1. Measurement Requirements and Assessment of Measurement Capability David Johnson, Réjean Boivin, Ken Young

2. Present “Measurement Requirements” and “Justifications” provide solid basis for Diagnostic Planning Justification: The electron temperature, with good spatial dependence, is a major indicator of plasma performance and a key component of transport analyses. The profile provides 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 internal transport barrier (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. The core temperature should be measured with 10% accuracy or better to enable a useful determination of the stored energy and to support useful analysis of plasma performance with transport codes. To resolve fine structure on the profile such as internal transport barriers it should be measured at 30 locations across the profile. The edge, with much steeper gradients should be measured with only 0.5 cm between measurements at about 20 locations. However, it has proven difficult to stimulate discussion of existing requirements table and justifications.

3. Need for Expanded Measurement Goals Because it is so condensed, the the existing requirements table does not permit flexibility to consider the next level of detail in requirements, such as: –more detail on different locations in the profile –different times in the discharge –different operating regimes –more detail on parameters vs gradients and moments –requirements for basic control vs advanced control vs physics evaluation There is a need to develop a format that can accommodate the next level of detail. When you consider the number of parameters, this is a daunting task How can we get experts to give more attention to measurement requirements?

4. Assessment of Measurement Capability There is also a need to begin to document expected performance for the planned techniques. This process will evolve with the designs.

5. Proposal to Develop a “Measurement Assessment” Goals –Move to next level of detail in definition of “extended measurement goals” for each parameter –For each parameter, also append a prediction on the performance of each of the techniques planned to measure this parameter Use a standard but flexible template –include measurement requirement, physics justification, expanded measurment goals, technique performance predictions, and performance summary together in one document for each parameter –initially aim at 1-3 pages for each parameter in present table Hope –dealing with requirements in the context of BOTH the physics (justification) AND the techniques (predicted performance) will make this task much more interesting and valuable. It’s interesting and relatively easy for experts to make assessments for parameters they are used to measuring. –such an assessment will document measurement capability identifying gaps in coverage –performance predictions can be updated as designs and predictions are refined.

6. Plan for development of “Measurement Assessment” Basic format (for each parameter - total 1-4 pages) –present measurement requirement –physics justification (we have a good start on this) –expanded measurement goals –performance predictions for relevant diagnostic techniques –assessment summary Develop template –by looking at 4-6 examples (will show a start using T e (R)) –volunteers sought for template development –choose parameters for template development this meeting propose 1) line-averaged density, 2) T e (R), 3) impurity density profile, 4) plasma current, 5) neutron emissivity, 6) ?? –present and propose template at next ITPA meeting Possible paths to develop full “Measurement Assessment” document –Delegate to parties providing various diagnostics the responsibility to develop the performance predictions for these techniques for each of the relevant parameters. –These parties could also provide initial draft of expanded measurement goals (conflict of interest??) –Alternately, a Working Group with reps from all parties and IT leadership could be delegated responsibility for overseeing the full document development.

11. Summary We propose the creation of a “Measurement Assessment” The development of this assessment would document the capability of the proposed diagnostics, permitting better planning for ITER research. Approaching each parameter from the point of view of the predicted performance would provide a fresh look at measurement requirements. The expanded measurement goals would provide a flexible way to record more detailed measurement needs. It would be valuable to have all this information in one document keyed to plasma parameters. A format has been proposed, but further development is needed. A plan for the development of the full document has been suggested, which relies on experts working on the designs to summarize predicted performance. Suggestions on how to develop expanded measurement goals are welcome. Is this a worthwhile task? ……. Is this the right time? ……. Is the ITPA Diagnostics TG the group to coordinate??