问题不在于连续性，这个实验室根本就是一个开心果

Using the traditional definition of Q, P_fus / P_heat, ICF devices have extremely low Q. This is because the laser is extremely inefficient; whereas {\displaystyle \eta _{heat}} for the heaters used in magnetic systems might be on the order of 70%, lasers are on the order of 1%.

For this reason, Lawrence Livermore National Laboratory (LLNL), the leader in ICF research, has proposed another modification of Q that defines P_heat as the energy delivered by the driver to the capsule, as opposed to the energy put into the driver by an external power source. That is, they propose removing the laser's inefficiency from the consideration of gain. This definition produces much higher Q values, and changes the definition of breakeven to be P_fus / P_laser = 1. On occasion, they referred to this definition as "scientific breakeven".^[17][18] This term was not universally used; other groups adopted the redefinition of Q but continued to refer to P_fus = P_laser simply as breakeven.^[19]

On 7 October 2013, LLNL announced that it had achieved scientific breakeven in the National Ignition Facility (NIF) on 29 September.^[20][21][22] In this experiment, P_fus was approximately 14 kJ, while the laser output was 1.8 MJ. By their previous definition, this would be a Q of 0.0077. For this press release, they re-defined Q once again, this time equating P_heat to be only the amount energy delivered to "the hottest portion of the fuel", calculating that only 10 kJ of the original laser energy reached the part of the fuel that was undergoing fusion reactions. This release has been heavily criticized in the field.^[23][24]

On 17 August 2021, the NIF announced that in early August 2021, an experiment had achieved a Q value of 0.7, producing 1.35 MJ of energy from a fuel capsule by focusing 1.9 MJ of laser energy on the capsule. The result was an eight-fold increase over any prior energy output.^[25]