1. High-beta Program 3 June 2002 Objective: Investigate effect of toroidal currents on high-b performance:
1. Low-iota: discharges with current ramp and constant density
Recover #54156 (B = T, iota = 0.30, Bz = -190 G, Icc = - 2 kA) but use 900 MHz target
a) apply proper gaspuffing to heal collapse of energy and density at iota(a) = 0.5
b) get profile- and MHD-data just before collapse
c) keep OH-current just below critical value and increase density (Murakami-limit ?)
2. High-iota: optimize discharge by dynamic Bz- and Icc-program without toroidal current drive
Recover #54023 (B = T, iota = 0.52, Bz = -220 G, Icc = kA), 900 MHz target
a) extend time of beta increase to 150 ms by proper stacking of NBI power
b) apply Bz - ramp G during increase of beta ! (constant Icc = kA)
c) apply Icc - ramp kA G using optimized Bz - program
100
200
300
400
500 ms
NBI
<b> Bz
Icc

2. High-beta Program 3 June 2002 - cont‘d
3. High-iota: OH current ramp during increase of beta
B = T, iota = 0.52, optimized Bz , Icc program (see 2.), 900 MHz target
a) apply current ramp of ≈ kA to maintain iota(a) > 0.5 (≈ 0.52) during increase of beta
(compensate beta induced decrease of edge iota, avoid iota = 1/2)
b) optimize Bz - ramp (≈ 4 different flat top values)
c) optimize Icc - ramp (with optimized Bz)
d) Scan Ip with optimized Bz and Icc ( kA , 20 kA  iota(0) ≈ 1.25, iota(a) ≈ 0.71)
100
200
300
400
500 ms
NBI
<b>
IOH

3. High-beta Program 3 June 2002 - cont‘d
4. High-iota: OH current ramp during flat top of beta
B = T, iota = 0.52, optimized Bz , Icc program (see 2.), 900 MHz target
a) fast beta increase by proper stacking of NBI power
d) Scan Ip kA (20 kA  iota(0) ≈ 1.25, iota(a) ≈ 0.71)
100
200
300
400
500 ms
NBI
<b>
IOH

4. High-beta Program 3 June 2002 - cont‘d
5. Very high-iota: reversed OH current
B = T, iota = 0.72, optimized Bz , Icc program , 900 MHz target
a) apply current ramp of ≈ kA to achieve shearless high-b configuration
(beta-ramp during Ip flat top phase) , MHD limit decreased (no shear stabilization) ?
b) increase reversed current to achieve cross iota = 0.5
tearing modes, pressure driven modes in case of reversed shear ?
6. Very high-iota: reversed OH current, low-b configurations
B ≥ 1.25 T, iota = 0.72, reduced NBI power
a) Scan Ip , reversed shear  neoclassical stabilization ?

5. 1. Recover high-b current ramp shot #54156 B = -1. 25 T, iotaext = 0
1. Recover high-b current ramp shot #54156 B = T, iotaext = 0.30, Bz = 190 G , Icc = -2 kA

6. 1. Recover high-b current ramp shot #54156 (70 GHz startup) B = -1
1. Recover high-b current ramp shot #54156 (70 GHz startup) B = T, iotaext = 0.30, Bz = 190 G , Icc = -2 kA (900 MHz startup)
ruby Thomson

7. Healing of energy (density) collapse by gas puffing possible ?

8. Healing of energy (density) collapse by gas puffing possible
Healing of energy (density) collapse by gas puffing possible ? - influence of iota ? -

9. MHD in #55846 Fast crash (≈ 20 ms) during Ip = 0 phase
 interchange/ballooning
resistive ? (low Te)
Tearing mode activity at iota = 1/2
sometimes after start of radiative collapse
causing contraction of current profile

10. Plasma current kept just below critical value (iota(a) < 1/2) - collapse avoided -

11. Plasma current kept just below critical value (iota(a) < 1/2) - collapse triggered by gas puff (contraction of current profile detabilizes tearing modes) -

12. 2. Recover high-iota, high-b currentless shot #54023 B = -1
2. Recover high-iota, high-b currentless shot # B = T, iotaext = 0.52, Bz = 220 G , Icc = -2.5 kA, 900 MHz startup

13. Apply Bz-ramp (100. 220 G) and Icc-ramp (-0. 7. -2
Apply Bz-ramp ( G) and Icc-ramp ( kA) - improved start-up, improved low-b performance ? -