R. H. Goulding

Comparing experiments with modeling for light ion helicon plasma sources

The ability to obtain high plasma densities with high fractional ionization using readily available, low-cost components makes the helicon a candidate plasma source for many applications, including plasma rocket propulsion, fusion component testing, and materials processing. However, operation of a helicon can be a sensitive function of the magnetic field strength and geometry as well as the driving frequency, especially when using light feedstock gases such as hydrogen or helium. In this paper, results from a coupled rf and transport model are compared with experiments in the axially inhomogeneous Mini-Radio Frequency Test Facility [Goulding et al., Proceedings of the International Conference on Electromagnetics in Advanced Applications (ICEAA 99), Torino, Italy, 1999 (Litografia Geda, Torino, 1999), p. 107] (Mini-RFTF). Experimental observations of the radial shape of the density profile can be quantitatively reproduced by iteratively converging a high-resolution rf calculation including the rf parallel electric field with a transport model using reasonable choices for the transport parameters. The experimentally observed transition into the high density helicon mode is observed in the model, appearing as a nonlinear synergism between radial diffusion, the rf coupling to parallel electric fields that damp near the plasma edge, and propagation of helicon waves that collisionally damp near the axis of the device. Power deposition from various electric field components indicates that inductive coupling and absorption in the edge region can reduce the efficiency for high-density operation. The effects of absorption near the lower hybrid resonance in the near-field region of the antenna are discussed. Ponderomotive effects are also examined and found to be significant only in very low density and edge regions of the Mini-RFTF discharge.

Physics and engineering results obtained with the ion cyclotron range of frequencies ITER-like antenna on JET

This paper summarizes the operational experience of the ion cyclotron resonant frequency (ICRF) ITER-like antenna on JET aiming at substantially increasing the power density in the range of the requirements for ITER combined with load resiliency. An in-depth description of its commissioning, operational aspects and achieved performances is presented.

Helicon Plasma Injector and Ion Cyclotron Acceleration Development in the VASIMR Experiment

In the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) radio frequency (rf) waves both produce the plasma and then accelerate the ions. The plasma production is done by action of helicon waves. These waves are circular polarized waves in the direction of the electron gyromotion. The ion acceleration is performed by ion cyclotron resonant frequency (ICRF) acceleration. The Advanced Space Propulsion Laboratory (ASPL) is actively developing efficient helicon plasma production and ICRF acceleration. The VASIMR experimental device at the ASPL is called VX-10. It is configured to demonstrate the plasma production and acceleration at the 10kW level to support a space flight demonstration design. The VX-10 consists of three electromagnets integrated into a vacuum chamber that produce magnetic fields up to 0.5 Tesla. Magnetic field shaping is achieved by independent magnet current control and placement of the magnets. We have generated both helium and hydrogen high density (>10(exp 18) cu m) discharges with the helicon source. ICRF experiments are underway. This paper describes the VX-10 device, presents recent results and discusses future plans.

High density hydrogen helicon plasma in a non-uniform magnetic field

A high density (1019 m−3) hydrogen plasma has been sustained successfully in axially non-uniform static magnetic field configurations for frequencies both above and below the high density limit of the lower hybrid resonance frequency (LH-HD). Wave field measurements suggest several modes are coupling to generate these helicon plasmas. The dependence of the plasma density on the static magnetic field strength for a fixed geometry can be explained by waves, with wavelength close to the antenna length, that couple to the fundamental radial mode for frequencies below the LH-HD frequency and to the second radial mode for frequencies above the LH-HD frequency.

