Rf online where to get beam

This type of the matching circuit requires a mechanical motion control preventing the matching circuit from being compact. Furthermore, the time lag of the communication between the spacecraft and the ground control station would be a serious problem for the impedance matching; it would be desirable to include the automatic controller for the impedance tuning.

To overcome the issue on the matching box, several types of the rf generators have adjusted the frequency to match the load impedance to the output impedance of the generator [ 50 — 53 ], where fixed capacitors are used in the matching circuit.

A recently developed fast and automatically controlled rf system has demonstrated the fast impedance matching for the rf plasma source [ 54 ], where the source tube is attached to a vacuum flange of a chamber and the rf antenna wound around the source tube is exposed to the atmosphere. On the other hand, the whole structure of the plasma source including the antenna has to be immersed in vacuum for the thruster assessment configuration.

Here the fast and automatically controlled rf system operational in the frequency range of 37—43 MHz and with the maximum power of about W is installed in the helicon plasma thruster immersed in vacuum, where the thruster is attached to a pendulum thrust balance.

The impedance tuning can be typically accomplished within several msec and the net power corresponding to the forward minus reflected powers is maintained at a constant level during the discharge, providing the stable steady-state operation of the thruster. The imparted thrust and the ion energy distribution function are measured by using a thrust balance and a retarding field energy analyzer RFEA , respectively, showing the thrust of a few mN for W rf power and the spontaneous generation of the supersonic ion beam.

Discontinuous increases in the thrust, the source plasma density, and the ion beam component, are clearly observed when increasing the rf power. The ion beam component enhanced simultaneously with the discharge mode transition implies that the presence of the high-density plasma at the high-potential side is useful to the increase in the ion beam current. The energy of the supersonic ion beam and the electron temperature increase with a decrease in the gas flow rate. The results are consistent with the previous experiments using Figure 1A shows the schematic diagram of the experimental setup, together with the calculated magnetic field lines.

A helicon thruster consists of a stepped-diameter 65—95 mm inner diameter and 70— mm outer diameter pyrex glass source tube wound by a single-turn water-cooled rf loop antenna and a solenoid providing a static magnetic field expanding downstream of the source, i. The detailed structure of the thruster design can be found in Ref. It is noted that the rf loop antenna is mechanically isolated from the source tube to ensure the pendulum motion of the thrust balance.

The upstream side of the source is terminated by an insulator plate having a small gas injection port. Argon gas is continuously introduced from the gas injection port into the source tube via a mass flow controller located outside the chamber. It should be mentioned that the thrust measurement for different pumping speeds, i. This implies that the thruster performance is not affected by the gas ingestion. The performance assessment at the lower gas pressure cannot be performed due to the limit of the vacuum facility.

The rf antenna is powered from the rf generator briefly described later via an impedance matching circuit, resulting in a plasma production in the source tube, where the capacitances in the matching circuit are unchanged to demonstrate the automatic and fast control of the frequency tuning.

Figure 1. A Schematic diagram of the experimental setup together with the calculated magnetic field lines blue solid lines. B Calculated magnetic field strength on the z axis. The rf generator is very similar to that used in the previous experiment [ 53 ], while the maximum output power can be increased up to about W in the present setup.

Briefly, it consists of a voltage-controlled oscillator VCO , a voltage-variable attenuator VVA , a main amplifier, a bi-directional coupler, and power detectors, as shown in Figure 2. The amplified rf power is transferred to a load including the capacitors and the plasma source via the bi-directional coupler.

The rf signals corresponding to the forward and reflected powers are converted into dc voltages by using coaxial schottky barrier diode detectors and the low pass filters LPF , which are measured by the AI channels.

A gate signal is inputted into the DI channels; the same signal outputted from the DO channel is inputted into the main amplifier to turn on the rf power. During the detection of a high logic level by the DI channel, the frequency and the power are controlled by the board so as to minimize the reflection coefficient and to maintain the net rf power at a constant level, where the reflection coefficient and the net power are calculated on the board from the measured forward P f and reflected P r powers as.

It should be noted that the power delivered to the load is not the forward power P f but the net power P net.

To assess the overall efficiency of the source, estimation of the rf power delivered to the plasma, i. This has not been performed yet and remains a further experimental issue.

As shown in Figure 1A , the whole structure of the thruster is attached to a plate suspended by flexible thin metallic plates from a top plate of the thrust balance, where the length of the arms is about 24 cm. The displacement induced by the plasma production is measured by a commercial laser displacement sensor with a resolution of 0. The absolute value of the thrust can be obtained by multiplying a calibration coefficient to the measured displacement, where the calibration coefficient is obtained by measuring the displacement vs.

The validity of the thrust measurement technique has been shown in the previous experiment with the comparison between the thrust balance and the target techniques [ 58 ].

The plasma density n p can be obtained from an ion saturation current I is as. As the detector faces in the radial direction, the estimated density corresponds to that of the thermal ions.

The RFEA consists of a collector electrode and two meshes: the first mesh contacting the plasma is electrically floating and the second one is used as a repeller for the electrons. The IEDF is known to be proportional to the first derivative of the collector voltage V c -current I c characteristic, which is obtained by a pulsed Langmuir probe technique [ 59 ].

The net power P net is also found to approach the target value of W during the pulse. Figure 3. A probability density function PDF of t tune presented in Figure 4A shows the typical tuning time of about 7.

