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Thermal heat load onto primary limiter for three plasma configurations in doublet III
Journal of Nuclear Materials 128 St 129 (1984) 812-815
812
THERMAL HEAT LOAD ONTO PRINARY LIMITER FOR THREE PLASMA CONFI~U~~ONS
IN DOUBLET
III *
H. YOKOMIZO, M. KASAI **, H. AIKAWA, R. CALLIS +, D. DOLL +, A. KITSUNEZAKI, S. KONOSHIMA, T. MATSUDA, M. NAGAMI, M. SHIMADA and T. TAYLOR t Japan Atomic Energy Research Institute,
Tokai, Ibaraki, Japan
Key words: Doublet III, heat load, primary limiter, plasma con~guration The temperature increments of the limiter tiles are measured by the thermocouples for discharges with three different plasma-configurations. The heat depositions onto each tile are evaluated for each configuration. The heat depositions onto the primary limiter are significantly decreased from 25% to 2% of the total input power by changing the plasma configuration.
In the fusion reactor, the thermal heat load onto the material around the plasma is one of most serious concerns for the machine safety and the material maintenance (lifetime) [l]. The stored energy in the reactor plasma is large enough to produce a high heat flux over the allowable value of the material when the plasma control runs out of normal operation. The present tokamak machines are still smaller than the reactor in size. Their plasma energies, however, are large enough to study the thermal heat load onto the material in the tokamak device. Although the heat flux is usually low under normal operation, it greatly increases under some operation conditions, for example, disruption [2] and abnormal position control. In other word, the plasma behaviour is important from the point of view of controlling the heat flux onto the limiter and the first wall. In this paper, the heat deposition onto the primary limiter is measured by the thermocouples for the discharges with three different ~nfig~ations. All discharges are stable without disruption. The input powers into the plasma are Joule heating power (maximum - 1.2 MW) and the neutral beam power (- 2 MW) for all discharges. Three configurations show different plasma-wall interactions. The heat flux onto the primary limiter is too high in one type of the configurations, while it is nearly zero for other type of the configurations.
2. Experiment& amditions
shapes examined in this report are shown in fig. 1. The discharge indicated by (a) has a major radius of 1.45 m, a minor radius of 0.36 m, an elongation (height/width) of - 1.2. In this case, the primary limiter is set inwardly by 5 cm relative to the location in other cases (b) and (c). The plasma surface is in contact only with the primary limiter and far away from backup limiters and armor tiles. The discharge in the configuration (b) has a major radius of 1.43 m, a minor radius of 0.43 m and an elongation of - 1.0. The plasma is located towards the outer side and its surface is mainly in contact with the primary limiter. The discharge in the configuration (c) has a major radius of 1.41 m, a minor radius of 0.43 m and an elongation of - 1.4. The plasma is located towards the inner-side and its surface is mainly in contact with the inside armor tiles. The plasma current is in the range of 200 - 800 kA for all configurations. Fig. 2 shows typical waveforms of one discharge in configuration (a). The neutral beams [4] with a total power of 2 MW are injected with a time period of
Primary Limiter
Backup Limiter
-.
Doublet III [3] has a capability of making several kinds of plasma shapes. The three types of plasma * This work was authorized by a cooperative agreement between the Japan Atomic Energy Research Institute and the United States Department of Energy under DOE Contract No. DE-ATO3-8iJSF11512. ** Gn leave from Mitsubishi Atomic Power Industry, Japan, + GA Technologies, Inc. San Diego, California, USA. @22-3Il5/84/$03.00
(North-Holl~d
0 Elsevier Science Publishers B.V. Physics ~blis~ng Division)
Fig. 1. Three types of pIasma configurations. (a) SmalI size plasma with an elongation of - 1.2. The primary limiter is set inside by 5 cm from the location of configurations (b) and (c). (b) FulI size plasma with the elongation of - 1.0 mainly contacting with the primary limiter. (c) Full size plasma with the elongation of - 1.4 mainly contacting with the armor tiles.
