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Heating and Current Drive Systems for ARIES-AT T.K. Mau University of California, San Diego

Heating and Current Drive Systems for ARIES-AT T.K. Mau University of California, San Diego ARIES Project Meeting September 18-20, 2000 Princeton Plasma Physics Laboratory Princeton, NJ. OUTLINE. CD Analysis for ARIES-AT equilibria at b = 9.1% (90% of limit)

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Heating and Current Drive Systems for ARIES-AT T.K. Mau University of California, San Diego

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  1. Heating and Current Drive Systems for ARIES-AT T.K. Mau University of California, San Diego ARIES Project Meeting September 18-20, 2000 Princeton Plasma Physics Laboratory Princeton, NJ

  2. OUTLINE • CD Analysis for ARIES-AT equilibria at b = 9.1% (90% of limit) • and with R = 5.2 m, Ip ~ 13 MA, and Bo = 5.9 T • Power requirement, profile alignment and number of • CD systems • Normalized CD efficiency scaling vs Te and Zeff. • RFCD launcher system definitions • Conclusions and Discussions

  3. Seed CD Requirements for Latest ARIES-AT Equilibria • Latest series of ARIES-AT equilibria have profiles optimized to give • high bN ( 90% of b limit ), and maximum bootstrap alignment ( Ibs/Ip > 0.9 ) • at Zeff = 1.7, Te0 = 24, 26, 28 and 30 keV. • Seed current is defined as: Jsd = jeq - jbs - jdia - jps in f - direction. • Bootstrap alignment: 2 regions of seed CD : (1) On axis; (2) Off axis • CD power and system requirements determined by driving seed current • profile using RF techniques. ne Te0 = 26 keV bN = 5.4 fbs = 0.917 Te EQ BS Off-axis Seed: 1.05 MA n, T profiles RS core, L-mode edge On-axis Seed: 0.04 MA Dia+PS

  4. Seed CD Requirements at Zeff = 1.8 • Bootstrap current is sensitive to changes in Zeff. • To extrapolate from Zeff = 1.7, adjust n and T profiles to obtain bootstrap • alignment without overdrive. • Three regions of seed current: • (1) on-axis seed : r < 0.2, • (2) mid-radius seed : 0.5 < r < 0.8 • (3) edge seed : r > 0.8. Te0 = 26 keV bN = 5.4 fbs = 0.897 ne EQ Te BS edge +mid-radius Seed: 1.32 MA Modified n, T profiles RS core, L-mode edge On-axis Seed: 0.03 MA Dia

  5. Current Drive at Zeff = 1.7 • Needs two CD systems: • 1. ICRF/FW for on-axis drive : r < 0.2; Pfw ~ 1-2 MW • 2. LHW for off-axis drive : r > 0.8; Plh ~ 25-40 MW • Very good current alignment can be obtained. Teo = 26 keV fbs = 0.917 Pfw = 1.4 MW Plh = 32 MW Teo = 30 keV fbs = 0.911 Pfw = 2.2 MW Plh = 36 MW RF RF EQ EQ BS BS LH LH FW Dia FW Dia

  6. Current Drive at Zeff = 1.8 • Three CD systems are required: • 1. ICRF/FW for on-axis drive : r < 0.2; Pfw ~ 1 MW • 2. LHW for off-axis drive : r > 0.8; Plh ~ 30-40 MW • 3. HHFW for mid-radius drive : 0.5 < r < 0.8 ; Phh ~ 10-16 MW • Fair current profile alignment Teo = 28 keV fbs = 0.898 Pfw = 0.8 MW Plh = 32 MW Phh = 16 MW Teo = 24 keV fbs = 0.897 Pfw = 1.1 MW Plh = 40 MW Phh = 16 MW EQ RF EQ RF BS BS LH LH Dia Dia FW HH FW HH

  7. CD Efficiency Scaling vs Te0 and Zeff • Based on four equilibria optimized at Zeff = 1.7 and Te0 = 24, 26, 28, 30 keV. • Thus, Zeff = 1.7 case has the highest CD efficiency. • For Zeff = 1.7 and 1.6, only 2 RF systems are required (FW+LH). • For Zeff = 1.8, 3 RF systems are required (ICRF/FW+LH+HHFW). • Alignment not as good: results are less reliable. gB = <n>IpRo/PCD

