asipp ht-7/ east overview of psi activities at asipp g. –n. luo, j. g. li, and psi group institute...

ASIPP

HT-7/EAST

Overview of PSI activities at ASIPP

G. –N. Luo, J. G. Li, and PSI Group

Institute of Plasma Physics, Chinese Academy of Sciences P. O. Box 1126, Hefei, Anhui, 230031 China

PRC-US Fusion Magnetic Collaboration WorkshopMay 18-19, 2006, Dalian, China

May 18-19, 2006 PRC-US Magnetic Fusion Collaboration Workshop 2

HT-7/EAST

ASIPP

Introduction

• PSI studies play a significant role in achieving high performance and long pulse or steady-state operation in future tokamaks like EAST, ITER and beyond.

• Goals of the currently-running HT-7 superconducting tokamak at ASIPP are steady-state advanced operation and related physics ( Ip>100kA, ne>1.0×1019m-3, Te>1keV, t>100s).

• Recently, some activities related to PSI issues have been carried out on the HT-7 tokamak.


HT-7/EAST

ASIPP

Limiter system of HT-7

• In 2004 and 2005, the limiter area was enlarged and covered by SiC coated graphite to hold plasma from all direction. And an active cooling system with Cu heat sink were equipped.

• The plasma facing surface area of limiters was 2.35m2

(2004) plus 1.88m2 (2005).• The effective plasma facing

area of limiters and liners is about 12m2.

Upper toroidal limiter

lower toroidal limiter

poloidal limiter

belt limiter


HT-7/EAST

ASIPP

PSI activities

• RF wall conditioning like boronization;• Oxygen wall cleaning for deposits removal and hydrogen rele

ase; • In-time retention evaluation by particle balance analysis; • Dust measurements;• Carbon based materials with doping and coating;• Thick tungsten coatings (>1mm) on copper heat sink prepare

d by vacuum plasma spraying (VPS); • Testing and PSI issues of the thick VPS-W/Cu plasma facing

components in HT-7 tokamak.

------------------------------------------------------------------------------------• Future plan and collaboration opportunities


HT-7/EAST

ASIPP

RF wall conditioning (1)

RF wall conditioning like boronization and siliconization is used for recycling control, isotropic control, H removal in HT-7. Now the boronization using carborane (C2B10H12) has become a routine conditioning before long pulse operation in HT-7. The boron film of ~350nm thick may last for 1500~2000 shots.

RF-system

f =15~30MHz

PRF =10~100kW

Working gas: D2, He

Pvv = 8×10-4~0.2Pa

BT = 0.5~1.8T

RF plasma parameters

Te: He (4~10eV)

H2 (2~5eV)

Ti: H2 (0.5~ 2keV)

D2: 0.3~0.5 keV

ne: ~ 0.5~ 3×1017m-3


HT-7/EAST

ASIPP

RF wall conditioning (2)

Improved performance

• Zeff close to 1;• Pr < 15% POH;• ne max ~ 1.2 ne GW;• Higher LHCD efficiency;• Higher heating efficiency;• Extended operation limit.

0

100

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0

1

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0

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4

0123

0.0 0.2 0.4 0.6 0.8 1.0 1.20123

(a)

(b)

IP(k

A)n

e(0)(*

10-1

9m

-3)

Vp(a

.u.)

OII(

a.u.

)

CIII(

a.u.

) (c)

(d)

before boronization after boronization

Time(s)

(e)

• 60 min. RF He cleaning, Tw=100 C, Tliner = 200C

• Boronization:1.5~2 hours with He:Caborane =1:1

• 30~60 min. RF cleaning (He) to remove hydrogen after boronization


HT-7/EAST

ASIPP

Oxygen wall cleaning (1)

• High inventory of tritium is unacceptable for fusion reactors due to issues of safety and limited operation.

• The dominant mechanism for hydrogen retention is co-deposition with carbon.

• Important to develop techniques of removing co-deposits and hydrogen, and recovering plasma performance after cleanup.

• Application of O-ICR with permanent magnetic field in HT-7.


HT-7/EAST

ASIPP

Oxygen wall cleaning (2)

Oxygen removal

After removing oxygen, plasma can be recovered satisfactorily with controllable density, after some initial disruptions.


HT-7/EAST

ASIPP

In-time retention evaluation (1)

SdtPQ

VPQ

QQQ

vvextract

tanktankpuff

retentionextractpuffl

Absolute evaluation• Error of Qpuff could be limited lower tha

n 10%.

• Error of Qextract could be limited lower than 35%.

• Error of the evaluation with particle balance method could be limited <50% after careful design of gas injection system and regular calibration of gauges on HT-7.

Relative evaluation• Error of Qpuff < 7% (from DAQ).

• Error of Qextract < 10% (from QMS).

• Thus, retention could be compared relatively with the error of <20%.

• The evaluation is suited for long pulse discharges, which generate big pressure variation and provide long enough time for Residual Gas Analysis.

Wall retention is a critical topic for ITER. The long pulses of HT-7 provide good opportunity for the study. Particle balance equation is utilized for retention evaluation since 2004.


HT-7/EAST

ASIPP

In-time retention evaluation (2)

• In HT-7, the effective pumping speed is very low during the discharge;

• Particle balance shows that about 60% of the fuelled gas is retained relatively permanently inside the chamber. Longer pulse tends to cause higher retention quantity;

• The majority of the dynamic inventory is released and pumped within a couple of seconds after the pulse termination.