H. Yukomizo et al. / Thermal heat load onto primaty limiter
*
80 60
l*
i
40 20 i NBI
0.2
0.4
0.6
t (secf
0.8
f 8
1
:
40
,
. .
20 140 -
t.0
150 - 180 ms into all discharges. The Joule input power varies shot by shot according to the plasma current. The radiation power measured by a bolometric measurement is - 30% of the total input power in cases of (a) and (c) and - 50% in the case of (b) as shown in fig. 3. The major part of remaining input power apart from the radiation power is expected to be lost through conduc0 Radiation
Input
:
I
60
Fig. 2. Typical waveforms of one discharge in ~nfiguration (a). (a) The plasma current, (b) one-turn voltage, (c) the neutral beam power, (d) the radiation loss Power.
l
I
(bl
80
i!i;!i/‘“; , ,r; 0
@
0
1
813
E
1
___g___g.---&-%--
5: E2
(Cl
t20 100 80 60 40 20-
l
. .
l*
l
. .
0
400
600
800
1000
1,~ lkAl Fig. 4. Plasma stored energy at the beam heating phase for three configurations.
tion and the convection. Doublet III has one poloidal limiter (called the primary limiter), which is located on the outer vessel wall at one toroidal angle. It is composed of six graphite tiles in a 75 cm X 18 cm array mounted on a water-cooled metal structure with barrel nuts [5). The graphite tiles are Poco AXF-SQ coated with 20 p of Tic. Several thermocouples are installed in the tiles of the primary limiter in order to measure the bulk temPerature of the graphite tiles. Their temperatures were automatically recorded at 10 s before and after each discharge. The increment of the temperature before and after a discharge provides ~fo~ation about the integrated heat deposition during one discharge. The plasma stored energy at the neutral beam heating phase proportionally increases with the plasma current as shown in fig. 4. These data are obtained from a diamagnetic loop measurement. The differences between the configur&ons are due to elongation [6].
3. Experimental resuIts and &seusaii
-0
200
400
600
800
1000
Ip (kAj Fig. 3. Total input Power and radiation loss power. (a), (b) and (c) correspond to the configurations shown in fig. 1.
Fig. 5 shows a typical example of the temperature increments of the six tiles for three configurations. The operation conditions are nearly same for these discharges. The plasma current is - 800 kA. The integrated input ener- is - 960 M during a complete 13. HIGH HEAT FLUX EFFECTS
814
H. Yokomizo et al. /
Temperature (a)
Thermal heat load onto primary
Increment (b)
80 _(a)
(cl
9°C 31°C
2l 15°C
tot 6OC
71°C
33°C
9°C
61°C
7*C
8’C
48°C
3°C
5°C
22OC
1°C
5OC
s”
l
I
I
I
_
discharge. The temperature increments are larger in configuration (a) than in configurations (b) and (c). The heat flux mainly deposits onto three tiles from the third to the fifth tile. The temperature increment of the third tile in configuration (b) is reduced to half of that in configuration (a). The heat flw mainly deposits onto two tiles from the second to the third tile. The plasma in configuration (b) is centered at the higher vertical position by 10 cm relative to that in configuration (a), and the plasma shape is circular so that the surface curvature is the smallest among the three configurations. The temperature increments of all tiles are significantly lower in configuration (c), and the heat flw is spread over five tiles from the second to be sixth tile. Fig. 6 shows the correlation between the temperature increment of the third tile and the plasma current for each configuration. The third tile presents the highest temperature increment among the six tiles in all configurations. A strong correlation is observed in the case of configuration (a), in which the plasma strongly interacts with the primary limiter. The temperature increment linearly increases with the plasma current. The heat deposition seems to be affected by the plasma stored energy, which is proportional to the plasma current as show in fig. 4, and also by the input energy, which is linearly correlated with the plasma current as shown in fig. 3. Although data are scattered in configuration (b), their temperature increments seem to become large as the plasma current increases. This correlation is weak, and it looks similar to the trend observed in the input energy as shown in fig. 3. In configuration (c), no correlation is observed. The temperature increment is nearly constant for the plasma current from 200 - 1000 kA. The plasma surface’in this configuration is detached from the primary limiter so that the heat flux to the primary limiter is only due to’ the neutral particle, radiation during steady state and due to the particle flux during the non-steady state at the initial and final stages of the discharge. Therefore, the heat deposition has little dependence on the input energy and the plasma energy.
