Modelling plasma scenarios for MAST-Upgrade

Transcription

1 Modelling plasma scenarios for MAST-Upgrade Neutral beam requirements, sensitivity studies and stability D. Keeling R. Akers, I. Chapman, G. Cunningham, H. Meyer, S. Pinches, S. Saarelma, O. Zolotukhin and the MAST team EURATOM/UKAEA Fusion Association Culham Centre for Fusion Energy Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK. International Spherical Tori Workshop 2009, Madison, WI 1

2 Outline Overview of the MAST-U project Baseline scenarios modelling methodology Scenario sensitivity studies Example 1 - PINI position and tangency radius Example 2 - T e /n e profiles ASTRA studies MHD stability studies International Spherical Tori Workshop 2009, Madison, WI 2

3 MAST Upgrade principal features Long pulse ( t ~ 5 R), fully non-inductive to prove current drive physics on and off-axis. More flux, higher TF 12.5 MW NBI High B t and off-axis NBI (5 MW) to access q(r) > 2 avoiding low n MHD test CTF-like q(r). Cryo pumped closed divertor density control EBW (~ 1 MW) to test heating and current drive and start-up On axis co- and counter current NBI (each 2.5 MW) for q-profile control, rotation and fast particle physics Cryo-pumps Closed divertor International Spherical Tori Workshop 2009, Madison, WI 3

4 MAST Upgrade principal features Long pulse ( t ~ 5 R), fully non-inductive to prove current drive physics on and off-axis. Expanded flux divertor High B t and off-axis NBI (5 MW) to access q(r) > 2 avoiding low n MHD test CTF-like q(r). Advanced divertor concepts can be tested DEMO, ST Low poloidal field EBW (~ 1 MW) to test heating and current drive and start-up On axis co- and counter current NBI (each 2.5 MW) for q-profile control, rotation and fast particle physics Increased connection length and flux expansion reduces heat loads International Spherical Tori Workshop 2009, Madison, WI 4

5 MAST-U plasma modelling International Spherical Tori Workshop 2009, Madison, WI 5

6 Plasma scenario modelling methodology step 1 SCENE equilibrium International Spherical Tori Workshop 2009, Madison, WI 6

7 Plasma scenario modelling methodology step 1 The initial scenario was produced using the SCENE code to create a CTF-like plasma:- Input boundary and n e, T e /T i profiles produced from analytical expressions (using e.g. elongation/triangularity values for boundary and T 0 /T ped in temperature expression) informed by appropriate MAST/NSTX experimental pulses. Other parameters (I p, Z eff, I rod etc) prescribed. I p =12MA 1.2MA I rod =2.2MA Z eff =1.781 T i =T e International Spherical Tori Workshop 2009, Madison, WI 7

8 Plasma scenario modelling methodology step 2 SCENE equilibrium FIESTA equilibrium guided by SCENE International Spherical Tori Workshop 2009, Madison, WI 8

9 Plasma scenario modelling methodology step 2 SCENE equilibrium then used to guide FIESTA modelling. Pressure profile used as input and a realistic coil set is used to attempt to match SCENE boundary and global parameters (kappa, li, p etc) as closely as possible. SCENE FIESTA International Spherical Tori Workshop 2009, Madison, WI 9

10 Plasma scenario modelling methodology step 3 SCENE equilibrium FIESTA equilibrium i guided by SCENE TRANSP run from FIESTA eqm. International Spherical Tori Workshop 2009, Madison, WI 10

11 Plasma scenario modelling methodology step 3 FIESTA equilibrium then used to derive inputs to TRANSP code TRANSP used to investigate Neutral Beam requirements to produce a fully relaxed simulation with global parameters matching the SCENE and FIESTA equilibria. TRANSP considered useful for NB investigation due to integrated plasma equilibrium solver and Monte-Carlo NUBEAM package. By specifying various NB layouts and tweaking input profiles to match SCENE/FIESTA global parameters, the NB requirements could be assessed. TRANSP run for a sufficient time (>5s) to reach a fully relaxed state. International Spherical Tori Workshop 2009, Madison, WI 11

12 TRANSP Neutral Beam investigation 4 beam system: 1 on-axis axis, 1 on-axis counter, 2 off-axis 1 on-axis counter-current PINI 2 double PINI boxes (1 on-axis, 2 off-axis PINIs. 1 unpopulated onaxis position) International Spherical Tori Workshop 2009, Madison, WI 12

13 Plasma scenario modelling methodology step 4 Each scenario demonstrates a different aspect of CTF/ITER/DEMO physics. SCENE equilibrium FIESTA equilibrium i guided by SCENE TRANSP run from FIESTA eqm. Common parameters: Ip=1.2MA κ=2.5 A=1.6 li(3)=0.5 (except where stated otherwise) TRANSP TRANSP TRANSP TRANSP TRANSP TRANSP TRANSP Scenario A Scenario B Scenario C Scenario D Scenario E Scenario F Scenario G A1,A2 : baseline, CTF-like q profile, 2 density variants B : high fast particle content - confinement, f NI =0.9, β N =6, C1, C2 : long pulse, f NI >1, β N =6.7, reduced TF, 2 I p variants D : high β T, I p =2MA, q0~1, test fast particle β limit E : 'touch-base', high l i, low β F : high =0.6, β limit and confinement scaling G : high thermal β T (β N up to 7), I p =2MA, n g =1, β limit testing International Spherical Tori Workshop 2009, Madison, WI 13

