Radiative divertor studies in JET high confinement mode plasmas

Aaro Järvinen

Radiative divertor studies in JET high confinement mode plasmas

Julkaisun otsikon käännös: Radiative divertor studies in JET high confinement mode plasmas

Aaro Järvinen

Teknillisen fysiikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Lämmönsiirto on eräs keskeisimmistä fuusioreaktoreiden haasteista. Seinämien kuormat eivät saa ylittää 10 MW/m2 reaktoreiden tuottaessa useita gigawatteja fuusioenergiaa. Lisäksi seinämän eroosion sekä polttoaineen kertymisen reaktoriin täytyy olla riittävän hidasta, jotta toimintajakso huoltoseisokkien välissä on riittävän pitkä. Lupaavin ratkaisu näihin haasteisiin on käyttää volframia seinämämateriaalina ja suihkuttaa reaktoriin tehoa säteileviä epäpuhtauksia. Nykyisessä teknologisessa ja tieteellisessä ymmärryksessä on kuitenkin puutteita, eikä voida täysin luottaa siihen, että mallien avulla suunnitellut reaktorit suoriutuvat täysin tehtävistään. Ennusteet fuusioreaktoreille perustuvat laskentamallien validointiin ja fysiikan ilmiöiden tulkintaan olemassa olevilla fuusioreaktoreilla. Tässä työssä tutkitaan sekä kokeellisesti että EDGE2D-EIRENE -koodipaketilla tehosäteilyä divertorilla JET-tokamakissa korkean koossapidon plasmoissa. Tutkimuksissa vertaillaan ennustettuja ja mitattuja diverttoriolosuhteita, tutkitaan seinämäkomponenttien materiaalien ja geometrian vaikutusta säteilevän diverttorin suorituskykyyn, sekä vertaillaan diverttorin suorituskykyä typpi- ja neonsuihkutuksella. Lisäksi volframin kulkeutumista on tutkittu ennustavilla Monte-Carlo simulaatioilla DIVIMP-koodia käyttäen. Simulaatiot toistavat kokeellisesti havaitun diverttorisäteilyjakauman sekä teho- ja hiukkaskuorman vähenemisen matalan kentän puoleisella (LFS) diverttorilevyllä, mikäli kokeellisesti mitatut säteilytasot sovitetaan epäpuhtaussuihkutuksen avulla. Simulaatiot kuitenkin aliarvioivat deuteriumin aiheuttaman säteilyosuuden, kuten on havaittu aikaisemmissakin tutkimuksissa. Hiilen ja typen samankaltaisista säteilyominaisuuksista johtuen JET-tokamakin täyshiiliseinällä havaitut säteilyjakaumat voidaan toistaa typpisuihkutuksella JETin ITER-seinämä -kokeissa. Diverttoriplasman erkaantuminen saavutetaan samoilla säteilytasoilla molemmilla seinämämateriaaleilla. Vastoin odotuksia diverttorigeometrialla havaittiin olevan vain vähän vaikutusta LFS-diverttorilevyn lämpökuormituksen vähenemiseen säteilyn kasvaessa. Lisäksi samankaltaiset diverttorin lämpökuormituksen vähenemiset havaitaan sekä typpi- että neonsuihkutuksella. Toisin kuin typpisäteily, merkittävä osa neonsäteilystä kuitenkin tapahtuu koossapidetyn plasman puolella, minkä uskotaan heikentävän plasman suorituskykyä. Lisäksi korkean tehon ja matalan lämpötilan diverttoriolosuhteet on laskentamallien mukaan eduksi volframin pitämiseksi diverttorikammiossa. Reunamoodit (ELMs) dominoivat laskentamalleissa volframin eroosiota ja kulkeutumista ulos diverttorikammiosta JET-tokamakissa.

