Feedback Control System for the Antenna Phase Difference of Lower Hybrid Current Drive

1. Feedback Control System for the Antenna Phase Difference of Lower Hybrid Current Drive Min Jiang, Guangli Kuang, Jiafang Shan, Jian’an Lin and HT-7 Team Institute of Plasma Physics, Chinese Academy of Science, P.O.Box 1126, Hefei, Anhui, 230031, P.R.China

2. Abstract It is well accepted that LHCD(lower hybrid current drive) is the most efficient method for non-inductive current drive in fusion devices and the effect of the current drive is dependent on not only microwave power but also its grill phase shift. This paper presents a new kind of feedback control system for antenna phase difference on LHCD experiments. In this high-speed control system, a lot of new technologies and methods are applied. The experiments results show a very good agreement with the design ones.

3. Introduce • LHW in Tokamak is one of the most important ways to realize the steady state nuclear fusion. • The current drive efficiency depends on plasma density, toroidal magnetic field and launched LHW power coupling spectrum[1]. • With various antenna phase differences at each waveguide, the power coupling spectrums are diverse.

4. FCSAPD • FCSAPD ---- Feedback Control System for the Antenna Phase Difference • PDAC system ---- Phase Data Acquisition and Control system • Database Program ---- developed for the efficient management of measured data • DCS ---- Data Communicate System

5. PDAC system HARDWARE: • Multi-junction Grill Antenna:3 row*4column, phase controlled • Klystron: KU-2.45,Made in Russia, 100KW • Phase shifter: 360 deg, 2.8 deg step • Phase Discriminator: parallel, response time 15us • Computer : with 2 cards installed • ADC card: 1MHZ • DO card Fig. 1 PDAC System Hardware Frame

6. PDAC system SOFTWARE: • Step 1: • Preparing work(to adjust the parameters) • Waiting for the trigger signal • Determine control Arithmetic • Step 2(loop time 300us): • Sampling the phase data • Analyzing with Deviation-adjust algorithm • Generating control signal through DO card for phase shifter • Step 3: • Managing and compressing the data • To get ready for the transfer to DCS

7. PDAC system Three-Stage Phase Adjustment: • LHW can play different roles in different stages of one shot with different power spectrum N// peak, such as LH heating and LHCD[4]. And it is what the development of HT-7 physics experiments requires.

8. Database Program • Database Server: Windows 2000 OS, PENTIUM 4 and 256M RAM • Data : • Some data with a LZO compressing format contains the represent time, data points and raw measured values. • Other are stored with a given database format. • GUI program • C-S: Client-Server mode, detailed information • B-S: Browser-Server mode, through IE and Netscape

9. DCS • DCS is a bridge between PDAC and Database program. • DCS contains two networks: control network and common network. • PDAC system is separated safely from the dangers such as viruses and hack attacks.

10. Arithmetic of Phase Difference Control in Real Time Fig. 3 Principium to Measure the Phase Background

11. Arithmetic of Phase Difference Control in Real Time • Let’s assumeθ1 =θ2= …… =θ11=θ12, (1) • then the phase at the left of the bi_directional equals (αi-Φi) (2) • and the phase at the mixing port equals (αi - Φi + δi + γi). (3) • So the phase we should shift is given by (4) ~ (6) αi –Φi +δi+γi－(α12 –Φ12 +δ12+γ12)=βi (4) αibackground=（Φi－Φ12）－（δi－δ12）－（γi－γ12） =ΔΦi-△δi-△γi (5) αishift =αipreset-（αi -α12） (6) αishift=αipreset-βi -αibackground (7)

12. Reference • [1] Ding B.J. Ph.D Thesis (Institute of Plasma Physics, Chinese Academy of Sciences, 2001). • [2] Wang Mao et al Nuclear Fusion and Plasma Physics, 2003,23:55 • [3] Luo Jiarong et al Plasma Science & Technology , 2002,4:1445 • [4] Shen W.C. et al Plasma Science & Technology , 2003,5:1633 • [5] J.Y. Journeaux et al Fusion Engineering and Design, 2001,56-57:767-771 • [6] Lin Jian’an Ph.D Thesis (Institute of Plasma Physics, Chinese Academy of Sciences, 2001).