Editing Hall-effect thruster (section)

=== Variants ===
As well as the Soviet SPT and TAL types mentioned above, there are: 

====Cylindrical Hall thrusters====
[[File:Hall Effect Thruster in a vacuum chamber.jpg|thumb|An Exotrail ExoMG – nano (60&nbsp;W) Hall Effect Thruster firing in a vacuum chamber]]

Although conventional (annular) Hall thrusters are efficient in the [[kilowatt]] power regime, they become inefficient when scaled to small sizes. This is due to the difficulties associated with holding the performance scaling parameters constant while decreasing the channel size and increasing the applied [[magnetic field]] strength. This led to the design of the cylindrical Hall thruster. The cylindrical Hall thruster can be more readily scaled to smaller sizes due to its nonconventional discharge-chamber geometry and associated [[magnetic field]] profile.<ref>{{cite web|first1=Y. |last1=Raitses |first2=N. J. |last2=Fisch |title=Parametric Investigations of a Nonconventional Hall Thruster|url=http://htx.pppl.gov/publication/Journal/CHT_PoP_2001.pdf|publisher=Physics of Plasmas, 8, 2579 (2001)|url-status=live|archive-url=https://web.archive.org/web/20100527094903/http://htx.pppl.gov/publication/Journal/CHT_PoP_2001.pdf|archive-date=27 May 2010}}</ref><ref>{{cite web|first1=A. |last1=Smirnov |first2=Y. |last2=Raitses |first3=N. J. |last3=Fisch |title=Experimental and theoretical studies of cylindrical Hall thrusters|url=http://htx.pppl.gov/publication/Journal/CHT_Artem_PoP2007.pdf|publisher=Physics of Plasmas 14, 057106 (2007)|url-status=live|archive-url=https://web.archive.org/web/20100527095129/http://htx.pppl.gov/publication/Journal/CHT_Artem_PoP2007.pdf|archive-date=27 May 2010}}</ref><ref name=NTRS>{{cite conference |last1=Polzin |first1=K. A.|last2=Raitses |first2=Y. |last3=Gayoso |first3=J. C. |last4=Fisch |first4=N. J. |title=Comparisons in Performance of Electromagnet and Permanent-Magnet Cylindrical Hall-Effect Thrusters |conference=46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference |website=NASA Technical Reports Server|date=25 July 2010 |hdl=2060/20100035731 |hdl-access=free}}</ref> The cylindrical Hall thruster more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster. The primary reason for cylindrical Hall thrusters is that it is difficult to achieve a regular Hall thruster that operates over a broad envelope from c.1&nbsp;kW down to c. 100&nbsp;W while maintaining an efficiency of 45–55%.<ref>{{cite conference |last1=Polzin |first1=K. A. |last2=Raitses |first2=Y. |last3=Merino |first3=E. |last4=Fisch |first4=N. J. |title=Preliminary Results of Performance Measurements on a Cylindrical Hall-Effect Thruster with Magnetic Field Generated by Permanent Magnets |conference=3rd Spacecraft Propulsion Subcommittee (SPS) meeting/JANNAF Interagency Propulsion Committee |website=NASA Technical Reports Server|date=8 December 2008 |hdl=2060/20090014067 |hdl-access=free}}</ref>

====External discharge Hall thruster====
Sputtering erosion of discharge channel walls and pole pieces that protect the magnetic circuit causes failure of thruster operation. Therefore, annular and cylindrical Hall thrusters have limited lifetime. Although magnetic shielding has been shown to dramatically reduce discharge channel wall erosion, pole piece erosion is still a concern.<ref>{{Cite book |chapter=Pole-piece Interactions with the Plasma in a Magnetically Shielded Hall Thruster |title=50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference |doi=10.2514/6.2014-3899 |isbn=978-1-62410-303-2 |date=2014 |last1=Goebel |first1=Dan M. |last2=Jorns |first2=Benjamin |last3=Hofer |first3=Richard R. |last4=Mikellides |first4=Ioannis G. |last5=Katz |first5=Ira }}</ref> As an alternative, an unconventional Hall&nbsp;thruster design called external discharge Hall thruster or external discharge plasma thruster (XPT) has been introduced.<ref>{{Cite book |chapter=Preliminary Investigation of an External Discharge Plasma Thruster |title=52nd AIAA/SAE/ASEE Joint Propulsion Conference |doi=10.2514/6.2016-4951 |isbn=978-1-62410-406-0 |date=2016 |last1=Karadag |first1=Burak |last2=Cho |first2=Shinatora |last3=Oshio |first3=Yuya |last4=Hamada |first4=Yushi |last5=Funaki |first5=Ikkoh |last6=Komurasaki |first6=Kimiya }}</ref><ref>{{Cite web|url=https://repository.exst.jaxa.jp/dspace/bitstream/a-is/549895/1/SA6000036090.pdf|title=Numerical Investigation of an External Discharge Hall Thruster Design Utilizing Plasma-lens Magnetic Field|url-status=live|archive-url=https://web.archive.org/web/20170814095202/https://repository.exst.jaxa.jp/dspace/bitstream/a-is/549895/1/SA6000036090.pdf|archive-date=14 August 2017}}</ref><ref>{{Cite web|url=http://ltu.diva-portal.org/smash/record.jsf?pid=diva2%3A1037721&dswid=1358|title=Low–voltage External Discharge Plasma Thruster and Hollow Cathodes Plasma Plume Diagnostics Utilising Electrostatic Probes and Retarding Potential Analyser|url-status=live|archive-url=https://web.archive.org/web/20170829163334/http://ltu.diva-portal.org/smash/record.jsf?pid=diva2%3A1037721&dswid=1358|archive-date=29 August 2017}}</ref> The external discharge Hall thruster does not possess any discharge channel walls or pole pieces. Plasma discharge is produced and sustained completely in the open space outside the thruster structure, and thus erosion-free operation is achieved.