Julkaisun otsikon käännös	Radiative divertor studies in JET high confinement mode plasmas
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Ohjaaja	Groth, Mathias, Vastuuprofessori Groth, Mathias, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-6475-8
Sähköinen ISBN	978-952-60-6476-5
Tila	Julkaistu - 2015
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

fuusio
epäpuhtaudet
lämmönsiirto
diverttori
säteily

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-6476-5Lisenssi: Määrittelemätön

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@phdthesis{a0040f658ed04761a6cc5be5221571b1,

title = "Radiative divertor studies in JET high confinement mode plasmas",

abstract = "Controlled power exhaust is one of the key challenges in reactor scale fusion devices. These devices must maintain heat loads less than 10 MW/m2 at the plasma-facing materials (PFM), while producing gigawatts of fusion power. Furthermore, sufficiently low erosion of and fuel retention in PFMs are required to reach reactor relevant component duty cycles. The presently preferred solution to these challenges is to utilize tungsten PFMs with injection of extrinsic radiating impurities, such as nitrogen or neon. However, significant gaps do still exist in the technology and scientific understanding needed to fully rely that these devices will perform according to their design specifications. Predictive capability for these devices relies on model validation and physics interpretation studies conducted on existing fusion test reactors. In this doctoral thesis, radiative divertor studies with nitrogen and neon injection are investigated experimentally and interpreted with the multi-fluid code package EDGE2D-EIRENE for high confinement mode plasmas in the JET tokamak. The studies include comparison of predicted and measured divertor conditions, investigations of the impact of PFMs and divertor geometry on the divertor performance, and comparison of divertor performance with nitrogen and neon injection. Furthermore, predictions for tungsten retention in the divertor chamber with the Monte-Carlo code DIVIMP were conducted. When imposing the divertor radiation by impurities, the simulations capture the experimentally observed reduction of the low-field side (LFS) divertor peak heat load, radiated power, and their spatial distribution. However, consistent with earlier studies, the simulations underestimate the radiated power by deuterium, indicating a shortfall in the radiation from the fuel species. Due to similar radiative characteristics of nitrogen and carbon, the divertor radiation distributions observed in JET with carbon PFMs can be obtained with nitrogen seeding in JET with the ITER-like wall. Detachment is obtained at similar divertor radiation levels in both PFM configurations. Unexpectedly, divertor geometry is observed to have only a marginal impact on the reduction of the LFS heat load with increasing radiation. It is also observed that similar levels of LFS heat load reduction can be obtained at JET with either nitrogen or neon injection. However, unlike nitrogen radiation, a significant fraction of neon radiation is predicted to occur in the confined plasma, expected to reduce plasma performance. Furthermore, high density, low temperature divertor conditions are predicted to be beneficial for improving tungsten retention in the divertor of JET, and edge-localized modes (ELMs) are predicted to dominate tungsten erosion and leakage out of the divertor chamber in JET.",

keywords = "fusion, tokamak, impurities, power exhaust, divertor, radiation, fuusio, ep{\"a}puhtaudet, l{\"a}mm{\"o}nsiirto, diverttori, s{\"a}teily, fusion, tokamak, impurities, power exhaust, divertor, radiation",

author = "Aaro J{\"a}rvinen",

year = "2015",

language = "English",

isbn = "978-952-60-6475-8",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "156",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Radiative divertor studies in JET high confinement mode plasmas