0: . .
. .
0 Fig. 5. Temperature increments of six tiles of the primary limiter for three configurations. The plasma conditions are nearly equal for three configurations.
limiter
(b) :
40
“‘11 l*.,*y3~ 0
9,
,
200
400 I+,
600
800
1000
(kA)
Fig. 6. Correlation between the temperature increment of the third tile and the plasma current for three configurations.
The total heat depositions onto the primary limiter are evaluated as shown in table 1 using the temperature increment of fig. 5. Specific heat and thermal conductivity are considered as a function of temperature [7]. About 25% of total input energy deposits onto the primary limiter in the case of configuration (a). In this case, the plasma surface is more than 10 cm away from any structures except the primary limiter. Thus, the heat flows from the plasma concentrate only on the primary limiter. The heat deposition onto the primary limiter is - 4% of the total input energy in the case of configura-
Table 1 Heat depositions Tile
1 2 3 4 5 6 Total
(kJ) of six tiles for three configurations
Plasma confiiuration
‘)
(a)
(b)
Cc)
13 30 63 59 46 31 -240kJ
2 12 23 3 2 1 -40kJ
1 3 4 4 3 4 - 20 kJ
‘) The plasmas are the same as those shown in figs. 5 (a), (b) and (c). Total input energy into the plasma is - 960 kJ.
H. Yokomizo et al. / T~e~~~ tion
(b) and - 2% in configuration (c). In these cases, the plasma surface is close to the area: amor tiles, backup limiters and the vessel wall. Thus, following the heat flows from the plasma spread to the large area so that the heat depositions onto the primary limiter are reduced. This experiment suggests that the distance between the plasma surface and the structures is important for the control of the heat flux onto the materials. Heat fluxes to the primary limiter during the ohmic heating phase and the beam heating phase are estimated by comparing the thermocouple data of two successive discharges with and without a neutral beam injection in the case of configuration (a), which is the most dangerous operation against the limiter tiles. Table 2 shows the heat fluxes to six tiles of the primary limiter. The heat flux to the third tile is 0.8 kW/cm’ during the ohmic heating phase with the ohmic input power 1.1 MW. It increases to 2.3 kW/cmz during the neutral beam heating phase with the input power of 2.8 MW. It is assumed that the heat flux homogeneously deposits to one third of the whole surface area of the primary limiter f8]. A thermal calculation shows that the temperature of the third tile increases 1000°C after the beam injection in this discharge. The heat flux during a beam heating phase is so large that the third and forth tiles of the primary limiter eventually became broken in the series of experiments with configuration (a). A stress calculation [9] based on an analytical formula indicates that a probable cause of the tile crack is a high tensile stress at the barrel nut hole which is located inside the tile to be used for mounting on the supporting structure. The injected beam power in this experiment is 2 MW which is not very high compared to the present tokamak experiments and future plans. The heat concentration onto a small area, however, results in serious damage to the material. In future tokamaks [I], the heating power and the produced fusion power are so large that this kind of heat concentration will cause a significant impact on the machine safety. The plasma operation must Table 2 Heat influx onto six tiles during ohmic and beam heating phases Tile
1 2 3 4 5 6
Heat flux (kW/cm’)‘) ohmic
NBI
0.06 0.3 0.8 0.8 0.4 0.2
0.5 1.2 2.3 2.1 2.0 0.9
a) The plasma is the same as that shown in fig. 5 (a).
815
heat ioad onto primary limiter
be careful to avoid unnecessary onto the materials.
heat concentrations
4. Conclusion The heat depositions onto the primary limiter are compared for three configurations. The input Rower into the plasma is compared of the Joule heating power and the neutral beam power. The heat depositions onto the primary limiter are reduced from 25% to 2% of the total input energy by changing the plasma wnfiguration. The heat flux exceeds the allowable value of the limiter tile for the worst case and the two tiles are eventually broken due to thermal stress. Careful control must be exercised over the plasma in order to avoid abnormal thermal concentration onto a small area of the limiter and the first wall.
