The Ignitor ICRF Antenna System

G. Vecchi, M.M. Gola, R. Maggiora, T. Berruti, V. Kyrytsya

Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy

Objectives and Constraints

Design ICRH antenna and outline RF system

· "freeze" vacuum chamber design

· Robust/reliable

Ignitor ICRH system

· 18 MW total, 3 MW / port, 6 port

· "narrow" ports ® complex design

ICRF Heating Scenarios

Collaboration with PPPL

70 - 140 MHz range

BT	min H	min ^3He
5 T	76 MHz	---
9 T	137 MHz	91 MHz
11 T	---	110 MHz
13 T	---	131 MHz

Antenna Conceptual Schematics (Dimensions in m)

Design Considerations

· Dimensions optimized for all frequency range

· K_|| spectrum selected to be an out-of-phase, bell-shaped spectrum with a maximum around ±8 m^-1

· Single layer Faraday shield

· Strap length about a quarter-wavelength

· Characteristic impedance of the coaxial transmission lines feeding the antenna selected to be 50 W

RF Power System

· One generator/amplifier per antenna strap (4 strap per port)

· Phase locked generators

· Separate tuning and matching system for each coax/strap

· Adaptive tuning and matching system (ferrite ® costs) ?

Connections to Mechanical Design

· Electrical optimized configuration achieved

· Accurate calculation for Faraday shield dimensioning under disruption forces and thermal loads

· Detailed antenna thermo-mechanical analysis under way, Mechanical Dept., POLITO

Motivation

· "Virtual lab" (VL) - assisted detailed design of Antenna and RF system

· Design phase between conceptual design and antenna test in actual Tokamak (plasma facing)

Objective:

design antenna as operating in conditions close to actual plasma-facing conditions

design:

optimize antenna geometry to maximize power transfer to plasma and power handling

Virtual Lab (1)

"Virtual lab" (VL):

accurate, dependable computer simulation of antenna performance and impact on power RF system including:

- precise rendering of antenna actual 3D geometry

- reasonable description of plasma and Tokamak

Need:

- accurate, full-wave simulation code allowing "virtual-lab" prototyping

Virtual Lab (2)

Results in:

confidence that difference between simulated/actual antenna parameters will depend only on:

- plasma modeling and plasma parameters uncertainties

- tokamak vacuum chamber geometry modeling

Self-consistent code

Rationale:

input parameters of antenna at feeding port (coax)

® Standing wave ratio

® discharge in coax and/or matching/tuning system

® power handling

Input impedance strongly depends on antenna near fields, requires self-consistent simulation

Need to consider accurate effect of 3D geometry to analyze and optimize antenna shape to maximize power coupling to plasma

Conclusions (1)

- Analysis of heating schemes and scenarios (PPPL)

- Antenna design and mechanical drawings

- Performance evaluation using new, self-consistent, 3D antenna simulation code

- Conceptual design of RF power system based on antenna performance

Results: physics goal appear feasible at best of present simulation