Diagnostics and Control for Burning Plasmas

1. Diagnostics and Control forBurning Plasmas Introduction Tony Donné Information taken from ITPA TG on Diagnostics, ITPA WG on Control, ITER IT

2. ITER will require: • An extensive set of diagnostics to provide measurements for • Machine protection • Separatrix/wall gap, first wall temperature, etc. • (Advanced) plasma control • Plasma shape and position, plasma current, etc. • Physics studies • Confined alpha particles, alpha-driven modes, etc.  About 45 individual measurements A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

3. Many diagnostic challenges • Relatively harsh environmental conditions • Phenomena new to diagnostic design have to be handled • Control role of the measurements • Requires high accuracy and reliability • Simultaneous (advanced) control of many parameters • Long plasma pulse length • Requires high stability • Nuclear environment • Stringent demands on the engineering, robustness A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

4. Machine protection Plasma control Physics evaluation Measurement requirements & justifications Diagnostic design process A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

5. Key aspects in control* – 1/3 • Equilibrium control • AC losses, power management, full scenario robustness, development of control matrix for shape and position with minimum coupling between the terms, modeling of breakdown phase • MHD control • Control of NTM’s, sawteeth, RWM’s, disruption avoidance and mitigations, ELM control, etc. • Current profile control • Development of response matrix, effect of a-heating on current profile, mode conversion current drive, real-time equilibrium codes incl. bootstrap current and loop voltage profile *taken from ITPA meeting on control (2003) A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

6. Key aspects in control – 2/3 • Transport barrier control • Identification of key parameters to control ITBs, role with current profile, simulation of ITB control in presence of a-heating, interrelation between ETB and ITB • Power control and particle exhaust • Methods for erosion/deposition control, control & monitoring of tritium inventory, edge power dissipation control in ELMy H-mode and ITB scenarios, validation of models of He-ash removal, real-time measurement and control of D/T ratio, compatibility of good confinement A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

7. Key aspects in control – 3/3 • Control of steady state scenarios • Fuelling: how to increase density without destroying barrier, Impurity accumulation and exhaust, disruptivity, develop scenarios with minimum control, control of current and loop voltage under high bootstrap conditions. • Other • Integration of all aspects of control (control architec-tures and methodologies), pre-emptive control (e.g. disruption avoidance), diagnostic requirements on basis of adequacy for control, use modeling calculations for sensor development, measurement requirements, indicators for possible loss of a confinement. A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

8. Measurements needed in ITER Conclusion The more advanced the operating scenario, the more parameters need to be simultaneously controlled A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

9. Parameters vs. actuators • There are many (profiles of) parameters that need to be controlled with a rather limited number of actuators • Experimental programs have started to address simultaneous control of current and pressure (temperature) profiles with various H&CD systems • Least-square integral minimisation of several profile errors simultaneously • Model-based algorithms based on physics-based state-space models including multiple time-scales algorithms will be tested • Stepwise approach to integrate more and more systems such as combined shape, profile and flux control, as foreseen on JET • Testing of control algorithms should take place in present devices, and in particular in simulated burning plasma conditions (e.g. ICRH) or D-T plasmas (JET). • This extensive experimental program should be strongly supported and aim, on the longer term, at the development of the ultimate "advanced control“ that ITER will need Source: D. Moreau A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

10. GROUP 1a GROUP 1b GROUP 2 Measurements For Machine Protection And Measurements For Advanced Control Additional Measurements For Performance Basic Control Evaluation And Physics Studies Plasma shape and position, separatrix- a a Neutron and -sourc e profile Confined -particles wall gaps, gap between separatrixes Helium density profile (core) TAE Modes, fishbones Plasma current, q(a), q(95%) Plasma rotation (toroidal and T profile (edge) e Fusion power poloidal) n , T profiles (X-point) e e b = b (aB/I) Current density profile (q-profile) N tor T in divertor i Electron temperature profile (core) Line-averaged electron density Plasma flow (divertor) Electron density profile (core and edge) Impurity and D,T influx (divertor, & main plasma) n /n /n (edge) T D H Ion temperature profile (core) Surface temperature (divertor and upper plates) n /n /n (divertor) T D H Radiation power profile (core, X-point Surface temperature (first wall) T fluctuations e & divertor) Runaway electrons n fluctuations Z profile e 'Halo' currents eff Radial electric field and field Radiated power (main plasma, X-point Helium density (divertor) fluctuations & divertor Heat deposition profile (divertor) Edge turbulence Divertor detachment indicator Ionization front position in divertor MHD activity in plasma core (J , n , T at divertor plate) Impurity density profiles sat e e Pellet ablation Neutral density between plasma and Disruption precursors (locked modes, first wall m=2 mode) n , T of divertor plasma H/L mode indicator e e Z (line-averaged) Alpha-particle loss eff Low m/n MHD activity n /n in plasma core T D Sawteeth ELMs Net erosion (divertor plate) Gas pressure (divertor & duct) Neutron fluence Gas composition (divertor & duct) Loop voltage Toroidal magnetic field Dust ITER measurements A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