Acknowledgement The authors would like to express their sincere gratitude to Doublet III operation, diagnostics and neutral beam groups for their support. They would lie to thank Drs. T. Ohkawa, J.R. Gilleland, S. Mori, and M. Yoshikawa for their encouragement.
References [l] INTGR GROUP, International Tokamak Reactor: Phase One, Rep. Int. Tokamak Reactor Workshop, Vienna, 1980/ 1981 (Int. Atomic Energy Agency, Vienna, 1982). {2] T. Taylor, General Atomic Company Rep. GA-Al6816 (1981) p. 27. [3] R.W. Calhs, General Atomic Company Rep. GA-Al3996 (1976). I41 A. Colleraine et al., in: Heating in ToroidaI Plasmas, Proc. 3rd Joint Varrerma-Grenoble Int. Symp., Grenoble, 1982, Yet. 1 (1982) p. 49. 151 D.L. Sevier, P.W. Trester, G. Hopkins, T.E McKelvey and T.S. Taylor, General Atomic Company Rep. GA-Al6384 (1981). 161 M. Nagami and the JAERI TEAM, D. Overskei and the GA TEAM, in: Plasma Physics and Controlled Nuclear Fusion Research, Proc. 9th Int.‘Conf. Baltimore, 1982, Vol. 1 (IAEA, Vienna, 1983) p. 27. f71 R.E. Nightingale, ed. Nuclear Graphite (Academic Press, New York, 1962). PI T. Taylor, N. Brooks and K. Ioki, J. Nucf. Mater. lllfll2 (1982) 569. 191 H. Yokomiw, M. Kasai, T. Taylor, R. Callis, D. Doll, II. Aikawa, A. Kit.nmezaki, S. Konoshima, T. Matsuda, M. Nagami and M. Shimada, Nucl. Engrg. Des. Fusion 1 (1984) 279.
13.
HIGH HEAT FLUX EFFECTS
812
THERMAL HEAT LOAD ONTO PRINARY LIMITER FOR THREE PLASMA CONFI~U~~ONS
IN DOUBLET
III *
H. YOKOMIZO, M. KASAI **, H. AIKAWA, R. CALLIS +, D. DOLL +, A. KITSUNEZAKI, S. KONOSHIMA, T. MATSUDA, M. NAGAMI, M. SHIMADA and T. TAYLOR t Japan Atomic Energy Research Institute,
Tokai, Ibaraki, Japan
Key words: Doublet III, heat load, primary limiter, plasma con~guration The temperature increments of the limiter tiles are measured by the thermocouples for discharges with three different plasma-configurations. The heat depositions onto each tile are evaluated for each configuration. The heat depositions onto the primary limiter are significantly decreased from 25% to 2% of the total input power by changing the plasma configuration.
In the fusion reactor, the thermal heat load onto the material around the plasma is one of most serious concerns for the machine safety and the material maintenance (lifetime) [l]. The stored energy in the reactor plasma is large enough to produce a high heat flux over the allowable value of the material when the plasma control runs out of normal operation. The present tokamak machines are still smaller than the reactor in size. Their plasma energies, however, are large enough to study the thermal heat load onto the material in the tokamak device. Although the heat flux is usually low under normal operation, it greatly increases under some operation conditions, for example, disruption [2] and abnormal position control. In other word, the plasma behaviour is important from the point of view of controlling the heat flux onto the limiter and the first wall. In this paper, the heat deposition onto the primary limiter is measured by the thermocouples for the discharges with three different ~nfig~ations. All discharges are stable without disruption. The input powers into the plasma are Joule heating power (maximum - 1.2 MW) and the neutral beam power (- 2 MW) for all discharges. Three configurations show different plasma-wall interactions. The heat flux onto the primary limiter is too high in one type of the configurations, while it is nearly zero for other type of the configurations.
