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Plans for a new ECRH system at ASDEX upgrade
Fusion Engineering and Design 66 /68 (2003) 537 /542 www.elsevier.com/locate/fusengdes
Plans for a new ECRH system at ASDEX upgrade F. Leuterer a,*, K. Kirov a, F. Monaco a, M. Mu¨nich a, H. Schu¨tz a, F. Ryter a, D. Wagner a, R. Wilhelm a, H. Zohm a, T. Franke a, K. Voigt a, M. Thumm b, R. Heidinger c, G. Dammertz b, K. Koppenburg b, G. Gantenbein d, H. Hailer d, W. Kasparek d, G.A. Mu¨ller d, A. Bogdashov e, G. Denisov e, V. Kurbatov e, A. Kuftin e, A. Litvak e, S. Malygin e, E. Tai e, V. Zapevalov e a
Max Planck Institut fu ¨ r Plasmaphysik, Association EURATOM-IPP, D-85748 Garching, Germany Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, D-76021 Karlsruhe, Germany c Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, IMF1, D-76021 Karlsruhe, Germany d Institut fu ¨ r Plasmaforschung, Universita ¨ t Stuttgart, D-70569 Stuttgart, Germany e Institute of Applied Physics, 603600 Nizhny Novgorod, Russia b
Abstract A new ECRH system is being constructed for ASDEX Upgrade with a total power of 4 MW, generated by four gyrotrons, and a pulse duration of 10 s. Particular features are the use of gyrotrons which can work at various frequencies in the range 104 /140 GHz and correspondingly broad band transmission components. The transmission will be at normal air pressure, and at the torus we will have a tunable double disk vacuum window. A further aim is the installation of fast moveable mirrors for a feedback controlled localized power deposition. # 2003 Elsevier Science B.V. All rights reserved. Keywords: ECRH system; ASDEX upgrade; Localized power deposition
1. Requirements For electron cyclotron resonance heating (ECRH) the power deposition in the plasma is determined by the magnetic field and the gyrotron frequency. If the magnetic field should be a free parameter to allow tokamak operation with different equilibria and plasma currents, or if an experimental program, like suppression of neo-
* Corresponding author. Tel.: /49-89-3299-2223; fax: /4989-3299-2558. E-mail address: [email protected] (F. Leuterer).
classical tearing modes (NTM), requires to drive current on the high field side without changing the magnetic field, then the gyrotron frequency has to be variable. The available power of 2 MW for 2 s of the present ASDEX Upgrade ECRH system imposed a real limitation for current drive, NTM stabilisation or generation of internal transport barriers [1]. The new system will therefore have a power of 4 MW with a pulse duration of 10 s. A further requirement is very localised and feedback controlled power deposition. For this purpose we will install fast moveable mirrors.
0920-3796/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0920-3796(03)00100-5
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
538
Fig. 1. Output power for different operating modes of the experimental gyrotron.
2. The gyrotrons The first gyrotron to be installed can work at 104 GHz and at 140 GHz, making use of the 3l/2
and 4l /2 resonances of the single disc CVDdiamond vacuum window. Such a gyrotron with operating modes TE18,7 and TE22,10, constructed by GYCOM and equipped with a boron nitride
Fig. 2. Intensity pattern at the gyrotron output window (5% levels): (a) f /111.5 GHz, (b) f /140 GHz.
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 3. Gyrotron arrangement.
window, achieved 980 kW/0.5 s and an efficiency of 46% at both frequencies. With a diamond window a pulse length of 10 s is expected. A second gyrotron will be step-tuneable, i.e. it can work at several frequencies within the same interval using different cavity modes. Short pulse tests have demonstrated power generation in excess of 1 MW at all these frequencies [2,3]. Fig. 1 shows results from Ref. [3]. A frequency change requires resetting of the cryomagnetic field in the cavity, the gun and the collector magnetic fields. A
539
CVD-diamond window [4] mounted at the Brewster angle allows a broadband output of the gyrotron. For each frequency the output beam leaves the gyrotron at a slightly different angle. Fig. 2 shows the calculated output beam for two frequencies. The gyrotrons will have a depressed collector and a single-anode gun. Two of them will be fed from one thyristor-controlled power supply 70 kV/ 80 A, but each will have its own series modulator for switching the voltage on and off, for modulation and protection. The body will be driven from a switching power supply /45 kV/0.3 A. Modulation up to 1 kHz will be done with both the cathode and the body voltage. An ignitron crowbar chain will protect both the gyrotron and the modulators.
