Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA

Fox

et al. 2015

Nat Commun

Magnetic reconnection, the annihilation and rearrangement of magnetic fields in a plasma, is a universal phenomenon that frequently occurs when plasmas carrying oppositely directed field lines collide. In most natural circumstances, the collision is asymmetric (the two plasmas having different properties), but laboratory research to date has been limited to symmetric configurations. In addition, the regime of strongly driven magnetic reconnection, where the ram pressure of the plasma dominates the magnetic pressure, as in several astrophysical environments, has also received little experimental attention. Thus, we have designed the experiments to probe reconnection in asymmetric, strongly driven, laser-generated plasmas. Here we show that, in this strongly driven system, the rate of magnetic flux annihilation is dictated by the relative flow velocities of the opposing plasmas and is insensitive to initial asymmetries. In addition, out-of-plane magnetic fields that arise from asymmetries in the three-dimensional plasma geometry have minimal impact on the reconnection rate, due to the strong flows.

Section: Laser-driven Asymmetric Magnetic Reconnection Experimentsmentioning

confidence: 99%

A laboratory study of asymmetric magnetic reconnection in strongly driven plasmas

Fox

et al. 2015

Nat Commun

“…17,18 A spherical glass backlighter capsule with a 420-µm diameter and a 2 µm-thick wall, filled with 18 atm of D 3 He gas, was imploded by 22 OMEGA lasers, delivering 11 kJ in a 1-ns pulse. This implosion generated an isotropic burst of monoenergetic 15-MeV protons from the D 3 He fusion.…”

Section: Fig 1 (Color Online)mentioning

confidence: 99%

First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

Fox

et al. 2015

Physics of Plasmas

Self Cite

Novel experiments to study the strongly-driven collision of parallel magnetic fields in β∼10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell (PIC) simulations predict a stronger flux compression and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.

“…[21][22][23][24][25][26][27][28][29] The CR-39 response to protons, in particular, has been studied extensively and is well documented 17,[30][31][32][33][34] and this work rests on this previous work.…”

Section: A Omega Cr-39 Measurements Of Ddp Yieldsmentioning

confidence: 99%

A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

Waugh

Review of Scientific Instruments

Zylstra

et al. 2015

Self Cite

Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.