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Ebook Fusion physics: Part 2

(BQ) Part 2 book "Fusion physics" has contents: Plasma heating and current drive by neutral beam and alpha particles, plasma–wall interactions, helical confinement concepts, inertial fusion energy, the broader spectrum of magnetic configurations for fusion. | CHAPTER 5 PLASMA HEATING AND CURRENT DRIVE BY NEUTRAL BEAM AND αLPHA PARTICLES M. Kikuchi, Y. Okumura Fusion Research and Development Directorate, Japan Atomic Energy Agency, Japan 5.1. HEATING AND CURRENT DRIVE PHYSICS BY NEUTRAL BEAM AND ALPHA PARTICLES 5.1.1. Basic processes of neutral beam injection The purpose of plasma heating is to raise the plasma temperature enough to produce a deuterium and tritium reaction (D + T → 4He + n). The required plasma temperature T is in the range of 10–30 keV. Since the high temperature plasma is confined by a strong magnetic field, injection of energetic ions from outside to heat the plasma is difficult due to the Lorenz force. The most efficient way to heat the plasma by energetic particles is to inject high energy “neutrals” which get ionized in the plasma. Neutral beam injection (NBI) with a beam energy much above the average kinetic energy of the plasma electrons or ions is used (beam energy typically ~40 keV – 1 MeV). This heating scheme is similar to warming up cold water by pouring in hot water. There are two types of neutral beam, called P-NBI and N-NBI (P- and Nmeans “positive” and “negative”, respectively). P-NBI uses the acceleration of positively charged ions and their neutralization, while N-NBI uses the acceleration of negative ions (electrons attached to neutral atoms) and their neutralization. Details are given in NBI technology Section 5.2. The first demonstration of plasma heating by P-NBI was made in ORMAK [5.1] and ATC [5.2] in 1974, while that by N-NBI was made in JT-60U [5.3] for the first time in 1996. ITER has also adopted the N-NBI system as the heating and current drive system with a beam energy of 1 MeV. Figure 5.1 shows a typical bird’s eye view of a tokamak with N-NBI and N-NBI (JT-60U). Since the magnetic confinement system is a torus and the tokamak has a toroidal plasma current, there are three injection geometries, namely co-tangential, counter-tangential and perpendicular injection, as .