  Advancements in high temperature superconducting technology have opened a
path toward high-field, compact fusion devices. This new parameter space
introduces both opportunities and challenges for diagnosis of the plasma. This
paper presents a physics review of a neutron diagnostic suite for a SPARC-like
tokamak [Greenwald et al 2018 doi:10.7910/DVN/OYYBNU]. A notional neutronics
model was constructed using plasma parameters from a conceptual device, called
the MQ1 (Mission $Q \geq 1$) tokamak. The suite includes time-resolved
micro-fission chamber (MFC) neutron flux monitors, energy-resolved radial and
tangential magnetic proton recoil (MPR) neutron spectrometers, and a neutron
camera system (radial and off-vertical) for spatially-resolved measurements of
neutron emissivity. Geometries of the tokamak, neutron source, and diagnostics
were modeled in the Monte Carlo N-Particle transport code MCNP6 to simulate
expected signal and background levels of particle fluxes and energy spectra.
From these, measurements of fusion power, neutron flux and fluence are feasible
by the MFCs, and the number of independent measurements required for 95%
confidence of a fusion gain $Q \geq 1$ is assessed. The MPR spectrometer is
found to consistently overpredict the ion temperature and also have a
1000$\times$ improved detection of alpha knock-on neutrons compared to previous
experiments. The deuterium-tritium fuel density ratio, however, is measurable
in this setup only for trace levels of tritium, with an upper limit of $n_T/n_D
\approx 6\%$, motivating further diagnostic exploration. Finally, modeling
suggests that in order to adequately measure the self-heating profile, the
neutron camera system will require energy and pulse-shape discrimination to
suppress otherwise overwhelming fluxes of low energy neutrons and gamma
radiation.
  *Co-first-authorship
