Ignitor Diagnostics. Presented by Francesca Bombarda Ignitor Project ENEA UTS Fusione Frascati (Italy)* *Present address: M.I.T.

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1 Ignitor Diagnostics Presented by Francesca Bombarda Ignitor Project ENEA UTS Fusione Frascati (Italy)* *Present address: M.I.T., Cambridge, MA ITPA Diagnostics, GA San Diego, March 4 h 2002

2 The Ignition Goal! Fusion ignition is a major scientific and technical goal for contemporary physics. The ignition process will be similar for any magnetically confined, predominantly thermal plasma.! Meaningful fusion burn experiments are those where heating methods and control strategies for ignition, burning and shutdown can be established on time scales sufficiently long relative to the plasma intrinsic characteristic times : τ α,sd << τ E, τ burn >> τ E

3 Outline The Ignitor Experiment: " The ignition goal " Ohmic ignition " Machine design, status and site " Auxiliary systems " Possible regimes Diagnostics " Ports " General requirements " Main systems

4 The Ignitor Objectives Use compact, high field limiter configurations to reach burning and ignition conditions at low temperature, high density, and trigger the thermonuclear instability. Investigate plasma heating, transport process and stability of fusion generated alpha-particles Identify methods for control, heating and fueling of high density burning plasmas. Reference Design Parameters R 0 a κ δ 0.4 I p!11 MA B T Bp Ip 5 ab V 0 10 m 3 S 34 m 2 0! ICRH 1.32 m 0.47 m 1.8!13 T!3.5 T! MW

5 The Ignitor Strategy High density n 0 ~ m -3, far from density limit, relatively peaked density profiles Low temperature High poloidal magnetic field Low beta-poloidal and a small q < 1 region provide a defense against ideal MHD and resistive m=1 internal modes Mostly ohmic heating, to avoid confinement degradation

6 Ohmic Ignition Ignition is most effectively achieved soon after the end of the current rise. In this phase, the current density profile is broad and the loop voltage is non uniform across the minor radius. The maximum ohmic heating power density is off the magnetic axis T, 11 MA Scenario Bt (T) Ip (MA) time (sec) Extensive simulations 1,2 were carried out with the TSC, BALDUR and JETTO codes 1 B. Coppi, M. Nassi, L.E. Sugiyama, Physica Scripta 45, 112 (1992) 2 A. Airoldi, G. Cenacchi, Nuclear Fusion 37, 1117 (1997).

7 JETTO Simulations 25 (Airoldi and Cenacchi, Nucl. Fusion 37,1117(1997) MW 15 P OH P α 10 Z [m] MA 2 MA 3 MA 4 MA 5 MA 6 MA kev 10 P rad Q α t [s] T e,i (0) R [m] 5 <T e,i > t (s)

8 10 21 m , 1.2% I P 11 MA B T 13 T T e0, T i0 11.5, 10.5 kev n e0 n α m -3 P α 19.2 MW W pl 11.9 MJ P OH =dw/dt 10.5 MW P rad 6 MW β pol, β q ψ, q 0 3.5, ~ 1.1 τ E, τ sd 0.62, 0.05 s 1.2 Z eff Parameters at ignition p α, p α 0.2, 0.02 β α0 0.3% P. Detragiache, JSOLVER, private com.

9 Confinement and other issues The path to ignition has been extensively analyzed using a variety of transport models. The sensitivity to other assumptions, such as -ion transport, -density and density profile, -impurities -ICRH n τ [m - 3 s] e0 E Ignition condition a) Coppi Model b) B-gB Model c) radial Model d) Coppi + RF heating has also been tested 1,2, kev 1 B. Coppi, M. Nassi and L.E. Sugiyama, Physica Scripta 45, B. Coppi, P. Detragiache, et al., Fusion Technology 25, 353 (1992) 3 A. Airoldi, G. Cenacchi, Nuclear Fusion 41, 687 (2001)

10 The machine is characterized by a complete integration among major components. The parameter Ip Aqψ / R0 Bp was found, on the basis of purely engineering considerations [1] to be the appropriate factor of merit to gauge the quality of toroidal magnetic confinement machines. Bucking and Wedging Passive and Active Compression Cooling to 30 K No Divertor, optimized for OOP forces [1] J. Schultz et al., Advanced Magnets and Implications for BPX, BPS Workshop II, San Diego (May 2001) Machine Design ELECTROMAGNETIC RADIAL PRESS C-CLAMP BRACING RING TOROIDAL FIELD COIL CENTRAL SOLENOID EXTERNAL POLOIDAL COIL