2. Experiment& amditions
shapes examined in this report are shown in fig. 1. The discharge indicated by (a) has a major radius of 1.45 m, a minor radius of 0.36 m, an elongation (height/width) of - 1.2. In this case, the primary limiter is set inwardly by 5 cm relative to the location in other cases (b) and (c). The plasma surface is in contact only with the primary limiter and far away from backup limiters and armor tiles. The discharge in the configuration (b) has a major radius of 1.43 m, a minor radius of 0.43 m and an elongation of - 1.0. The plasma is located towards the outer side and its surface is mainly in contact with the primary limiter. The discharge in the configuration (c) has a major radius of 1.41 m, a minor radius of 0.43 m and an elongation of - 1.4. The plasma is located towards the inner-side and its surface is mainly in contact with the inside armor tiles. The plasma current is in the range of 200 - 800 kA for all configurations. Fig. 2 shows typical waveforms of one discharge in configuration (a). The neutral beams [4] with a total power of 2 MW are injected with a time period of
Primary Limiter
Backup Limiter
-.
Doublet III [3] has a capability of making several kinds of plasma shapes. The three types of plasma * This work was authorized by a cooperative agreement between the Japan Atomic Energy Research Institute and the United States Department of Energy under DOE Contract No. DE-ATO3-8iJSF11512. ** Gn leave from Mitsubishi Atomic Power Industry, Japan, + GA Technologies, Inc. San Diego, California, USA. @22-3Il5/84/$03.00
(North-Holl~d
0 Elsevier Science Publishers B.V. Physics ~blis~ng Division)
Fig. 1. Three types of pIasma configurations. (a) SmalI size plasma with an elongation of - 1.2. The primary limiter is set inside by 5 cm from the location of configurations (b) and (c). (b) FulI size plasma with the elongation of - 1.0 mainly contacting with the primary limiter. (c) Full size plasma with the elongation of - 1.4 mainly contacting with the armor tiles.
H. Yukomizo et al. / Thermal heat load onto primaty limiter
*
80 60
l*
i
40 20 i NBI
0.2
0.4
0.6
t (secf
0.8
f 8
1
:
40
,
. .
20 140 -
t.0
150 - 180 ms into all discharges. The Joule input power varies shot by shot according to the plasma current. The radiation power measured by a bolometric measurement is - 30% of the total input power in cases of (a) and (c) and - 50% in the case of (b) as shown in fig. 3. The major part of remaining input power apart from the radiation power is expected to be lost through conduc0 Radiation
Input
:
I
60
Fig. 2. Typical waveforms of one discharge in ~nfiguration (a). (a) The plasma current, (b) one-turn voltage, (c) the neutral beam power, (d) the radiation loss Power.
l
I
(bl
80
i!i;!i/‘“; , ,r; 0
@
0
1
813
E
1
___g___g.---&-%--
5: E2
(Cl
t20 100 80 60 40 20-
l
. .
l*
l
. .
0
400
600
800
1000
1,~ lkAl Fig. 4. Plasma stored energy at the beam heating phase for three configurations.
tion and the convection. Doublet III has one poloidal limiter (called the primary limiter), which is located on the outer vessel wall at one toroidal angle. It is composed of six graphite tiles in a 75 cm X 18 cm array mounted on a water-cooled metal structure with barrel nuts [5). The graphite tiles are Poco AXF-SQ coated with 20 p of Tic. Several thermocouples are installed in the tiles of the primary limiter in order to measure the bulk temPerature of the graphite tiles. Their temperatures were automatically recorded at 10 s before and after each discharge. The increment of the temperature before and after a discharge provides ~fo~ation about the integrated heat deposition during one discharge. The plasma stored energy at the neutral beam heating phase proportionally increases with the plasma current as shown in fig. 4. These data are obtained from a diamagnetic loop measurement. The differences between the configur&ons are due to elongation [6].
3. Experimental resuIts and &seusaii
-0
200
400
600
800
1000
Ip (kAj Fig. 3. Total input Power and radiation loss power. (a), (b) and (c) correspond to the configurations shown in fig. 1.
