The magnitude of a fusion reaction rate in a plasma depends strongly on the relative energy of the reacting plasma ions and less strongly on the ion number density. The ratio of two reaction rates, however, is less dependent on the relative velocities while retaining the linear dependence on the relative densities of the plasma ion species. In this manner, the ratio of t (d,n )a to d (d,n)3 He fusion reactions depends only on the ratio nt/nd so that tritium levels in a deuterium plasma can be determined from the d-t/d-d reaction ratio [nd≃ne. Similarly, the density of 3He can be determined in a deuterium plasma from the ratio of 3He (d, p]α to d (d,n)3 He fusion reactions. Such measurements of the 3He density are of interest since they relate to the alpha ash removal problem expected on a tokamak reactor. © 1983, American Vacuum Society. All rights reserved.

The d(d, p)t and d(d, n) 3He fusion reactions produce 1 MeV tritons and 0.8 MeV 3He ions which can subsequently undergo d(t, n) α and d(3He, p) α fusion reactions. The magnitude of this triton and 3He ion ‘burn-up’ was measured on the PLT and PDX tokamaks by detection of the 14 MeV neutron and 15 MeV proton emission. In discharges with Bφ > 2 T, the measured 3He and triton burn-up is consistent (within a factor of three) with predictions based on classical theories of ion confinement and slowing down. In discharges with weaker toroidal fields but constant plasma current, the burn-up of both ions fell by more than a factor of ten so that the observed burn-up was significantly less than expected classically. © 1983 IOP Publishing Ltd.

A code that integrates the Lorentz force equation has been developed to trace a single charged particle's trajectory under the influence of toroidally symmetric magnetic fields found in tokamaks. This code is used primarily to design and estimate the efficiency of charged fusion product probes, which detect escaping energetic ions such as the 1 MeV tritons, 3 MeV protons, 15 MeV protons, and 3.5 MeV alphas created in TFTR. This interactive code has also been used as a teaching tool to illustrate classes of orbits such as trapped and passing, as well as subtle orbital motions, e.g., precession of banana orbits in tokamaks, or orbits in dipole magnetic field configuration. This paper describes the code as well as recent modifications which (1) include Shafranov shifts of the magnetic surfaces, (2) use more realistic current density profiles, and (3) allow modeling of the detector and limiters.

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.