Download Chen_APS 2006

HIBP Designs for Measurement of the Electric Field in HSX
Xi Chen, Jon Hillesheim1, Paul Schoch, Diane Demers, Kenneth Connor, David Anderson1
Rensselaer Polytechnic Institute, Troy; 1HSX Plasma Laboratory, Univ. of Wisconsin, Madison, USA
HSX Ports for HIBP
Overview
Comparison of Launch Geometries
Launch Trajectory Scaling
Magnetic Flux(psi)profile along X-axis inside plasma(Boxport plane)
Top Launch
Front Launch
Particle Trajectory Projected into the Plane of the Boxport
1
0.3
0.8
0.2
Cs-133 at 0.5 T
psi
0.1
0.4
2 ¾”
Ports
Ion Species: Cs-133
Initial Energy: 40 keV
Deflection out of plane: ~2 cm
Magnetic Field on axis: 0.5 T
No radial electric field included
0.2
-0.1
-0.05
0
X (m)
0.05
0.1
0.15
-0.1
Plasma Potential(phi) profile along X-axis inside plasma(Boxport plane)
2000
Ion Species: Cs-133
Initial Energy: 8 keV
Deflection out of plane: ~1 cm
Magnetic Field on axis: 0.5 T
No radial electric field
Ion Species: Cs-133
Initial Energy: 5 keV
E= -2048.3*∇ψ
Magnetic Field on axis: 0.5 T
Theta= 10degree
Theta= 5degree
-0.2
Theta= 0
Theta= -5degree
1500
•
•
•
•
•
Boxport
Front
Flange
0
0
Y (m)
•
•
•
•
•
•
•
•
•
0.6
phi
• A feasibility study has shown that it is practical to measure the radial electric field in the Helically
Symmetric eXperiment, HSX, using ion beams.
• Two options have been explored, a standard Heavy Ion Beam Probe, HIBP, and a system that
measures the deflection of an ion beam due to the plasma electric field.
– The standard HIBP measures the local space potential at multiple points, allowing a
calculation of the radial electric field. Estimated signal levels are similar to some previous
systems, most notably the EBT HIBP. It is also capable of measuring fluctuations in
potential and density.
– The second option studied measures the change in a probing ion beam trajectory due to the
electric field. HSX vacuum magnetic fields are virtually unchanged by the plasma,
therefore changes in the beam trajectory due to plasma would be dominated the plasma
electric field. The changes are path integrated and the local electric field is determined by
running multiple trajectories and inverting. A beam deflection system is simpler and needs
a lower ion accelerator voltage than a HIBP, but it provides less information.
CAD Picture of HSX Boxport Cross
Section
-0.3
Theta= -10degree
1000
-0.4
500
-0.5
0
-0.1
-0.05
0
X (m)
0.05
0.1
0.15
-0.1
Assume inside plasma ψ=k*Φ+2000
where k= -2048.3
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
X (m)
Particle Trajectory Projected into the Plane of the Boxport
0.3
Motivations for a Heavy Ion Beam Probe
Diagnostic
Particle Trajectory Projected into the Plane of the Boxport
0.3
0.2
0.1
•
•
•
•
•
0
K= 5120.9
-0.1
0
-0.1
-0.2
-0.2
•
•
•
•
•
Ion Species: Cs-133
Initial Energy: 25 keV
Deflection out of plane: ~1 cm
Magnetic Field on axis: 1.0 T
No radial electric field included
V= 6keV
V= 7keV
-0.3
V= 4keV
V= 3keV
K= -5120.9
-0.3
V= 5keV
-0.4
K= -2048.3
-0.4
-0.5
K= 2048.3
no E field
-0.5
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
X (m)
-0.6
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Particle Trajectory Projected into the Plane of the Boxport
X (m)
0.3
Front
Launch
0.2
Tl-205 at 1.0 T
0.1
• Orbits followed in detailed magnetic field structure
•
•
•
•
0
-0.1
Y (m)
Implementation of an HIBP
System on HSX looks Feasible
•Ion Species: Tl-205
•Initial Energy: 100 keV
•Deflection out of plane: ~2 cm
•Magnetic Field on axis: 1.0 T
•No radial electric field included
Trajectory Calculations
• Particle trajectories have been calculated to investigate the feasibility of a HIBP system for HSX.