14 Plasma scenario modelling methodology step 4 TRANSP pressure and current profiles then passed back to guide further FIESTA modelling using a modified coil set (engineering g design evolved since last modelling round!). New boundary ypassed to TRANSP model. In principle this iteration could continue but it was considered that no significant improvements to the boundary or pressure profile would result. International Spherical Tori Workshop 2009, Madison, WI 14

15 Plasma scenario modelling methodology SCENE equilibrium FIESTA equilibrium i guided by SCENE TRANSP run from FIESTA eqm. Pressure Profile + updated coil set TRANSP TRANSP TRANSP TRANSP TRANSP TRANSP TRANSP Scenario A Scenario B Scenario C Scenario D Scenario E Scenario F Scenario G Sensitivity studies Time evolution studies Stability studies International Spherical Tori Workshop 2009, Madison, WI 15

16 Sensitivity studies International Spherical Tori Workshop 2009, Madison, WI 16

17 Sensitivity studies Equilibria presented are based on carefully chosen assumptions. Necessary to test how scenarios react to changes in these assumptions. NB layout based on engineering considerations Necessary to test that layout chosen is sufficiently close to optimum for physics. International Spherical Tori Workshop 2009, Madison, WI 17

18 Sensitivity studies Ex 1 T e /n e profile peaking T e /n e profiles are assumed to be achievable based on observation of MAST/NSTX plasmas. In practice there is a risk of the profiles being more peaked. What is the effect on the baseline scenarios? Simple peaking algorithm applied to n e profile, scaling applied to keep line average n e constant and T e adjusted to maintain H 98 ~1. Simple peaking algorithm applied, T e scaled to maintain H 98 ~1. International Spherical Tori Workshop 2009, Madison, WI 18

19 Sensitivity studies Ex 1 n e profile peaking Scenario Sc A with very Parameter peaked density I P 1.2MA 1.2MA B T 0.78T n e (0)/<n e > H q 0 q min q t 11% 11% p N thermal f bs f NBCD NBCD q-profile with flat and peaked density profiles Some risk to scenario as q min drops below 2 but is still above 3/2 Non-inductive current drive increases International Spherical Tori Workshop 2009, Madison, WI 19

20 Sensitivity studies Ex 1 T e profile peaking Scenario Sc A With very Parameter peaked temperature I P 12MA 1.2MA 12MA 1.2MA B T 0.78T T e (0)/<T e > H q 0 q min q t 11% 12% p N thermal f bs f NBCD Catastrophic drop in q-profile, q min <1 Reduction in non-inductive current Such highly peaked T e unlikely due to H-mode profile shape (generally much flatter in H-mode) and off-axis heating from off-axis NBI. International Spherical Tori Workshop 2009, Madison, WI 20

21 Sensitivity studies Ex 2 - PINI position and Tangency radius A single PINI is defined for the TRANSP run. Vertical position and tangency radius (using horizontal LOS) varied to obtain total I beam and electron/ion heating from a PINI in a wide range of positions. Equilibrium shape differs only a little from the baseline scenario so, although most of the parameters from the run are unrealistic (, H 98 etc), the beam driven current, shine-through and heating power is reasonably reliable. International Spherical Tori Workshop 2009, Madison, WI 21

22 Sensitivity studies Ex 2- PINI position and Tangency radius Scenario A beam driven current presented. (Other parameters such as heating power, shine-through etc can also be determined.) Contours show total I beam for a PINI in a particular Z/R Tan position. This is NOT a map of I beam contours in the plasma! Total I beam /PINI Z (m) Simulation indicates more efficient beam current drive may be realised with beams at higher R Tan R Tan (m) International Spherical Tori Workshop 2009, Madison, WI 22

23 Sensitivity studies Ex 2 - PINI position and Tangency radius Studies on all Baseline scenarios showed a clear advantage to increasing R Tan for some PINIs. New configuration specified as: Z (cm) R Tan (cm) Off-axis Off-axis On-axis 0 90 On-axis (cntr.) 0-70 Different PINI positions produce an NB system with greater flexibility. International Spherical Tori Workshop 2009, Madison, WI 23

24 Other sensitivity studies A number of other sensitivity studies have been carried out including: Plasma rotation (eqm. assumption test) T i scaling (eqm. assumption test) PINI power scaling (q-profile control) Anomalous Fast Ion diffusivity (MHD sensitivity) Reduced number of PINIs (project staging approach) Increased number of PINIs (project staging approach) Whereas assumptions used to set up the TRANSP model, particularly T e and n e shape, introduce uncertainties into the results Uncertainties can be mitigated by carrying out sensitivity studies allowing optimum engineering decisions to be made. International Spherical Tori Workshop 2009, Madison, WI 24

