Index of content:
Volume 77, Issue 1, January 2006
- NUCLEAR PHYSICS, FUSION AND PLASMAS
77(2006); http://dx.doi.org/10.1063/1.2149607View Description Hide Description
This article describes the control system for a ion source of the NBI (neutral beam injector) for steady-state superconducting tokamak-1 (SST-1). The system uses both hardware and software solutions. It comprises a DAS (data acquisitionsystem) and a control system. The DAS is used to read the voltage and current signals from eight filament heater power supplies and 24 discharge power supplies. The control system is used to adjust the filament heater current in order to achieve an effective control on the discharge current in the plasma box. The system consists of a VME (Verse Module Eurocard) system and C application program running on a VxWorks™ real-time operating system. A (proportional, integral, and differential) algorithm is used to control the filament heater current. Experiments using this system have shown that the discharge current can be controlled within 1% accuracy for a loop time of . Response of the control system to the pressure variation of the gas in the chamber has also been studied and compared with the results obtained from those of an uncontrolled system. The present approach increases the flexibility of the control system. It not only eases the control of the plasma but also allows an easy changeover to various operation scenarios.
77(2006); http://dx.doi.org/10.1063/1.2140488View Description Hide Description
A thermographic camera and four hard x-raydetectors have been developed to measure the runaway electrons in the HT-7 tokamak. The synchrotron radiation originated from the runaway electrons was measured by an infrared (IR) camera working in the wavelength ranges of . With a tangential viewing into the plasma in the direction of the electron approach on the equatorial plane, the synchrotron radiation from the runaway electrons was measured in a full poloidal cross section. Three NaI scintillators are used to monitor the hard x-rayradiation(HXR) in the energy ranges of , and a CdTe detector is used to monitor the low-energy HXR in the energy ranges of . The combination of infrared camera and hard x-raydetectors provides a powerful tool to investigate the runaway electron dynamics in HT-7. Runaways in the core and edge regions are monitored simultaneously. The parameters of runaway beam in the core are deduced from the IR pictures. The interaction of runway electrons with toroidalmagnetic field ripple is monitored from the HXR emission.
Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster77(2006); http://dx.doi.org/10.1063/1.2149006View Description Hide Description
The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a Hall thruster operating over the range of and . The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of Xe ( Xe) to Xe ( Xe) in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operating condition. The differences between the current density profiles obtained by each probe are attributed to the ion filtering systems employed. Analysis of the results shows that the MFFP, operating at a solenoid current, provides the best agreement with flight-test data and across operating pressures.
77(2006); http://dx.doi.org/10.1063/1.2162451View Description Hide Description
The influence of preionization around the insulator sleeve by a mesh-type source for the x-ray emission from a (2.3-3.9 kJ) plasma focus device is investigated. Quantrad Si diodes along with suitable filters are employed as time-resolved x-ray detectors and a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray emission in geometry is measured as a function of argon and hydrogen gas filling pressures with and without source at different charging voltages. It is found that the pressure range for the x-ray emission is broadened, x-ray emission is enhanced, and shot to shot reproducibility is improved with the source. With argon, the emission is estimated to be 27.14 J with an efficiency of 0.7% for source and 21.5 J with an efficiency of 0.55% without source. The maximum x-ray yield in geometry is found to be about 68.90 J with an efficiency of 1.8% for source and 54.58 J with an efficiency of 1.4% without source. With hydrogen, emission is 11.82 J with an efficiency of 0.32% for source and 10.07 J with an efficiency of 0.27% without source. The maximum x-ray yield in geometry is found to be 30.20 J with an efficiency of 0.77% for source and 25.58 J with an efficiency of 0.6% without source. The x-ray emission with Pb insert at the anode tip without source is also investigated and found to be reproducible and significantly high. The maximum x-ray yield is estimated to be 46.6 J in geometry with an efficiency of 1.4% at 23 kV charging voltage. However, degradation of x-ray yield is observed when charging voltage exceeds 23 kV for Pb insert. From pinhole images it is observed that the x-ray emission due to the bombardment of electrons at the anode tip is dominant in both with and without source.
77(2006); http://dx.doi.org/10.1063/1.2165549View Description Hide Description
The design, development, and testing of the top hat electric propulsion plume analyzer (TOPAZ) are presented for far-field electric propulsion plume diagnostics. The trend towards high-power thruster development will require plume diagnostic techniques capable of measuring high-energy particles as well as low-energy ions produced from charge-exchange collisions due to elevated facility background pressures. TOPAZ incorporates a “top hat” design with a geometrical analyzer constant of 100 resulting in a wide energy range and a high-energy resolution. SIMION, an ion trajectory analysis program, was used to predict characteristics of the analyzer. An ion beam accelerator system confirms the computational results. TOPAZ provides an energy resolution of 2.7%, field of view of (azimuthal by elevation) with an angular resolution in each direction of 2°, and a demonstrated energy-per-charge acceptance range of . An energy profile measurement of the NASA-173Mv1 Hall thruster demonstrates instrument operation in a Hall thruster plume.