Effective ripple in the CHS-qa configuration

Abstract

The effective ripple is analysed for the final version of the quasi-axisymmetric stellarator configuration with a low aspect ratio, CHS-qa. For the computation, a method is used that is based on the integration along magnetic field lines in a given magnetic field. Computations are done for magnetic fields presented in Boozer magnetic coordinates as well as for magnetic fields produced directly by currents in the modular coils of the device. The computations show the significant advantage of CHS-qa over a conventional stellarator resulting from the reduced effective ripple.

Quasi-isodynamic Configuration With N = 12 and High β

“…At this value of β , there are no collisionless losses of α-particles born at 1/2 of the minor plasma radius for typical power plant parameters (B = 5T,V = 1000m 3 ) up to a time of flight of 1 sec. The neoclassical transport is similar to that of W7-X [4] and the value of the bootstrap current is small. The aspect ratio of the configuration found is about 36.…”

“…5 shows the radial profile of effective ripple, as defined in Ref. [4]. It is worth mentioning that the diffusion coefficient is proportional to ε 3/2 and inversely proportional to the square of aspect ratio for fixed small plasma radius.…”

“…In the optimization the VMEC code [5] was used to calculate equilibria for fixed boundaries; the transition to magnetic coordinates was performed by the JMC code [6]; a set of codes was used to calculate the contours of B on magnetic surfaces, the contours of the second adiabatic invariant, Mercier and ballooning-mode stability as well as values of the effective ripple [4] and the structural factor of bootstrap current in the 1/ν regime (see, e.g. [7]).…”

Studies of the neoclassical transport for CNT

“…using the transformation s(ψ) = dV /dψ = S/ |∇ψ| and the transformation of the Boozer diffusion coefficient D B to the real space diffusion coefficient D, D B = D |∇ψ| 2 (see in [16]). Note, that before solving equation ( 1) for obtaining κ ⊥ , the vector (coordinate free) solution for transport fluxes should be obtained followed by the flux surface averaging as it is performed in [1].…”

Optimization of finite-sized modular coils for advanced stellarators

“…The geometry of the coils is varied by nonlinear optimization algorithms to minimize a penalty-function that describes a balance between the physics requirement, i.e., the minimization of the total normal magnetic field on the plasma boundary and the engineering constraints which mainly include radius of coil curvature and distance between adjacent coils. Modular coil systems for the compact stellarators NCSX [20,21] and CHS-qa [22,23] were designed using this approach.…”