Boronization

'''Boronization''' is a wall conditioning technique for fusion machines (such as tokamaks), where a thin film of boron is deposited on the walls of the vacuum vessel in order to reduce the impurity content (for example oxygen) in the vacuum which can be deleterious for fusion plasma operation.<ref>{{Cite web |title=Wall conditioning {{!}} A coat of boron to capture impurities |url=http://www.iter.org/newsline/-/3948 |access-date=2024-04-13 |website=ITER |language=en}}</ref><ref name=":0">{{Cite journal |last=Pitts |first=R. A. |last2=Loarte |first2=A. |last3=Wauters |first3=T. |last4=Dubrov |first4=M. |last5=Gribov |first5=Y. |last6=Köchl |first6=F. |last7=Pshenov |first7=A. |last8=Zhang |first8=Y. |last9=Artola |first9=J. |last10=Bonnin |first10=X. |last11=Chen |first11=L. |last12=Lehnen |first12=M. |last13=Schmid |first13=K. |last14=Ding |first14=R. |last15=Frerichs |first15=H. |date=2025-03-01 |title=Plasma-wall interaction impact of the ITER re-baseline |url=https://www.sciencedirect.com/science/article/pii/S2352179124002771 |journal=Nuclear Materials and Energy |volume=42 |article-number=101854 |doi=10.1016/j.nme.2024.101854 |issn=2352-1791|doi-access=free }}</ref><ref>{{Cite journal |last=Strait |first=E.J. |last2=Barr |first2=J.L. |last3=Baruzzo |first3=M. |last4=Berkery |first4=J.W. |last5=Buttery |first5=R.J. |last6=de Vries |first6=P.C. |last7=Eidietis |first7=N.W. |last8=Granetz |first8=R.S. |last9=Hanson |first9=J.M. |last10=Holcomb |first10=C.T. |last11=Humphreys |first11=D.A. |last12=Kim |first12=J.H. |last13=Kolemen |first13=E. |last14=Kong |first14=M. |last15=Lanctot |first15=M.J. |date=2019-11-01 |title=Progress in disruption prevention for ITER |url=https://iopscience.iop.org/article/10.1088/1741-4326/ab15de |journal=Nuclear Fusion |volume=59 |issue=11 |page=112012 |doi=10.1088/1741-4326/ab15de |issn=0029-5515|hdl=21.11116/0000-0003-D899-D |hdl-access=free }}</ref>

This technique can be seen as a plasma-assisted chemical vapor deposition of boron. The typical workflow involves performing a glow discharge and injecting a gas containing boron into the vacuum vessel chamber.

