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)
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
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
Te
n, T profiles
RS core, L-mode edge
Te0 = 26 keV
bN = 5.4
fbs = 0.917
EQ
BS
Off-axis
Seed:
1.05 MA
On-axis
Seed: 0.04 MA
Dia+PS
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.
ne
Te
Te0 = 26 keV
bN = 5.4
fbs = 0.897
EQ
BS
Modified n, T profiles
RS core, L-mode edge
On-axis
Seed: 0.03 MA
edge
+mid-radius
Seed: 1.32 MA
Dia
Current Drive at Zeff = 1.7
• Needs two CD systems:
1.
2.
•
ICRF/FW for on-axis drive :
LHW for off-axis drive :
r < 0.2;
r > 0.8;
Pfw ~ 1-2 MW
Plh ~ 25-40 MW
Very good current alignment can be obtained.
Teo = 26 keV
fbs = 0.917
Pfw = 1.4 MW
Plh = 32 MW
RF
EQ
Teo = 30 keV
fbs = 0.911
Pfw = 2.2 MW
Plh = 36 MW
RF
EQ
BS
BS
LH
LH
FW
Dia
FW
Dia
Current Drive at Zeff = 1.8
• Three CD systems are required:
1.
2.
3.
•
ICRF/FW for on-axis drive :
LHW for off-axis drive :
HHFW for mid-radius drive :
r < 0.2; Pfw ~ 1 MW
r > 0.8; Plh ~ 30-40 MW
0.5 < r < 0.8 ; Phh ~ 10-16 MW
Fair current profile alignment
Teo = 24 keV
fbs = 0.897
Pfw = 1.1 MW
Plh = 40 MW
Phh = 16 MW
EQ
RF
BS
Teo = 28 keV
fbs = 0.898
Pfw = 0.8 MW
Plh = 32 MW
Phh = 16 MW
EQ
RF
BS
LH
FW
Dia
HH
LH
FW
Dia
HH
CD Efficiency Scaling vs Te0 and Zeff
4.5
Z
20
2
A /W /m )
• 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.
= 1.7
1.6
4
N orm a lize d C D Effic ienc y ,

B
(1 0
eff
3.5
ARIES-AT
A = 4, R = 5.2 m
b = 9%
3
B = <n>IpRo/PCD
1.8
2.5
23
24
25
26
27
28
Peak Electron T emperature, T
29
30
e0
(keV)
31
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
4T
3D
5T
4D,6T
135 MHz
2D,3T
96 MHz
2T
68 MHz
D
T
22 MHz
Axis
ICRF Fast Wave Drives On-axis Seed Current
Axis
• 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.
ARIES-AT
Driven Current
• 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.
X (m)
R (m)
Pe/P = 0.90
PT/P = 0.02
Pa/P = 0.08
I / P = 0.036 A/W
r
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
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.
Te0 = 26 keV
Zeff = 1.8
Pa/P = 0.41
Te0 = 26 keV
Zeff = 1.8
I/P = 0.018 A/W
e
a
Absorption
Current Drive
F = 0.9 GHz
N|| = -2
Current Drive System Definition for ARIES-AT
• Reference Option :
•
•
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 + LHW
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?
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.
Isometric View of Folded Waveguide Unit
• Design and dimensions are similar to ARIES-RS (f = 95 MHz)
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
2
3
4
5
3.6
3.6
3.6
3.6
2.5
1.7
2.0
2.5
3.5
5.0
1.1
5.9
7.0
7.5
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.
Front View of LH Launcher Modules
• Shown are the designs for ARIES-RS, for illustration purpose only.
* The 4.6 GHz LH launcher array consists of 4 units, 2 for N
* Total pow er transmitted = 20 MW;
|| =2.0 spectrum and 2 forN
|| =1.8 spectrum.
Directivity = 0.7.
emitter
piece
hyperguide
2 4 cm
mouthpiece

R
22.5 cm
69.8 cm
N || = 2.0
35.0 cm
67.8 cm
N || = 1.8
f
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.
Special Blanket Sector with RF Launchers
• 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 :
- LHW :
- HHFW :
0.99 m2
1.34 m2
1.16 m2
m2
Total aperture area = 3.49
= 1% of first-wall area.
Blanket
Sector
HHFW
ICRF/FW
LHW
LHW
LHW
LHW
LHW
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.
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?
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