3. Gyrotron setup and matching optics unit The gyrotrons will be arranged in a square, as shown in Fig. 3, with a distance of 5 m between them, and far away from the tokamak to avoid any magnetic perturbations [5 /7]. A high power calorimetric load able to handle the full 1 MW power and 10 s pulse length is placed in the centre. A rotatable mirror on the top can be directed to each gyrotron.
Fig. 4. Matching optics unit and loads.
540
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 4 shows the matching optics unit (MOU). The gyrotron beam passes a tunnel designed to absorb diffuse radiation up to 50 kW. There is one set of phase correcting mirrors for each frequency, mounted on rotatable disks, since the beam leaves the gyrotron in slightly different directions. The second mirror includes a directional coupler giving a polarisation independent measure of the power. The following two mirrors are polariser mirrors with periodic grooves designed for broad band use. A focusing mirror finally couples the beam into the waveguide transmission line. The mirrors will be 40 mm thick copper. The thermal deformation during a 10 s pulse is sufficiently small and no forced water cooling is necessary. Switchable mirrors in the MOU allow each beam to be redirected into a dummy load capable of 1 MW/1 s pulses. These will be used in the everyday start up procedure and also to absorb pulses inbetween the plasma shots. Another switchable mirror allows to direct a single beam into the central high power load.
4. Transmission line The transmission line is a 87 mm diameter corrugated waveguide line of about 70 m length at normal air pressure. The corrugation, Fig. 5, is designed for minimum losses within the required frequency band. Sliding sections are inserted to compensate thermal expansion. Only 6 mitre bends are necessary between the MOU and the mirror which couples the beam into the torus. The mitre bend at the torus end of the line incorporates a directional coupler to monitor the transmitted power. Couplers sensitive to both polarization components are in development. The waveguide transmission ends in a mirror box where an adjustable mirror directs the beam through the torus window. This mirror can be rotated by 908 to direct the beam radially outward into a calorimetric load which can take a 100 ms pulse. It is used in our standard startup procedure to test the transmission line. The mirror box serves also as a dc-break to isolate the transmission line from the torus.
Fig. 5. Broadband corrugation with high aspect ratio.
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
541
tuneable double disk window. The maximum distance between the discs can be 15 mm if we take a gyrotron frequency drift during the pulse of 100 MHz into account. The calculated reflection for such a window is shown in Fig. 6. The maximum tuning range is 0.9 mm for which we intend to use a piezo-electric control. The precision has to be :/10 mm for a reflected power B/1% in the case of the most critical frequency around 120 GHz. In this case there is a high standing wave ratio of :/2.4 in the space inbetween the discs which therefore must be evacuated. Fig. 6. Calculated reflection for a double disk window with disc separations of 5 and 15 mm.
