Study on electromagnetic plasma propulsion using rotating magnetic field acceleration scheme

Abstract

As one of the electromagnetic plasma acceleration systems, we have proposed a rotating magnetic field (RMF) acceleration scheme to overcome the present problem of direct plasma-electrode interactions, leading to a short lifetime with a poor plasma performance due to contamination. In this scheme, we generate a plasma by a helicon wave excited by a radio frequency (rf) antenna which has no direct-contact with a plasma. Then, the produced plasma is accelerated by the axial Lorentz force f z ¼ j h  B r (j h is an azimuthal current induced by RMF, and B r is an external radial magnetic field). Erosion of electrodes and contamination are not expected in this total system since RMF coils and an rf antenna do not have contact with the plasma directly. Here, we have measured the plasma parameters (electron density n e and axial ion velocity v i) to demonstrate this RMF acceleration scheme by the use of AC currents in two sets of opposing coils to generate a RMF. The maximum increasing rate Dv i /v i was $28% (maximum v i of $3 km/s), while the density increasing rate of Dn e /n e is $ 70% in the case of a RMF current frequency f RMF of 3 MHz, which showed a better plasma performance than that with f RMF ¼ 5 MHz. Moreover, thrust characteristics such as a specific impulse and a thrust efficiency were discussed, although a target plasma was not optimized.

Electrodeless plasma acceleration system using rotating magnetic field method

“…The highest ∆n e /n e was ∼ 33 % for φ = 90 deg., and the lower was ∼ 1.7 % for φ = -90 deg.. Here, the nearly sinusoidal curves of n e and v i w/RMF was obtained as a function of φ, as is expected from the RMF scheme 10,13 (see Sec. II), especially, concerning v i .…”

“…11 Recently, dependences of an electron density n e and ion velocity v i on f RMF have been investigated by changing f RMF form 5 MHz to 3 MHz. 13 Higher increasing rates of n e and v i denoted as ∆n e /n e and ∆v i /v i , respectively, have been obtained: up to ∼ 70 % and 28 %, respectively with f RMF = 3 MHz than these with 5 MHz. 10 We have also examined the RMF operation conditions, e.g., RMF current I RMF and RMF current phase difference φ.…”

“…As a propellant gas, argon gas is injected continuously from a flange port located on an upstream side of the quartz tube via a mass flow controller, where the gas flow rate can be controlled up to 100 sccm. A half-helical antenna, whose azimuthal mode of m = 1, 16 is wound around the quartz tube to generate a plasma, whose n e can be raised up to ∼ 10 13 cm -3 if we use electromagnets as well as permanent magnets, 13 whose grade is N35 made by NeoMag Co. Ltd, located as shown Fig. 2.…”

“…7,8,12,13 This RMF method comes from the field of magnetically a Electronic mail: s172832r@st.go.tuat.ac.jp confined plasma fusion research in order to induce an azimuthal current to maintain the Field Reversed Configuration (RFC). In this acceleration scheme, an rf antenna, which is outside of a discharge tube, is used to produce a plasma, and the plasma acceleration is conducted by two pairs of opposed, facing RMF coils, wound around the discharge tube in the downstream of the plasma generation region.…”

“…Moreover, we have found that ∆n e /n e and ∆v i /v i were increased in proportion to I RMF , 2 and they behaved nearly sinusoidal curves by changing φ. 13 Here, we have further decreased f RMF from 3 MHz to 1 MHz as well as 0.7 MHz with applying higher I RMF , since we can easily change the rf matching conditions, e.g., series/parallel capacitances and series inductance in matching boxes in a wide range of RMF excitation frequency, and made RMF penetration condition better, at the expense of lower induced j θ , which is proportional to f RMF if a full penetration condition is satisfied. We have also investigated the dependencies of n e and v i on I RMF and φ, where radial measurement positions were the same as previous experiments with f RMF = 3 MHz.…”