Accelerator Systems
FAR-TECH has expertise in developing systems for particle accelerators, including:

• novel acceleration structures
• cavity-based BPM's
• RF sources
• systems integration

• Real-time Mode Identification: To sustain high-performance fusion plasmas, which is required for viable fusion energy, deleterious instabilities must be controlled/suppressed. The prerequisites for feedback control are accurate identification and early detection, preferably at the onset. For this reason, we implemented a Kalman filter technique to discriminate a specific Resistive Wall Mode (RWM) accurately in its early growth, where noise is comparably large. The algorithm has been implemented on DIII-D, and successfully tested, routinely used and maintained. Additionally, in collaboration with the DIII-D team, we succeeded in discriminating Edge-Localized Modes (ELMs) from RWMs for the first time, in real-time experiments.

• Feedback Control: We have been developing a model-based feedback control method. It has been applied to control the RWM, which is critical for creating and sustaining high-performance fusion plasmas. In addition to the active-feedback stabilization experiments, we are currently developing a rotation-compatible RWM model. The model will allow us not only to accurately identify the RWM, but also to effectively suppress the mode in real-time experiments.

• Disruption Mitigation: We are developing a novel plasma accelerator using a solid state pulsed power source and a coaxial plasma gun. The hyper-velocity high-density plasma jets produced by our plasma gun provide a promising solution for delivering the mass and time required for disruption mitigation in current and future tokamaks and ITER.

• Simulation Validation and Virtual Diagnostics: Our capabilities in the theoretical, numerical and experimental aspects of magnetic fusion energy research, combined with our direct involvement at DIII-D, provide a unique opportunity to perform simulation validation. We have already worked on virtual diagnostics using soft x-rays. In this work, we simulated x-ray signals at sensors and compared them to experimental measurements, taking into account the specific geometry and instrumental details involved.

We utilize LSP extensively and have produced improved models, including an electrode Plasma Ablation/Erosion Model for more realistic treatment of conductor boundary conditions (now incorporated in LSP). In addition, we have developed plasma slug and plasma membrane models, to assist in understanding plasma dynamics and to guide application of sophisticated codes. Currently, we are developing an innovative adaptive, meshless hybrid code to improve computational efficiency while capturing the critical physics.

Some of the specific areas of current work include:

• Formation and subsequent acceleration of plasmas in various plasma gun geometries
• Stability of the density and magnetic structure of the accelerating plasmas
• Effects of ejection of plasma jets from gun structures on their density and magnetic structure
• Merging of plasma jets
• Penetration of plasma jets into magnetic barriers

• GEM: Our Generalized ECRIS Model is a comprehensive numerical model of the ECRIS plasma. The user inputs experimental settings such as the microwave power and gas pressure, and the code calculates the distribution of electrons and all ion species self-consistently. A sophisticated Fokker-Planck module allows the code to model the evolution of the highly non-Maxwellian electron distribution function all the way to steady state, and sophisticated fluid modeling of the ions allows the extracted charge state distribution to be predicted without resorting to arbitrary assumptions about the ion confinement time.

• MCBC: Our Monte-Carlo Charge Breeding Code can model the capture and charge breeding of a beam of ions injected into an ECRIS. Combined with the GEM code, it allows the user to predict the charge state distribution of the charge bred ions after they are extracted from the ECRIS. The code models a wide variety of collisional effects including electron impact ionization, Coulomb collisions, charge exchange, and recombination.

• IonEx: The newest addition to our suite of codes, IonEx models the extraction of ions from an ECRIS. Electron and ion space charge fields are both included self-consistently so as to accurately model the shape of the “plasma-meniscus” which determines the emittance of the extracted beam. IonEx is the only beam extraction code that uses the Particle-In-Cloud-Of-Points (PICOP) algorithm, an adaptive, meshfree technique that allows very complex geometries to be accurately modeled.

  IonEx has a user-friendly Graphical User Interface which makes it easy to enter simulation parameters, run the simulation, and view the results with a variety of post-processing plots. The code is capable of running simulations with multiple species. It can be run as a stand-alone code or linked to FAR-TECH’s MCBC and GEM codes.

• FAR-TECH is currently adapting its suite of codes to model electron beam ion sources (EBIS). There are many similarities between the two types of sources, allowing much of our work on ECRIS to be transferred to EBIS. Due to the pulsed nature of EBIS operation, we are extending the codes to model both time-dependent and steady state sources.