5. Torus windows The torus windows must permit the transmission of all the possible frequencies. For the first line with the 2-frequency gyrotron this will be a single disk diamond window resonant at both frequencies. For the lines connected to the steptunable gyrotrons we need either a Brewster angle window or a tuneable double disk window. The Brewster window can only transmit linearly polarised waves and requires polariser mirrors in the torus. Furthermore, the limited available diameter for diamond disks needs strong focusing and then reshaping of the beam. This can be avoided with a
6. Launching mirrors All four launchers will be inserted into one 800 /400 mm main port of ASDEX Upgrade. Beyond the vacuum window each beam is further guided in a waveguide until it is finally radiated into the plasma via a focusing mirror and a plane steerable mirror. These allow injection at toroidal angles from /258 to /258, which are set before the pulse. They also allow to scan the whole poloidal cross-section at moderate speed. Over a limited range the poloidal scan will be fast (108 in 100 ms) to realise a feedback controlled power deposition. The drive mechanism is a coaxial arrangement so that the poloidal drive is independent of the toroidal drive [8]. The fast poloidal drive uses a rolling spindle and a rotary vacuum feed through connected directly to a servo motor,
Fig. 7. Steerable mirror with ball screw drive.
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F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 7. To reduce disruption forces the launching mirror will be made of graphite with a copper coating on an intermediate layer of tungsten. However, the low heat conductivity will lead to a surface temperature rise of :/500 8C in a 10 s pulse. The tungsten coating has been tested to withstand such thermal loading.
7. Summary A new ECRH system for ASDEX Upgrade with four gyrotrons of 1 MW/10 s is in construction. At first a 2-frequency gyrotron is expected to be available in Spring 2003, and in Autumn 2003 a
first high power step tunable gyrotron with f /104 /140 GHz is expected.
References [1] F. Leuterer, et al., Fus. Eng. Des. 53 (2001) 277. [2] M. Thumm, et al., Fus. Eng. Des. 53 (2001) 407. [3] V. Zapevalov et al., 12th Wshp. ECE and ECRH, Aix en Provence, France, May 2002. [4] M. Thumm, et al., Fus. Eng. Des. 53 (2001) 517. [5] F. Leuterer et al., 9th Wshp. ECE and ECRH, Borrego Springs, Cal., Jan. 1995, p. 529. [6] F. Leuterer, et al., Fus. Eng. Des. 53 (2001) 485. [7] F. Leuterer, et al., Fus. Eng. Des. 56 /57 (2001) 615. [8] R. Ellis, et al., AIP Conf. Proc. 595 (2001) 318.
Plans for a new ECRH system at ASDEX upgrade F. Leuterer a,*, K. Kirov a, F. Monaco a, M. Mu¨nich a, H. Schu¨tz a, F. Ryter a, D. Wagner a, R. Wilhelm a, H. Zohm a, T. Franke a, K. Voigt a, M. Thumm b, R. Heidinger c, G. Dammertz b, K. Koppenburg b, G. Gantenbein d, H. Hailer d, W. Kasparek d, G.A. Mu¨ller d, A. Bogdashov e, G. Denisov e, V. Kurbatov e, A. Kuftin e, A. Litvak e, S. Malygin e, E. Tai e, V. Zapevalov e a
Max Planck Institut fu ¨ r Plasmaphysik, Association EURATOM-IPP, D-85748 Garching, Germany Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, D-76021 Karlsruhe, Germany c Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, IMF1, D-76021 Karlsruhe, Germany d Institut fu ¨ r Plasmaforschung, Universita ¨ t Stuttgart, D-70569 Stuttgart, Germany e Institute of Applied Physics, 603600 Nizhny Novgorod, Russia b
Abstract A new ECRH system is being constructed for ASDEX Upgrade with a total power of 4 MW, generated by four gyrotrons, and a pulse duration of 10 s. Particular features are the use of gyrotrons which can work at various frequencies in the range 104 /140 GHz and correspondingly broad band transmission components. The transmission will be at normal air pressure, and at the torus we will have a tunable double disk vacuum window. A further aim is the installation of fast moveable mirrors for a feedback controlled localized power deposition. # 2003 Elsevier Science B.V. All rights reserved. Keywords: ECRH system; ASDEX upgrade; Localized power deposition
1. Requirements For electron cyclotron resonance heating (ECRH) the power deposition in the plasma is determined by the magnetic field and the gyrotron frequency. If the magnetic field should be a free parameter to allow tokamak operation with different equilibria and plasma currents, or if an experimental program, like suppression of neo-
* Corresponding author. Tel.: /49-89-3299-2223; fax: /4989-3299-2558. E-mail address: [email protected] (F. Leuterer).
