlinearity and using non-linear Schrödinger equation with paraxial approximation, a second-order differential equation is obtained for the pulse width parameter (in time) to demonstrate the longitudinal pulse compression. The compression of laser pulse in a magnetized plasma can be observed by the numerical solution of the equation for the pulse width parameter. The effects of magnetic field and chirping are investigated. It is shown that in the presence of magnetic field and negative initial chirp, compression of pulse is significantly enhanced.

Electromagnetic pulse compression and energy localization in quantum plasmas

The evolution of the intensity of a relativistic laser beam propagating through a dense quantum plasma is investigated, by considering different plasma regimes. A cold quantum fluid plasma and then a thermal quantum description(s) is (are) adopted, in comparison with the classical case of reference. Considering a Gaussian beam cross-section, we investigate both the longitudinal compression and lateral/longitudinal localization of the intensity of a finite-radius electromagnetic pulse. By employing a quantum plasma fluid model in combination with Maxwell's equations, we rely on earlier results on the quantum dielectric response, to model beam-plasma interaction. We present an extensive parametric investigation of the dependence of the longitudinal pulse compression mechanism on the electron density in cold quantum plasmas, and also study the role of the Fermi temperature in thermal quantum plasmas. Our numerical results show pulse localization through a series of successive compression cycles, as the pulse propagates through the plasma. A pulse of 100 fs propagating through cold quantum plasma is compressed to a temporal size of ≈1.35 attosecond and a spatial size of ≈ 1.08 ⋅ 10 − 3 cm . Incorporating Fermi pressure via a thermal quantum plasma model is shown to enhance localization effects. A 100 fs pulse propagating through quantum plasma with a Fermi temperature of 350 K is compressed to a temporal size of ≈0.6 attosecond and a spatial size of ≈ 2.4 ⋅ 10 − 3 cm .

Relativistic laser pulse compression in plasmas with a linear axial density gradient

The self-compression of a relativistic Gaussian laser pulse propagating in a non-uniform plasma is investigated. A linear density inhomogeneity (density ramp) is assumed in the axial direction. The nonlinear Schrödinger equation is first solved within a one-dimensional geometry by using the paraxial formalism to demonstrate the occurrence of longitudinal pulse compression and the associated increase in intensity. Both longitudinal and transverse self-compression in plasma is examined for a finite extent Gaussian laser pulse. A pair of appropriate trial functions, for the beam width parameter (in space) and the pulse width parameter (in time) are defined and the corresponding equations of space and time evolution are derived. A numerical investigation shows that inhomogeneity in the plasma can further boost the compression mechanism and localize the pulse intensity, in comparison with a homogeneous plasma. A 100 fs pulse is compressed in an inhomogeneous plasma medium by more than ten times. Our findings indicate the possibility for the generation of particularly intense and short pulses, with relevance to the future development of tabletop high-power ultrashort laser pulse based particle acceleration devices and associated high harmonic generation. An extension of the model is proposed to investigate relativistic laser pulse compression in magnetized plasmas.

Beam behavior under a non-stationary state in high-current heavy ion beams

Three-dimensional beam dynamics in a space-charge-dominated regime during a longitudinal pulse compression is investigated numerically using a multi-particle code developed. Results are compared with those of a two-dimensional particle simulation including a longitudinal current increase model. The rms transverse emittance additionally increases along the drift distance due to the longitudinal motion of the beam particles. The three-dimensional beam behavior can be also compared with a longitudinal one-dimensional calculation under a condition of a constant geometry factor for the transverse direction. Results indicate that the longitudinal beam dynamics are not affected by the transverse motions in the parameter regime.

Simulations and experiments of intense ion beam current density compression in space and time

The Heavy Ion Fusion Science Virtual National Laboratory has achieved 60-fold longitudinal pulse compression of ion beams on the Neutralized Drift Compression Experiment (NDCX) [P. K. Roy et al., Phys. Rev. Lett. 95, 234801 (2005)]. To focus a space-charge-dominated charge bunch to sufficiently high intensities for ion-beam-heated warm dense matter and inertial fusion energy studies, simultaneous transverse and longitudinal compression to a coincident focal plane is required. Optimizing the compression under the appropriate constraints can deliver higher intensity per unit length of accelerator to the target, thereby facilitating the creation of more compact and cost-effective ion beam drivers. The experiments utilized a drift region filled with high-density plasma in order to neutralize the space charge and current of an ∼300 keV K+ beam and have separately achieved transverse and longitudinal focusing to a radius <2 mm and pulse duration <5 ns, respectively. Simulation predictions and recent experiments demonstrate that a strong solenoid (Bz<100 kG) placed near the end of the drift region can transversely focus the beam to the longitudinal focal plane. This paper reports on simulation predictions and experimental progress toward realizing simultaneous transverse and longitudinal charge bunch focusing. The proposed NDCX-II facility would capitalize on the insights gained from NDCX simulations and measurements in order to provide a higher-energy (>2 MeV) ion beam user-facility for warm dense matter and inertial fusion energy-relevant target physics experiments.

Long-pulse ion induction linac

Important issues for the long-pulse induction ion accelerator are (1) the development of high-current long-pulse ion injectors, (2) a method for precise modulation of ion energy for longitudinal pulse compression, (3) core material selection of reasonable construction cost and size, and (4) a realistic scheme for the ion beam transport at low- β region. At the present stage of our project, emphasis has been placed on the characterization of magnetic materials and the development of the long pulse, high flux, low emittance ion injectors. For the precise voltage modulation and cost effective selection of magnetic cores, we measured the response of various ferromagnetic materials under fast-pulse excitation. For the intense, long-pulse ion injectors, we propose drifting point-expanding plasma sources, which compress (smooth out) and expand (cool) the source plasma. These issues are discussed based on some experimental results.

Design and performance characteristics of a compact induction acceleration module for longitudinal pulse compression experiments

A compact induction acceleration module has been designed and constructed for electron beam experiments at the University of Maryland aimed at investigating the physics of longitudinal bunching and compression. The module imparts a front-to-tail energy shear to the pulsed electron beam (15–50 ns) causing longitudinal compression in a 5 m long periodic solenoid channel. The design parameters, operating principle and performance characteristics of this device are reported in this paper.