S2-3
Challenge to Erosion-less Hall Thruster
無損耗ホールスラスタへの挑戦
Kimiya Komurasaki
小紫公也
The University of Tokyo
7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan東京大学 〒113-8656 東京都文京区本郷7-3-1
In order to investigate the applicability of the magnetic shielding technique to thruster with anode layer(TAL), the guard-ring current of a TAL type thruster of UT-58 was measured. The magnetic shielding is
the technique of reducing the channel wall erosion caused by ion sputtering by aligning the magnetic lines
with the channel wall. The magnetic shielding has been applied to stationary plasma thruster (SPT), but it
is unclear that this technique can be applied to TAL because the electric potential of channel wall isdifferent between SPT and TAL. From the result, the guard-ring current of magnetic shielding
configuration thruster was reduced. Therefore the feasibility of the magnetic shielding to TAL wasconfirmed.

1. Introduction
Hall thruster is considered to be suitable forin-space transportation of large mass structuresuch as Solar Power Satellite owing to its highthrust efficiency and less difficulty of increasing
the size [1]. Because hall thruster need long
operation period due to its small thrust for large
mass transportation, the lifetime is one of themost important performances.
Lifetime of hall thruster mainly depends on thewall erosion caused by ion sputtering. In order toenhance the lifetime performance, the techniqueof magnetic shielding [2] was developed, and a
SPT type thruster of BPT-4000 with magnetic
shielding achieved a zero-erosion configuration[3]. The principle of the magnetic shielding for
SPTs is shown in Fig. 1. The magnetic field lines of
the unshielded thruster cross the channel walls asshown in Fig. 1 (left), while the magnetic field linesof the magnetically shielded thruster are parallel tothe channel walls shown in Fig. 1 (right), which canbe realized by modifying the geometric andFig. 1. The principle of the magnetic shielding,unshielded (left) and magnetically shielded(right)

magnetic configuration of the channel wall.
Because the equipotential lines form along themagnetic field lines if the electron temperature
along the magnetic field line is low, the parallel
magnetic field lines near the channel walls cause
the electric field which repels the ions fromchannel walls, resulting in the reduction of thechannel wall erosion. However because theelectric potential of TAL is different from that ofSPT, it is unclear that magnetic shielding can beapplied to TAL.
The objective of this paper is to investigate theapplicability of the magnetic shielding technique
to TAL to enhance the lifetime performance.
2. Experiment
2.1 Experimental setup
A TAL type thruster of UT-58 [4] developed at theUniversity of Tokyo was used for the test of themagnetic shielding technique. A picture of UT-58 isshown in Fig. 2 (left) and the cross section drawingof UT-58 is shown in Fig. 2 (right). To installmagnetic shielding for UT-58, the configuration ofmagnetic lines and channel wall was changed. Bychanging the width of magnetic pole piece, thedifferent shape of magnetic line can be applied. In
this research, UT-58 with unshielded and magnetic
shielding was tested. The lines of magnetic force
and cross section schematics of unshielded andmagnetic shielding are shown in Fig. 3 respectively.
While there are lines of magnetic force which
terminate the channel walls in the case ofunshielded thruster, there are few lines which
terminate the channel wall in the case of themagnetic shielding. In this research, the vacuum

chamber with a diameter of 2.0 m and a length of
3.0 m was used. The diffusion pump (SPD-36 madeby ULVAC Co., pumping speed is 37000 L/s) wasused to evacuate the chamber. The correctedpressure with thruster operation with xenon
propellant of 2.0 Aeq (2.72 mg/s) was 4.6×10-5
Torr.
2.2 Experimental method
To evaluate the channel wall loss, the guard-ringcurrent was measured to obtain the ratio of ion loss
current and the discharge current εion-wall, which isdefined by Eq. (1),
Ig
Ig
(1)
 ion - wall  Id Ib  Ie  Ig
where Ig is guard-ring current and Id is discharge
current. During the guard-ring current measurement
the front surface of the thruster was covered withboron nitride (BN) powder to prevent ions fromthe front surface of the thruster was covered withboron nitride (BN) powder to prevent ions fromgoing into the thruster from the front surface asshown in Fig. 4. Insulating surface blocks thecurrent of the charge exchange (CEX) ions, which
increases a guard-ring current.
3. Results and discussion
The channel wall loss of UT-58 with theunshielded and magnetic shielding was measured.
The operation condition with the unshielded andmagnetically shielded was the same: the discharge
voltage of 200 V, the xenon mass flow rate of 2.0
Aeq (2.72 mg/s).
The εion-wall of the magnetic shielding thruster was
3.7% while the εion-wall of the unshielded thruster was7.1%. This result shows that ion loss toward the wallwith the magnetic shielding thruster is small comparedwith the unshielded thruster. Therefore the channel
wall erosion of UT-58 with magnetic shielding can beinferred to be reduced because of the installation ofgeometric and magnetic configuration of the channel
wall of magnetic shielding.
Table I. Summary of guard-ring current measurement(the discharge voltage of 200 V, the xenon mass flowrate of 2.0 Aeq (2.72 mg/s))
εion-wall [%]Id [A]
Ig [A]

Fig.2. UT-58 thruster of a picture of UT-58 (left)
and the cross section drawing (right)Fig. 3. The geometric and magnetic configurationof UT-58 with the width of 14 (left) and 24 (right)

Fig. 4. Picture of the thruster surface covered byboron nitride (BN) powder

Unshielded

2.68

0.19

7.1

Magneticallyshielded

2.70

0.10

3.7

4. Conclusions
In order to investigate the applicability of themagnetic shielding technique to TAL, theguard-ring current measurement was conductedwith unshielded and magnetically shielded TAL
thruster of UT-58. From the result, the channel wall
erosion rate of UT-58 with magnetic shielding islower than that of UT-58 without the configurationof magnetic lines and channel wall of the magnetic
shielding. Therefore a magnetic shielding isapplicable to TAL based on this result.
References[1] Ito. Y, Nakano. M, Schönherr. T, Cho. S,Komurasaki. K, Koizumi. H: 29th ISTS, Nagoya,
2013, p.o-1-05.
[2] Mikellides. I, et al.: 48th AIAA/ASME/SAE/ASEE
Joint Propulsion Conference & Exhibit, Atlanta,
2012, p. 3789.
[3] Grys K, d. et al.: 46th AIAA/ASME/SAE/ASEE Joint
Propulsion Conference & Exhibit. Nashville, 2010, p.
6698.
[4] Daiki Fujita: 29th ISTS Nagoya, 2013, p.s-07-b.