1. 49th Annual Meeting of the Division of Plasma Physics, November 12 – November 16, 2007, Orlando, Florida Ion Species: Cs-133 Initial Energy: 10 keV Launch and Detect on Boxport Front Flange Deviation from Plane Perpendicular to Axis: 3 mm Projected Maximum Deflection in E-Field: 1 cm Simulation and Implementation of HIBP Electric Field Measurements for the HSX Stellarator Christopher Clark, Jon Hillesheim, David Anderson, Paul Schoch 1, Diane Demers 1, Kenneth Connor 1, Michael Bingham 1, Alex Dunckle 1 HSX Plasma Laboratory, Univ. of Wisconsin, Madison, USA; 1 Rensselaer Polytechnic Institute, Troy, USA Optimization of Beam Parameters Beam Divergence Overview HSX Boxport Cross Section with Puncture Plot Superimposed Sensitivity to Electric Field Profile Develop inversion techniques to recover profile from deflections Develop error analysis techniques incorporating effects that have been simulated Construct mounting hardware and detector for HSX Feasibility of Approach Plan of Action Based on a full, three dimensional particle orbit simulation Realistic electric field models incorporated results based on neoclassical calculations Deflections of up to 1 cm are predicted, which should be measurable Hardware parameters are compatible with the beam hardware provided by RPI Error sources and their relative magnitude have been identified Full three dimensional simulations were then undertaken to maximize beam deflection, while ensuring an accessible launch and detector location based on the fixed parameters: 2 ¾” Ports Boxport Front Flange Magnetic Field on Axis: 1.0 T Magnetic Configuration: QHS Electric Field Model Peak Value: 90 V/cm Electric Field Profile Shape: Peaked around r/a = 0.2 - 0.4 The HSX boxports are the only feasible locations at which to mount the beam and detector. Simulations of single particle trajectories show that sweeping the beam insertion angle can recover information about the electric field profile. The simulations found the following to be the optimal trajectory, given the above criterion: Boxport Front Flange.5 m Corresponding Deflections Measurement of a Beam Simulations with a collimated truncated Gaussian current density, show similar behavior to the single particle simulations. Two Electric Field Profiles (At Mid-Plane) Simulate Sweep Measures energies of secondary ions Crowley, 1994 Conventional HIBP Proposed HIBP Measures deflections of primary ions Ion energies must be high enough for secondaries to have large r L A wire grid detector should be sufficient Ion energies lower, as only primaries must traverse plasma Results are a path effect, and must be inverted Requires low enough density for most primaries to traverse plasma Requires energy analyzer Requires high enough density to produce large number of secondaries Sweep Insertion Angle Simulate Small Changes to Poloidal Launch Angle Launch Beam with Square Cross-SectionCentroid Shift at Point of Impact is Symmetric A similar analysis holds for the case of changing the toroidal launch angle. In general, so long as the divergence is symmetric, the location of the centroid will not exhibit a measurable shift with respect to the centroid of a perfectly collimated beam. Magnitude of Error Sources Ion Energy Error Beam Deflection +/- 1% (100 V) +/- 0.1% (10 V) +/- 1.4 mm +/- 0.1 mm Magnetic Field Strength Beam Deflection +/- 1% (.01T) +/- 0.1% (.001T) +/- 2.2 mm +/- 0.6 mm -0.1 Degrees +0.1 Degrees Nominal Centroids Simulate Sweep Compare ‘Virtual’ Measurements at Maximum Deflection Two Electric Field Profiles (At Mid-Plane) Simulated Current Density at Boxport Cover Currents Expected on a Detector Grid A Simple Grid of Wires as a Detector Sample volume can be selected by aperture angle Allows measurement of fluctuations Deflection due to fluctuations are too small to measure Beam Hardware on.Test Beam-line at HSX Simulation Results Using these results, the measurement of the beam by a wire grid are simulated. The projected peak deflections of about 1 cm are relatively small, so it is important to know the relative contributions of potential error sources. It is difficult to predict the beam divergence, so its effect was simulated to determine the effect on the measurement. A novel form of heavy ion beam probe is under development at HSX –The deflection of a 10 keV beam of singly charged Cesium ions is used to infer the radial electric field –Enabled by the equivalence of the HSX magnetic field with and without plasma Simulations of this novel technique have been performed using a realistic radial electric field model based on neoclassical calculations of the ambipolar condition –These simulations suggest that this form of beam probe will be suitable for HSX –Simulations also show that varying the insertion angle of the beam allows different radial locations in the plasma to be diagnosed Beam hardware has been moved from RPI to HSX and set up on a test-stand Beam has been operated with Sodium ions on the test-stand 1 mm wide Conductor Micro-gap