physics_performance.html

KSTAR Physics Performance

The KSTAR tokamak is being designed to provide a flexible fusion physics research facility for advancing the understanding and optimization of tokamak plasmas. The machine configuration is based on a strongly-shaped, double-null poloidally diverted plasma favored for high-beta stability and flexibility. The divertor features a "deep-vee" outer leg for particle control and heat removal and an "open" inner leg for shape flexibility. Conducting structure is provided on the outboard side of the plasma for passive stabilization of the vertical instability and of high-beta non-axisymmetric instabilities. Limiters protect the passive stabilizers and vacuum vessel walls from start-up losses and plasma radiation. Plasma-facing surfaces will be made of carbon-based materials.

In its initial configuration, the KSTAR facility will be designed for 20 second pulses. As the current-drive and divertor physics operating scenarios are developed to permit longer-pulse operation (up to 300 seconds), the in-vessel systems will be upgraded correspondingly, from pulsed (inertial cooling) to steady state (real-time cooling) technology. External systems such as power supplies and plasma heating systems may need to be upgraded as well. However, to ensure a viable upgrade path to steady state operation, the permanent structures such as magnets, vacuum vessel, and inboard limiter, will employ steady-state technology from the outset.

Plasma discharges in KSTAR will be initiated with a low-loop-voltage, electron-cyclotron-heating assisted scenario. This reduces the field transients experienced by the poloidal-field magnets and may simplify the conducting structure design. The toroidal plasma current will be raised inductively to its rated value (2 MA) as the plasma is shaped and positioned in the center of the vacuum vessel. Heating will be applied to raise beta, and then the plasma will be maintained with inductive current drive for about 20 seconds before being terminated in a controlled manner. This standard inductive scenario provides KSTAR with a highly reliable, moderate-pulse startup plasma to permit a smooth transition to steady-state plasma control and exhaust methods, development of which is a key element of the KSTAR mission. The magnets are designed to provide considerable flexibility in plasma profiles and pressure at full current and pulse length and a high source rate of deuterium-deuterium fusion neutrons, resulting in a wide operating space for advanced-tokamak optimization. Annual neutron yields will be limited, however, to levels compatible with hands-on maintenance of the machine.

The plasma heating system will utilize three different technologies for plasma profile control flexibility. Neutral beams will provide ion heating, bulk current and rotation drive, core fueling, and diagnostic capability. A beam configuration that would also provide pressure profile control is being investigated. Ion-cyclotron range-of-frequencies radiofrequency waves will provide electron or ion heating and core current drive. Lower hybrid waves will be used for heating and off-axis current-profile control. Port space is provided to permit expansion of all three systems beyond the initial complement and, in particular, flexibility in the radiofrequency heating configuration.

The KSTAR plasma diagnostic system will provide measurement capabilities for control and machine operation, for performance evaluation, and for enhancing physics understanding. State-of-the-art systems will be developed to provide the control needed for steady-state performance and the measurement detail necessary to advance tokamak physics understanding in the next decade.

Preliminary estimates of plasma performance have been made using a zero-dimensional, prescribed-profile model by W. Nevins. A possible scenario is summarized in the following table.

High-Performance KSTAR Plasma Scenario
Toroidal field (Tesla)	3.5
Plasma Current (MA)	2.0
Safety factor q₉₅	3.4
Paux (MW)	16
Energy confinement time tau_E (s)	0.30
tau_E/ITER-89P (H)	2.72
beta (%)	4.6
Normalized beta	4.0
Volume-averaged density (m^-3)	1.0x10²⁰
Average electron temperature (keV)	6.4
Average ion temperature (keV)	7.4
2.45-MeV neutron source rate (s^-1)	3.5x10²⁰

<--Back to About KSTAR
<--Back to the US KSTAR Home Page