Question: The Department of Energy sponsors a laboratory that is currently working on magnetic fusion devices based on what principle?

Context paragraphs:
Bumpy torus: The bumpy torus is a class of magnetic fusion energy devices that consist of a series of magnetic mirrors connected end-to-end to form a closed torus.  Such an arrangement is not stable on its own, and most bumpy torus designs use secondary fields or relativistic electrons to create a stable field inside the reactor.  The main disadvantage of magnetic mirror confinement, that of excessive plasma leakage, is circumvented by the arrangement of multiple mirrors end-to-end in a ring.  It is described as "bumpy" because the fuel ions comprising the plasma tend to concentrate inside the mirrors at greater density than the leakage currents between mirror cells.

Neutral beam injection: Neutral beam injection (NBI) is one method used to heat plasma inside a fusion device consisting in a beam of high-energy neutral particles that can enter the confinement magnetic field.  When these neutral particles are ionized by collision with the plasma particles, they are kept in the plasma by the confining magnetic field, and can transfer most of their energy by further collisions with the plasma.  By tangential injection in the torus, neutral beams provide also momentum to the plasma and current drive, one essential feature for long pulses of burning plasmas.  Neutral beam injection is a ﬂexible and reliable technique, which has been the main heating system on a large variety of fusion devices.  To date, all NBI systems were based on positive precursor ion beams.  In the 90s there has been impressive progress in negative ion sources and accelerators with the construction of multi-megawatt negative ion based NBI systems at LHD (H, 180 keV) and JT-60U (D, 500 keV).  The NBI designed for ITER is a substantial challenge (D, 1MeV, 40A) and a prototype is being constructed to optimize its performance in view of the ITER future operations.  Other ways to heat plasma for nuclear fusion include RF heating, electron cyclotron resonance heating (ECRH), and ion cyclotron resonance heating (ICRH).

Magneto-inertial fusion: Magneto-inertial fusion (MIF) describes a class of fusion devices which combine aspects of magnetic confinement fusion and inertial confinement fusion in an attempt to lower the cost of fusion devices.  MIF uses magnetic fields to confine an initial warm, low-density plasma, then compresses that plasma to fusion conditions using an impulsive driver or "liner."

KSTAR: The KSTAR, or Korea Superconducting Tokamak Advanced Research is a magnetic fusion device being built at the National Fusion Research Institute in Daejeon, South Korea.  It is intended to study aspects of magnetic fusion energy which will be pertinent to the ITER fusion project as part of that country's contribution to the ITER effort.  The project was approved in 1995 but construction was delayed by the East Asian financial crisis which weakened the South Korean economy considerably; however the construction phase of the project was completed on September 14, 2007.  First plasma occurred on July 15, 2008.  or more likely on June 30, 2008.

Predhiman Krishan Kaw: Predhiman Krishan Kaw (15 January 1948 – 18 June 2017) was an Indian plasma physicist.  He had been the founding director of the Institute for Plasma Research and served the institute as the director from 1986 to 2012.  He was born on January 15, 1948 in Srinagar (Jammu and Kashmir), India.  He matriculated from Punjab University (1958) and completed his M.Sc.  from Agra University in 1964.  He received PhD from Indian Institute of Technology, Delhi in 1966 under Supervision of Prof. M. S. Sodha, and was the first Ph.D. from the Indian Institute of Technology, Delhi.  Kaw received his Ph.D. at the age of 18, following which he completed his PostDoc at Princeton University.  He was awarded the prestigious Padma Shri award, India's fourth-highest honor, in 1985 and Shanti Swarup Bhatnagar Award in 1986.  On December 28, 2016 he was awarded the Subrahmanyan Chandrasekhar Prize of Plasma Physics for his seminal contributions in the areas of laser-plasma interactions, strongly coupled dusty plasmas, and turbulence, nonlinear effect in magnetic fusion devices.  He is also a recipient of the 2008 TWAS Prize.

Oak Ridge National Laboratory: Oak Ridge National Laboratory (ORNL) is an American multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT-Battelle as a federally funded research and development center (FFRDC) under a contract with the DOE.  ORNL is the largest science and

Magnetic nozzle: A magnetic nozzle is a convergent-divergent magnetic field that guides, expands and accelerates a plasma jet into vacuum for the purpose of space propulsion.  The magnetic field in a magnetic nozzle plays a similar role to the convergent-divergent solid walls in a de Laval nozzle, wherein a hot neutral gas is expanded first subsonically and then supersonically to increase thrust.  Like a de Laval nozzle, a magnetic nozzle converts the internal energy of the plasma into directed kinetic energy, but the operation is based on the interaction of the applied magnetic field with the electric charges in the plasma, rather than on pressure forces acting on solid walls.  The main advantage of a magnetic nozzle over a solid one is that it can operate "contactlessly," i.e. avoiding the material contact with the hot plasma, which would lead to system inefficiencies and reduced lifetime of the nozzle.  Additional advantages include the capability of modifying the strength and geometry of the applied magnetic field in-flight, allowing the nozzle to adapt to different propulsive requirements and space missions. Magnetic nozzles are the fundamental acceleration stage of several next-generation plasma thrusters currently under development, such as the helicon plasma thruster, the electron-cyclotron resonance plasma thruster, the VASIMR, and the applied-field magnetoplasmadynamic thruster.  Magnetic nozzles also find another field of application in advanced plasma manufacturing processes, and their physics are related to those of several magnetic confinement plasma fusion devices.

Resonant magnetic perturbations: Resonant magnetic perturbations (RMPs) are a special type of magnetic field perturbations used to control burning plasma instabilities called edge-localized modes (ELMs) in magnetic fusion devices such as tokamaks.  The efficiency of RMPs for controlling ELMs was first demonstrated on the tokamak DIII-D in 2003.

National Spherical Torus Experiment: The National Spherical Torus Experiment (NSTX) is an innovative magnetic fusion device based on the "spherical tokamak" concept.  It was constructed by the Princeton Plasma Physics Laboratory (PPPL) in collaboration with the Oak Ridge National Laboratory, Columbia University, and the University of Washington at Seattle.

Reversed field pinch: A reversed-field pinch (RFP) is a device used to produce and contain near-thermonuclear plasmas.  It is a toroidal pinch which uses a unique magnetic field configuration as a scheme to magnetically confine a plasma, primarily to study magnetic fusion energy.  Its magnetic geometry is somewhat different from that of the more common tokamak.  As one moves out radially, the portion of the magnetic field pointing toroidally (see inset) reverses its direction, giving rise to the term "reversed field".  This configuration can be sustained with comparatively lower fields than that of a tokamak of similar power density.  One of the disadvantages of this configuration is that it tends to be more susceptible to non-linear effects and turbulence.  This makes it a perfect laboratory for non-ideal (resistive) magnetohydrodynamics.  RFPs are also used in the study of astrophysical plasmas as they share many features.

Supporting paragraphs: National Spherical Torus Experiment Oak Ridge National Laboratory
Answer: spherical tokamak