Developing MagLIF Laser Preheat for Z and Beyond*

.Laser preheat is a critical component of the Magnetized Liner Inertial Fusion (MagLIF) inertial confinement fusion (ICF) approach [1] that sets the initial adiabat of the fuel before implosion. In the laser preheat phase, energy from a multi-kJ laser is coupled into the ~10-mm-long underdense gaseous fuel (typically D₂) within the MagLIF target by inverse Bremsstrahlung absorption. The amount of energy coupled within that length is a crucial parameter. The process is complicated by the presence of a strong applied magnetic field and by potential laser plasma instabilities and beam self-focusing and filamentation that can dramatically alter how much energy is coupled within the fuel.

 

This talk will describe how the understanding and implementation of laser preheat has changed in the decade since the first integrated MagLIF experiments on the Z pulsed power facility [2]. Significant advances include the development of an experimental platform that assesses the preheat energy coupled in each MagLIF experiment [3]; the implementation of spatial smoothing to reduce laser plasma instabilities (LPI) [4]; controlling the temporal profile of the laser pulse to reduce mix [5]; and cryogenically cooling the fuel to enable thinner laser entrance hole foils and more efficient heating [6]. These efforts have resulted in a >2 times increase in preheat energy coupled to the fuel in integrated MagLIF experiments on Z [6] and the elimination of some mix sources. Ongoing research at the Omega and National Ignition Facility lasers are investigating preheat induced mix, the effects of magnetization on LPI, and energy scaling up to 10’s of kJ [7]. These efforts have given confidence in our understanding of laser preheat in MagLIF experiments on Z and its viability for future, larger facilities.

[1]: S. A. Slutz et al., Physics of Plasmas 17, 056303 (2010)

[2]: M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)

[3]: A. J. Harvey-Thompson et al., Physics of Plasmas 26, 032707 (2019)

[4]: M. Geissel et al., Physics of Plasmas 25, 022706 (2018)

[5]: A. J. Harvey-Thompson et al., Physics of Plasmas 25, 112705 (2018)

[6]: A. J. Harvey-Thompson et al., Rev. Sci. Instrum. 94, 053506 (2023)

[7]: B. B. Pollock et al., Physics of Plasmas 30, 022711 (2023)