The topics for this subgroup applied to each proposed BPX are to 1) simulation of the reference scenario, 2) determination of the global operating space, 3) determine capability and flexibility to pursue advanced tokamak operating regimes, 4) examine ability to control operating point, and 5) identify specific physics and prediction/extrapolation issues

This will require the use of time-dependent integrated simulations, typically 1-1/2 D (2D equilibrium and 1D transport). In addition, analysis may also include static equilibrium based calculations. Both static and time-dependent 0D calculations will be required. These simulations will be done on a standardized common basis for all proposed BPXs, to the maximum extent possible.

The topical areas outlined above would be applied to ITER, FIRE, Ignitor, and any other proposed BPX to the fullest extent possible. Full participation by proponents of the various BPXs would be required.

TASK #1

1-1/2D simulation of the reference full discharge scenario for each BPX (typically ELMing H-mode) consistent with its engineering constraints and commonly applied physics constraints.

1. What energy transport model and pedestal model
2. How is particle transport handled, fueling and pumping.
3. What burn control is applied.
4. How is sawtooth treated, time-averaged or explicitly, and how is its amplitude and period determined.
5. Fixed boundary or free boundary.
6. Clearly cite parameters that are not explicitly modeled (i.e. taup*/tauE, details of sawtooth crash, alpha physics).
7. If choices in the simulations are uncertain, should a scan be part of the assessment.

TASK #2

0D POPCON-like analysis to determine the operating space for each BPX consistent with its engineering constraints and commonly applied physics constraints. Including an assessement of accessibility.

• Standard <n> versus <T> with associated boundaries for betaN, Paux, Pin/P(L-H), n/nGr, etc.
• Find a way to demonstrate the impact of uncertainties for different scalings, assumptions, etc.
• Dimensionless parameters comparison, can this be displayed pictorially.
• Can alpha/energetic particle boundaries be displayed on a POPCON-like diagram.
• What is the approach for AT or alternative operating scenarios, since POPCONs may be too limited to demonstrate the operating space, Pcd versus H98.
• 0D time dependent analysis to determine access and examine trajectory and burn control.

TASK #3

1-1/2D simulations of alternative operating regimes for each BPX (such as Advanced Tokamak, long pulse). This assessment would include static equilibrium based analysis as well to address specific areas.

• This will involve RFCD calculations for NBI, LHCD, ICRF/FW, ECCD, and bootstrap current, coupled to 1-1/2 D time-dependent or equilibrium analysis.
• What energy transport model should be used here, consistent with ITB formation, H-mode, etc. GLF23, MMM, and IFS/PPPL are possibilites.
• Some density profile peaking is typically required relative to standard H-mode making pellet fueling and ITB in the particle channel something we need to analize.
• Ideal MHD is normally examined for target equilibria to decide what to generate in the 1-1/2 D time-dependent analysis. One then takes snapshots of the simulation and analizes for stability to see how well the configuration was obtained.
• NTM and RWM analysis is out of our work scope, however we can simulate the impact of stabilization, or in the case of NTMs should we simulate the impact of operation with saturated island widths.
• The rampup or formation of quasi-stationary plasmas for the burn phase.
• The flattop can have 100% noninductive or partial inductive operation.
• One can also have transient AT or alternative plasmas with inductive current. Each BPX must determine its own alternative mode of operation, and should we allow multiple modes of operation, leading to an assessment of flexibility to do alternative modes.
• The alternative modes are the most complex and expected to provide the strongest case for "integration" aspect of a burning plasma experiment, how do we demonstrate this.

TASK #4

0D, equilibrium based, and 1-1/2D analysis to examine the ability of each BPX to control its operating point, which would include identifying control needs, timescales, required sources (actuators), and diagnostics.

• For burn control the primary tools are density and auxiliary power control, although impurity control can also be effective. Thermal stability could be assessed here, and the level of detail must be determined.
• Particle control is critical to a burning plasma experiment, and is probably the highest priority, second to magnetic control, so we will try to include a detailed assessment of this, involving fueling, pumping, impurites, etc.
• Magnetic control would involve vertical position, radial position, plasma current, and plasma shape control. The control of strike points to guarantee pumping and heat deposition, avoidance of PFC contact, and antenna coupling are high priorities.
• Alternative scenarios would involve current profile control, which must be couped to stored energy control.
• We may not be able to simulate pressure profile control self-consistently, but we should be ble to say how the BPXs are prepared to pursue this type of control.
• There may be physics issues that appear in #5 that would pertain to control, or the ability to change or maintain an operating point.

