Highlights from the 2013 Workshop on RF Heating Technology of Fusion Plasmas

1. Workshop on RF Heating Technology of Fusion Plasmas 2013 US-EU-JPN RF Heating Technology Workshop September 9 – 11, 2013 Speyer Germany HEPHAISTOS

2. The Workshop on RF Heating Technology of Fusion Plasmas Meets Annually • The workshop started in the late 80s between the US and Japan to develop ICRF technology quicker and cheaper • Early success was the 2 MW EIMAC Tetrode. Built by the US, tested on a JT 60 transmitter • Hosting the workshop follows a US-Japan-Europe rotation • All frequencies of RF plasma heating are included • Ion Cyclotron Range of Frequencies • Lower Hybrid Range of Frequencies • Electron Cyclotron Range of Frequencies • Topic cover • RF sources • Transmission Components • Launchers

3. To Encourage Workshop Attendance, it is Ususally Held Close to Another RF Conference • The RF Heating Technology Workshops usually follows one of the following: • IRMMW-THz Conference • US-JPN RF Heating Physics WS • Joint WS on Electron Cyclotron Emission and Electron Cyclotron Heating • The 2013 RF Heating Technology WS followed the 38th IRMMW-THz Conference held in Mainz, Germany, and was hosted by the Karlsruher Institute of Technology

4. Agenda RF Heating Technology WS 1 of (2)

5. Agenda RF Heating Technology WS 2 of (2)

6. There Were 36 Presentations • 36 Presentations • Six on ECH Systems • Four on ICH Systems • Ten on EC Sources (gyrotrons) • Seven on EC Transmission Lines • Nine on Launchers • The final session was used to review past collaborations and identify potential new collaborations

7. Highlights from ECH System Presentations (1 of 2) • ITER • PCR-505: Proposes to change Equatorial Launcher to poloidal steering (doubles ECCD in 0.4 < ρ < 0.6) • LHD • The addition of a 1 MW 154 GHz gyrotron extended ECR plasma parameters up to high electron temperature Te0> 20 keV and up to high density ne~ 5.4 x 1019 m-3

8. Highlights from ECH System Presentations (2 of 2) • JT 60 SA • Plan - 7MW injection by 9 gyrotrons (initially 4 110 GHz {old}, and 5 110 & 138 GHz dual frequency) and 4 antennas enables ECH/CD for 100s • First Dual Freq gyrotron delivered and tested 2012 • AUG • New ECH System planned - 4x 1 MW, 140 and 105 GHz, cryogen-free magnets, semiconductor based body modulator, DC-heating of cathode

9. Highlights from ICH System Presentations (1 of 2) LHD • To control toroidal wavenumber and reduce RF sheath by dipole excitation a HAandShake form antenna (HAS) was installed 2012 • High-quality heating was achieved by dipole phasing > 90% • Higher density plasma with ne=3.6x1019m-3 , Te~Ti~1keV was sustained with PICH=2MW and PECH=0.37MW, Plasma density was increased proportionally to PRF(PICH+PECH). • HAS (dipole mode) antenna has better performance than HAS (monopole) and Poloidal Array antennas, (> 90% coupling). • Faraday-shield less ICRF antenna will be tested, in next experimental campaign. Rods were removed from one of two Poloidal Array antennas Toroidal Array Antenna

10. Highlights from ICH System Presentations (2 of 2) DIII-D • Kurchatov Institute has suggested that helicons could be very effective for off-axis current drive in tokamaks (including DEMO) • Models predict off-axis current drive with efficiency 2 to 4 times higher than that from neutral beam injection or ECCD • Traveling wave antenas are a tested technology for launching helicons (accepts large gaps, launches narrow spectrum) • The proposed length of the 500 MHz antenna is 2 m, • For the balanced combline with 1 MW input, the highest peak voltage is expected to be < 14 kV • Only one feed and one return needed 2 m 20 cm W/O Faraday Shield

11. Highlights from Gyrotron Development (1 of 2) • KIT • Now developing the 1 MW 170 GHz EU gyrotrons for ITER • Testing a 1 MW 105 to 165 GHz step tunable gyrotron with dimond brewster window. • Plans to design/develop a coaxial cavity 1.5 MW, 240 GHz, step tunable (3 GHz steps) gyrotron • JAEA • ITER • Gyrotron:170GHz, 1MW, 50%, (<1hr) • Gyrotron system: Power supply, Control system • Equatorial Launcher • JT--‐60SA • Construction of 9 gyrotron EC system • 110GHz/138GHz, 1MW (100s) gyrotron • Development of Launcher • DEMO • >200GHz Gyrotron (203GHz, 300GHz)

12. Highlights from Gyrotron Development (2 of 2) • CPI • VGT-8170: 170 GHz, 500 KW/1 MW GYROTRON (USIPO) • VGT-8115: 110 GHz, 1.2 MW GYROTRON (DIII-D) • VGT-8141: 140 GHz, 900 KW GYROTRON (W7X) • VGT-8117: 117.5 GHz, 1.5 MW GYROTRON (DIII-D) • GYCOM • Significant progress in MW ( e.g. ITER ) gyrotrons • Demonstrated parameters 1 MW, > 50%, 1000 sec/ 1.2 MW, 100sec • Reliability tests of ITER gyrotrons • Successful tests of gyrotrons (prototypes) with enhanced power (1.5 MW, 2.5 sec) • Multi-frequency gyrotron development in progress (AUG) • Several other gyrotorn systems developed end delivered (140 GHz/1MW/3s SWIP, 42GHz/0.5MW/1s IPR, 140 GHz/1MW/1000s EAST)

13. EC Transmission Line Topics • Transmitting and maintaining good HE11 mode purity [MIT, Kyushu Univ, JAEA] • Measuring mode purity [Kyushu Univ, GA] • Validation of models to predict mode generation, and means to reduce mode content [MIT] • Developing and validating CVD diamond windows [KIT] Pressure test

14. EC Launcher Topics • Seismic sensitivity – can designs be improved to make components more robust • Design changes can reduce max stress from 385 MPa to 156 Mpa • Remote handling optimization – Use modularization to reduce maintenance time • Remotely steerable ECRH launchers for W7X • JT 60SA launcher design supporting 110 GHz and 138 GHz Max equiv. stress = 385 MPa Max equiv. stress = 156 MPa

15. Non HE11 Mode Content in Equatorial Launcher Sprays Stray Radiation into unprotected Zones • JAEA constructed one layer (8 tubes) of the equatorial launcher and tested at high power ( 120 kW, 50 sec) • LP01/LP11/LP02/others : 64%/32%/1.2%/2.8% • Main beam (92~93% of power) was radiated toward the target within 3 cm discrepancy. • 1% of power absorbed behind each mirror • 0.6% of power absorbed in the beam duct • 1% of power was deviated from the path to M2. • 4~5% of power could not be caught.