HT-7/EAST

ASIPP

Dust measurements (1)

Dust inventory

• Scale up by 2 or 3 orders of magnitude in a next step device along with the erosion and the discharge duration;

• In accidental scenarios, chemical reactions with steam and air create potential explosion and dispersal of radioactivity hazards;

• Reliable measurement of dust and reliable methods to remove dust are necessary.

In principle

Photo of a detector for HT-7Size: 150×150 mm

160VDC


HT-7/EAST

ASIPP

Dust measurements (2)

Dust signal

Dust signal measured near the edge of HT-7 tokamak plasma in long pulse discharge. From top to bottom are plasma current, plasma electron density, Ha, ECE radiation, and dust signal.


HT-7/EAST

ASIPP

Carbon based materials

The graphite PFCs in HT-7

• The graphite PFCs have been developed and used for the main belt toroidal and poloidal limiter in HT-7.

• Helpful to achieving better control of plasma and in turn longer pulse duration.

Doped graphite

• The GBST1308 graphite (1%B, 2.5%Si, 7.5%Ti) samples coated with SiC of ~100m thick have high thermal conductivity of 180 W/m.K (RT).

• The samples were mechanically joined to copper heat sink with a super carbon sheet as a compliant layer.

• The e-beam test shows encouraging results that the surface temperature is less than 1000 ºC even when the heat flux is about 3MW/m2.


HT-7/EAST

ASIPP

Thick tungsten coatings

• VPS-W coatings of 1 mm thick have been developed on Cu heat sink with a gradient Cu – W transition layer to decrease the property mismatch between the two materials.

• The W/Cu PFC passed an e-beam test of 20 cycles, each lasting 100 s at heat flux > 10 MW/m2 (4 kW power onto area < 4 cm2 in the test).

W

Cu


HT-7/EAST

ASIPP

W/Cu movable limiter for HT-7

HFSLFS

R270

min

~ 2

55

Movablelimiter

Position ofthe fixed limiter

External VV

Internal VV

Co-axial cooling piping

Port for IR camera

• The W/Cu PFC was welded to a motion mechanism to serve as a movable limiter in HT-7 tokamak.

• The limiter is actively cooled through a co-axial water cooling system at a flow rate of ~ 2 m3/hr.

• The W/Cu PFC can be monitored using an IR-camera and six thermocouples inserted into Cu to different depths.

• The limiter has been mounted in HT-7, and now the testing is still underway.


HT-7/EAST

ASIPP

Plasma-tungsten interactions

• Material issues: Component integrity under high performance and/or long pulse plasmas exposure. Surface and cross-section microstructure analysis and deuterium retention and distribution analysis.

• Heat load measurements: Evaluation on the heat deposited onto the movable limiter. Contribution to estimating the power/energy distribution inside HT-7.

• Impurity behavior: Study on W impurity generation and transport, and ways to hold it back. Test on capability of the now-equipped diagnostics in detection of the impurity in the core and edge plasmas.


HT-7/EAST

ASIPP

Preliminary result of ML by IR-camera

Shot 86308 (OH, Ip~130kA, ne~1.5e19m-3, Te~500eV, t=860ms) (r=254.5mm, a=270mm)

200ms

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100200ms 400ms

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HT-7/EAST

ASIPP

Future plan (1)

Plasma–wall interactions • To understand the flows and exchanges of fuel and i

mpurity particles between the plasma and the facing materials for fuel and impurity control;

• To understand the erosion and redeposition, and the lifetime of graphite and tungsten under steady state operation;

• To develop RF conditioning techniques in divertor device for ITER (cleaning, tritium removal, boronization, isotropic control,etc.).


HT-7/EAST

ASIPP

Future plan (2)

Plasma-facing materials / components development strategy

• To make the best of HT-7 as a test bench in developing different materials for divertor / first wall of EAST and beyond.

• EAST first wall materials: < 2MW/m2

– SiC coated graphite + bolted Cu heat sink, technically ready; – W coatings on the reduced activation ferritic steel.

• EAST divertor: 4-6 MW/m2 (8-12 MW/m2)– W coatings (1-2 mm thick) on Cu heat sink, under development;– SiC coated graphite + brazed Cu heat sink, under development;– W coatings (mm thick) on the RAFS;– W coated graphite + brazed Cu heat sink.

• EAST may switch from the initial PFC (screw-fastened graphite + Cu heat sink) to the directly-cooled tungsten-coated PFC after the first some years’ operation to withstand higher heat flux with increasing the heating power, and finally it may become a whole tungsten PFC machine.


HT-7/EAST

ASIPP

Collaborations

Seeking for collaborations in PSI studies, especially issues related to plasma-tungsten interactions, e.g.,– Methods to prepare for the analysis samples without conta

mination to the surfaces; – Ion beam analysis of the irradiated large W-PFCs in a non-

destructive way;– Detection of tungsten impurity in tokamak plasma;– Behavior of the W PFCs under normal operation conditions

and in the off-normal events like disruptions and VDEs, by means of simulation devices and tokamaks;

– Modeling and computer simulation of the plasma-tungsten interactions.


HT-7/EAST

ASIPP

Thank you !

asipp ht-7/ east overview of psi activities at asipp g. –n. luo, j. g. li, and psi group institute...

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