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Observations of single-pass ion cyclotron heating in a trans-sonic flowing plasma
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10.1063/1.3389205
/content/aip/journal/pop/17/4/10.1063/1.3389205
http://aip.metastore.ingenta.com/content/aip/journal/pop/17/4/10.1063/1.3389205
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Block diagram of the VASIMR® system.

Image of FIG. 2.
FIG. 2.

Engineering drawing of the VX-50, showing the major systems and the location of the diagnostic instruments. The RPA used to obtain most of the data in this paper was located, as shown at .

Image of FIG. 3.
FIG. 3.

A sample shot of RPA data, showing the relationship of chamber ground to plasma potential.

Image of FIG. 4.
FIG. 4.

Two sample shots of RPA data with 0 V set to chamber ground, showing the relationship between plasma potential as measured by an rf compensated Langmuir probe and the sweep potential where .

Image of FIG. 5.
FIG. 5.

The first derivative of the current-voltage characteristics measured by an RPA with 30° collimation oriented at 10° pitch angle. The lower energy, lighter curve shows a helium shot without ICH, and the upper energy, darker curve shows a helium shot with ICH.

Image of FIG. 6.
FIG. 6.

The ion velocity phase space distribution functions inferred from the data shown in Fig. 5.

Image of FIG. 7.
FIG. 7.

Circuit diagram of the ICH coupler, indicating how the plasma impedance couples to the circuit.

Image of FIG. 8.
FIG. 8.

Time history of the plasma loading of the ICH coupler and coupler efficiency. Present refers to the VX-50 in 2005 and 2006.

Image of FIG. 9.
FIG. 9.

Fit parameters obtained by least-squares fitting a drifting Maxwellian representation to each voltage sweep obtained by the wide angle RPA during a pulsed ICH helium plasma shot. From top to bottom, the panels show ion drift velocity, ion density and ion temperature in the frame of the beam. The plusses and X’s show up and down sweeps. The vertical dashed lines show the times when the ICH turned on and off.

Image of FIG. 10.
FIG. 10.

The ion velocity phase space distribution function obtained in a 3 kW helium discharge with 1.5 kW of ICH on. The distribution function grayscale bar scale is logarithmic. Note the intense 60–100 km/s ion jet at 10°-pitch angle.

Image of FIG. 11.
FIG. 11.

The difference in helium velocity phase space distribution functions between ICH-on and ICH-off conditions. The distribution function grayscale bar scale is linear. The distribution has been mapped back to the location of cyclotron resonance using conservation of the first adiabatic invariant. The perpendicular heating effect of the ICH shows up as the intense features at perpendicular velocities of 60–100 km/s.

Image of FIG. 12.
FIG. 12.

Raw RPA anode current plotted as a current-voltage characteristic. Data were obtained during a low density ICH-on helium shot. Solid lines show least-squares fits of drifting bi-Maxwellian representations, showing that the data can be modeled as the sum of a hot, slow component and a cold, fast component.

Image of FIG. 13.
FIG. 13.

Fit parameters obtained by least-squares fitting drifting bi-Maxwellian representations to the RPA data obtained during a scan of ICH transmitter power. From top to bottom, the panels show ion drift velocity, ion density and ion temperature in the frame of the beam. The plusses show the slow, hot component. The X’s show the fast, cold accelerated component. The round dots show the flow velocity expected for an energization rate of 70 eV/ion/kW of transmitted rf power.

Image of FIG. 14.
FIG. 14.

RPA traces showing the difference between ICH-on and ICH-off. The top panel shows the average of 6 raw sweeps in each curve. The dashed line shows ICH-off and the solid line shows ICH-on. The bottom panel shows the derivative with respect to sweep voltage of the top two curves, which is proportional to energy distribution function. The sweep voltage is referenced to chamber ground instead of plasma potential in these figures. Plasma potential was at .

Image of FIG. 15.
FIG. 15.

The energy difference between the location of the peak of the ion energy distribution function for ICH on and the location in the peak for ICH off is plotted as a function of applied ICH power.

Image of FIG. 16.
FIG. 16.

The raw output of a microwave interferometer is plotted as a function of time during an ICH on shot. The drop in signal corresponds to a drop in density resulting from the combined effect of an acceleration of the plasma and conservation of flux.

Image of FIG. 17.
FIG. 17.

The ratio of ICH-off to ICH-on plasma velocities (circles) and the ratio of ICH-on to ICH-off plasma densities (squares) are plotted as functions of the applied ICH power.

Image of FIG. 18.
FIG. 18.

Time series of fit parameters from an ICH-on deuterium plasma shot presented in the same format as Fig. 9. The vertical dashed line show the time when the ICH turned on.

Image of FIG. 19.
FIG. 19.

Same as Fig. 6. Distribution function obtained during the ICH-on portion of the deuterium shot shown in Fig. 18 with an ICH-off shot run under otherwise identical conditions. The ICH-off curve is shown as a lighter-colored line.

Image of FIG. 20.
FIG. 20.

Fit parameters obtained by least-squares fitting drifting bi-Maxwellian representations to the RPA data obtained during a scan of mirror magnet field intensity. From top to bottom, the panels show ion drift velocity, ion density and ion temperature in the frame of the beam. The plusses show the slow, hot component. The X’s show the fast, cold accelerated component.

Image of FIG. 21.
FIG. 21.

Fit parameters obtained by least-squares fitting drifting Maxwellian representations to RPA data taken while scanning the radial location of the RPA during both ICH-on (X’s) and ICH-off (’s) conditions. Each symbol represents the average of all sweeps during a single shot.

Image of FIG. 22.
FIG. 22.

Graph showing time history of the plasma loading of the ICH coupler and corresponding coupler efficiency.

Image of FIG. 23.
FIG. 23.

The first derivative of the current-voltage characteristics measured by an RPA with 30° collimation. The lower, darker curve shows a deuterium shot without ICH, and the upper, lighter curve shows a deuterium shot with ICH.

Image of FIG. 24.
FIG. 24.

The ion velocity phase space distribution function obtained in a 20 kW deuterium discharge with no ICH. The distribution function grayscale bar scale is logarithmic.

Image of FIG. 25.
FIG. 25.

The ion velocity phase space distribution function obtained in a 20 kW deuterium discharge with 1.5 kW of ICH on. The distribution function grayscale bar scale is logarithmic.

Image of FIG. 26.
FIG. 26.

Ion density plotted as a function of radial position during high density discharges similar to those shown in Figs. 23–25. Density was measured by an array of small ( diameter) planar Langmuir probes. Profiles for both ICH-off and ICH-on are compared.

Image of FIG. 27.
FIG. 27.

Fit parameters obtained by least-squares fitting drifting Maxwellian representations to RPA data taken while scanning the radial location of the RPA during ICH-on (X’s) conditions during high density discharges similar to those shown in Figs. 23–25. Each symbol represents the average of all sweeps during a single shot.

Image of FIG. 28.
FIG. 28.

Comparison of ion energy distributions for 0, 8.3, and 20 kW of ICH power in deuterium plasma, input flow rate 0.625 mg/s, and 20 kW helicon power.

Image of FIG. 29.
FIG. 29.

Comparison of ion velocity distributions for the same three shots as in Fig. 28.

Image of FIG. 30.
FIG. 30.

Ion velocity phase space distribution function, 14 kW ICH on, in deuterium plasma, input flow rate 0.625 mg/s, and 20 kW helicon power.

Image of FIG. 31.
FIG. 31.

Ion velocity phase space distribution function, ICH off in deuterium plasma, input flow rate 0.625 mg/s, and 20 kW helicon power.

Image of FIG. 32.
FIG. 32.

Time series of fit parameters obtained by least-squares fitting a drifting Maxwellian representation to the raw RPA data during ICH deuterium plasma shots. From bottom to top, the panels show ion drift velocity, ion density, and ion temperature in the frame of the beam.

Image of FIG. 33.
FIG. 33.

A radial scan of the RPA, showing fit parameters obtained by least-squares fitting a drifting Maxwellian representation to the raw RPA data during ICH deuterium plasma shots as functions of radius from the center of the beam. From bottom to top, the panels show ion drift velocity, ion density, and ion temperature in the frame of the beam.

Image of FIG. 34.
FIG. 34.

Scans of ICH power for two different flow rates and helicon power levels, showing fit parameters obtained by least-squares fitting a drifting Maxwellian representation to the raw RPA data during ICH deuterium plasma shots as functions of ICH power. From bottom to top, the panels show ion drift velocity, ion density and ion temperature in the frame of the beam. The meaning of the two separate curves is discussed in the text.

Image of FIG. 35.
FIG. 35.

Scans of ICH power for two different flow rates and helicon power levels, showing parameters inferred from the fit parameters shown in the previous figure as functions of ICH power. From bottom to top, the panels show output power, thrust and specific impulse. The meaning of the two separate curves is discussed in the text.

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/content/aip/journal/pop/17/4/10.1063/1.3389205
2010-04-29
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Observations of single-pass ion cyclotron heating in a trans-sonic flowing plasma
http://aip.metastore.ingenta.com/content/aip/journal/pop/17/4/10.1063/1.3389205
10.1063/1.3389205
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