  8. Frequency Options for Fast Wave On-Axis CD • Criteria : Avoid ion and a absorption no resonance on OB side • Reasonable antenna size higher frequency • 68 MHz, 96 MHz, and 135 MHz appear feasible; similar power requirements • 68 MHz is used in most calculations. R+a R-a 5T 4D,6T 3D 4T 135 MHz 2D,3T 96 MHz 2T 68 MHz D T 22 MHz Axis

  9. ICRF Fast Wave Drives On-axis Seed Current • Wave frequency is chosen to place • 4fcT resonance at R > Ro+a, and • 2fcD resonance at R << Raxis, to • minimize ion and alpha absorption. • Launcher is located on outboard • midplane with N|| = 2 spectrum for • best current profile alignment. • Plasma & wave parameters : • R = 5. 2 m, A = 4, k = 2.2, d =0.8, • Bo = 5.9 T, Ip = 13 MA, bN = 5.4, • Teo = 26.8 keV, neo,20 = 2.83, • Zeff = 1.8 • f = 96 MHz, N|| = -1.5. Axis Y (m) Z (m) X (m) R (m) ARIES-AT Pe/P = 0.90 PT/P = 0.02 Pa/P = 0.08 I / P = 0.036 A/W Driven Current r

  10. Off-Axis/Edge Seed CD with LH Waves • Frequency = 3.6 GHz [ > 2 * fLH (r=0.8) ] • - Less than 1% alpha absorption • Usually five waveguide modules, each launching a different N||, are required. • - Located ~2 m. below OB midplane to give maximum penetration. • Penetration to r < 0.8 is not possible for this class of AT equilibria. • Low N|| rays encounter mode conversion to fast wave at r>0.8 and propagates • back to edge; higher N|| rays get totally damped before reaching r = 0.8. Accessible N|| = -1.6 Inaccessible e-damping limit end MC limit start

  11. Mid-Radius CD Using High Harmonic Fast Waves (HHFW) • At f ~ 20fci, HHFW can penetrate deeper than LH waves. • CD efficiency is found to be acceptable. • Issues: • - Strong absorption by energetic a’s • - Experimental database being developed on NSTX • at 30 MHz. • - No credible FW launcher design at f ~ 0.9 GHz. F = 0.9 GHz N|| = -2 Te0 = 26 keV Zeff = 1.8 I/P = 0.018 A/W Te0 = 26 keV Zeff = 1.8 Pa/P = 0.41 e a Absorption Current Drive

  12. Current Drive System Definition for ARIES-AT • Reference Option : ICRF/FW + LHW • -Requires two RF systems and highly compatible with core configuration • - Requires lowest CD power (30-40 MW) • - Likely narrow range of operation • - Issues : (1) LH wave penetration limited to r > 0.8. • Second Option : ICRF/FW + HHFW + LHW • - Requires three RF systems; should be compatible with core design • - Requires more CD power (40-60 MW) • - Broader range of operation • - Issues: (1) alpha absorption of HHFW power • (2) HHFW antenna concept remains to be developed. • Comments: • - Because of small on-axis seed current, ECCD can be a viable • alternative to ICRF/FW. • - Should extra ICRF power be set aside for auxiliary heating? • Can existing CD systems heat plasma to design point?

  13. Definition of the ICRF Fast Wave Launcher System • Assumed requirements for Zeff = 1.8, Te0 = 26 keV (strawman): • - 1 MW of power @ 96 MHz and N|| = 1.5 for on-axis CD. • At 96 MHz, similar jfw profile and I/P are obtained. • Higher frequency is used to reduce size of launcher. • Base launcher module is similar to ARIES-RS folded waveguide design : • - Has 8 waveguides in a toroidal array, with 45o phase shift • - Each waveguide has 10 folds • - Located at outboard midplane • - Radial thickness with diaphragm = 0.97 m • - Module dimensions are : 2.08 m (width) x 0.51m (height) • with total aperture area = 0.99 m2 • Taking a maximum power density of ~40 MW/m2, prudence requires • us to set the power limit at ~20 MW. Extra power can be used for • auxiliary heating and/or rotation drive. • Structural material is SiC with W coating (as in divertors); high • surface resistive dissipation [TBD]; structures (Faraday shields, straps • and support) to be cooled with LiPb. Other choices will be explored.

