R. Ellis

Design of a dual high-power, long pulse, steerable ECH launcher for DIII-D

ECH launchers typically use a moveable mirror to steer a gyrotron beam. Increased power handling capability in an ECH launcher requires adding mass or active cooling to the mirrors. The additional forces on the moveable mirror resulting from either approach typically require a compromise between the power handling capability and the steering capability. The P2001 launcher designed by PPPL for DIII-D will launch two 800 kW beams for 10 seconds every 10 minutes. Poloidal and toroidal steering during and between pulses, and a fast poloidal scan capability, will be provided. These conflicting design requirements are satisfied by the use of an innovative steering mechanism. The entire scanning range about two axes is obtained with a mechanism that is strong enough to withstand the electromagnetic forces on the mirror. An innovative mirror design uses high thermal conductivity materials arranged in a manner that limits the eddy currents during a disruption. In this paper, the design of the P2001 launcher is pre...

Metrology for the NCSX Project

The National Compact Stellerator Experiment (NCSX) is being constructed at the Princeton Plasma Physics Laboratory (PPPL) in partnership with the Oak Ridge National Laboratory (ORNL). The complex geometry and tight fabrication tolerances of the NCSXs non-planar coils and vacuum vessel necessitate the use of computerized, CAD-based metrology systems capable of very accurate and reasonably quick measurements. To date, multi-link, portable coordinate measuring machines (pCMM) are used in the fabrication of the non-planar coils. Characterization of the CNC machined coil winding form and subsequent positioning of the conductor centroid (to within +/-0.5 mm) are accomplished via multiple sets of detailed measurements. A laser tracker is used for all phases of work on the vacuum vessel including positioning magnetic diagnostics and vessel ports prior to welding. Future tasks requiring metrology include positioning of the magnet systems and assembly of the three vacuum vessel sub-assemblies onto the final machine configuration. This paper describes the hardware and software used for metrology, as well as the methodology for achieving the required dimensional control and will present an overview of the measurement results to date.

HIGH POWER LONG PULSE PERFORMANCE OF THE DIII-D GYROTRON INSTALLATION

At DIII-D, five 110 GHz gyrotrons are operating routinely for 2.0 s pulses at generated power levels {ge}750 kW per gyrotron. A sixth gyrotron is being installed, which should bring the generated power level to >4 MW and the injected power to about 3.0 MW. The output power now can be modulated by the plasma control system to fix T{sub e} at a desired value. The system is being used as a tool for control of current diffusion, for current profile control and other experiments leading to advanced tokamak operation.

Development of steady-state mirrors for the KSTAR ECH launchers

Steerable Electron Cyclotron Heating (ECH) launchers typically use a fixed, focusing mirror and a flat steerable mirror to direct a high power beam. The launchers presently in service on KSTAR are intended for use in pulsed operation and are passively cooled. KSTAR, and its ECH system, will eventually operate at pulse lengths where a steady-state balance between input power and heat removal must be achieved. Initial design studies for ECH launcher mirrors have been performed, and a prototype has been fabricated and tested. This paper describes the design studies for steady-state ECH launcher mirrors considered for the KSTAR system. Results of analyses and prototype tests are described.

Design of the C-Mod Advanced Outer Divertor

Operational requirements and research considerations make a high-temperature, toroidally continuous outer divertor an important aspect for future operation of the Alcator C-Mod tokamak. Leading edge melting of tiles, nonuniform heat loads, large electromagnetic forces, and localized impurity sources limit the performance of bulk plasmas. These issues can be addressed by the installation of a well-aligned, toroidally continuous outer divertor. In addition, future proposed long pulse operation of C-Mod will cause the temperature of the outer divertor to reach bulk temperatures as high as 500-600°C. This future operational requirement combined with the strong temperature dependence of plasma surface interactions (especially fuel retention), makes a controllable, high-temperature outer divertor desirable and necessary. The design and development of the C-Mod Advanced Outer Divertor (AOD) is discussed.