TASK #5

Identification and simulation of the most significant physics impacts or uncertainties on the operating regimes for each BPX. These will be agreed upon by this subgroup’s leaders and participants, and would be largely derived from Snowmass 1999, UFA1, and UFA2 assessments. Direct interaction with Snowmass 2002 subgroups is required to coordinate efforts and avoid unproductive overlap.

• Alpha particle effects: these range from prompt losses and ripple to TAE’s and EPM’s. These are not likely to be modeled directly in the 1-1/2 D simulations, however, the impact of these, which is alpha loss or broadening of alpha heating profile, can be artificially modeled.
• MHD effects: these include the sawtooth, NTMs, ideal MHD and the RWM, and modifications to standard MHD due to alpha particles. The sawtooth period and amplitude are the critical features for integrated modeling. Analysis of NTMs could include the impact of saturated islands with enhanced transport and examining how these modes are being addressed. For RWMs we can assess the impact of obtaining the higher accessible betas and bootstrap fractions if the device has the means to achieve it.
• Transport effects: these include scaling, modeling, fundamental/turbulence, and particle transport. In scaling we can address the impact of uncertainties in tauE and P(L-H). In addition, we can include effects of missing variables such as triangularity, proximity to nGr, and density profile peakedness. What are each BPX’s ability to compensate for these uncertainties. The modeling area involves different models for energy diffusivity and pedestal height, should we assess all of them. For the turbulence area models exist that try to track the competition between the instability growth rate and ExB shearing rate, so should we examine one of these. Pressure profile control comes under this area. Particle transport is poorly understood and involves choosing a diffusivity and pinch veloctiy, along with fueling models, and boundary conditions that are tied to the wall and divertor. What can we do here.
• Wave-Particle Interactions: assesing the sources available, their feasibility, constraints for their application, etc. We should recognize that these are sources of heating, CD, rotation, and possibly pressure profile control. The simulations for this area are primarily self-consistency oriented, although variations of injected power for various T and n assumptions, impact of Pcd on power balance, and identification of critical assumptions can be done.
• Boundary Physics effects: involves the plasma edge/SOL/divertor issues that impact the core plasma performance. Integration of dynamic edge models into existing 1-1/2 D simulations is somewhat immature, so how can we integrate this feature into our assessment. Simulations of impurity seeding, impact of varying pumping, ELMs, mantle/divertor radiation, etc. are possibilities for examination.

Tentatively establish Subgroup E2 working group meeting at ITPA Database and Modelling meeting at PPPL, March 11-14/2002. Several subgroup members are already in this ITPA membership, allowing all "codes" to be represented.

TASK #2) 0D/Systems Analysis (significant progress 1/30-2/14/2002, target ITPA Database and Modelling meeting 3/11/2002 to present to wider audience and get feedback)

1. set up formulations, check and verify, and check ITER systems assumptions
2. identify diagrams useful for operating space assessment
3. find effective ways to demonstrate impact of uncertainties and flexibilities for each BPX
4. dimensionless parameters comparison
5. capability of each BPX to access AT operating regimes
6. 0D time-dependent for P/Pthr and burn control examination

TASK #1) 1-1/2D simulation of reference operating scenario (all participants will contribute, significant progress 2/28/2002, target ITPA Database and Modelling meeting 3/11/2002 to present to wider audience)

1. free-boundary simulations by TSC and Corsica, requires structure, PF coils and currents
2. collect BPX device data for participants, supply boundary evolutions to fixed boundary codes
3. all codes will be applied to reference scenarios, at least one device per code
4. subtopics for analysis:

TASK #3) 1-1/2D simulation of alternative operating regime (such as Advanced Tokamak) --- detailed outline pending results of TASK #1 and 2.

TASK #4) Burn and other plasma control, the ability of each BPX to control its operating point --- detailed outline pending results of TASK #1 and 2.

TASK #5) Significant physics impacts --- detailed outline pending results of TASK #1, 2, 3, and 4.

Note: Coordination with Physics and Engineering Working Groups on all elements is needed. Assessments include a reference and uncertainty/flexibility examination.

Working Group: in addition to subgroup leaders C. Kessel (PPPL) and C. Greenfield (General Atomics)

Interested Participants:

BPX Contacts:

Computer Codes: