045-05/rs PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION Taming The Physics For Commercial Fusion Power Plants ARIES Team Meeting Georgia Tech., Atlanta, GA December A.D. Turnbull, General Atomics

045-05/rs Is There A Comprehensive Approach to Asking The Right Plasma Control Issues Begin with Engineering Question: –Select possible solution: oFormulate Physics Questions: –Select alternative solution: oFormulate Physics Questions: Example: Engineering Question: How is the power flow to be handled ? –Possible solution: H-mode with a radiative divertor to distribute heat and radiation oPhysics Questions: Can H-mode thresholds be maintained ? oCan divertor detachment be maintained ? –Possible solution: L-mode oPhysics Questions: Is fusion performance sufficient ?

045-05/rs Basic Question For Plasma Control Issues: How Are Performance And Heat Loads Balanced And Controlled Possible solution: Measure fusion performance and heat loads and feed back on input power and deposition: –Physics Questions: oHow is fusion performance to be measured ? oHow are heat and radiation loads to be measured ? oHow is the input deposition to be controlled ? oHow does input power deposition modify performance ? oHow does input power deposition modify heat and radiation loads ? oWhat algorithm translates performance to input power ? oWhat algorithm can be used to translate heat and radiation loads to input power ? oWhat are the limits to the control of performance and power fluxes from this solution ?

045-05/rs Other Engineering Questions Relevant To Plasma Control Issues How is control regained after excursions occur outside the normal parameters ? How is plasma startup done ? How is plasma shutdown achieved ? How is fusion ash removed ? How is the distribution of power fluxes to external surfaces controlled ? How is cleanup after disruptions achieved ? How is the required level of diagnostic capability achieved in a fusion environment ? Not all issues can be formulated as: Engineering question  Proposed solution  Physics questions –Some do not have physics content: solution is just a few numbers –eg What are the wall loading limits ?

045-05/rs Is There A General Formal Approach to Formulating The Right Plasma Control Issues ? Maybe ! Many of the plasma control issues boil down to requiring control of a finite number of physics parameters: –Essentially requiring measuring a quantity and modifying it ! Additional issues not encapsulated in questions of control of plasma parameters can and need to be addressed separately: –How is cleanup after disruptions achieved ? –How is the required diagnostic capability achieved in a fusion environment ? Profiles are closely coupled and should be considered simultaneously These all have the same set of general physics questions: –What values of the parameter are required ? –What is the allowable range of values –How are the parameters measured ? –How are they modified - what is the input controller ? –What is the algorithm for translating the required change in parameters to the needed change in controller ?

045-05/rs Plasma Physics Parameters Requiring Diagnostics And Control Global parameters: –Fusion power –Plasma beta –Confinement quality –Overall heat and radiation loads Power handling control: –Heat and radiation load distributions –Edge recycling –ELM size and frequency –Sawtooth size and frequency Equilibrium profiles: –Current density (safety factor) –Pressure –Density –Temperature –D-T ratios –Impurities –Plasma rotation

045-05/rs Some Answers To Current Profile Control Questions Required current profile set by ARIES-AT design Allowable range needs to be determined from calculations Profile measurements using Motional Stark Effect (MSE): –Requires at least a diagnostic Neutral Beam –Requires full equilibrium reconstruction to obtain resultant current profile from magnetic field pitch angle Current profile modified by noninductive current drive: –ECCD –Lower Hybrid Translation of desired current profile to input current drive requires: –Ray tracing and current drive deposition calculations –Possible coupling with pressure profile changes due to heating

045-05/rs Some Answers To Pressure, Density, And Temperature Profile Control Questions Required profiles set by ARIES-AT design Allowable ranges need to be determined from calculations: –T i from fusion cross section requirements –nT  restrictions –Control of spontaneous transport barrier formation Profile measurements using Thomson scattering and Charge Exchange Recombination (CER) diagnostics Profiles modified by: –Pellet injection, gas puffing, and Neutral Beam input –RF wave heating –Divertor pumping –Alpha particle heating Translation of desired profiles to fueling input requires: –Deposition calculations for pellets, RF, beams, and gas –Alpha particle slowing down and heating calculations –Full equilibrium reconstruction to obtain resultant pressure profile

045-05/rs Some Answers To Questions Of Control Of D-T Ratios Required values set by fusion yield calculations Allowable range needs to be adjustable during operation D-T mix diagnostics: –Global D-T ratio measurements from neutron rates –Profile measurements using ?? Global mix and profile modified by: –Tritium neutral beam input –Control of isotopic differential transport rates Translation of desired D-T ratios to fueling input requires: –Deposition calculations for beams –Alpha particle slowing down and heating calculations

045-05/rs Some Answers To Impurity And Alpha Particle Ash Control Questions Required values set by fusion yield requirements: –Presumably minimized Allowable range set by fusion yield requirements Impurity profile measurements using ? Impurity profile modified by: –Altering balance between particle and energy confinement oHow ? –MHD fluctuations from Sawteeth and ELMs Translation of desired ash and impurity concentration to MHD fluctuation size and frequencies requires: –Impurity transport calculations –ELM and sawtooth frequency and size control through: oCross section shaping oEdge seeding oDivertor pumping oNonaxisymmetric shaping

045-05/rs Some Answers To Plasma Rotation Profile Control Questions Required rotation values and profile set by resistive wall mode (RWM) stability and possibly confinement requirements Minimum generally needs to be satisfied only: –Low momentum input  a reactor is unlikely to rotate too fast Rotation profile measurements using: –CER for impurity rotation –Main ion rotation ? Rotation profile modified by: –Momentum input from Neutral Beams –Possibly external rotating nonaxisymmetric fields –Particle losses ? Translation of desired rotation to beam input requires: –Beam deposition calculations –Angular momentum transport calculations –Particle loss calculations –Magnetic drag calculations

045-05/rs Some Answers For Control Of Global Parameters: Fusion Power, Beta Confinement, And Power Loads Required values set by fusion power requirements Range set by POPCON calculations Measurements using: –Neutron rates –Equilibrium reconstruction –Input power flows –Rates of profile changes –Power flows to material surfaces Parameters modified by: –D-T ratios –Control of transport barriers –Input heating power Translation of desired global parameters to input heating and D-T ratios requires: –Time dependent 1 1/2 D transport calculations

045-05/rs Some Answers To Power Handling Control Questions: Power Distribution, Recycling, ELM And Sawtooth Sizes Required values set by materials engineering specifications Range set by materials engineering specifications Measurements using: –Diagnostics placed near external surfaces –Magnetic diagnostics, edge impurity density diagnostics –Divertor diagnostics (Thomson, cameras, etc.) Power distribution parameters modified by: –Profile control –Fusion power control –Divertor geometry control Translation of desired power flow parameters to input requires: –Edge and SOL simulations –Radiation calculations –Time dependent transport calculations

045-05/rs Two Key Issues Not Encapsulated In Terms Of Control Of Plasma Profiles Or Parameters Require Serious Attention How is cleanup after disruptions achieved ? –This is an issue that needs to be resolved by ITER –Requires techniques that work in a hostile fusion environment oIs glow discharge cleaning sufficient ? oIs Lithium conditioning a working option ? –Requires developing wall conditions that minimize cleanup oLow Z ? oNo carbon ? How is the required level of diagnostic capability achieved in a fusion environment –This is a big issue that may not get resolved by ITER

045-05/rs An Advanced Tokamak Reactor Will Require An Unprecedented Array Of Diagnostics DIII-D Diagnostics