Electron Cyclotron Heating system status and upgrades on DIII-D

The Electron Cyclotron Heating (ECH) system on the DIII-D tokamak consists of six 110 GHz gyrotrons with corrugated coaxial 31.75 mm waveguide transmission lines and steerable launching mirrors. The system has been gradually updated, leading to increased experimental flexibility and a high system reliability of 91% in the past year. Operationally, the gyrotrons can generate up to a total of 4.8 MW of rf power for pulses up to 5 seconds in length. The maximum ECH energy injected into the DIII-D is 16.6 MJ. The HE11 mode content is over 85% for all the lines, and the transmission coefficient is better than -1.1 dB for all the transmission lines, close to the theoretical value. A new depressed collector gyrotron was recently installed and was injecting up to 640 kW of power into the plasma during 2014-2015 tokamak operations. Three dual waveguide launchers, which can steer the RF beams ±20 degrees poloidally and toroidally, were used for real-time neoclassical tearing mode control and suppression. The launchers now have increased poloidal scanning speed and beam positioning accuracy of ~±2 mm at the plasma center. A new method of in-situ calibration of the mirror angle was used in conjunction with the upgrading of the encoders and motors for the launchers. Two more gyrotrons are expected to be installed and operational in 2015-2016. The first is a repaired 110 GHz, 1 MW gyrotron that had a gun failure after more than 11 years of operation at DIII-D. The second is a newly designed depressed collector tube in the 1.5 MW class, operating at 117.5 GHz, manufactured by Communications and Power Industries (CPI). It operates in the TE20,9 mode and has achieved 1.8 MW for short pulses during factory testing. This gyrotron is undergoing rework to address a high voltage standoff problem.

Upgrades and performance of the electron cyclotron heating system on DIII-D

The Electron Cyclotron Heating (ECH) system on DIII-D consists of six 110 GHz gyrotrons with 6 MW installed power for pulses limited administratively to 5 s in length. The transmission coefficient is better than -1.1 dB for four of the transmission lines, close to the theoretical value. A new depressed collector gyrotron was recently installed and is injecting up to 720 kW of power into DIII-D during 2013 tokamak operations. Three of the four dual waveguide launchers, which can steer the rf beams ±20 degrees both poloidally and toroidally, were used for real-time neoclassical tearing mode control and suppression with increased poloidal scanning speed up to 60 deg/s and positioning accuracy of the beams of ±2 mm at the plasma center. The ECH capabilities on DIII-D are being steadily updated, leading to increased experimental flexibility and high reliability of the system. In the past year the ECH system reliability reached 87%, for 2352 successful individual gyrotron shots into DIII-D. Planning is under way for the addition of two new depressed collector gyrotrons, one at 110 GHz, 1.2 MW and another at 117.5 GHz, 1.5 MW generated power, both of which are being manufactured at Communications and Power Industries (CPI).

Development of an explosion bonded toroidal field coil inner leg for CIT

The high currents and high magnetic fields present in the Compact Ignition Tokamak (CIT) toroidal field (TF) system will necessitate an exceptionally strong conductor for the inner leg of the coils. One solution is to bond UNS 7718 to the copper conductor for reinforcement. Explosion bonding is a method of joining dissimilar metals. The joining of UNS 7718 to copper over large areas is one of the more challenging combinations for explosion bonding. Four vendors were selected to perform a series of 15 shots, starting with small-scale setups to determine bonding parameters, and scaling up to a size comparable to the inner leg of a CIT TF coil. The results of the development program offer encouragements as to the use of an explosion-bonded laminate in the CIT TF coils, pending the resolution of several problems: trailing-end cracking must either be eliminated or shown to fail repeatedly in an area of clad which will be removed during taper grinding; the nose insert caused much trouble with the bonding process; and the additional material needed for bond startup must eventually be machined off, which is not a trivial matter given the physical properties of the 718. Production feasibility is discussed, and the next phase of the development program is described.<<ETX>>

Development of a beryllium copper inner leg for the CIT toroidal field coil

A combination of high strength and high conductivity will be required for the inner leg of the toroidal field coils on the CIT (Compact Ignition Tokamak). An alternative to the baseline laminate design is a C17510 beryllium copper conductor with enhanced strength and conductivity. Two vendors were engaged in a program which resulted in full size, tapered prototype conductors. The results of the program are discussed, and a summary of material properties is presented. The issues of production feasibility and the need for additional development are also addressed.<<ETX>>