1. Neutral beam heating on the TCV tokamak
29th Symposium on Fusion Technology, September 2016, Prague, Czech Republic
Neutral beam heating on the TCV tokamak
Alexander N. Karpushova, René Chavana, Stefano Codaa, Vladimir I. Davydenkob, Frédéric Dolizya, Aleksandr N. Dranitchnikovb, Basil P. Duvala, Alexander A. Ivanovb, Damien Fasela, Ambrogio Fasolia, Vyacheslav V. Kolmogorovb, Pierre Lavanchya, Xavier Llobeta, Blaise Marletaza, Philippe Marmilloda, Yves Martina, Antoine Merlea, Albert Pereza, Olivier Sautera, Ugo Siravoa, Igor V. Shikhovtsevb, Aleksey V. Sorokinb, Matthieu Toussainta
a Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC),CH-1015 Lausanne, Switzerland
b Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia
Introduction
I. Neutral Beam Injector
TCV tokamak: RO0.88m, a0.25m, BT1.54T, IP1MA, in operation since 1992
before 2016: 0.7≤ne≤151019m-3; 0.3≤Te≤15keV; 0.15≤Ti≤1keV; Ti/Te:0.1…0.8
flexible shaping: elongation () up to 2.8, positive and negative triangularity (=-0.7…+1.0)
4MW/2s real time-controllable ECH-ECCD system, since 2000: X2 (ne≤4.21019m-3, cut-off) and X3 (ne≥3.51019m-3)
continuous improvements in diagnostics and plasma control
Motivation for upgrades — widening the parameter range of reactor relevant regimes
Direct ion heating: 1 MW, 25 keV, deuterium neutral beam (installed in 2015, in experiment from 2016)
access to Ti/Te≥1 (up to 3…5), including reactor relevant Te/Ti1, Ti up to 2…4keV
1 MW, keV, neutral beam (2018)
fast ion physics, optimized for high density plasma, especially in H-mode
ECH upgrades: two new X3/X2, replacing two X2 ( )
X3: 1.35MW  3.50MW 30.50MW/118GHz + 21MW/126&84GHz (dual frequency)
X2: 2.70MW  4.85MW 30.45MW/82.7GHz + 21MW/126&84GHz + 20.75MW/84GHz
 high  (ITER scenarios), lower collisionality
II. Power sweep and modulation
Neutral Beam Injector on TCV
6.6
6.4
6.2
6.0
5.8
5.6
Perveance (I/U3/2), ×105 A×V3/2
Beam width (cm) on calorimeter
vs ion current
Optimization at 4-6 power levels: perveance scan
divergence minimum at fixed energy
beam energy, RF power (ion current),
suppression grid voltage, BM current
UHV(energy), Ii(ion current)
 functions of PO.
interpolation between “optimization” points
Control signals (DACs) - f(UHV, Ii, Mi, time)[Volts]
Ion Source
30kV, 50A, deuterium
Time, sec
Pion: 290kW→1.22MW
PO: 230kW→1.05MW
EO: 15→25keV
Iion: 19→49A
IO: 17→42eq.A
NBI shot #1678 ( :58:46)
1.2
1.0
0.8
0.6
0.4
0.2
Power, MW
Energy, keV 50 40 30 20 10
Current, A 25 15 5
Beam energy vs neutral beam power
Neutral Power, MW 25 24 23 22 21 20 19 18 17 16 15
Energy, keV
NBI shots #1675…1678
Injector layout: 1 – RF plasma source, 2 – magnetic screen, 3 – ion-optical system, 4 – neutral beam; 5 –adjusting device; 6 – ions source gate-valve; 7 – vacuum tank; 8 – cryopump cold head; 9 – liquid nitrogen volume; 10 – cryo-panels, 11 – neutralizer, 12 – bending magnet, 13 – diaphragm, 14 – ion dump for positive ions, 15 – calorimeter.
Plasma Source
inductively driven 40kW
4 MHz RF-discharge
Neutral beam power fractions
76:17:7%, 24.8kV, deuterium
Ion Optical System
3 spherical copper grids
Ø250mm, focal length 3.6m
NBI power steps with 5 ms transition time
Time, sec
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Power, MW
NBI shots #1677, 1734…1743 ( )
NBI power modulation kW
and sweep
50 Hz 840/530 kW and
(neutral power)
Time, sec
0.85
0.80
0.75
0.70
0.65
0.60
0.55
Power, MW
NBI shots #1723…1732 ( )
III. First shots with NB heating
Before NB heating:
NBI assembling and preliminary tests – June-August 2015;
Modification of calorimeter, integration with TCV – September-November 2015
NBI tests and optimisation on the calorimeter – December 2015 – January 2016
Tests of TCV first wall overheat protection system.