The continued development of the Spallation Neutron Source external antenna H- ion source

The U.S. Spallation Neutron Source (SNS) is an accelerator-based, pulsed neutron-scattering facility, currently in the process of ramping up neutron production. In order to ensure that the SNS will meet its operational commitments as well as provide for future facility upgrades with high reliability, we are developing a rf-driven, H(-) ion source based on a water-cooled, ceramic aluminum nitride (AlN) plasma chamber. To date, early versions of this source have delivered up to 42 mA to the SNS front end and unanalyzed beam currents up to approximately 100 mA (60 Hz, 1 ms) to the ion source test stand. This source was operated on the SNS accelerator from February to April 2009 and produced approximately 35 mA (beam current required by the ramp up plan) with availability of approximately 97%. During this run several ion source failures identified reliability issues, which must be addressed before the source re-enters production: plasma ignition, antenna lifetime, magnet cooling, and cooling jacket integrity. This report discusses these issues, details proposed engineering solutions, and notes progress to date.

The Development of the Material Plasma Exposure Experiment

The availability of future fusion devices, such as a fusion nuclear science facility or demonstration fusion power station, greatly depends on long operating lifetimes of plasma facing components in their divertors. ORNL is designing the Material Plasma Exposure eXperiment (MPEX), a superconducting magnet, steady-state device to address the plasma material interactions of fusion reactors. MPEX will utilize a new highintensity plasma source concept based on RF technology. This source concept will allow the experiment to cover the entire expected plasma conditions in the divertor of a future fusion reactor. It will be able to study erosion and redeposition for relevant geometries with relevant electric and magnetic fields in-front of the target. MPEX is being designed to allow for the exposure of a priori neutron-irradiated samples. The target exchange chamber has been designed to undock from the linear plasma generator such that it can be transferred to diagnostics stations for more detailed surface analysis. MPEX is being developed in a staged approach with successively increased capabilities. After the initial development step of the helicon source and electron cyclotron heating system, the source concept is being tested in the Proto-MPEX device. Proto-MPEX has achieved electron densities of more than 4×1019 m-3 with a large diameter (13 cm) helicon antenna at 100 kW power. First heating with microwaves resulted in a higher ionization represented by higher electron densities on axis, when compared with the helicon plasma only without microwave heating.

The Development of Plasma-Material Interaction Facilities for the Future of Fusion Technology

Abstract A new era of fusion research has started with ITER being constructed and DEMO for power demonstration on the horizon. However, the fusion nuclear science needs to be developed before DEMO can be designed. One of the most crucial and most complex outstanding science issues to be solved is the plasma surface interaction (PSI) in the hostile environment of a nuclear fusion reactor. Not only are materials exposed to unprecedented steady-state and transient power fluxes, but they are also exposed to unprecedented neutron fluxes. Both the ion fluxes and the neutron fluxes will change the micro-structure of the plasma facing materials significantly even to the extent that their structural integrity is compromised. New devices have to be developed to address the challenges ahead. Linear plasma-material interaction facilities can play a crucial role in advancing the plasma-material interaction science and the development of plasma facing components for future fusion reactors.

Experimental evidence of parametric decay processes in the variable specific impulse magnetoplasma rocket (VASIMR) helicon plasma source

This project was proudly supported by the International Science Linkages programme established under the Australian Government’s innovation statement Backing Australia’s Ability.

Implementation of load resilient ion cyclotron resonant frequency (ICRF) systems to couple high levels of ICRF power to ELMy H-mode plasmas in JET

The paper summarizes the continuous developments made to the ion cyclotron resonant frequency (ICRF) system at JET in order to improve the reliability of the power coupled to plasma. It details the changes and improvements made to the system so that more power is coupled during ELMy plasmas as well as increasing the power density to demonstrate reliable operation in the range of the requirements for ITER. Results obtained using the conventional matching (stubs and trombones) system, 3 dB couplers and the conjugate-T scheme with variable matching elements outside the wave launching structure (external conjugate-T) and inside the wave launching structure (ITER-like antenna) are described. The presence of the three different approaches to load resilient ICRF systems at JET creates a unique opportunity to compare these methods under very similar plasma conditions and to assess the results of ICRF power delivery to ELMy plasmas, an important issue for ITER. The impact of the availability of increased levels of reliable ICRF power on plasma physics studies in JET is illustrated.

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.