25 ASTRA studies O. Zolotukhin International Spherical Tori Workshop 2009, Madison, WI 25

26 ASTRA studies ASTRA is a 1.5D transport code Core transport properties determined by turbulence-driven transport coefficients from GLF23 Pedestal zone described by critical pressure gradient from empirical MAST scaling and width ~ pol For this study it has been coupled with the ESC 2D equilibrium code and the NUBEAM Monte-Carlo neutral beam code Parameters taken from appropriate TRANSP run to set-up ASTRA model: n e profile I p, Z eff, boundary etc Temperature edge value set to keV to simulate H-mode, T e profile calculated Studies Scenario D: time evolution during I p ramp-up and to stationary state. Scenario A: sensitivity to temperature boundary conditions Scenario A: Calculated plasma density profile International Spherical Tori Workshop 2009, Madison, WI 26

27 ASTRA studies scenario D time evolution 2.0 D I 10 I p T D e0 I p (M MA) I p and n e ramp to flat-top values by 300ms n m -1 ) n (10 1 T i0 (kev) T e0, t (s) D 0.08 Current profile equilibrates after 2.5s T i0 W therm Core temperature and stored thermal 0.2 energy equilibrate by 800ms t (s) I p W therm (MJ) l i (3) q 0, 2 1 E q 0 l i (3) E (s) I p (MA A), (Vs) Flux consumption reaches limit after 2.5s t (s) t (s) Run to fully relaxed state should be possible for high-current scenario International Spherical Tori Workshop 2009, Madison, WI 27

28 ASTRA studies Scenario A boundary conditions Pedestal temperature varied in model (ref: 175eV) to determine scenario sensitivity Change of T e0 and T e0 /T ea with T ea define boundary between L and H mode Change in current drive efficiency less sensitive to boundary values in H-mode (kev) T e0 /T ea T e L Reference value in [1] H A1 T e0 E T e0 /T ea E (ms) fractions of driven curren t Reference value in [1] f bs +f CD f bs f CD A T e,i (a) (kev) T e,i (a) (kev) With scenario in H-mode, lower than expected boundary temperature does not result in catastrophic loss of non-inductive current drive. International Spherical Tori Workshop 2009, Madison, WI 28

29 ASTRA studies Scenario A density profile calculation Previous studies have used prescribed density profile. Addition of particle flux term allows density to be calculated along with temperature using specified pressure parameters. m -3 ) n ( Stationary ti state t density profile more peaked than prescribed a) A1 0.5 s 1 s 2.5 s prescribed T e (ke ev) T e profile agrees well b) A1 model for density prescribed density t=2.5 s More peaked density profile may occur than is presently accepted in the baseline model Earlier sensitivity study indicated moderate density peaking can easily be tolerated International Spherical Tori Workshop 2009, Madison, WI 29

30 MHD stability studies I. Chapman, S. Pinches, S. Saarelma International Spherical Tori Workshop 2009, Madison, WI 30

31 MHD Stability Studies have been carried out using the MISHKA MHD code to test stability of the scenarios to all MHD modes Stability of the Baseline scenarios has been investigated It has been found in all cases the most problematic instability is an n=1 internal kink mode (so called infernal mode) Stabilisation effects of rotation, conducting wall structures and triangularity variation have been investigated. International Spherical Tori Workshop 2009, Madison, WI 31

32 MHD Stability Rotational stabilisation Example: Scenario C is most challenging with a calculated N limit of 4.0 and a target N of 6.7 TRANSP rotation model and prescribed rotation profile used: Rotation stabilises the n=1 mode but, for Scenario C, it is unlikely rotation alone will be sufficient to reach the target N. International Spherical Tori Workshop 2009, Madison, WI 32

33 MHD stability stabilisation plates Conducting 1 st wall and structures in the vessel can have a stabilising influence. MAST vessel is large wall is far from plasma Stabilisation plates can be included in the design Stabilisation plates significantly improve limit of n=1-3 modes ( plates 3 is the realistically achievable preferred option) International Spherical Tori Workshop 2009, Madison, WI 33

34 MHD stability - triangularity Tests carried out on Scenario C, triangularity varied between =0.3 and =0.72 (reference =0.52) N is varied and the limit taken to be the value where growth rate of the n=1 mode becomes positive. Significant increase in the limit is seen with increased triangularity Divertor upgrade (more divertor coils) should assist in exploiting this mechanism International Spherical Tori Workshop 2009, Madison, WI 34

35 Conclusions International Spherical Tori Workshop 2009, Madison, WI 35

36 Conclusions A set of baseline scenario models have been produced in support of the MAST-U physics case. Testing neutral beam layouts has optimised the MAST-U design for non-inductive current drive and heating. A series of sensitivity studies has demonstrated the scenarios are robust with respect to initial assumptions and temperature pedestal height. ht Transport modelling of the startup phase has shown the increased flux available is sufficient to reach a fully relaxed state in the demanding high I p scenario. Modelling of density profile broadly agrees with assumed densities with the possibility of moderate profile peaking MHD stability has been assessed and mitigating effects of plasma rotation, stabilisation plates and plasma shaping have been investigated. International Spherical Tori Workshop 2009, Madison, WI 36

37 END International Spherical Tori Workshop 2009, Madison, WI 37