Plasma Density Transition Research Articles

Enhanced self-focusing of Laguerre-Gaussian laser beam in relativistic plasma under exponential plasma density transition

In the current work, self-focusing of Laguerre-Gaussian laser beam under the influence of exponential plasma density transition in relativistic plasma is studied. It is observed that the spot size of laser beam shrinks as beam propagates into the plasma because of exponential plasma density ramp. The exponential plasma density ramp reduces the beam width parameter due to its slowly variation ramp profile. Also, with the rise in intensity of the laser beam, self-focusing enhances significantly. Our results in the present manuscript may be helpful in the field where strong self-focusing of the laser is required such as high-power laser driven fusion, explanation of devices involved in beam propagation in the various applications.

Strong self-focusing of a chirped pulse laser in thermal quantum plasma under density transition

In the present manuscript, an analysis has been done on strong self-focusing of a chirped pulse laser in thermal quantum plasma under exponential plasma density transition. It is observed that the beam width parameter reduces up to great extent which in turns enhances the process of self-focusing. It is observed that in the embellishment of self-focusing of laser beam, thermal quantum plasma contributes significantly. Further, it is seen that with change in different parameters like intensity of the laser beam, chirped parameter value and plasma frequency, self-focusing is sensitive and becomes stronger at higher values of these parameters. The present work may have important applications in field of laser interaction with the quantum plasma, laser driven particle accelerators etc.

Relativistic Self-Focusing of Hermite-cosine-Gaussian Laser Beam in Collisionless Plasma with Exponential Density Transition

This work reveals an exploration of self-focusing of Hermite-cosine-Gaussian laser beam in a collisionless plasma under relativistic nonlinearity. Self-focusing along with self-trapping of Hermite-cosine-Gaussian laser beam are analyzed for different values of laser intensity, plasma density, and decentered parameters. Mathematical analysis displays that these parameters play a major role in achieving the stronger and earlier self-focusing. Further, a comparative study between self-focusing of Hermite-cosine-Gaussian laser beam with and without exponential density ramp profile is introduced. Plasma density transition with exponential profile is found to be more effective in order to have stronger self-focusing. The present analysis may lead to very useful applications in the field of efficient harmonic generation, laser driven fusion etc.

Resonant second harmonic generation in plasma under exponential density ramp profile

Resonant second harmonic generation of a relativistic self-focused laser beam in plasma under exponential density ramp profile is investigated. It has been found that the self-focusing of Gaussian laser beam becomes stronger in plasma with exponential density ramp profile hence, leads to enhance the resonant second harmonic generation. The periodic variation of the normalized second-harmonic amplitude with normalized distance has been analyzed for different laser and plasma parameters. Therefore, enhanced second harmonic generation on account of relativistic self-focusing of fundamental laser beam in plasma under plasma density transition is observed. One may notice that exponential density ramp plays an important role in making the self-focusing stronger which in turn enhances the second harmonic generation in plasma.

Enhanced resonant second harmonic generation in plasma based on density transition

Abstract Resonant second harmonic generation of a relativistic self-focusing laser in plasma with density ramp profile has been investigated. A high intense Gaussian laser beam generates resonant second harmonic beam in plasma with density ramp profile. The second harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second harmonic amplitude varies periodically with distance and attains maximum value in the focal region. Enhancement in the second harmonic amplitude on account of relativistic self-focusing of laser based on plasma density transition is seen. Plasma density ramp plays an important role to make self-focusing stronger which leads to enhance the second harmonic generation in plasma.

Enhanced relativistic self-focusing of Hermite-cosh-Gaussian laser beam in plasma under density transition

Enhanced and early relativistic self-focusing of Hermite-cosh-Gaussian (HChG) beam in the plasmas under density transition has been investigated theoretically using Wentzel-Kramers-Brillouin and paraxial ray approximation for mode indices m=0, 1, and 2. The variation of beam width parameter with normalized propagation distance for m=0, 1, and 2 is reported, and it is observed that strong self-focusing occurs as the HChG beam propagates deeper inside the nonlinear medium as spot size shrinks due to highly dense plasmas and the results are presented graphically. A comparative study between self-focusing of HChG beam in the presence and absence of plasmas density transition is reported. The dependency of beam width parameter on the normalized propagation distance for different values of decentered parameter “b” has also been presented graphically. For m=0 and 1, strong self-focusing is reported for b=1.8, and for m=2 and b=1.8, beam gets diffracted. The results obtained indicate the dependency of the self-focusing of the HChG beam on the selected values of decentered parameter. Moreover, proper selection of decentered parameter results strong self-focusing of HChG beam. Stronger self-focusing of laser beam is observed due to the presence of plasma density transition which might be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, etc.

