1. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Progress in Development of Time-of- Flight Refractometer for ITER Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco (FTU) 2006 SRC RF TRINITI, Troitsk Moscow region, Russia E-mail: vpetrov@triniti.ru ITPA-10

2. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 OUTLINE SPECIFIC FEATURES PROBLEMS, TASKS PROGRESS RECENT EXPERIMENTS, STATUS CONCLUSION, PLANS, TASKS

3. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 A robust measurement of line integrated electron density (without fringe jumps) needed for many application, in particular for real time control. Measure time delay SPECIFIC FEATURES Unambiguous line int. density for feedback control Microwave pulse - just above Xl cutoff freq. from LFS: single or double pass ITER– using transparency window on X-mode in low frequency band (60 – 100 GHz): to avoid “first mirror” problem Less sensitive to the reflection surface quality

4. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 SNR – long distances, long waveguides, accuracy of measurements ~ Refraction – attenuation, change of wave trajectory- need ray- tracing/(Full wave-analysis) to take into account Additionally, for high Te (45keV) regimes: absorption, relativistic effects). Transparency window – 60-80-100 GHz - ? Choose of probing geometry: double- or single pass Multi-freq. probing to avoid profile dependence Experiments on tokamaks Integration with ITER-chamber, LFS-X reflectometer (76-220 GHz; F.02 system, Eq#11) PROBLEMS, TASKS -1

5. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 SNR – accuracy of measurements: Optimization of probe geometry, optimization of antenna- waveguide system, use scheme with low-noise microwave amplifier, measure time delay by phase measurements Probe geometry: –1. Double-pass (DB). Pro - use only LFS antennas. Contra –absorption higher. Influence of refraction larger? –2. Single pass (SP), using HFS antenna and LFS antenna. Pro – absorption less. Contra – complicate HFS antenna system. Compare two systems: k = P 1 /P 2 ~ A 1 ·L 2 2 /A 2 ·L 1 2, A 1 ~ 9*9 cm 2, A 2 ~9*1 cm 2 ; L 1 ~2·(2a+l), L 2 ~(2a+l). k~10 dB (DB - better), w/o absorption and refraction PROBLEMS, TASKS - 2

6. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Integrated absorption for equatorial trajectories at different frequencies (60- 100 GHz) and Te values (25-45 keV), n e (0) = 1.03·10 20 m -3 - 50dB (single pass) - 10dB - 0.4dB Total single pass transmission: G. Vayakis, J. Sánchez, ITPA-6 Absorption, choice frequencies PROBLEMS, TASKS - 3 At least 3 freq. in a range 60-78? GHz to secure immunity to density profile, 95- 96 GHz – up to 25 keV Reference Te profiles ~4.7 dB

7. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 PROGRESS - 1 SNR 1. Development of the prototype of a receiver for a refractometer with a pulse microwave amplifier (PMA) based on a IMPATT- diode (SNR): –Frequency 60.0±0.5 GHz –Gain>20 dB –Noise <5 dB –Net effect – 15 dB 2. Improved prototype of a time delay measurements unit with a fast peak detector (PD) - enhanced accuracy of time delay measurements (for low SNR), net effect - 2-3 times better accuracy 3. Method of a double-frequency differential refractometry (DFR) for time delay measurements is offered and tested in T-11M (higher SNR, sensitivity) [1,2] (CW, net effect +10 dB and more) Measurements of phase shift between 2 waves with close frequencies (fringe jump-free) :  1   2,  12 < 2  [1]. V. Petrov et al. Plasma Physics Reports, 2006, Vol. 32, No. 4, p. 317. [2]. V. Petrov et al. Instr. and Exper. Techn., 2006, Vol. 49, No. 2, p. 238.

8. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 PROGRESS - 2 Interferometer density, vertical probing, -1 cm DFR density, vertical probing, +3 cm, single pass, differential freq. 1.3 GHz, CW oscillators High sensitivity, 1-2 order higher SNR compared to pulse TFR. Time delays as low as 100 ps and less have been measured with accuracy of 1%. DFR showed stable operation up to 7·10 19 m -3 (140 GHz) Disadvantage: possible problem with parasitical reflections

9. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 RECENT EXPERIMENTS - 1 Experiments in tokamaks – T-11M, FTU T-11MFTUITER B T [T]1.25.0– 8.05.3 R [м]0.700.9356.2 a [м]0.20.3052.0 R/a3.53.073.1 N e [м -3 ]0.5*10 20 >1*10 20 Tokamak Parameter Te [keV] 0.510-1215 Testing 60 GHz prototype of refractometer (X-mode) in ITER- like conditions on the FTU tokamak (Frascati, Italy) >1*10 20

10. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 The behavior of cut-off and ECE frequencies on FTU for typical plasma parameters N= N 0 (1-  2 )  Transparence window on FTU:  f =50- 120 GHz N0  f f lc B0  f f lc f uc B0 > 3.5 T needed Experiments in tokamaks – FTU RECENT EXPERIMENTS - 2

11. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 MO – microwave oscillator, I-isolator, DC- directional coupler, PCS- pulse current source, A1, A2 – amplifiers, D1, D2 – detectors, PD – adaptive threshold pulse discriminator, TVC – time- to-voltage converter Experiments in tokamaks – T-11M, FTU P ~ 200 mW, t pulse = 5 ns, t fr < 2 ns, f (PRR) ~ 500 kHz RECENT EXPERIMENTS - 3

12. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 CO 2 /CO interferometer RECENT EXPERIMENTS - 4 Experiments in tokamaks – FTU, geometry and picture Refractometer Antenna system of ECE and reflectometer for the first experiments in FTU, antennae directed along minor radius – refraction minimal Signal detector with pulse amplifier Pulse microwave oscillator Electronic unit for signal handling (PD)

13. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Time delays ~1.5 ns Now accuracy ~10 ps (~1 ms time resolution) Sensitivity of density measurements ~ 1.5 ns/10 20 m -3. Lower density limit: 0.7% of max density. The behavior of the calculated time delays for X-mode versus density for typical plasma parameters N= (N(0)-N(a))·(1-  2 )   N(a) J= J 0 (1-  2 )   = q(a)-1 Ip = 500 kA Bt = 6 T = 0.8 Time delay, ns RECENT EXPERIMENTS - 5 FTU experiments

14. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Raw data of TFR: Time delay (code ADC) versus shot time for the typical shot # 27992 (Bt = 6 T, Ip = 500 kA, Ohmic heating RECENT EXPERIMENTS - 6 Time, ms ADC, code 0.8 ns Mean density, 10 20 m -3 : Refractometer (blue) and Interferometer (red) for the shot #27982 Time, s 0.8 0.4 FTU experiments

15. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Mean density: Refractometer (blue line) and Interferometer (red) for the shot #27983 RECENT EXPERIMENTS - 7 Cut-off at the density 1-1.110 20 m -3 ; Adequate density measurements up to cut-off Time, s Mean density 10 20 m -3 FTU - Reflectometry regime 1 1 -3 Time, s Td, ns

16. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Blue – refractometer Red –IR- interferometer (22.5 cm) RECENT EXPERIMENTS - 8 Time, ms Mean density, a.u.

17. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Integration in ITER: STATUS -1 Eq#11 TFR probing geometry is part of HFS/LFS antennae- wave guide system (A. Malaquias)

18. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Eq#11 C.I.Walker, et.al, ITPA-6 STATUS - 2

19. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 1. Development of the prototype of a receiver with a pulse microwave amplifier (PMA) based on a IMPATT-diode (SNR): + 15 dB. 2. Improved prototype of a time delay measurements unit with a fast peak detector (PD) - enhanced accuracy of time delay measurements (for low SNR), net effect - 2-3 times better accuracy 3. Method of a double-frequency differential refractometry (DFR) for time delay measurements is offered and tested in T-11M. +10 dB and more. 4. Testing of TFR in ITER-like configuration (X-mode, double-pass horizontal probing, the same frequency) has been performed successfully in FTU. The first measurements of plasma density with TFR on X-mode have been performed, up to the cut-off density, influence of refraction is low for reflectometry type antenna system (looking along density gradient). Good signal-to-noise ratio is obtained with time resolution of ~50  s CONCLUSION, PLANS, TASKS -1

20. Alexei Petrov, Vladimir Petrov, Massimo De Benedetti, Onofrio Tudisco. 10-Apr-06 ITPA-10 Density measured by TFR corresponds to the one measured by interferometer (along vertical chord) within 10%. Double-pass scheme of TFR is preferential. Plans: to proceed testing of TFR in different regimes of FTU (ITER- relevant regimes), to develop algorithms of data elaboration (refraction, relativistic effects), hardware modernization (ADC, signal handling electronic); test measurements in JET (D-shape large plasma); testing in T-11M of prototypes of TFR; development of multifrequency prototype; Tasks. Integration in ITER. Study influence of refraction – experimentally and numerically. CONCLUSION, PLANS, TASKS - 2