DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 54: Steady State FDF Based on Hybrid Scenario | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) | Presentation time: | Requested | Co-Author(s): | -- |
| Description: | Demonstrate the existence of a fully noninductive hybrid plasma that satisfies the requirements for FDF. This will be achieved by adding central current drive from EC and FW to a previously obtained high beta hybrid discharge (129323) to eliminate the residual ohmic current and to slighly raise the normalized beta to 4.0. This demonstration will quickly put the physics basis for FDF on a firm foundation.
The starting point for this proposal is shot 129323, which was a hybrid scenario discharge that obtained normalized beta > 3.5 with co-NBI. This beta value is well above the ideal no-wall stability limit. Presumably the rapidly rotating plasma is wall stabilized. The confinement factor is good, H_89P=2.4, and the fusion gain factor of G=0.38 at q_95=4.9 is suitable for modest fusion gain on FDF (Q<10). The parameters given below are from a self-consistent 0-D calculation using shot 129323 as the starting point. Typical values of the achieved current drive efficiencies for EC, FW, and NB on DIII-D are used. These parameters could be scaled up to full field if desired. Parameter 129323 Goal Ip (MA) 1.06 1.06 Bt (T) 1.54 1.54 q_95 4.9 5 n (10^19 m^-3) 3.9 3.9 beta_N 3.7 4.0 H_89P 2.4 2.4 G 0.38 0.38 P_tot (MW) 9 11 P_NB (MW) 9 7 P_EC (MW) 0 3 P_FW (MW) 0 1 I_BS (MA) 0.47 0.56 I_NB (MA) 0.31 0.24 I_EC (MA) 0 0.19 I_FW (MA) 0 0.07 | ||
| Experimental Approach/Plan: | - Start with shot 129323. Modify NBI program to use mainly left (co) beams.
- Inject maximum amount of EC and FW power available in co-current drive phasing. The EC should be deposited as close to the center as possible. - Increase PCS feedback target for stored energy to obtain beta_N=4. - The plasma current and toroidal magnetic field strength can be scaled up or down (at fixed q_95) to fine tune the noninductive fraction and eliminate the residual ohmic current. | ||
| Background: | The current proposal for FDF envisions a high q_min advanced tokamak scenario with 70% bootstrap current fraction. While this is compatible with the US view of DEMO, the physics of the high q_min AT scenario is still being developed. There is also an issue regarding the high off-axis current drive efficiency needed for FDF in this proposal.
Here I propose that the low q_min hybrid scenario is compatible with the requirements of FDF, and it has several advantages. First, the physics basis is well advanced. Long duration hybrid discharge with high beta and high confinement are routinely achieved. Second, because q_min=1 in the hybrid scenario, all of the external current drive can be deposited near the plasma center where the current drive efficiency is the highest (because of the lack of trapped particles and the high electron temperature). While the bootstrap current fraction will be lower in this low q_min hybrid scenario (50% rather than 70%), the increase in the current drive efficiency for central deposition more than makes up for this. Experiments on DIII-D have shown that the current profile in hybrids is insensitive to the external current drive profile. The internal MHD appears to regulate the current profile shape so that sawteeth are eliminated in hybrids regardless of the ohmic current fraction. Therefore, I anticipate no adverse changes to the beneficial characteristics of hybrid plasmas as the ohmic current is reduced to zero. | ||
| Resource Requirements: | Neutral beams: 3 co left sources critical, 3 co right sources desired.
EC: Minimum 5 gyrotrons. FW: Demonstrate ability to couple >1 MW into ELMy H-modes. | ||
| Diagnostic Requirements: | MSE is critical. | ||
| Analysis Requirements: | Will analyze discharges using TRANSP. Various programs will be used to analyze the MSE data to verify the noninductive current fraction. | ||
| Other Requirements: | -- | ||
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