A number of factors have been considered:
– Entry and exit locations
– Beam energy
– Ion mass
– Magnetic field strength (all trajectories are in QHS mode)
– Radial electric field estimates
• Beam deflection system considered as a simpler, less costly alternative to a full HIBP detector
system
Ion Species: Cs-133
Initial Energy: 100 keV
Deflection out of plane: ~2 cm
Magnetic Field on axis: 1.0 T
No radial electric field included
Y (m)
Top Launch Point (2 ¾” Port not visible)
0.1
• Ion Species: Cs-133
• Initial Energy: 7 keV
• Magnetic Field on axis: 0.5 T
Y (m)
• Understanding the relative roles of neoclassical and anomalous transport in advanced stellarators
is critically dependent on knowledge of the radial electric field.
– Neoclassical transport depends strongly on the ambipolar radial electric field; potential
measurements would resolve whether HSX is operating in the ion or electron root
– Understanding of the anomalous transport present in devices with low effective ripple
requires a detailed understanding of the neoclassical predictions
– The CHERS system presently being installed on HSX infers the electric field through
plasma flow measurements
– An HIBP system would provide direct measurements of the potential and have better
spatial, temporal, and potential resolution
• Simultaneous measurements of density and potential fluctuations would provide estimates of the
electrostatic fluctuation induced particle flux and data for turbulent anomalous transport models
• RPI has a 200 keV accelerator which could be made available for HSX if it would provide the
needed information at a reasonable cost
Experiment Geometry Outline
• Ion Species: Cs-133
• E= -2048.3*∇ψ
• Magnetic Field on axis: 0.5 T
0.2
Cs-133 at 1.0 T
E=
E= -2048.3*∇ψ
-2048.3*grad(phi)
-0.2
-0.3
no E field
-0.4
• Electric fields incorporated with flux surface geometry
•Ion Species: Tl-205
•Initial Energy: 25 keV
•Deflection out of plane: ~2 cm
•Magnetic Field on axis: 1.0 T
•No radial electric field included
2 ¾” Ports
Boxport Front Flange Top
Edge, Center, and Bottom
Edge
Note: Aspect ratios not to scale
• Two MATLAB routines were developed independently and generated
corroborating results
– Three dimensional particle trajectories calculated first, trajectories
then projected into the plane of the boxport
– Magnetic field projected into the plane of the boxport, two
dimensional trajectories then calculated
• Top launch orbits at ~100 keV exit the front of the boxport
at B=1.0 T; Front launch only requires ~25 keV
• Top launch might require a detector inside the vacuum
vessel to recover all secondaries
Cs-133 with a Constant Electric Field in ∇ψ Direction
•
•
•
•
•
•
• Both types of launching geometries exhibit reasonable
orbits
• Low dispersion with E~T/a imply energy analysis may be
necessary for top launch
Ion Species: Cs-133
Initial Energy: 40 keV
Deflection out of plane: ~2 cm
Magnetic Field on axis: 0.5 T
Radial electric fields of 0, 3, 10 kV/m
Deflection by electric field ~0.5 cm at 10 kV/m
• Deflections out of the boxport plane <2 cm and not an
issue
0 V/m
3 kV/m
10 kV/m
•
•
•
•
•
•
Ion Species: Cs-133
Initial Energy: 8 keV
Deflection out of plane: ~1 cm
Magnetic Field on axis: 0.5 T
Constant Radial electric fields of 0, 3, 10 kV/m
Deflection by electric field ~6 cm at 10 kV/m
• Lower energy beam (at B=0.5 T) gives good coverage of
the plasma cross-section with small variations in injection
angle (assumption of electrostatic beam steering)
• Additional flexibility in coverage through variation of
beam energy and calculations with Thallium and Cesium
beams
48th Annual Meeting of the Division of Plasma Physics, October 30 – November 3, 2006, Philadelphia, Pennsylvania
Ion Species: Cs-133
Initial Energy: 5 keV
Initial Angle: 0, -5, -10degree
Magnetic Field on axis: 0.5 T
-0.5
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
X (m)
Tasks Yet to Accomplished for
Assessment
• Electric field and fluctuation measurement sensitivity
estimates
• Secondary signal strength forecasts
• Beam divergence appraisal using finite beam calculations
• Determination of RPI hardware applicable to the HSX
system
• Consideration of analyzer (full HIBP)/no-analyzer (beam
deflection) options with respect to cost; quantity and quality
of obtainable data with each option
• Cost and schedule estimates for the selected system