P.M. Ryan

Global ICRF system designs for ITER and TPX

The design of feed networks for ICRF antenna arrays on ITER and TPX are discussed. Features which are present in one or both of the designs include distribution of power to several straps from a single generator, the capability to vary phases of the currents on antenna elements rapidly without the need to rematch, and passive elements which present a nearly constant load to the generators during ELM induced loading transients of a factor of 10 or more. The FDAC (Feedline/Decoupler/Antenna Calculator) network modeling code is described, which allows convenient modeling of the electrical performance of nearly arbitrary ICRF feed networks.

Novel broadband multilayer microstrip directional couplers

Design method of novel multilayer, broadband six port microstrip directional coupler at VHF- UHF range for high power applications is given. Directional coupler is modeled and simulated with the method of moments based planar electromagnetic simulator on a two-layer Alumina substrate. It is shown that the high directivity and desired coupling level of the directional coupler are maintained within 300MHz of bandwidth using the proposed design method in this paper. Results of this work can be used in the design of broadband directional couplers for high power RF/Microwave applications.

Initial operation of the JET ITER‐like High‐Power Prototype ICRF Antenna

Fabrication and assembly of a High Power Prototype (HPP) of the JET ITER‐like Ion Cyclotron Range of Frequencies (ICRF) launcher have been completed at Oak Ridge National Laboratory (ORNL), and high power tests have begun. The HPP consists of one quadrant of the full 7.5 MW antenna (1). The prototype is the product of a collaboration between ORNL, Princeton Plasma Physics Laboratory, and EFDA‐JET/UKAEA. Internal matching capacitors are utilized in a circuit that maintains a voltage standing wave ratio (VSWR) at the input 45 kV peak voltage at the internal matching capacitors, which is greater than the original design voltage. High power pulses up to 2s have been run. Diagnostics include thermocouples, voltage probes at the capacitors and along the integral λ/4 matching transformer, and an optical temperature sensor for in‐situ measurements of capacitor temperatures. Low power measurements of electrical characterist...

Spectral shaping and phase control of a fast‐wave current drive antenna array*

The requirements for antenna design and phase control circuitry for a fast-wave current drive (FWCD) array operating in the ion cyclotron range of frequencies are considered. The design of a phase control system that can operate at arbitrary phasing over a wide range of plasma-loading and strap-coupling values is presented for a four-loop antenna array, prototypical of an array planned for the DIII-D tokamak (General Atomics, San Diego, California). The goal is to maximize the power launched with the proper polarization for current drive while maintaining external control of phase. Since it is desirable to demonstrate the feasibility of FWCD prior to ITER, a four-strap array has been designed for DIII-D to operate with the existing 2-MW transmitter at 60 MHz. 3 refs., 6 figs.

Conversion of the four‐strap array in DIII‐D to a tunable traveling wave antenna

The in situ conversion of the two‐standing wave resonator driven four‐strap array in DIII‐D to a new type of traveling wave antenna (TWA) is introduced. First observations are reported on (1) broad frequency range tunability; (2) narrow frequency band phase control; (3) single pass transmission loss and modification caused by resistive and reactive sheet simulators of plasma loading; and (4) recirculating power resonance and gain in a traveling wave resonator (TWR) driven TWA.

Results from HHFW system operation on NSTX

The HHFW system on NSTX has operated with the full 12-antenna, 6-transmitter configuration, delivering over 2 MW reliably for pulse lengths over 100 ms with various phasings of the antenna system. A circuit model of the full 12- antenna coupled system has been developed that gives good agreement with vacuum measurements. When it is used to extract the effects of the plasma on the rf circuit, pronounced asymmetries in antenna loading are observed, even when antenna phasing is symmetrical (e.g., 0π0π0π…..). The loading of the plasma on the antenna has been calculated with the RANT3D code using measured edge density profiles in front of the antenna; these agree with measured loading values.

Measurement of rf voltages on the plasma‐touching surfaces of ICRF antennas

Measurements of the rf voltages on Faraday shields and protection bumpers have been made for several loop antennas, including the mock‐up antenna and A1 for JET, the original antenna for Tore Supra, the present ASDEX‐U antenna, and the folded waveguide. The loop antennas show voltages that scale to ≊12 kV for a maximum input voltage of 30 kV with 0/0 phasing. The voltages are dramatically reduced for 0/π phasing. These voltages are significant in that they can substantially increase the rf sheath potential beyond the levels associated with the simple electromagnetic field linkage from the current straps that results in plasma heating. In this paper, we investigate and measure the source of these voltages, their scaling with antenna impedance, and the differences between the loop arrays.