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SUMMARY:Overview of the SPARC physics basis towards the exploration of bur
ning-plasma regimes in high-field\, compact tokamaks
DTSTART;VALUE=DATE-TIME:20210510T140000Z
DTEND;VALUE=DATE-TIME:20210510T142000Z
DTSTAMP;VALUE=DATE-TIME:20210413T215900Z
UID:indico-contribution-17016@conferences.iaea.org
DESCRIPTION:Speakers: P. Rodriguez Fernandez (MIT Plasma Science and Fusio
n Center)\nAchieving net energy production in magnetic confinement fusion
devices is a key milestone in the quest for fusion energy. With the missio
n of demonstrating net fusion energy\, the SPARC tokamak is being designed
jointly by the MIT Plasma Science and Fusion Center and Commonwealth Fusi
on Systems. Its study of reactor-relevant\, alpha-heating-dominated scenar
ios and high power density regimes will help retire risk for ITER operatio
ns and for fusion power plants. A team of over 100 engineers and scientist
s is on track to deliver a toroidal field model coil using high-temperatur
e superconductor (HTS) technology by 2021\, with the engineering design of
the tokamak progressing in parallel. Negotiations with potential host sit
es in the Northeast US are underway\, with start of construction planned i
n 2021 and operation expected in 2025.\nSPARC will be a pulsed machine ope
rating with Deuterium-Tritium (DT) fuel and with ICRF auxiliary heating. T
he high strength of the magnetic field ($B_T>12.0T$ on axis)\, will allow
operation at high plasma current and high absolute density\, leading to ne
t fusion output in a device with a size comparable to current tokamaks ($R
_0<2.0m$). In particular\, the SPARC mission objective has been establishe
d as demonstration and study of Q>2 plasma conditions\, where Q is the rat
io between the total fusion power and the external power absorbed in the p
lasma. Figure [1] depicts the poloidal cross-section of the Version 1C (SP
ARC V1C) design iteration\, and Figure [2] indicates main plasma parameter
s for the baseline DT H-mode plasma discharge.\n\n![SPARC V1C poloidal cro
ss-section.][1]\n![SPARC V1C main plasma parameters for nominal DT H-mode
operation.][2]\n\nFollowing a traditional design workflow (1)\, SPARC para
meters are first selected using empirical scaling laws and plasma operatio
n contour (POPCON) analysis. Figure [3] represents the operational space f
or SPARC V1C for its baseline scenario\, demonstrating that $Q\\approx11$
can be reached with conservative assumptions ($H_{98}=1.0$ confinement\, a
nd $\\nu_{Ti}=2.5$\, $\\nu_{ne}=1.3$ profile peaking factors\, consistent
with empirical predictions). Total fusion power remains below administrati
ve limits for the machine ($P_{fus}<140MW$)\, and safety factor ($q^*=3.05
$)\, normalized density ($f_G=0.37$) and normalized pressure ($\\beta_N=1.
05$) are at reasonably safe levels of operation.\n\n![SPARC V1C operationa
l space\, bounded by LH threshold (green)\, maximum fusion power (blue) an
d available ICRF power (black). $Q_{max}=11.4$ (circle).][3]\n\nThe develo
pment and validation of theory-based reduced models allow integrated simul
ations to also inform the design of SPARC. To this end\, simulations with
the TRANSP code (2) coupled with the TGLF model (3) for turbulence and EPE
D (4) for pedestal stability are performed. Figure [4] depicts simulated t
emperature and density profiles. $H_{98}\\approx1.0$ is predicted\, and fu
sion gain results in $Q\\approx8.2$. The good agreement between the two in
dependent workflows (empirical and theory-based simulations) provides high
confidence that SPARC will accomplish its $Q>2$ mission. During nominal o
peration\, D-T(3He) ICRF minority heating at 120 MHz will be utilized for
on axis heating of both 3He and T. AORSA and CQL3D (5) simulations are in
good agreement with TRANSP\, which uses TORIC (6) to model ICRF. Single-pa
ss absorption is excellent\, and minimum losses of ICRF power (~1%) to alp
has are predicted.\n\n![Predicted profiles for SPARC V1C.][4]\n\nLoss of f
ast ions (alphas and RF-tail ions) due to toroidal field (TF) ripple can b
e a major issue for the design of DT tokamaks\, as it can lead to excessiv
e localized wall heating. The effect of first-orbit\, classical and TF ri
pple in SPARC has been studied with ASCOT (7). Simulations indicate that
the total losses are small (<2%)\, due to the low edge TF ripple (0.15%) i
n the SPARC design. There is no concentration of losses toroidally and onl
y modest concentration poloidally in the current TF design.\n\nManaging di
vertor heat flux will be challenging in SPARC\, but unmitigated levels are
comparable to ITER. To ensure divertor survivability with conservative as
sumptions (i.e.\, not relying on partial or complete divertor detachment)\
, the poloidal field coil set and central solenoid are being designed to e
nsure that a fast strike point sweep (~1 Hz) can be achieved. Thermal simu
lations of the divertor target indicate that sweeping during the flat-top
is sufficient to ensure divertor survivability with only a moderate divert
or radiation fraction. SPARC will be equipped with impurity gas injection
to attain detached-divertor scenarios. The feasibility of an “advanced
” divertor is also being assessed.\n\nIn summary\, SPARC will be an impo
rtant experiment to study burning plasma physics and will be a proof-of-pr
inciple for high-field\, compact fusion power plants. The SPARC design is
converging towards a self-consistent model of the machine with robust engi
neering and physics. Conservative estimates of fusion gain show significan
t margin for the Q>2 mission\, leaving room for extensive exploration of b
urning plasma physics regimes.\n\nThis work was supported by Commonwealth
Fusion Systems.\n(1) ITER Physics Expert Group on Confinement and Transpor
t et al. Nucl. Fusion 39\, 2175 (1999).\n(2) J. Breslau et al. USDOE SC-FE
S (2018).\n(3) G.M. Staebler et al. Phys. Plasmas 14\, 055909 (2007).\n(4)
P.B. Snyder et al. Phys. Plasmas 16\, 056118 (2009).\n(5) E. F. Jaeger et
al. Phys. Plasmas 13\, 056101 (2006).\n(6) M. Brambilla et al.\, Plasma P
hys. Con. Fus. 41\, 1 (1999). \n(7) A. Snicker et al. Nucl. Fusion 52\, 0
94011 (2012).\n\n\n [1]: https://www1.psfc.mit.edu/iaea-fec20/pablorf/CX.
png\n [2]: https://www1.psfc.mit.edu/iaea-fec20/pablorf/Table.png\n [3]:
https://www1.psfc.mit.edu/iaea-fec20/pablorf/Popcon.png\n [4]: https://w
ww1.psfc.mit.edu/iaea-fec20/pablorf/Profiles.png\n\nhttps://conferences.ia
ea.org/event/214/contributions/17016/
LOCATION:Virtual Event
URL:https://conferences.iaea.org/event/214/contributions/17016/
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