AU - Järvinen, Aaro

PY - 2015

Y1 - 2015

N2 - Controlled power exhaust is one of the key challenges in reactor scale fusion devices. These devices must maintain heat loads less than 10 MW/m2 at the plasma-facing materials (PFM), while producing gigawatts of fusion power. Furthermore, sufficiently low erosion of and fuel retention in PFMs are required to reach reactor relevant component duty cycles. The presently preferred solution to these challenges is to utilize tungsten PFMs with injection of extrinsic radiating impurities, such as nitrogen or neon. However, significant gaps do still exist in the technology and scientific understanding needed to fully rely that these devices will perform according to their design specifications. Predictive capability for these devices relies on model validation and physics interpretation studies conducted on existing fusion test reactors. In this doctoral thesis, radiative divertor studies with nitrogen and neon injection are investigated experimentally and interpreted with the multi-fluid code package EDGE2D-EIRENE for high confinement mode plasmas in the JET tokamak. The studies include comparison of predicted and measured divertor conditions, investigations of the impact of PFMs and divertor geometry on the divertor performance, and comparison of divertor performance with nitrogen and neon injection. Furthermore, predictions for tungsten retention in the divertor chamber with the Monte-Carlo code DIVIMP were conducted. When imposing the divertor radiation by impurities, the simulations capture the experimentally observed reduction of the low-field side (LFS) divertor peak heat load, radiated power, and their spatial distribution. However, consistent with earlier studies, the simulations underestimate the radiated power by deuterium, indicating a shortfall in the radiation from the fuel species. Due to similar radiative characteristics of nitrogen and carbon, the divertor radiation distributions observed in JET with carbon PFMs can be obtained with nitrogen seeding in JET with the ITER-like wall. Detachment is obtained at similar divertor radiation levels in both PFM configurations. Unexpectedly, divertor geometry is observed to have only a marginal impact on the reduction of the LFS heat load with increasing radiation. It is also observed that similar levels of LFS heat load reduction can be obtained at JET with either nitrogen or neon injection. However, unlike nitrogen radiation, a significant fraction of neon radiation is predicted to occur in the confined plasma, expected to reduce plasma performance. Furthermore, high density, low temperature divertor conditions are predicted to be beneficial for improving tungsten retention in the divertor of JET, and edge-localized modes (ELMs) are predicted to dominate tungsten erosion and leakage out of the divertor chamber in JET.

AB - Controlled power exhaust is one of the key challenges in reactor scale fusion devices. These devices must maintain heat loads less than 10 MW/m2 at the plasma-facing materials (PFM), while producing gigawatts of fusion power. Furthermore, sufficiently low erosion of and fuel retention in PFMs are required to reach reactor relevant component duty cycles. The presently preferred solution to these challenges is to utilize tungsten PFMs with injection of extrinsic radiating impurities, such as nitrogen or neon. However, significant gaps do still exist in the technology and scientific understanding needed to fully rely that these devices will perform according to their design specifications. Predictive capability for these devices relies on model validation and physics interpretation studies conducted on existing fusion test reactors. In this doctoral thesis, radiative divertor studies with nitrogen and neon injection are investigated experimentally and interpreted with the multi-fluid code package EDGE2D-EIRENE for high confinement mode plasmas in the JET tokamak. The studies include comparison of predicted and measured divertor conditions, investigations of the impact of PFMs and divertor geometry on the divertor performance, and comparison of divertor performance with nitrogen and neon injection. Furthermore, predictions for tungsten retention in the divertor chamber with the Monte-Carlo code DIVIMP were conducted. When imposing the divertor radiation by impurities, the simulations capture the experimentally observed reduction of the low-field side (LFS) divertor peak heat load, radiated power, and their spatial distribution. However, consistent with earlier studies, the simulations underestimate the radiated power by deuterium, indicating a shortfall in the radiation from the fuel species. Due to similar radiative characteristics of nitrogen and carbon, the divertor radiation distributions observed in JET with carbon PFMs can be obtained with nitrogen seeding in JET with the ITER-like wall. Detachment is obtained at similar divertor radiation levels in both PFM configurations. Unexpectedly, divertor geometry is observed to have only a marginal impact on the reduction of the LFS heat load with increasing radiation. It is also observed that similar levels of LFS heat load reduction can be obtained at JET with either nitrogen or neon injection. However, unlike nitrogen radiation, a significant fraction of neon radiation is predicted to occur in the confined plasma, expected to reduce plasma performance. Furthermore, high density, low temperature divertor conditions are predicted to be beneficial for improving tungsten retention in the divertor of JET, and edge-localized modes (ELMs) are predicted to dominate tungsten erosion and leakage out of the divertor chamber in JET.

KW - fusion

KW - tokamak

KW - impurities

KW - power exhaust

KW - divertor

KW - radiation

KW - fuusio

KW - epäpuhtaudet

KW - lämmönsiirto

KW - diverttori

KW - säteily

KW - fusion

KW - tokamak

KW - impurities

KW - power exhaust

KW - divertor

KW - radiation

M3 - Doctoral Thesis

SN - 978-952-60-6475-8

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Radiative divertor studies in JET high confinement mode plasmas

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