11 First Wall The first wall, covered with molybdenum tiles, acts as an extended limiter. No active cooling. Pumped/vented limiters can be housed in pockets around the horizontal ports. C. FERRO

12 Why not a divertor Divertor machines do not produce cleaner plasmas than limiter, high density devices.. At high density, the low temperature reduces sputtering from the wall and impurities are effectively screened from the main plasma. A new view of the divertor and of the role played by particle recycling from the main chamber and cross-field diffusion have been pointed out by the Alcator C-Mod group [1], challenging the standard picture of the divertor as the sole power and particle sink, in plasma regimes that are similar to those expected in Ignitor. [1]LABOMBARD, et al., Nucl. Fusion 40 (2000) Z eff MW 20 MW 24 MW n e (10 20 m -3 ) G.F. Matthews, et al., J. Nuclear Mat , 450 (1997)

13 Edge density n a = m -3 Edge temperature T e0 ~ ev These values suggest a complex SOL in Ignitor, where radiation, ionization and charge exchange are all important in reducing particle energy and spreading out the power transported across the LCFS by energetic particles Edge Radiative Regime Edge conditions Detachment C.S. PITCHER, EDI code

14 A pellet injector can be used for: fast core fueling; density profile control; time-dependent burn control; controlled injection of T; promoting the formation of ITB s diagnostic purposes. Pellet Injector Pellets may be injected several times during the approach to ignition, with velocities up to 4 Km/s. Schematics of the FTU pellet injector. A. Frattolillo at al., Rev. Sci. Instr. 70, 2355 (1999)

15 ICRH ICRH is envisaged to extend the region of accessible parameter space; have better control on the evolution of the temperature and current density profiles; simulate α-particle heating at the same power level as under relevant ignition conditions in non-reacting plasmas (18 24 MW). M. Riccitelli, G. Vecchi, R. Maggiora, et al, Fus. Eng. and Design 45, 1 (1999) Antenna Design by Politecnico di Torino

16 Non-ohmic regimes Ignitor is, in fact, a flexible machine. The available RF heating allows the explorations of other regimes including, but not limited to: Reversed Shear: small amounts of RF power in the early phase of the current allow reaching ignition Non-ohmic ignition scenarios (~ 5 MW) H-mode (9 MA, 13 T, DN) First exploration of fusion burn condition in tritium-poor plasmas. About 1 MW from D- 3 He reaction can be obtained with ICRH heating (n e0 ~ , T e0 ~ 20 KeV). REVERSED SHEAR B T I p q ψ 4.9 q min f bs 1.5 β N P RF <8 MW H ipb98y Q 12 T 7 MA 1.1 L.E. Sugiyama, MIT-RLE Report PTP95/3 (1995)

17 Physics Comparison ITER Ignitor Magnetic field (T), Plasma current (MA) 5.3, 15 13, 11 Magnetic energy B 2 V/2µ 0 (GJ) Mean Poloidal Field Safety factor q ψ STABILITY β N, β pol 1.82, , 0.2 nn G ( ) Qα Pα Ploss Pα Thermonuclear instability no 0.4 yes IGNITION BURN CONTROL τ E τ α, sd Normal. Collisionality v* Normalized size (a/ρ i,pol ) PROTECTION AGAINST α PARTICLE DRIVEN MODES

18 Diagnostic Systems Contributions from: F. Alladio, R. Bartiromo, P. Batistoni, E. Bittoni, F. Bombarda, G. Bonizzoni, P. Buratti, S. Coda, B. Coppi, P. Detragiache, C. Ferro, E. Giovannozzi, G. Gorini, M. Haegi, J.A. Snipes, J. Källne, H. Kroegler, E. Mazzucato, M. Nassi, S. Rollet, O. Tudisco, M. Zerbini, M. Zucchetti. The scientific objectives of Ignitor are centered on the study of fusion burning plasmas. Diagnostics with special characteristics will be required. Diagnostics will have to withstand large fluxes of neutrons and γ-rays produced in the surrounding materials; on the other hand, fluences are low and radiation damage should not be a concern for most systems. Some will have to be remotely handled. The experience developed so far at JET and TFTR should be fully exploited.