classical tearing modes (NTM), requires to drive current on the high field side without changing the magnetic field, then the gyrotron frequency has to be variable. The available power of 2 MW for 2 s of the present ASDEX Upgrade ECRH system imposed a real limitation for current drive, NTM stabilisation or generation of internal transport barriers [1]. The new system will therefore have a power of 4 MW with a pulse duration of 10 s. A further requirement is very localised and feedback controlled power deposition. For this purpose we will install fast moveable mirrors.
0920-3796/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0920-3796(03)00100-5
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
538
Fig. 1. Output power for different operating modes of the experimental gyrotron.
2. The gyrotrons The first gyrotron to be installed can work at 104 GHz and at 140 GHz, making use of the 3l/2
and 4l /2 resonances of the single disc CVDdiamond vacuum window. Such a gyrotron with operating modes TE18,7 and TE22,10, constructed by GYCOM and equipped with a boron nitride
Fig. 2. Intensity pattern at the gyrotron output window (5% levels): (a) f /111.5 GHz, (b) f /140 GHz.
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 3. Gyrotron arrangement.
window, achieved 980 kW/0.5 s and an efficiency of 46% at both frequencies. With a diamond window a pulse length of 10 s is expected. A second gyrotron will be step-tuneable, i.e. it can work at several frequencies within the same interval using different cavity modes. Short pulse tests have demonstrated power generation in excess of 1 MW at all these frequencies [2,3]. Fig. 1 shows results from Ref. [3]. A frequency change requires resetting of the cryomagnetic field in the cavity, the gun and the collector magnetic fields. A
539
CVD-diamond window [4] mounted at the Brewster angle allows a broadband output of the gyrotron. For each frequency the output beam leaves the gyrotron at a slightly different angle. Fig. 2 shows the calculated output beam for two frequencies. The gyrotrons will have a depressed collector and a single-anode gun. Two of them will be fed from one thyristor-controlled power supply 70 kV/ 80 A, but each will have its own series modulator for switching the voltage on and off, for modulation and protection. The body will be driven from a switching power supply /45 kV/0.3 A. Modulation up to 1 kHz will be done with both the cathode and the body voltage. An ignitron crowbar chain will protect both the gyrotron and the modulators.
3. Gyrotron setup and matching optics unit The gyrotrons will be arranged in a square, as shown in Fig. 3, with a distance of 5 m between them, and far away from the tokamak to avoid any magnetic perturbations [5 /7]. A high power calorimetric load able to handle the full 1 MW power and 10 s pulse length is placed in the centre. A rotatable mirror on the top can be directed to each gyrotron.
Fig. 4. Matching optics unit and loads.
540
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 4 shows the matching optics unit (MOU). The gyrotron beam passes a tunnel designed to absorb diffuse radiation up to 50 kW. There is one set of phase correcting mirrors for each frequency, mounted on rotatable disks, since the beam leaves the gyrotron in slightly different directions. The second mirror includes a directional coupler giving a polarisation independent measure of the power. The following two mirrors are polariser mirrors with periodic grooves designed for broad band use. A focusing mirror finally couples the beam into the waveguide transmission line. The mirrors will be 40 mm thick copper. The thermal deformation during a 10 s pulse is sufficiently small and no forced water cooling is necessary. Switchable mirrors in the MOU allow each beam to be redirected into a dummy load capable of 1 MW/1 s pulses. These will be used in the everyday start up procedure and also to absorb pulses inbetween the plasma shots. Another switchable mirror allows to direct a single beam into the central high power load.