Boronization as a wall conditioning technique was first developed for the TEXTOR tokamak<ref>{{Cite journal |last=Winter |first=J. |last2=Esser |first2=H. G. |last3=Könen |first3=L. |last4=Philipps |first4=V. |last5=Reimer |first5=H. |last6=Seggern |first6=J. v. |last7=Schlüter |first7=J. |last8=Vietzke |first8=E. |last9=Waelbroeck |first9=F. |last10=Wienhold |first10=P. |last11=Banno |first11=T. |last12=Ringer |first12=D. |last13=Vepřek |first13=S. |date=1989-04-01 |title=Boronization in textor |url=https://www.sciencedirect.com/science/article/pii/0022311589903528 |journal=Journal of Nuclear Materials |volume=162-164 |pages=713–723 |doi=10.1016/0022-3115(89)90352-8 |issn=0022-3115|url-access=subscription }}</ref> at the Forschungszentrum Jülich. It is now a well-established technique and has been successfully applied on many machines,<ref>{{Cite journal |last=Apicella |first=M.L |last2=Mazzitelli |first2=G |last3=Esposito |first3=B |last4=Gabellieri |first4=L |last5=Leigheb |first5=M |last6=Ridolfini |first6=V. Pericoli |last7=Pieroni |first7=L |last8=Romanelli |first8=M |last9=Zagórski |first9=R |last10=team |first10=Ftu |date=July 2005 |title=Effects of wall boron coating on FTU, an all metallic and carbon free medium size tokamak |url=https://iopscience.iop.org/article/10.1088/0029-5515/45/7/018 |journal=Nuclear Fusion |volume=45 |issue=7 |pages=685–693 |doi=10.1088/0029-5515/45/7/018 |issn=0029-5515|url-access=subscription }}</ref><ref>{{Cite journal |last=Yamauchi |first=Y. |last2=Yamaguchi |first2=K. |last3=Hirohata |first3=Y. |last4=Hashiba |first4=M. |last5=Hino |first5=T. |last6=Tsuzuki |first6=K. |last7=Kusama |first7=Y. |date=2006-02-01 |title=Deuterium retention of low activation ferritic steel and boronized wall in JFT-2M |url=https://www.sciencedirect.com/science/article/pii/S0920379605005181 |journal=Fusion Engineering and Design |series=Proceedings of the Seventh International Symposium on Fusion Nuclear Technology |volume=81 |issue=1 |pages=315–319 |doi=10.1016/j.fusengdes.2005.09.031 |issn=0920-3796|url-access=subscription |hdl=2115/5925 |hdl-access=free }}</ref><ref>{{Cite journal |last=Hong |first=Suk-Ho |last2=Lee |first2=Kun-Su |last3=Kim |first3=Kwang-Pyo |last4=Kim |first4=Kyung-Min |last5=Kim |first5=Hong-Tack |last6=Sun |first6=Jong-Ho |last7=Woo |first7=Hyun-Jong |last8=Park |first8=Jae-Min |last9=Park |first9=Eun-Kyong |last10=Kim |first10=Woong-Chae |last11=Kim |first11=Hak-Kun |last12=Park |first12=Kap-Rai |last13=Yang |first13=Hyung-Lyeol |last14=Oh |first14=Yeong-Kook |last15=Na |first15=Hoon-Kyun |date=2011-08-01 |title=First boronization in KSTAR: Experiences on carborane |url=https://www.sciencedirect.com/science/article/pii/S0022311510006525 |journal=Journal of Nuclear Materials |series=Proceedings of the 19th International Conference on Plasma-Surface Interactions in Controlled Fusion |volume=415 |issue=1, Supplement |pages=S1050–S1053 |doi=10.1016/j.jnucmat.2010.10.059 |issn=0022-3115|url-access=subscription }}</ref> examples include DIII-D<ref>{{Cite journal |last=Jackson |first=G. L. |last2=Winter |first2=J. |last3=Burrell |first3=K. H. |last4=DeBoo |first4=J. C. |last5=Greenfield |first5=C. M. |last6=Groebner |first6=R. J. |last7=Hodapp |first7=T. |last8=Holtrop |first8=K. |last9=Kellman |first9=A. G. |last10=Lee |first10=R. |last11=Lippmann |first11=S. I. |last12=Moyer |first12=R. |last13=Phillips |first13=J. |last14=Taylor |first14=T. S. |last15=Watkins |first15=J. |date=1992-12-01 |title=Boronization in DIII-D |url=https://www.sciencedirect.com/science/article/abs/pii/S0022311506800383 |journal=Journal of Nuclear Materials |series=Plasma-Surface Interactions in Controlled Fusion Devices |volume=196-198 |pages=236–240 |doi=10.1016/S0022-3115(06)80038-3 |issn=0022-3115|url-access=subscription }}</ref> and ASDEX.<ref>{{Cite journal |last=The ASDEX Team |last2=The ICRH Team |last3=The LH Team |last4=The NI Team |last5=Schneider |first5=U. |last6=Poschenrieder |first6=W. |last7=Bessenrodt-Weberpals |first7=M. |last8=Hofmann |first8=J. |last9=Kallenbach |first9=A. |last10=Krieger |first10=K. |last11=Müller |first11=E. |last12=Niedermeyer |first12=H. |last13=Ryter |first13=F. |last14=Roth |first14=J. |last15=Söldner |first15=F. |date=1990-12-03 |title=Boronization of ASDEX |url=https://www.sciencedirect.com/science/article/abs/pii/002231159090071T |journal=Journal of Nuclear Materials |volume=176-177 |pages=350–356 |doi=10.1016/0022-3115(90)90071-T |issn=0022-3115|url-access=subscription }}</ref>

