The physics design guidelines for a next step, high-field tokamak, burning plasma experiment (FIRE, Fusion Ignition Research Experiment) have been developed as an update of the ITER Physics Basis (IPB). The plasma performance attainable in FIRE (or any next-step device) is affected by many physics issues, including energy confinement, L-to-H-mode power transition thresholds, MHD stability/beta limit, density limit, helium accumulation/removal, impurity content, sawtooth effects, etc. Design basis and guidelines are provided in each of these areas, along with sensitivities and/or uncertainties involved. The overall basic device parameters and features for FIRE (R = 2 m, a = 0.525 m, κ95 ~ 1.8, δ95 ~ 0.4, q95 > 3, B = 10-12 T, I = 6.45-7.7 MA, Pfus ~ 100-200 MW, Q ~ 5-10) are consistent with these guidelines and uncertainties if the potential design upgrade option (12 T, 8 MA) is considered as part of the main design option.