19 Accessibility Ignitor is a high field machine, therefore the number and size of its ports can be regarded as: a) A diagnostician nightmare b) The usual problem c) A great opportunity for developing smart solution There are 12 sectors, each carrying a large horizontal port, and one or two up-down symmetric vertical ports, at different radial locations. 6 of the 12 horizontal ports are allocated to the RF system Most of the plasma can be observed from the side, but only ~1/4 of its radial extent is directly visible from the top or bottom.

20 Port Lay-out Horizontal ports: mm Vertical ports: mm Ø 35 mm

21 Diagnostic Systems Conventional Diagnostics Neutron Diagnostics Spectroscopy Alpha-particle diagnostics Others. Electron cyclotron emission Thomson Scattering Two Color CO 2 Interferometer Faraday Rotation Reflectometry Bolometry Magnetics and MHD coils Neutron Counters and Foil Activation High Resolution Neutron Spectrometer Multicollimator Arrays H α, Visible, VUV, Soft X, Hard X..

22 Tentative Lay-out

23 Neutron Diagnostics P. Batistoni, G. Gorini, J. Källne, S. Rollet, M. Zucchetti!!Neutron Yield (Y n ~ n/sec) Fission Chambers ( 235 U, 238 U) of different efficiencies at several toroidal and poloidal locations in the machine hall (absolute calibration difficult but feasible) T i (n i ) or n i (T i ) vs time Foil Activation System mounted close to the plasma at different location to measure the integrated neutron yield after each shot provides good calibration for the neutron counters; neutron energy spectrum near the source (important for assessing radiation damage and activation if operational from the beginning).

24 Neutron Spectrometry T i, n D n T, fusion spectrum (thermal and suprathermal components) G. Gorini, J. Källne, Il Nuovo Cimento 14D, 1115 (1992).

25 Neutron Camera!! Neutron Emissivity Profile Multicollimator with Magnetic Proton Recoil Detectors (MPR) T i (r) L ~ 7.5 m 11 channels 65% of plasma z ~ 6.5 cm

26 High resolution curved crystal spectrometer T i from λ Doppler of impurity lines λ= 1 4 Å Trace amounts of impurities provide adequate signal levels 2-D detectors for profile measurements 1 1 R. Bartiromo, et al., ISPP-9, 959 (1991)

27 Electron Cyclotron Emission T e from Fundamental harmonic, o-mode: Second harmonic, x-mode: P. Buratti, M. Zerbini R R R 0 + a, n e 0.1 B 2 (10 20 m -3 ) R R R 0 + a, n e 0.2 B 2 (10 20 m -3 ) 114 ν GHz for B 0 = T, ν 2 = 2 ν 1 Lay-out: equatorial light collection line followed by two transmission lines (one for the o-mode and the other for the x-mode) connected to compact, 4- channel Michelson interferometers, absolutely calibrated ( x~3 cm, t~5ms). An equatorial o-mode line connected to a polychromator, to be used for fast MHD activity.

28 Density Measurements O. Tudisco Two Color CO 2 Interferometer 10.6 µm µm, 1 horizontal port (retroflectors) or 2 vertical ones Faraday Rotation rotation always less than one fringe (~3 rad); 2. only one horizontal port required; 3. the rotation angle is insensitive to vibration and the optics can be anchored directly to the vacuum vessel. the toroidal magnetic field must be known with a high accuracy and interpretation problems can arise from ripples and diamagnetic fields. Reflectometry The lower cut-off for the extraordinary mode (156 and 178 GHz at 13 1/2 and 10 T respectively) may be used f 2 L = fpe (0.5 fce) fce

29 Summary The Ignitor physics program relies for the most part on assessed diagnostics systems, with a high degree of reliability. High neutron fluxes pose some challenges, but low fluences limit structural damage on most systems. Neutron diagnostics will be especially useful for the burning plasma phase of the experiment. Alpha-particle diagnostics remain largely to be determined. A set of basic diagnostic systems has been considered. Many more could be included: Feel free to put forward your ideas!