Creation of plasma density transitions short compared to the plasma skin depth

A plasma based electron beam source apparatus is described which creates a plasma with two distinct density regions separated by a transition which is shorter than the plasma skin depth kp−1 of either region. This sharp density modulation is achieved by using a perforated stainless steel screen to filter half of a diffusing plasma column. A simple physical model predicts that the length of the plasma density transition will vary with the distance from the screen. For a weakly magnetized plasma, the transition length will be twice the distance, on a line normal to the screen plane, from the screen edge to the location where the transition is measured. The plasma column is generated using an argon discharge plasma source. It has a peak density of approximately 3.5×1013cm−3 and a full width half maximum width of 5 cm. The discharge source utilizes a 7.5 cm diameter LaB6 disk cathode heated to 1300 °C using a graphite heater. The plasma column is filtered with a 78μm thick stainless steel sheet with 152μm holes and 21% open area. Plasma density transitions with lengths between 0.74 and 0.95kp−1 were measured.

Laser wake field acceleration with controlled self-injection by sharp density transition

Laser Wake Field Acceleration of relativistic electron bunches is a promising method to produce a large amount of energetic particles with table top equipment. One of the possible methods to inject particles in the appropriate acceleration phase of the wake behind the pulse takes advantage of the partial longitudinal breaking of the wake crests across a density downramp. In this paper results of 2.5D PIC simulations, showing the production of an electron bunch with reduced energy spread, are reported. Also, a possible method to produce the required plasma density transition by laser explosion of a suitable couple of thin foils is discussed.

Emittance Growth of High-Energy Electrons Produced From the Laser Wakefield Acceleration

When a laser wake field passes a sharp downward plasma density transition, a significant amount of plasma electrons are trapped and accelerated to relativistic high energies over a distance of the plasma wavelength. Phase space area of the plasma electrons remains constant during acceleration in the ion channel, but it was found that the phase space area, which is related with emittance, increases rapidly by the nonlinear space-charge field when the electron beam moves out of the plasma. As a result, the emittance of the accelerated electron beam grows severely during propagation in free space, and ultimately this limits the beam intensity. The emittance growth problem is investigated with two-dimensional particle-in-cell simulations, and several methods are suggested to suppress such a rapid emittance growth.

Plasma density transition trapping as a possible high-brightness electron beam source

Plasma density transition trapping as a possible high-brightness electron beam source

Femtosecond X-ray generation via the thomson scattering of a terawatt laser from electron bunches produced from the LWFA utilizing a plasma density transition

We propose a novel experimental scheme for a compact and tunable X-ray source capable of producing X-ray pulses with a few tens of femtosecond duration. This new source is simple; it does not require an RF-based accelerator or injector. It is based on the Thomson back-scattering of a terawatt femtosecond laser from the megaelectronvolt-level plasma-accelerated electrons. Here, we present particle-in-cell simulation results for the ultrashort e-beam generation from the laser-wakefield accelerators with a plasma-density transition and the basic characteristics of the X-ray generation. Using a 20-TW 40-fs laser system, we are going to perform an experiment for generating ultrashort X-rays via the Thomson scattering.

Electron acceleration based on self-trapping by plasma wake fields

A method for self-injection of background plasma electrons in a plasma wake field is introduced. In this scheme, a plasma wake wave, which can be generated by an intense laser pulse or an electron beam pulse propagating in a plasma, is passed through a sharply downward plasma density transition. When the plasma wake wave passes the density transition, some background plasma electrons are trapped by the ultrastrong plasma wake field that is several orders of magnitude stronger than the accelerating electric field in conventional rf-based accelerators. In this paper, the basic mechanism of the trapping is introduced and two-dimensional particle-in-cell simulation results including trapped-beam quality studies are presented. In addition, the experimental program to investigate the self-injection-based acceleration at the Center for Advanced Accelerators of KERI is introduced.