Fig. 5 shows a typical example of the temperature increments of the six tiles for three configurations. The operation conditions are nearly same for these discharges. The plasma current is - 800 kA. The integrated input ener- is - 960 M during a complete 13. HIGH HEAT FLUX EFFECTS
814
H. Yokomizo et al. /
Temperature (a)
Thermal heat load onto primary
Increment (b)
80 _(a)
(cl
9°C 31°C
2l 15°C
tot 6OC
71°C
33°C
9°C
61°C
7*C
8’C
48°C
3°C
5°C
22OC
1°C
5OC
s”
l
I
I
I
_
discharge. The temperature increments are larger in configuration (a) than in configurations (b) and (c). The heat flux mainly deposits onto three tiles from the third to the fifth tile. The temperature increment of the third tile in configuration (b) is reduced to half of that in configuration (a). The heat flw mainly deposits onto two tiles from the second to the third tile. The plasma in configuration (b) is centered at the higher vertical position by 10 cm relative to that in configuration (a), and the plasma shape is circular so that the surface curvature is the smallest among the three configurations. The temperature increments of all tiles are significantly lower in configuration (c), and the heat flw is spread over five tiles from the second to be sixth tile. Fig. 6 shows the correlation between the temperature increment of the third tile and the plasma current for each configuration. The third tile presents the highest temperature increment among the six tiles in all configurations. A strong correlation is observed in the case of configuration (a), in which the plasma strongly interacts with the primary limiter. The temperature increment linearly increases with the plasma current. The heat deposition seems to be affected by the plasma stored energy, which is proportional to the plasma current as show in fig. 4, and also by the input energy, which is linearly correlated with the plasma current as shown in fig. 3. Although data are scattered in configuration (b), their temperature increments seem to become large as the plasma current increases. This correlation is weak, and it looks similar to the trend observed in the input energy as shown in fig. 3. In configuration (c), no correlation is observed. The temperature increment is nearly constant for the plasma current from 200 - 1000 kA. The plasma surface’in this configuration is detached from the primary limiter so that the heat flux to the primary limiter is only due to’ the neutral particle, radiation during steady state and due to the particle flux during the non-steady state at the initial and final stages of the discharge. Therefore, the heat deposition has little dependence on the input energy and the plasma energy.
0: . .
. .
0 Fig. 5. Temperature increments of six tiles of the primary limiter for three configurations. The plasma conditions are nearly equal for three configurations.
limiter
(b) :
40
“‘11 l*.,*y3~ 0
9,
,
200
400 I+,
600
800
1000
(kA)
Fig. 6. Correlation between the temperature increment of the third tile and the plasma current for three configurations.
The total heat depositions onto the primary limiter are evaluated as shown in table 1 using the temperature increment of fig. 5. Specific heat and thermal conductivity are considered as a function of temperature [7]. About 25% of total input energy deposits onto the primary limiter in the case of configuration (a). In this case, the plasma surface is more than 10 cm away from any structures except the primary limiter. Thus, the heat flows from the plasma concentrate only on the primary limiter. The heat deposition onto the primary limiter is - 4% of the total input energy in the case of configura-
Table 1 Heat depositions Tile
1 2 3 4 5 6 Total
(kJ) of six tiles for three configurations
Plasma confiiuration
‘)
(a)
(b)
Cc)
13 30 63 59 46 31 -240kJ
2 12 23 3 2 1 -40kJ
1 3 4 4 3 4 - 20 kJ
‘) The plasmas are the same as those shown in figs. 5 (a), (b) and (c). Total input energy into the plasma is - 960 kJ.