Real-time boron powder injection is an advanced technique that offers several advantages over traditional boronization. This method involves injecting submillimeter boron powder directly into the plasma during operation, where it evaporates and deposits a thin boron layer on plasma-facing surfaces. Unlike earlier approaches, it avoids the use of toxic diborane gas and allows continuous conditioning without interrupting plasma operations. This approach is particularly valuable in long-pulse or steady-state devices, where traditional coatings may degrade quickly, helping to maintain wall integrity and limit impurities entering the plasma. It has been studied in many devices like ASDEX Upgrade and DIII-D and is now also being considered as a routine procedure for ITER.<ref>{{cite journal |last1=Bortolon |first1=A. |last2=Rohde |first2=V. |last3=Maingi |first3=R. |last4=Wolfrum |first4=E. |last5=Dux |first5=R. |last6=Herrmann |first6=A. |last7=Lunsford |first7=R. |last8=McDermott |first8=R.M. |last9=Nagy |first9=A. |last10=Kallenbach |first10=A. |last11=Mansfield |first11=D.K. |last12=Nazikian |first12=R. |last13=Neu |first13=R. |title=Real-time wall conditioning by controlled injection of boron and boron nitride powder in full tungsten wall ASDEX Upgrade |journal=Nuclear Materials and Energy |volume=19 |pages=384–389 |date=May 2019 |doi=10.1016/j.nme.2019.03.022|doi-access=free }}</ref><ref>{{cite news |last=Kremen |first=Rachel |title=Stopping off-the-wall behavior in fusion reactors |url=https://phys.org/news/2024-10-wall-behavior-fusion-reactors.html |work=Phys.org |publisher=Princeton Plasma Physics Laboratory |date=October 7, 2024 |access-date=October 12, 2024}}</ref><ref>{{cite news |last=Tamim |first=Baba |title=US plans to sprinkle boron in nuclear reactors like 'saltshaker' to stop energy loss |url=https://interestingengineering.com/energy/boron-nuclear-reactors-stop-energy-loss |work=Interesting Engineering |date=October 8, 2024 |access-date=October 12, 2024}}</ref><ref name=":0" />

A consequence of the repeated boronization procedures will be the accumulation of boron on the first wall and in the divertor regions of tokamak devices, as well as the mixing of boron with plasma-facing materials.<ref>{{Cite journal |last=Marin |first=Alexandru |last2=Saefan |first2=Ashrakat |last3=Unterberg |first3=Ezekial |last4=Parish |first4=Chad M. |last5=Bernard |first5=Elodie |last6=Diez |first6=Mathilde |last7=Tsitrone |first7=Emmanuelle |last8=Wang |first8=Xing |date=January 2025 |title=XPS post-mortem analysis of plasma-facing units extracted from WEST after the C3 (2018) and C4 (2019) campaigns |url=https://linkinghub.elsevier.com/retrieve/pii/S0022311524006263 |journal=Journal of Nuclear Materials |language=en |volume=604 |article-number=155525 |doi=10.1016/j.jnucmat.2024.155525}}</ref> The properties of the formed mixtures can differ significantly from the original wall-material, which may lead to unwanted side-effects of the boronization such as the retention of plasma fuel species in the walls of the reactor.<ref>{{Cite journal |last=Gautam |first=D. N. |last2=Tran |first2=T. T. |last3=Fellinger |first3=M. |last4=Aumayr |first4=F. |last5=Rubel |first5=M. |last6=Primetzhofer |first6=D. |last7=Pitthan |first7=E. |date=2025-12-01 |title=Deuterium retention in sputter-deposited W-B layers: in-situ implantation and ion beam analysis during annealing |url=https://www.sciencedirect.com/science/article/pii/S2352179125001425 |journal=Nuclear Materials and Energy |volume=45 |article-number=102000 |doi=10.1016/j.nme.2025.102000 |issn=2352-1791|doi-access=free }}</ref>

== References == {{Reflist}}

Category:Electrical discharge in gases Category:Fusion power