Heating

JT-60SA will use up to 34 MW of neutral beam (NB) heating and up to 7 MW of electron cyclotron resonance heating (ECRH). The upgraded NBI system (right) for JT-60SA consists of twelve positive-ion-based NBI (P-NBI) units and one negative-ion-based NBI (N-NBI) unit. The P-NBI units control deposition profile and plasma rotation. The P-NBI system is the same as that of JT-60U. High power N-NBI is also required to provide sufficient NB current drive capability for high beta steady-state (full non-inductively driven) plasma development.

High power N-NBI also contributes to heating of a central region in high density plasma with a dominant electron heating fraction, which is relevant to ITER and DEMO plasmas heated by alpha particles. The beam line of the co-tangential N-NBI unit is offset downward from the equatorial plane by ~0.6 m to drive off-axis plasma current, and hence to produce reversed shear with a high bootstrap current fraction.

The main modification compared to JT-60U is the upgrade of the power supply system. In addition, the negative ion source will be modified to improve performance such as the voltage holding capability. A key issue is to shield the stray magnetic field on the beam line from the JT-60SA tokamak, which is about three times larger than JT-60U.

The ECRH system (shown below) will generate or sustain high performance plasmas, provide assistance to plasma start-up, and provide cleaning of the first wall of the vacuum vessel. It is composed of 110GHz systems, basically similar to the present JT-60U ECRF system. However the maximum pulse duration of 100 s is much longer than the present 5 s. In the initial research phase 2 gyrotrons from JT-60U will run with two new gyrotrons, capable of 100s operation, provided by JA, with power supplies provided by EU. It is planned to upgrade these 4 units to nine for extended pulse duration.