H. Yokomizo et al. / T~e~~~ tion
(b) and - 2% in configuration (c). In these cases, the plasma surface is close to the area: amor tiles, backup limiters and the vessel wall. Thus, following the heat flows from the plasma spread to the large area so that the heat depositions onto the primary limiter are reduced. This experiment suggests that the distance between the plasma surface and the structures is important for the control of the heat flux onto the materials. Heat fluxes to the primary limiter during the ohmic heating phase and the beam heating phase are estimated by comparing the thermocouple data of two successive discharges with and without a neutral beam injection in the case of configuration (a), which is the most dangerous operation against the limiter tiles. Table 2 shows the heat fluxes to six tiles of the primary limiter. The heat flux to the third tile is 0.8 kW/cm’ during the ohmic heating phase with the ohmic input power 1.1 MW. It increases to 2.3 kW/cmz during the neutral beam heating phase with the input power of 2.8 MW. It is assumed that the heat flux homogeneously deposits to one third of the whole surface area of the primary limiter f8]. A thermal calculation shows that the temperature of the third tile increases 1000°C after the beam injection in this discharge. The heat flux during a beam heating phase is so large that the third and forth tiles of the primary limiter eventually became broken in the series of experiments with configuration (a). A stress calculation [9] based on an analytical formula indicates that a probable cause of the tile crack is a high tensile stress at the barrel nut hole which is located inside the tile to be used for mounting on the supporting structure. The injected beam power in this experiment is 2 MW which is not very high compared to the present tokamak experiments and future plans. The heat concentration onto a small area, however, results in serious damage to the material. In future tokamaks [I], the heating power and the produced fusion power are so large that this kind of heat concentration will cause a significant impact on the machine safety. The plasma operation must Table 2 Heat influx onto six tiles during ohmic and beam heating phases Tile
1 2 3 4 5 6
Heat flux (kW/cm’)‘) ohmic
NBI
0.06 0.3 0.8 0.8 0.4 0.2
0.5 1.2 2.3 2.1 2.0 0.9
a) The plasma is the same as that shown in fig. 5 (a).
815
heat ioad onto primary limiter
be careful to avoid unnecessary onto the materials.
heat concentrations
4. Conclusion The heat depositions onto the primary limiter are compared for three configurations. The input Rower into the plasma is compared of the Joule heating power and the neutral beam power. The heat depositions onto the primary limiter are reduced from 25% to 2% of the total input energy by changing the plasma wnfiguration. The heat flux exceeds the allowable value of the limiter tile for the worst case and the two tiles are eventually broken due to thermal stress. Careful control must be exercised over the plasma in order to avoid abnormal thermal concentration onto a small area of the limiter and the first wall.
Acknowledgement The authors would like to express their sincere gratitude to Doublet III operation, diagnostics and neutral beam groups for their support. They would lie to thank Drs. T. Ohkawa, J.R. Gilleland, S. Mori, and M. Yoshikawa for their encouragement.
References [l] INTGR GROUP, International Tokamak Reactor: Phase One, Rep. Int. Tokamak Reactor Workshop, Vienna, 1980/ 1981 (Int. Atomic Energy Agency, Vienna, 1982). {2] T. Taylor, General Atomic Company Rep. GA-Al6816 (1981) p. 27. [3] R.W. Calhs, General Atomic Company Rep. GA-Al3996 (1976). I41 A. Colleraine et al., in: Heating in ToroidaI Plasmas, Proc. 3rd Joint Varrerma-Grenoble Int. Symp., Grenoble, 1982, Yet. 1 (1982) p. 49. 151 D.L. Sevier, P.W. Trester, G. Hopkins, T.E McKelvey and T.S. Taylor, General Atomic Company Rep. GA-Al6384 (1981). 161 M. Nagami and the JAERI TEAM, D. Overskei and the GA TEAM, in: Plasma Physics and Controlled Nuclear Fusion Research, Proc. 9th Int.‘Conf. Baltimore, 1982, Vol. 1 (IAEA, Vienna, 1983) p. 27. f71 R.E. Nightingale, ed. Nuclear Graphite (Academic Press, New York, 1962). PI T. Taylor, N. Brooks and K. Ioki, J. Nucf. Mater. lllfll2 (1982) 569. 191 H. Yokomiw, M. Kasai, T. Taylor, R. Callis, D. Doll, II. Aikawa, A. Kit.nmezaki, S. Konoshima, T. Matsuda, M. Nagami and M. Shimada, Nucl. Engrg. Des. Fusion 1 (1984) 279.
13.
HIGH HEAT FLUX EFFECTS