First experiments with NB plasma heating:
Beam duct cleaning – a few shots into plasma 50…200ms
5th NB shot in TCV plasma #051458,
L-mode, plasma current IP:-240kA;
1.03 MW, 25 keV, deuterium, 0.52 sec.
Preliminary observations:
Ion (and electron) heating, increase of the plasma energy;
Strong increase of toroidal rotation;
Plasma fueling, limitation on plasma density.
PNBI: 1.03 MW
“ion power””neutralization efficiency”
POH: 295→180→300 kW
Plasma energy
(WP, DML): 8→14→7kJ
Bulk ion energy (Wi, CXRS): 3.5→6.5→2.5kJ
Electron energy (We, TS): 3→6→3kJ
Bulk energy
(Wi+We): 8→13→6kJ
Fast ions: ~1kJ
IP: -240 kA
favorable for fast ion first orbit losses
neL: 3.91019 m-2
ne(0): 5.81019 m-3
shine-through ≤ 0.5%
VI. NBI in EUROfusion MST1-TCV experiments
580 TCV shots with NB heating, since
> 60% of experiments (program) requested NBH, 20 of 33 missions
~ 25% of TCV shots with NBH, availability – 85-90%
7-10% faults of control electronics and power supplies
0.3% breakdowns in ion optics per shot
Experimental results and observations:
ion temperature ×2–4, up to 2-2.5keV in L-mode, keV in H-mode (with 1MW NBI)
CO-NBI toroidal rotation 100–300 km/s, -30…+30km/s without beam
easier access of H-mode, control of sawtooth and ELM frequency
Electron temperature:
0.9→1.2→0.9keV
Plasma radius, 
2.0
1.5
1.0
0.5
Electron temperature (Thomson scattering), keV
Ion temperature:
0.65→2.0→0.55keV
Plasma radius, 
2.0
1.5
1.0
0.5
Ion temperature (CXRS, CVI), keV
Plasma radius, 
Electron density (Thomson scattering), ×1019m-3 7 6 5 4 3 2 1
Toroidal rotation (CXRS)
+20→-160→+15 km/s
Plasma radius, 
Ion temperature (CXRS, CVI), keV 40
-40
-80
-120
-160
Ion temperature:
0.35→3.7→0.5keV
Plasma radius, 
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Ion Temperature, keV
TCV #53362
Electron temperature:
1.1→1.4→0.9keV
Plasma radius, 
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Electron Temperature, keV
TCV #53362
NB heating in ELMy H-mode
Close to ASTRA prediction – Te/Ti:1.3/1.9keV in
A.N.Karpushov, et al.; Upgrade of the TCV tokamak, first phase: Neutral beam heating system; Fusion Engineering and Design, (2015) DOI: /j.fusengdes
References:
A. Fasoli for the TCV Team; TCV heating and in-vessel upgrades for addressing DEMO physics issues; Nucl. Fusion 55 (2015) ; DOI: / /55/4/043006
A.N.Karpushov, et al.; Upgrade of the TCV tokamak, first phase: Neutral beam heating system; Fusion Engineering and Design 96–97 (2015)493–497; DOI: /j.fusengdes
Alexander N. Karpushov, Basil P. Duval, René Chavan, Emiliano Fable, Jean-Michel Mayor, Olivier Sauter, Henri Weisen; A scoping study of the application of neutral beam heating on the TCV tokamak; Fusion Engineering and Design, 86 (2011) 868–871 DOI: /j.fusengdes
M. Toussaint, et al.; Beam duct for the 1 MW neutral beam heating injector on TCV, P3.27 (this conference)
D. Fasel, et al.; Commissioning of the heating neutral beam injector on the TCV tokamak, P3.28 (this conference)
Acknowledgements
The authors are very grateful to Manfred Sauer (ex. Inst. fur Plasmaphys., Forschungszentrum Julich GmbH) for participation in the NBI installation and commissioning on the TCV, to Dr. David L. Keeling and Tim Robinson (EURATOM/CCFE Fusion Association, Culham Science Centre) for useful discussions and help with NBI operation during EUROfusion MST1 campaign, to members of SPC-EPFL and Budker INP teams involved in the work on manufacturing, installation, commissioning and operation of heating beam.
This work supported in part by the Swiss National Science Foundation.
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