11. Condition Range (keV) Dt (ms) Dx Accuracy Core Te r/a < 0.9 0.5 – 40 10 a/30 10% Edge Te r/a > 0.9 0.05 - 10 10 5 mm 10% Requirements & justifications A typical example: the electron temperature The electron temperature, with good spatial dependence, is a major indicator of plasmaperformance and a key component of transport analyses. The profile is key information in instability analyses. Steep transport barriers are observed inside the plasma core and electron temperature pedestals at the edge play a role in analysis of the transport. A time resolution of 10 ms is short compared to times of interest and allows for study of MHD. For kinetic control of the stored energy or ITB gradient, 10 ms time resolution is expected to be sufficient since this is much faster than the typical core confinement times and of the same order as the actuator (heating) response time. ….. Specifications and justifications exist for all parameters to be measured and are under continuous development A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

12. Machine protection Plasma control Physics evaluation Measurement requirements & justifications Established techniques BPX/Reactor relevance Selected diagnostic techniques Radiation Effects R&D System Specific R&D System conceptual design Integration on to Tokamak & with other diagnostics Engineering requirements Performance Assessment Relative to Requirements Design meets requirements Detailed design Yes No Diagnostic design process Figure taken from A.Costley A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

13. High priority diagnostic topics* • Assessment of the various options for Vertical and a Radial Neutron Cameras to measure the 2D n/a source profile and asymmetries in this quantity. • Development of methods of measuring the energy and density distribution of confined and escaping α’s 3. Assessment of radiation effects on coils used for measurements of the plasma equilibrium and development of new methods to measure steady state magnetic fields accurately in a nuclear environment. 4. Determination of life-time of plasma facing mirrors used in optical systems 5. Development of measurement requirements for measurements of dust, and assessment of techniques for measurement of dust and erosion. *taken from ITPA TG on Diagnostics A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

14. Intermediate diagnostic topics – 1/2 6. Establishment of a radiation effects database 7. Determination of the minimum target measurement requirement to support the ‘advanced’ tokamak operation 8. Development of methods for measuring core nD/nT ratio (r/a < 0.3) 9. Devise new concepts for measuring light in-core impurities (e.g. He-ash) that do not rely on a diagnostic neutral beam (DNB) 10. Determination of measurement requirements in divertor region and recommendation of diagnostic techniques. A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

15. Intermediate diagnostic topics – 2/2 11. Determination of the outgassing rates of mineral insulated cables and develop methods to reduce the outgassing rates. 12. Devise new concepts for measuring j(r) that can be applied to a BPX with sufficient spatial resolution. 13. Determination of impurities in divertor using only visible and UV spectroscopy 14. Measurement of runaway electrons • Demonstration of direct measurement of local electric field • Measurement of core density fluctuations A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

16. Diagnostic R&D • There are still many topics where developments are urgently needed. • However, the Parties’ fusion labs are still reluctant to develop BPX diagnostics as part of current programmes. • In the meantime (and especially since last week) the time to a BPX is reducing and so opportunities and time for development are diminishing. • Since it is an established fact that the knowledge gained with and the performance of fusion machines is directly linked to the diagnostic capability, it is a necessity that diagnostic developments are encouraged and enhanced. A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

17. Today’s programme A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005

18. Aim for discussion • What impact do the various control scenarios have on the measurement requirements and on the diagnostics? • Do we have adequate measurements of all parameters needed for control? • What are the key issues in the field of control and diagnostics where further R&D and testing is urgently needed (on present machines)? A.J.H. Donné, W60 Workshop on Burning Plasma Physics and Simulation, Tarragona, 4-5 July 2005