Constraining preheat energy deposition in MagLIF experiments with multi-frame shadowgraphy

Abstract

A multi-frame shadowgraphy diagnostic has been developed and applied to laser preheat experiments relevant to the Magnetized Liner Inertial Fusion (MagLIF) concept. The diagnostic views the plasma created by laser preheat in MagLIF-relevant gas cells immediately after the laser deposits energy as well as the resulting blast wave evolution later in time. The expansion of the blast wave is modeled with 1D radiation-hydrodynamic simulations that relate the boundary of the blast wave at a given time to the energy deposited into the fuel. This technique is applied to four different preheat protocols that have been used in integrated MagLIF experiments to infer the amount of energy deposited by the laser into the fuel. The results of the integrated MagLIF experiments are compared with those of two-dimensional LASNEX simulations. The best performing shots returned neutron yields $40-55% of the simulated predictions for three different preheat protocols.

Performance Scaling in Magnetized Liner Inertial Fusion Experiments

“…This Letter describes the first successful experimental demonstration of performance scaling in a MIF concept; significantly increased neutron production was observed with greater applied magnetic field, laser preheat energy, and drive current. The maximum performance in MagLIF now exceeds 10 13 primary deuterium-deuterium (DD) neutrons (2 kJ deuterium-tritium equivalent), representing a factor of 3 increase over the highest previously reported MagLIF experimental yield [27]. Trends observed in parametric scans of individual input parameters, as well as the improved performance observed when all inputs were simultaneously increased, are consistent with expectations based on 2D magnetohydrodynamics calculations [28] performed in LASNEX.…”

“…This configuration utilizes a distributed phase plate to create a more uniform intensity laser spot and a laser pulse shape with a low energy (0.02 kJ) prepulse, 0.3 kJ foot, and 2.2 kJ main pulse to deposit up to 1.4 kJ in the fuel. Note that all subsequent preheat energy values reported in this Letter refer to the energy deposited in the fuel (determined using the measured energy at the output of the laser and deposition fractions based on off-line experiments using similar target configurations and laser pulses [27,30]). Finally, an advanced magnetic field coil [32] and more efficient final transmission line were developed [ Fig.…”

Exploring the Parameter Space of MagLIF Implosions using Similarity Scaling

“…29,36 The thin-shell model can be readily retrieved by summing Eqs. (19) and (20) and approximating R(t) R out (t) R in (t). This leads to…”

“…Therefore, the fuel is not shock-heated; instead, it is preheated by a 2-4 kJ, TW-class laser to achieve sufficient adiabatic compression to fusion relevant temperatures. [17][18][19][20][21][22][23] Since the implosions are slower (on the order of 100 ns), the fuel must be premagnetized to reduce thermal conduction losses. 9 This is achieved by external electromagnetic coils that premagnetize the entire fuel volume with an axial 10-16 T magnetic field.…”

A pulsed-power implementation of “Laser Gate” for increasing laser energy coupling and fusion yield in magnetized liner inertial fusion (MagLIF)

“…Energy losses are believed to occur because of this LPI, energy absorption into the window material, and from window material mixing into the fuel (which leads to enhanced radiation loss). [5][6][7][8][9][10] To reduce these losses, the LEH window could be removed before the preheating laser passes through the LEH. This concept of early-time window removal is referred to as "Laser Gate".…”