Speaker
Celso Ribeiro
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1053.pdf
Features of the high field ultra-low aspect ratio tokamak
C. Ribeiro1
1
Laboratório de Física de Plasmas e Fusão, Instituto de Matemática, Estatística e Física,
Universidade Federal do Rio Grande, Rio Grande do Sul, Brazil
(celso_ribeiro@hotmail.com)
The basic features of the medium-size high field ultra-low aspect ratio tokamak
(HF-ULART) has been recently proposed[1]. The major objective is to explore very high
beta under the minimum toroidal field as a target plasma, and then explore higher pressure
values using the combined minor and major radius adiabatic compression (AC) technique.
This might be one of potential pathways scenario for an ultra-compact pulsed neutron source
based on the spherical tokamak(ST) concept. The major characteristics of typical target
plasma are: Ro=0.51m, a=0.47m, aspect ratio A=1.1, k=2, δ0.8, B(Ro)=0.1T (0.4T max.),
Ip=0.5MA (2MA, max.), ne(0)~1x1020m-3, Te(0)~1keV, and discharge duration τd~100ms.
The vessel is spherical, made of SS, and insulated from the natural diverted (ND) plasma by
thin (few centimetres) tungsten (W) semi-spherical limiters. The central stack is made of
cooper cover by a thin (~2mm) W sleeve. No internal PF coils or solenoid is envisaged. This
helps the compactness due to the close plasma-vessel fitting, capitalizing of wall stabilization
as previously envisaged in the RULART proposal[2], while also potentializes easier H-mode
(small edge neutral source volume), which has already been observed in Pegasus ohmic
H-mode ND plasmas, using inboard gas fuelling[3]. The major source of initial heating is
provided by Ip generated from RF (e.g. EC and EBW) in combination with transient
Coaxial/Local Helicity Injection (CHI/LHI) techniques, as both have been successfully
demonstrated in STs. By applying the AC technique over a very high beta plasma, that is,
Ip=0.5MA, B(Ro)=0.1T, Ro=0.51m, a=0.47m, A=1.1, k=2, δ0.8, q(Peng)=22, Te/Ti
=263/486eV (scaled from ref.4), ne(0)~0.15x1020m-3[4], the following final values can be
reached for short period (ms): Ip=1.0MA, B(Ro)=0.61T, Ro=0.33m, a=0.28m, A=1.2, k=1.6,
δ0.1, q(Peng)=12, Te/Ti=1.9/3.4keV, ne(0)~2.8x1020m-3. Preliminary neutron yield and
MHD stability calculations and some fixed and free-boundary equilibrium simulations by
VMEC[5] and FIESTA codes, respectively, will be also presented.
[1] Ribeiro C., 59th American Physical Society Meeting, Plasma Phys. Division, Milwaukee, WI, US, 2017.
[2] C. Ribeiro, Proc. 26th Symposium on Fusion Eng., Austin, TX, US, June 2015.
[3] K.E. Thome et al, Nucl. Fusion 57 022018, 2017.
[4] D.J. Schlossberg et al., Phys. Rev. Letters 119, 035001, 2017.
[5] private communication with M. R. Cianciosa.
