V.A. Soukhanovskii 2013 TCV JNM

abstract：

（1）novel snowflake divertor concept

(2) snowflake divertor ebables power sharing between divertor strike points,

divertor plasma-wetted area, effective connection length and divertor volumetric power loss to increase beyond those in the standard divertor.

potentially reducing heat flux and plasma temperature at the target.

it also enables higher magetic shear inside the separatrix ,potential affecting pedestal MHD stability.

(3) the snowflake divertor operation led to reduced core and pedestal impurity concentration,

(4) inaccessible partial detachment of the outer strike point with an up to 50% increase in the divertor radiation and a peak divertor heat flux reduction from 3-7 to 0.5-1 was achieved

(5) significantly dissipate in the high magnetic flux expansion region

(6) in the TCV, several advantageous snowflake divertor features (cf. the standard divertor) have been demonstrate : an unchanged L-H power threshold, enhanced stability of the peeling-ballooning modes in the pedestal region (and generally an extended second stability region ),

(7) as well as an H-mode pedestal regime with reduced ()and slightly increased (20-30%)normalized ELM energy, resulting in a favorable average energy loss comparison to the standard divertor .

(8) in the divertor, ELM power partitioning between snowflake divertor strike points was demonstrated. The NSTX and TCV experiments are providing support for the snowflake divertor as a viable solution for the outstanding tokamak plasma-material interface issue.

introduction :

(1) axisymmetric intense separate chamber envisage strategy

(2) partition the SOL power between inner, outer, lower and upper divertor legs

(3) reducing parallel heat and particle fluxes through divertor volumetric loss processes

increased plasma-wetted area

(4) divertor geometry  tilted vertical targets  partial radiative detachment

(5) the standard divertor solution is insufficient since the expected heat fluxes would exceed the presently allowed

(6) divertor target plate positioning :

horizontal or vertical orientation  poloidal or toroidal tilting of target elements  closed divertor

divertor magnetic configuration

(7) main features that  affect divertor volume, neutral penetration and incrasing radial heat (diffusion) and poloidal magnetic flux expansion

(8) the flux expansion is defined as  ,where

(9) increased leads to an increased flux tube volume and to the incrased plasma-wetted area ,

(10) is a fundamental SOL parameter determined by plasma transport and pdestal MHD stability

(11) new divertor magnetic geometry concepts have emerged.

(12) enable the divertor plasma-wetted area ,effective connection length and divertor volumetric power loss to increase beyong those in the standard divertor

(13) potential reducing heat flux and plasma temperature at the target

(14) this paper summarizes experimental SF divertor configuration studies performed in the National Spherical Torus Experiment (NSTX) and the Tokamak a Configuration Variable(TCV)

(15) the results demonstrate that the SF divertor may not only promise for solution of the outstanding plasma-material interface issues,but could also be used as a laboratory for pedestal stability and divertor heat transport

(16) poloidal magnetic flux surfaces in the vicinity of the second-order null point have hexagonal separatrix brabches with an appearance of a snowflake.

(17) in the SF-minus configuration, the corresponding divertor coil currents are slightly lower, and the second null-point located on the main separatrix, or, as in the asymmetric SF-minus, in the common flux region

(18) ideal SF is described by the parameter ,where d is the distance between the null-points and a is the plasma minor radius.

experiment:

（1） graphite evaporated

（2）ion grad B 漂移朝低XP. steady-state SF

（3）NSTX and TCV

results and discussion：

（1）in NSTX,asymmetric SF-minus

（2）a large region of very low in the SF nulls vicinity can be seen in the（w.r.t. standard divertor）

（3）在OMP中平面SOL，极向扩张1mm

（4）在SP附近连接长度和wetted区面积增加50-75%

（5）the SF divertor phase had a profound effect on plasma impurity content

the total carbon inventory was reduced by 50-70%.

the observed reduction was reduction was attributed to the reduction of carbon physical sputtering fluxes in SF divertor (due to very low divertor ) and to the particle expulsion effect

(6)降低PFCs 再循环，导致修改边界等离子体压力和电流剖面。

（7）had a profound effect on the

SOL and divertor properties :

(1) had a significant impact on the divertor heat and particle transport

(2) SF- 3MW NSTX a stable partial detachment of the outer strike point otherwise inaccessible in the standard divertor at

(3) divertor power decrease from 1.8-2.0MW to 1.2MW

(4) the peak flux was reduced from 4-7MW/m2

to 2-3MW/m2.

(5) this decrase was interpreted as driven by both geometric changes in as well as radiative losses

(6) SF 平行热流30-50MW/m2，SD热流100-115MW/m2

（7）SOL碰撞和体复合损失导致SP部分脱靶

（8）额外的体复合损失和偏滤器C辐射相关复合率在持续增加。超过SD 50%

（9）再部分脱靶发生后，热流降低到0.5-1MW/m2，while the total power received by the outer divertor decreased to below 1MW

(10) in spite of the formation of the highly-radiating detached region in the SF divertor

(11) in previous NSTX divertor experiments showed a linear scaling with

(12)partial detachment of the standard divertor using additional extrinsic puffing

(13)in the range of SOL power ,the outer strike point detachment did not occur without gas seeding because of insufficient divertor carbon in the open-geometry

(14)the peak heat flux reduction in the SF configuration was similar to the seeding partial detached divertor at =3MW

(15) in NSTX, an additional seeding into the SF phase showed excellent divertor gas screening ,increase divertor radiation .

(16) suggests a way to enhance non-cornal impurity radiation in the SF configuration due to its already reduced regime .

(17) power parting due to heat diffusion between the separatrix branches and additional strike points in the SF configuration can be benefical for steady-state divertor heat load handing

(18)