Hollow cathode effect

The hollow cathode effect allows electrical conduction at a lower voltage or with more current in a cold-cathode gas-discharge lamp when the cathode is a conductive tube open at one end than a similar lamp with a flat cathode.{{cite journal|last1=Eichhorn|first1=H.|last2=Schoenbach|first2=K. H.|last3=Tessnow|first3=T.|title=Paschen's law for a hollow cathode discharge|journal=Applied Physics Letters|volume=63|issue=18|year=1993|pages=2481–2483|issn=0003-6951|doi=10.1063/1.110455|url=http://www3.nd.edu/~sst/teaching/AME60637/reading/1993_APL_Schoenbach_et_al_hollow_cathode.pdf|accessdate=June 5, 2017|bibcode=1993ApPhL..63.2481E|archive-date=August 8, 2017|archive-url=https://web.archive.org/web/20170808052224/https://www3.nd.edu/~sst/teaching/AME60637/reading/1993_APL_Schoenbach_et_al_hollow_cathode.pdf|url-status=dead}} The hollow cathode effect was recognized by Friedrich Paschen in 1916.{{cite journal|last1=Paschen|first1=F.|title=Bohrs Heliumlinien|journal=Annalen der Physik|volume=355|issue=16|year=1916|pages=901–940|issn=0003-3804|doi=10.1002/andp.19163551603|bibcode=1916AnP...355..901P|url=https://zenodo.org/record/1447321}}

In a hollow cathode, the electron emitting surface is in the inside of the tube. Several processes contribute to enhanced performance of a hollow cathode:

• The pendulum effect, where an electron oscillates back and forth in the tube, creating secondary electrons along the way
• The photoionization effect, where photons emitted in the tube cause further ionization
• Stepwise ionization
• Sputtering{{cite journal|last1=Bartlow|first1=Robert B.|last2=Griffin|first2=Steven T.|last3=Williams|first3=J. C.|title=Axial evolution of the negative glow in a hollow cathode discharge|journal=Analytical Chemistry|volume=64|issue=22|year=2002|pages=2751–2757|issn=0003-2700|doi=10.1021/ac00046a017|pmid=1294005 }}{{cite journal|last1=Mavrodineanu|first1=R.|title=Hollow Cathode Discharges - Analytical Applications|journal=Journal of Research of the National Bureau of Standards|volume=89|issue=2|year=1984|pages=143–185|issn=0160-1741|pmid=34566122| doi=10.6028/jres.089.009 |pmc=6768240 |doi-access=free}}

The hollow cathode effect is utilized in the electrodes for neon signs, in hollow-cathode lamps, and more.