AT Task Force Summary. Amanda Hubbard C-Mod Ideas Forum 2005 Dec 2-6, 2004

Transcription

1 AT Task Force Summary Amanda Hubbard C-Mod Ideas Forum 2005 Dec 2-6, 2004

2 Main goals of the AT physics program (from 5-yr plan 2003) 1. Demonstrate and model current profile control using LH and ICRF waves, at high densities (>10 20 m -3 ). 2. Understanding, control and sustainment of Internal Transport Barriers, with coupled ions and electrons, τ e-i << τ E (T e ~T i ) and without momentum input (RF only). Global confinement H 89P > Achieve full non-inductive current drive (70% bootstrap) and extend pulse length to near steady state (5 sec, 4-6 τ CR ) - divertor power handling and wall particle issues. 4. Attain and optimize no-wall β limits, with β n of at least 3, and explore means of achieving higher values Program involves all physics areas (RF, transport, divertor, MHD)

3 Overview of Ideas05 How do new ideas fit into our AT program goals? (preliminary list, recognizing that AT session ended ~ 1 hour ago!) Relevant ideas from other sessions. What old ideas need to be completed? (will mention only a few key ones today!) Anything missing? Anything brand new?

4 Current Profile Control Most important expts here for 2005 are all those in the LH area: GET THE LH WORKING AS A CURRENT DRIVE TOOL! Similarly (but less urgently) RF group needs to demonstrate MCCD tool. Then, can carry out control experiments. New ones include: Hosea: Use of LHCD to form current hole Jardin: Formation and sustainment of current-hole and other very low li discharges Wukitch: High li discharges with near axis MCCD Kessel: Collaboration on Modeling of LH Discharges Given importance of density control for LH deposition, Labombard: Upper Divertor Pressures with Simulated Cryopump Baffle, is very relevant.

5 Internal Transport Barriers Note that this year, ITB proposals were assigned (rather arbitrarily) to either Transport or AT. A large number of outstanding prior ideas exist, primarily assigned to AT. Many relevant ideas are in Transport group. Internal Transport Barriers are a transport topic, of high relevance to Advanced Tokamak scenarios, hence the overlap. Martin and I need to (and will) re-consider the division after having heard the proposals, before considering priorities and run allocations. For now, the ones in the AT session were: Mikkelsen: Separating the ITB trigger from the initial transient phase of EDA H-mode plasmas Zhurovich : ITB formation T i critical gradient dependence Snipes: Driving Current Rise ITBs using Alfven Cascades Hosea: Early LHCD to allow transport barrier formation Marmar: Investigate the use of off-axis lower hybrid heating to trigger and sustain ITBs. A few of the past ITB proposals which are very AT-relevant include: Rice: Large-volume ITBs at 2.8 T ITBs with 50 MHz ICRH. Ernst: Feedback control of ITBs (could use new control system). Hubbard: Influence of j(r) on ITBs. (needs j(r) control via LHCD),

6 Non-inductive current drive, long pulse Seems optimistic this year to expect LHCD and MCCD to drive a large fraction of the current. Would be very useful to get some experience soon with non-inductive discharges, start studying both physics and operational issues. Several relevant ideas: Politzer: High Bootstrap Fraction Non-inductive Operation Wukitch: High bootstrap fraction discharges with off-axis MCCD Kessel: High Bootstrap Fraction Plasmas with ITBs also prior idea from Parker (similar title to Kessel s, details different). Long pulse: Prior idea for 3-sec pulses Extended Pulse Length Operation at Moderate Density with Increased RF Power (Terry), should be feasible this year due to upgraded RF pulse length. Several new and old divertor ideas (IR camera, brush tile tests ) very relevant.

7 High beta Rather a lack of dedicated AT proposals in this area. This has always been recognized to grow in emphasis later in the program. But, need to look at relevant MHD ideas, think about whether we can push beta to get started (eg. High power at 50 MHz, lower B T??) Eg Meade: NTM Stability modification using LHCD. (MHD) Generally, need to demonstrate NTMs, and other large-scale beta-limited MHD modes (eg kinks, RWM ), before we start any stabilization program, or can get others seriously interested in doing so.

8 Integrated scenarios Overall goal of AT program is to INTEGRATE the four parts goals into viable scenario with high non-inductive fraction, good transport, long pulse AND high beta. Relevant proposals, nominally in Burning Plasma session due to their ITER-relevance (need to discuss best placement): Meade and Kessel: Performance (beta_n, H and f_bs) of RS AT plasmas Wilson: Use of LHCD to achieve ITER-like AT and Hybrid current profiles Also past proposal by Sips on Hybrid scenario (ITPA proposal)

9 Next steps Make a complete list of AT proposals, including previous submissions. (I will do my best, but if there are old ideas which did not make it to MPs, and people are still keen to push them, a reminder would not hurt). Allocation of several proposals from other groups (Transport, MHD, Burning Plasma) needs discussion by Task Force leaders. Divide into groups: 1) needing demonstrated LH CD or heating, or 2) not (ie late or early in campaign). Hold meeting soon to discuss organization, priority of proposals in pre-lh group. Reserve some run time for LH group, to depend on progress of LH commissioning, heating and current drive demonstration.