Therefore, the fast and automatically controlled rf system can be utilized in the thruster development, where the plasma source structure including the rf antenna is immersed in vacuum. Figure 4. These are obtained from the data taken by 1, shots repetition. Steady state operation of the thruster is also an important issue. Figure 5 shows the measured P net and f for the long pulse of sec, where the target value of P net is set at W.

It is found that the frequency is immediately changed from the initial The slight change in the frequency seems to be due to the change in the wall temperature of the source tube, where the temperature of the water-cooled antenna is expected to be unchanged. It can be seen that P net is maintained at W during the discharge pulse of s, indicating the stable operation of the rf system. Figure 5. Temporal evolutions of the net power P net a blue solid line and the rf frequency f a red solid line , where the pulse width and the target value of the net power are set at s and W, respectively.

Measurement of the thrust as a function of P net is performed for the gas flow rate of 70 sccm and the result is plotted by filled squares in Figure 6. The maximum thrust obtained in the present experiment is about 3. Figure 6. The measured data can be well-fitted by a superimposition of two Gaussians dashed lines as drawn by a red solid line. Figure 7b shows the normalized IEDFs as a function of P net , where the fitting curves are used to draw the contour plot.

Therefore, it is demonstrated that the discharge mode inside the source significantly affects the ion energy distribution function downstream of the source tube; the presence of the high-density plasma in the source tube can yield the increase in the ions accelerated from the high- to low-potential sides.

Figure 7. When assuming a uniform electron temperature, the voltage V from the reference position density of n p0 can be given by the Boltzmann relation as. A red dashed line in Figure 8B indicates the axial position giving the This result implies that the accelerated ion beam comes from the high potential side near the thruster exit.

The velocity of the It should be mentioned that the IEDFs in the present experiment Figure 7 seem to be broadened, compared with that observed in the previous experiment showing the formation of the current-free double layer, which has a nearly discontinuous potential drop [ 61 ].

Possible reasons of the broadened IEDF are a poor energy resolution of the RFEA and the spatially broadened potential drop near the thruster exit over about 10 cm scale as in Figure 8. Figure 8. Both the ion beam energy and the electron temperature have been observed to increase with a decrease in the operating gas pressure or the gas flow rate [ 22 , 23 ]. This change in the ion beam energy can be interpreted as a result of the flux balance between the accelerated ions and the electrons overcoming the potential drop, as discussed in Ref.

The present results also show the similar trends to the previous observations [ 22 , 23 ] and the detected beam energy is about 3—3. This value is different from the potential drop estimation satisfying the flux balance between the ions and electrons for the Maxwellian electron energy distribution, i. This discrepancy seems to be due to the assumption of the Maxwellian electron energy distribution, since the previously measured energy distribution has a depleted tail and close to the Druyvesteyn rather than the Maxwellian [ 23 ].

Therefore, the detailed measurement of the electron energy distribution is required to verify the flux balance between the electrons and ions. The characteristics of the ion beam and the imparted thrust similar to the previous experiments show that the fast- and automatically-controlled rf power system does not impact the thruster performance, while it would be important technique to operate the thruster for the undefined composition of the propellant, e.

When the imparted thrust is expected to be changed by the propellant composition even if the impedance matching is well-performed, the rf output power has to be controlled to maintain the constant thrust level, which remains further development issue. Figure 9. Since the rf generator includes the similar components, such as the oscillator, the amplifier, and the power sensors, the weight and size of the rf generator would be similar to the traditional rf system.

However, the use of only the fixed capacitors in the matching circuit would reduce the size and weight of the matching circuit, as the traditional system includes the large size variable capacitors and the mechanical motors. Therefore, the present system will roughly reduce the size and weight in half for the W-class rf system. The fast and automatically controlled frequency-tunable rf system is attached to the magnetic nozzle rf plasma thruster immersed in vacuum, where the rf frequency can be adjusted in the range of 37—43 MHz and the maximum output power can be increased up to about W.

The frequency and the output power are automatically controlled, yielding the minimized reflection coefficient and the net power maintained at a constant level with the good reproducibility and the stable steady-state operation. The maximum thrust of 3. The presence of the supersonic ion beam is shown by the measurement of the ion energy distribution, where the enhancement of the ion beam component is detected simultaneously with the discharge mode transition.

This implies that the high-density plasma production at the high-potential side is the key element of the ion beam generation. The present results show that the fast- and automatically-controlled rf system does not impact the thruster performance, being useful to reduce the size and the weight of the rf system. KT designed the concepts of the experiment, the setup, and the frequency-tunable rf system. The data were taken by all authors and analyzed by KT. The results were discussed by all authors.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Magnetohydrodynamic production of relativistic jets. Charles C. A review of recent laboratory double layer experiments.

Plasma Sources Sci Technol. Oblique double layers: a comparison between terrestrial and auroral measurements. Phys Rev Lett. Plane and hemispherical potential structures in magnetically expanding plasmas. Appl Phys Lett. Plume structure and ion acceleration of a helicon plasma source. Charles C, Boswell RW.

Current-free double-layer formation in a high-density helicon discharge. Observation of ion-beam formation in a current-free double layer. Experimental investigation of double layers in expanding plasmas. Performance Calculator. Unlike other bulky helical antennas that require flight cases, the CP Beam is quickly deployed and stowed. Why do IEMs drop-out anyway? Helical antennas are overwhelmingly the antenna of choice for IEMs due to their circular polarization. This removes the greatest risk of dropouts, as many IEM belt packs are limited to a single whip antenna and changing orientation as performers move around a stage.

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