28th IAEA Fusion Energy Conference (FEC 2020)

Concept of the ICR plasma heating system for IGNITOR-like tokamak in relation to the Russian site

14 May 2021, 08:30

4h

Virtual Event

Regular Poster Fusion Energy Technology P7 Posters 7

Speaker

Mr Mikhail Subbotin (National Research Center "Kurchatov Instituti")

Description

1. INTRODUCTION
   The concept of the ICR plasma heating system for the Ignitor tokamak in order to determine possible solutions was developed. The concept meets the requirements of the Ignitor project for the capabilities of the engineering, physical and energy infrastructures of the Ignitor tokamak site. Currently, the site of the tokamak complex with a strong field T-14 of JSC "SRC RF TRINITI" ("Big Moscow" region, Russia) is considered as the main option for location of the Ignitor tokamak.

In order to determine the most optimal solution for developing of the concept of the Ignitor tokamak ICR plasma heating system, the experience of using ICR heating systems on existing JET and ASDEX-Upgrade tokamaks was studied. The analysis of the results of using the ICRH system and the adopted technological solutions on JET and ASDEX Upgrade tokamaks is carried out. It is shown that the applied technological solutions have high efficiency and can be used to solve the ICRH problem in the tokamak Ignitor project in relation to the Russian site. The obtained results allowed to optimize of the technical solutions embedded in the developed concept.

The Ignitor project is designed to achieve the ignition of fusion reaction in a high-density plasma (~ 1021 m-3) under conditions of a strong magnetic field (13 T) and a powerful discharge current (11 MA). The general view of the Ignitor tokamak is shown in Fig. 1, the design parameters are presented in table 1 1.

Table 1. The design parameters of the Ignitor tokamak
Major radius R, m 1.32
Minor radius a, m 0.47
Elongation k 1.83
Triangularity δ 0.4
Plasma volume V, m3 10
Plasma surface S, m2 34
Pulse length τ, s 4+4
Plasma current Ip, MA 11
Toroidal field Bt, T 13
Poloidal field Bp, T 6.5
Edge safety factor qψ 3.5
RF Heating PICRH, MW < 18

1. ICR-HEATING SYSTEM IN THE TOKAMAK IGNITOR PROJECT
   During of the development of the Ignitor project were provided of the theoretical calculations and computing simulations using the full-wave code TORIC in combination with the Fokker-Planck SSQLFP program, it was found that:
2. the frequency f = 115 MHz is optimal for the time of ICR heating tICRH > 3 s (completion of the current start-up stage and transition to the plateau), which corresponds to the magnitude of the magnetic field of 11-13 T, - the frequency f = 95 MHz is optimal for tICRH < 3 s and 9-11 T fields;

3. the energy release profile in the case of B = 11 T (t = 3 s) and f = 115 MHz, heating on an impurity of 3He (2%) has a quasi-linear character.
   For the Ignitor project, an ICR heating scheme was selected using a 3% 3He additive [2, 3, 4]

4. THE CONCEPT OF ICR- HEATING SYSTEM FOR IGNITOR TOKAMAK
   The system matching Antenna impedance with RF generator
   Based on the results of the data analysis performed on the ICR-heating systems on JET and ASDEX Upgrade, it was found that the external T-conjugation system for impedance matching, which was successfully integrated into the RF complex on JET is most optimal.
   Estimation of the absorbed RF power and technical requirements for the ICR heating system
   Based on the results obtained on JET using T-conjugation system for impedance matching, and having the area of the antenna of the ICR-heating system of the Ignitor tokamak equal to ≈0.62 m2 (it was received by approximately calculations), it is possible to estimate the value of the absorbed power on the Ignitor tokamak: for one antenna it will be ~0.73 MW, for four antennas ~3 MW.
   The antennas should be positioned in pairs and symmetrically relative to the torus axis in the Equatorial plane of the tokamak, as on JET and ASDEX Upgrade [5].
   Due to the small size of the branch pipe (cross-section is 800x160 mm) in the Ignitor tokamak, the geometric dimensions of the vacuum transmission line with a wave resistance of Z0 = 60ln (D/d) = 30 Ohms cannot exceed the outer diameter of the conductor D = 112 mm, and the inner diameter of the conductor d = 68 mm.
   Due to the small area of the antenna and the small distance between of the plasma separatrix and the outer wall of the vacuum chamber, the Faraday screen should be one for the entire area of the antenna facing on the plasma, as it was made on the ASDEX Upgrade.
   RF generator of the ICRN system
   The experience of exploitation of the ICR heating systems operating on JET and ASDEX Upgrade has shown good performance and sufficient flexibility of systems based on RF generators with controlled external excitation [6, 7, 8]. The proposed version of such RF power amplifier designed for Ignitor tokamak is shown in Fig. 2.

Power supply of ICR-heating.
It is planned to develop a power source for an RF generator consisting of eight separate identical power modules with a capacity of 2.8 MW each. Each pair of such modules will provide power to two RF amplifiers and have common switching equipment, a common control system that ensures their synchronous operation and joint operation of the protection system.
Composition of the ICR- heating system of the Ignitor tokamak
The ICR- heating system includes:
 antennas with a Faraday screen consisting of four short-circuited loops;
 vacuum transmission lines;
 external T-coupling system for matching the impedance of two identical loops of two antennas with the output impedance of the RF generator, consisting of transmission lines, matching elements;
 RF generators;
 cooling system for RF generators and power supplies;
 management system, coordination, diagnostics, collection and processing of information.

Reference
1. Coppi B. et al. Relevant advances of the ignitor program. — In: 34th EPS Conf. on Plasma Phys. Warsaw, Poland, 2—6 July, 2007, ECA, vol. 31F, P-1.156.
2. Cardinali A., Bombarda F. et al. ICRH physics in Ignitor. — In: 50th Annual Meeting of the Division of Plasma Physics. Dallas, Texas, USA, November 17—21, 2008.
3. Sassi M. et al., The ICRH System for the Ignitor experiment, In: 50th Annual Meeting of the Division of Plasma Physics. Dallas, Texas, 17-18 November, 2008.
4. Coppi B. et al., Nucl. Fusion, 2015, vol. 55, p. 053011
5. Kutsch H.-J., Wesner F., Noterdaeme J.-M., Muller E. Insulating Al2O3 layers ICRH antennas for ASDEX Upgrade. — Fusion Technology, 1992, p. 569—573.
6. Vrancken M., Mayoral M.-L., Blackman T. et al. Recent ICRF developments at JET. — Fusion Eng. Des., 2007, vol. 82, p. 873—880.
7. Monakhov I., Graham M., Blackman T. et al. Design and operations of load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET. — Nuclear Fusion, July 2013, vol. 53, p. 083813.
8. Bobkov V., Becoulet M., Blackman T. et al. Studies of ELM toroidal asymmetry using ICRF antennas at JET and ASDEX Up-grade. — In: 31st EPS Conf. on Plasma Physics. London, EPS, 2004.