4. Transmission line The transmission line is a 87 mm diameter corrugated waveguide line of about 70 m length at normal air pressure. The corrugation, Fig. 5, is designed for minimum losses within the required frequency band. Sliding sections are inserted to compensate thermal expansion. Only 6 mitre bends are necessary between the MOU and the mirror which couples the beam into the torus. The mitre bend at the torus end of the line incorporates a directional coupler to monitor the transmitted power. Couplers sensitive to both polarization components are in development. The waveguide transmission ends in a mirror box where an adjustable mirror directs the beam through the torus window. This mirror can be rotated by 908 to direct the beam radially outward into a calorimetric load which can take a 100 ms pulse. It is used in our standard startup procedure to test the transmission line. The mirror box serves also as a dc-break to isolate the transmission line from the torus.
Fig. 5. Broadband corrugation with high aspect ratio.
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
541
tuneable double disk window. The maximum distance between the discs can be 15 mm if we take a gyrotron frequency drift during the pulse of 100 MHz into account. The calculated reflection for such a window is shown in Fig. 6. The maximum tuning range is 0.9 mm for which we intend to use a piezo-electric control. The precision has to be :/10 mm for a reflected power B/1% in the case of the most critical frequency around 120 GHz. In this case there is a high standing wave ratio of :/2.4 in the space inbetween the discs which therefore must be evacuated. Fig. 6. Calculated reflection for a double disk window with disc separations of 5 and 15 mm.
5. Torus windows The torus windows must permit the transmission of all the possible frequencies. For the first line with the 2-frequency gyrotron this will be a single disk diamond window resonant at both frequencies. For the lines connected to the steptunable gyrotrons we need either a Brewster angle window or a tuneable double disk window. The Brewster window can only transmit linearly polarised waves and requires polariser mirrors in the torus. Furthermore, the limited available diameter for diamond disks needs strong focusing and then reshaping of the beam. This can be avoided with a
6. Launching mirrors All four launchers will be inserted into one 800 /400 mm main port of ASDEX Upgrade. Beyond the vacuum window each beam is further guided in a waveguide until it is finally radiated into the plasma via a focusing mirror and a plane steerable mirror. These allow injection at toroidal angles from /258 to /258, which are set before the pulse. They also allow to scan the whole poloidal cross-section at moderate speed. Over a limited range the poloidal scan will be fast (108 in 100 ms) to realise a feedback controlled power deposition. The drive mechanism is a coaxial arrangement so that the poloidal drive is independent of the toroidal drive [8]. The fast poloidal drive uses a rolling spindle and a rotary vacuum feed through connected directly to a servo motor,
Fig. 7. Steerable mirror with ball screw drive.
542
F. Leuterer et al. / Fusion Engineering and Design 66 /68 (2003) 537 /542
Fig. 7. To reduce disruption forces the launching mirror will be made of graphite with a copper coating on an intermediate layer of tungsten. However, the low heat conductivity will lead to a surface temperature rise of :/500 8C in a 10 s pulse. The tungsten coating has been tested to withstand such thermal loading.
7. Summary A new ECRH system for ASDEX Upgrade with four gyrotrons of 1 MW/10 s is in construction. At first a 2-frequency gyrotron is expected to be available in Spring 2003, and in Autumn 2003 a
first high power step tunable gyrotron with f /104 /140 GHz is expected.
References [1] F. Leuterer, et al., Fus. Eng. Des. 53 (2001) 277. [2] M. Thumm, et al., Fus. Eng. Des. 53 (2001) 407. [3] V. Zapevalov et al., 12th Wshp. ECE and ECRH, Aix en Provence, France, May 2002. [4] M. Thumm, et al., Fus. Eng. Des. 53 (2001) 517. [5] F. Leuterer et al., 9th Wshp. ECE and ECRH, Borrego Springs, Cal., Jan. 1995, p. 529. [6] F. Leuterer, et al., Fus. Eng. Des. 53 (2001) 485. [7] F. Leuterer, et al., Fus. Eng. Des. 56 /57 (2001) 615. [8] R. Ellis, et al., AIP Conf. Proc. 595 (2001) 318.