Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator

The transverse self-modulation of ultra-relativistic, long lepton bunches in high-density plasmas is explored through full-scale particle-in-cell simulations. We demonstrate that long SLAC-type electron and positron bunches can become strongly self-modulated over centimeter distances, leading to wake excitation in the blowout regime with accelerating fields in excess of 20 GV/m. We show that particles energy variations exceeding 10 GeV can occur in meter-long plasmas. We find that the self-modulation of positively and negatively charged bunches differ when the blowout is reached. Seeding the self-modulation instability suppresses the competing hosing instability. This work reveals that a proof-of-principle experiment to test the physics of bunch self-modulation can be performed with available lepton bunches and with existing experimental apparatus and diagnostics.Comment: 8 pages, 8 figures, accepted for publication in Physics of Plasma

Ion motion in the wake driven by long particle bunches in plasmas

We explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ J. Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics, and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas.Comment: 23 pages, 6 figure

માધયમિક શાળાના વિધાર્થીઓનાં માનસિક સ્વાસ્થય, કૌટુંબિક સમાયોજન અને વ્યવસાયિક અભિરૂચિનો અભ્યાસ

આજનાં આ આધુનિક યુગમાં એવી કોઈ વ્યક્તિ નહિ હોય કે જે માનસિક રીતે પૂરેપૂરી સ્વસ્થ હોય સમાજમાં કેટલીક વ્યક્તિઓ જ એવી હશે જેનું માનસિક સ્વાસ્થ્ય મહદ્ અંશે સ્વસ્થ હોય. કેટલી પ્રખ્યાત વ્યક્તિઓ જેવી કે વૈજ્ઞાનિક આઈનસ્ટાઇન, મનોવૈજ્ઞાનિક ફ્રોઈડ, ચિત્રકાર પિકાસો, સાહિત્યકાર ઇલિયેટ, ધાર્મિક મહામાનવ વિવેકાનંદ, રાજકીય વ્યક્તિઓમાં ગાંધીજી વગેરે મહાનુભાવોના જીવનચરિત્ર પરથી કહી શકીએ કે તેઓ માનસિક સ્વાસ્થ્યનાં ગુણોનો સુંગ્રથિત જથ્થો સાથે લઈને જીવ્યા હતા. આજના યુગમાં માનવી માનસિક સ્વાસ્થ્યની સાથે કૌટુંબિક સમાયોજનની કેટલીક મુશ્કેલીઓ પણ અનુભવે છે

Magnetically assisted self-injection and radiation generation for plasma based acceleration

It is shown through analytical modeling and numerical simulations that external magnetic fields can relax the self-trapping thresholds in plasma based accelerators. In addition, the transverse location where self-trapping occurs can be selected by adequate choice of the spatial profile of the external magnetic field. We also find that magnetic-field assisted self-injection can lead to the emission of betatron radiation at well defined frequencies. This controlled injection technique could be explored using state-of-the-art magnetic fields in current/next generation plasma/laser wakefield accelerator experiments.Comment: 7 pages, 4 figures, accepted for publication in Plasma Physics and Controlled Fusio

Baryon loading and the Weibel instability in gamma-ray bursts

The dynamics of two counter-streaming electron-positron-ion unmagnetized plasma shells with zero net charge is analyzed in the context of magnetic field generation in GRB internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios.Comment: 6 pages, 4 figures. Accepted for publication in MNRA

Long-time evolution of magnetic fields in relativistic GRB shocks

We investigate the long-time evolution of magnetic fields generated by the two-stream instability at ultra- and sub-relativistic astrophysical collisionless shocks. Based on 3D PIC simulation results, we introduce a 2D toy model of interacting current filaments. Within the framework of this model, we demonstrate that the field correlation scale in the region far downstream the shock grows nearly as the light crossing time, lambda(t) ~ ct, thus making the diffusive field dissipation inefficient. The obtained theoretical scaling is tested using numerical PIC simulations. This result extends our understanding of the structure of collisionless shocks in gamma-ray bursts and other astrophysical objects.Comment: 5 pages. 2 figures. Submitted to ApJ