# Presentation: 925721

## Diagnostics and Control forBurning Plasmas 

- Introduction
- Tony Donné
- Information taken from ITPA TG on Diagnostics, ITPA WG on Control, ITER IT

## 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

## 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

## Diagnostic design process

## 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 -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)

## 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 -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

## 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  confinement.

## Measurements needed in ITER

- Conclusion
- The more advanced the operating scenario, the more parameters need to be simultaneously controlled

## 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

## ITER measurements

## Requirements & justifications

- A typical example: the electron temperature

**The electron temperature, with good spatial dependence, is a major indicator of plasma**** ****performance 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

## Diagnostic design process

- Figure taken from A.Costley

## High priority diagnostic topics*

- Assessment of the various options for Vertical and a Radial Neutron Cameras to measure the 2D n/ 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

## 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.

## 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

## 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**.**

## Today’s programme

| 11.30 | Donné A. | Introduction and overview |
| --- | --- | --- |
| 11.50 | Baylor L. | Pellet Fueling Technology Leading to Efficient Fueling of ITER BurningPlasmas |
| 12.10 | Osborne T. | Suppression of Type I ELMs through application of edge resonant magnetic perturbations and application to ITER |
| 12.30 | Okabayashi M. | Present understanding of RWM physics and possible approaches for RWM control in burning plasmas |
| 12.50 | Raman R. | Advanced fueling system for use as a burn control tool |
| 13.10 | Moreau D. | Integrated real-time control for advanced steady state scenarios in JET and applications to burning plasmas |
| 13.30 |   | Lunch |
| 14.30 | Sasao M. | Development of Advanced diagnostics for Burning Plasmas |
| 14.50 | Goncalves B | Burning plasma diagnostics on JET: past results and future plans |
| 15.10 | Bindslev H. | Measuring fast ions by collective Thomson scattering, TEXTOR results and ITER plans.  |
| 15.30 | Donné A. | Discussion (until 16.10) |

## 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)?