Hall Effect Thruster Vacuum Chamber Systems

Design Requirements     

a. to accommodate thruster and associated diagnostics within the chamber:no equipment is normally placed in front of the thruster unless it is for the measurement of ion beam data.This equipment may include:

Langmuir ProbesFaraday Cups

Retarding potential Analyzers

Electromagnetic Spectrum Analyzers

Residual Gas Analyzer

b. to allow free expansion of the beam, i.e. to allow the ion beam to travel to the beam target before impinging on sidewalls;

c. to minimize electromagnetic interference/coupling between the thruster and the ground, in order to avoid neutralization of the beam by electron emission from the wall and to avoid warping of the applied electromagnetic field;

d. to minimize the contamination by back sputtering; the view factor of the thruster by the walls should be minimized;

e. to accommodate the thrust balance within the chamber; 

f. to accommodate thermal vacuum testing of the thruster;

g.to allow continuous uninterrupted testing (≧1000 hours) of a HET with up to 140mN maximum thrust;

h. to manage not less than 5-kW of absorbed energy load.

Features

1,Hall Effect Thruster Vacuum Chamber shall be equipped with a circular arm to host, move, and position beam diagnostics (Faraday Cups, RPA, Langmuir probes, etc). The arm shall allow installation of sensors and shall be rotated in the range of 180 deg during Thruster firing tests.

2,Hall Effect Thruster Vacuum Chamber shall be configurable as either: 

(1) Solar Electric Propulsion (SEP) Thruster Test Stand employing a Thrust balance or 

(2) a SEP Thruster Environmental Test Facility for Thermal Vacuum Testing.

3,The transition between the two configurations shall be as simple as possible and can be performed by the user and minimize facility downtime.

5,TVC shall allow to allocate and operate a thrust balance, as defined

6,The design of the Chamber shall be convenient and safe in operation and maintenance, allow convenient access to internal volume for test equipment set-up, and shall include a suitable platform for the fixation of the equipment under test.

7,The Hall Effect Thruster Vacuum Chamber shall be designed in accordance with the applicable standard code (see also par. 3.11)

Physical Requirements

The eventual sizing of the facility is left to the vendor and will be dependant on diagnostic encumbrance and trade offs. For guidance, the desired vacuum chamber diameter is at least 3.0 meters and desired vacuum chamber length (cylindrical) is at least 7.0 meters. The figures are derived from comparison with other operational facilities.

The chamber height shall be compatible with the laboratory height of 5 m;

Probes shall be mounted on one semi-circular arm, which shall be moved in any position w.r.t. the ion beam with a precision of 0.1 deg (TBC). The position of the arms shall be controlled by two Step motors and shall be possible to define their position in order to scan the plume.

Distance between thruster and probe installed on the arms shall be 1.0m (±15%).

The position or interfaces to install probes shall be defined and agreed with the Customer. The probe wires shall be protected from damage by plasma impingement.

The cylindrical vessel shall be equipped with one hinged door and one sliding door (TBC). The door opposite to the target shall be equipped with an ISOF DN630 interface flange to possibly install agate valve.

The vacuum chamber shall be equipped with a thermal shroud system. The shroud system shall be installed in the area impacted by the hot plasma, both on the cylindrical part (shroud ring) and on the rear door. These shrouds shall be covered with “graph oil” to be protected from sputtering phenomena.

The shroud system shall be designed to be water-cooled and capable of dissipating the beam power dump without exceeding a temperature of 50 degC (TBC)

The thermal shrouds shall be compliant with the following thermo-optical properties characteristics:

a) Internal surface of the shroud (sandblasted):Emissivity >0.3;

b) External surface of the shrouds (depositor electro polishing):Emissivity <0.15;

Configuration Requirements

The vacuum chamber shall be equipped with a pumping system completely oil-free. The pumping devices shall not generate chemical pollution. 

The pumping system shall adhere to the following general requirements:

a) The primary pumping section shall be comprised of two primary pumps for the  chamber  fore-vacuum operation. In  addition, one will be also dedicated for the turbo molecular pump backing and the second will be dedicated for preparation and regeneration of the cryogenic pump.

b) The turbo molecular pump, of capacity at least 2000 l/sfor N2 , shall be of a magnetically  levitated type and shall be furnished with a dedicated pneumatic gate valve.

c) The system shall include at least a cryogenic pump 5000 l/s with pneumatic gate valve.

d) The system shall be provided with a suitable number of cold heads to guarantee the dynamic pressure requirement. The Supplier shall ensure proper panel predisposition for   potential installation of additional cryopanels in the future.

e) The system shall have provision to allow cryopanel regeneration during long duration tests.

The System shall ensure the capability to work with pure Xenon (99.9999%), pure Krypton, pure argon, pure Nitrogen, and create mixtures of them, in any mass ratio. 

The Vacuum Chamber shall be equipped with a “bake out system” to accelerate outgassing of the internal surface of the chamber. The chamber shall be equipped with standard vacuum flanges to operate the test equipment, the diagnostics, the pumping system and flanges dedicated to the test chamber maintenance. 

Flanges to operate the test equipment and the diagnostics shall be located around the parking and operative position of the thruster.

a) Flanges position and number shall be defined in accordance with the Customer.

b) These flanges shall be equipped with adaptors for gas, electric, thrust balance, thrust stand and thruster diagnostics feedthroughs. 

We shall be in charge of selecting the number and type of flanges dedicated to the pumping system and the test chamber maintenance. The following list is reported as a guideline to define the minimum set of flanges to be provided:

Reference only

In addition to the above-mentioned flanges, in order to allow the thruster to be observed and photographed during operation, at least 5 viewing ports shall be installed on the test chamber at suitable locations. The viewing ports will be provisioned with internal shutters to protect from sputter deposition. At least two of the viewing ports will be optical grade, with transmission characteristics to be agreed with the customer, to allow spectroscopic investigation of the DUT.

Materials requirements

All relevant materials used for the test chamber manufacturing and integration shall below magnetic permeability (µr < 1.1). 

The vessel internal surfaces shall be manufactured and polished to ensure a low emissivity, less than 0,2. The internal surfaces of the chamber shall minimize the entrapment of gas and outgassing effects. 

The vessel will be made of stainless steel 304Lor similar. 

All components used for the construction of the test chamber shall be helium leak tested at component level to 10-9mbar l/s. 

The beam target and the vessel’s walls shall be protected from erosion due to ion beam impingement. The protective materials shall be vacuum compatible and designed to minimize erosion and sputter deposition on the device under test.

Performance Requirements

The Vacuum System shall ensure the following chamber environment:

a)  Ultimate vacuum limit: less than 1x10-7 mbar;

b)  High vacuum limit with 18 mg/s flow of Xenon: less than 4x10-5 mbar. 

Vacuum System shall ensure continued operation of Vacuum Chamber for a duration of at least equal or greater than 1000 hours. 

At the conclusion of a test campaign, the chamber vent back to atmosphere shall be accomplished in two stages: from vacuum up to a pre- defined pressure using gaseous nitrogen at ambient temperature and from this pressure to ambient atmospheric pressure by ambient air.

The pressure rising leak test shall demonstrate a global leak lower that 10-5mbar l/s.

The beam target placed in front of the thruster shall dissipate the HET beam energy up 5 kW and shall be designed to minimize back sputtering effects and to maximize the pumping speed.

Noise Level

The maximum noise level in the technical room area shall be lower than 80dB(A).

The maximum noise level in the testing area shall be lower than 70dB(A).