  14. Isometric View of Folded Waveguide Unit • Design and dimensions are similar to ARIES-RS (f = 95 MHz)

  15. Definition of the LH Wave Launcher System • Calculated lower hybrid system requirements for Zeff = 1.8, Te0 = 26 keV: • - 5 waveguide modules delivering a total power of 35 MW. • Module frequency (GHz) N|| Power (MW) • 1 3.6 1.7 1.1 • 2 3.6 2.0 5.9 • 3 3.6 2.5 7.0 • 4 3.6 3.5 7.5 • 5 2.5 5.0 13.9 • Base unit is the passive/active multijunction grille, modeled after • ITER-EDA design, and used in ARIES-RS. • The grilles are located at ~2 m from the outboard midplane. • Using ITER guideline for power flux capability: P (MW/m2) < 20 f 2/3(GHz), • total required port area = 1.34 m2.

  16. Front View of LH Launcher Modules • Shown are the designs for ARIES-RS, for illustration purpose only.

  17. Consideration of HHFW Launcher System • Calculated HHFW system requirements for Zeff = 1.8, Te0 = 26 keV: • - Launched wave spectrum at 0.9 GHz and N|| = 2.0. • - Launch location : outboard midplane. • - Power = 16 MW. • At present, there is no proven design of FW launcher in 0.9 GHz range. • Possibilities include: • - Combline structure : data at 200 MHz (GA/JFT-2M) • - Folded waveguide : no data close to 0.9 GHz • Assume similar power scaling as ITER guideline for LH waves: • - At 0.9 GHz, power density limit = 18.6 MW/m2 (conservative!) • - First wall penetration area = 1.16 m2.

  18. Special Blanket Sector with RF Launchers Blanket Sector • There are 16 blanket sectors. One sector • has a width of ~2.6 m at midplane. • Sketch of locations of RF launchers in • the sector is based on Zeff = 1.8, • Te0 = 26 keV (strawman). • Aperture area for the launchers: • - ICRF/FW : 0.99 m2 • - LHW : 1.34 m2 • - HHFW : 1.16 m2 • Total aperture area = 3.49 m2 • = 1% of first-wall area. HHFW ICRF/FW LHW LHW LHW LHW LHW

  19. Conclusions and Discussions • A series of ARIES-AT equilibria with bN = 5.4 and fBS = 0.91 at Zeff = 1.7 • and Te0 = 24, 26, 28 and 30 keV have been analyzed for CD power • and launch requirements. Extrapolations to Zeff = 1.6 and 1.8 are made. • CD efficiency scalings were calculated vs Te0 and Zeff; 2 RF systems are • required for Zeff = 1.6, 1.7, while 3 systems are required for Zeff = 1.8, • resulting in lower fBS and higher CD power requirements. • Based on the present strawman with Zeff=1.8 and Te0 = 26 keV, • 3 RF systems are required: LHW for edge CD, ICRF/FW for on-axis CD • and HHFW for mid-radius CD. • Power requirement is reasonable at ~ 52 MW level. Extra ICRF power for • auxiliary heating and/or rotation drive should be provided. • Launcher designs for both LH and ICRF systems have been on-going. • Initial design results in launcher penetration equal to 1% of first wall area. • It appears feasible to place all RF modules in one blanket sector.

  20. Suggested Remaining Tasks • CD power may be lowered, and number of RF systems may be reduced • to two by looking at equilibria optimized at Zeff = 1.8 or higher, and with • no mid-radius seed current drive ( 0.5 < r < 0.8 ). • Complete detailed design of ICRF/FW and LHW launchers. • - Dimensions of various modules • - Wall dissipation with W coating on structures, and compare to Cu. • Address the issue of auxiliary heating during start-up with existing • CD systems: • - How much extra ICRF power is required? At what frequency? • - What are the implications for using LHW to heat the plasma?

  21. Issues and Areas for Future Research • Heating and Current Drive: • - LHW penetration is limited in high-b plasma; HHFW is a possibility, • but needs innovative antenna concept; • - Investigate the dynamics of RF current profile control --- modeling, and • physics and technological constraints • - Refine modeling capability to self-consistently determine MHD stable • equilibrium with bootstrap and externally driven currents; • - Use wave spectrum calculated for RF launcher in ray tracing analysis; • - Study roles of RF in rotation generation and transport barrier control • RF Launcher: • - EM field analysis inside folded waveguide in realistic geometry, • and experiments in a tokamak environment • - Detailed launcher cooling and thermal stress analysis • - Structural material choice in SiC environment : SiC with metal coating • - Wave coupling and loading during plasma transients

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