Overview of the Physics and Engineering Design of NSTX Upgrade
Authors: J. Menard, et. al.
Abstract:
The spherical tokamak (ST) is a leading candidate
for a fusion nuclear science facility (FNSF) due to its compact
size and modular configuration. The National Spherical Torus
eXperiment (NSTX) is a MA-class ST facility in the U.S. actively
developing the physics basis for an ST-based FNSF. In plasma
transport research, ST experiments exhibit a strong (nearly
inverse) scaling of normalized confinement with collisionality,
and if this trend holds at low collisionality, high fusion neutron
fluences could be achievable in very compact ST devices. A
major motivation for the NSTX Upgrade (NSTX-U) is to span
the next factor of 3-6 reduction in collisionality. To achieve this
collisionality reduction with equilibrated profiles, NSTX-U will
double the toroidal field, plasma current, and NBI heating power
and increase the pulse length from 1-1.5s to 5s. In the area of
stability and advanced scenarios, plasmas with higher aspect ratio
and elongation, high βN, and broad current profiles approaching
those of an ST-based FNSF have been produced in NSTX using
active control of the plasma β and advanced resistive wall
mode control. High non-inductive current fractions of 70% have
been sustained for many current diffusion times, and the more
tangential injection of the 2nd NBI of the Upgrade is projected to
increase the NBI current drive by up to a factor of 2 and support
100% non-inductive operation. More tangential NBI injection is
also projected to provide non-solenoidal current ramp-up (from
IP = 0.4MA up to 0.8-1MA) as needed for an ST-based FNSF.
In boundary physics, NSTX and higher-A tokamaks measure
an inverse relationship between the scrape-off layer heat-flux
width and plasma current that could unfavorably impact nextstep
devices. Recently, NSTX has successfully demonstrated very
high flux expansion and substantial heat-flux reduction using
a snowflake divertor configuration, and this type of divertor is
incorporated in the NSTX-U design. The physics and engineering
design supporting NSTX Upgrade are described.
__________________________________________________
Submitted to: 38th International Conference on Plasma Science & 24th Symposium on Fusion Engineering/ICOPS 2011 SOFE, Chicago, IL, June 26-30, 2011
__________________________________________________
Download PPPL-4671 (pdf 184 KB 8 pp)
__________________________________________________