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R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
1
RFX – mod:what does the present device allow to do?
R. Piovan
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
2
Outline
RFX design
Main machine limits
What has been done up to now
What can be done?
Open issues
Conclusions
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
3
RFX design
Major radius R 2 m
Minor radius a 0.46 m
Flux swing (from Im to 0) 15 V s
Toroidal field 0.6 T (old 0.7)
Loop voltage 700 V
First wall graphite tiles
Shell time constant 70 ms (old 450 ms)
Target Plasma current 2 MAFlat top 250 ms @ 18 V
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
4
Winding performances and limits
Winding Max current[kA]
Max I2t per shot [MA2s]
Note
Magnetizing 50 3.500
Equilibrium 6.25 20 4°C @ 0.5 s
Toroidal 18.3 300
Magnetizing 15 Vs with 50 kASplitted into 4 sections
Equilibrium 5.2 kA (average) with 2 MA plasma currentSplitted into 8 sections
Toroidal 0.7 T with 18.3 kASplitted into 12 sectors
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
5
adiabatic tiles uniform temperature vs pulse durationat different thermal power load
0
200
400
600
800
1000
1200
1400
0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 0,50
pulse flat top duration [s]
Tem
per
atu
re
[°C
]
T for P=5 [MW/m2]
T for P=10 [MW/m2]
T for P=40 [MW/m2]
T ini = 20°C
Limit in the max overtemperature is related to the maximum stress in the probes between tiles and vessel
Tmax = 200 °C
Machine limits: first wall
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
6
1.6 MA
# 24533
Machine limits: first wall
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
7
Present performances
Vacuum shot with 50 kA magnetizing current 15 Vs
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
8
Present performances
• Toroidal circuit tested up to 12 kA (0.46 T).• Commissioning to 16 kA in the next future.• Very fast current inversion.
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
9
Flux consumption & rise time (#23800-#25672)Flux consumption & rise time (#23800-#25672)
800 1000 1200 1400 1600 18000
0.02
0.04
0.06
0.08
0.1
Iplasma [kA]
Ris
e ti
me
[s]
800 1000 1200 1400 1600 18004
5
6
7
8
9
10
Iplasma [kA]
Flux
con
sum
ptio
n [V
s]
Rt = 0.584 Rt = 0.420
Rt = 0.467 Rt = 1.011
Plasma current & volt seconds
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
10
Ptd
WdIVIV m
p
(theta_w = 1.4, constant)
pIV IVtd
Wd m
P
“Plasma” flux consumption
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
11
Plasma current & volt seconds
Very simple plasma with truncated Bessel function model
a plasma minor radiusrw internal vessel minor radius
Further hypothesis: plasma current rise with reversed toroidal field (RFP) and constant theta
Values assumed in the model:
a = 0.42 mrw = 0.459 mtheta_w = 1.4
Plasma side
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
12
td
Ida
td
dV po
2
pIJ
J
R
aI
1
0
2
1
02
1
20 ln
11
2 pwo
m Ia
r
J
J
J
JRW
td
I
PI
J
J
R
a
a
r
J
J
J
JRdtV
pp
wo
1
02
2
1
02
1
20 1
2
1ln
11
tdI
PILdtV
ppeq HLeq 3
Ptd
WdIVIV m
p
assumedisondistributicurrentuniformifHR
L oTeq
63.04_
“Plasma” flux consumption
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
13
Fluxes in the machine
B
IM
Ip
IF
LeqLstay
ST L+ R
BB
KR
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
14
Simplified circuit
Before the converter start:
IF = 10.4 Ip / 2 [kA] (Ip in MA)IMF = IF + IR = 10.4 Ip / 2 + VR/RT
at the plasma current peak significant magnetizing current and transformer residual flux
IM IFIRIconv
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
15
Varying the transfer resistorFixed magnetizing current: 40.4 kA 12.1 Vs
ST = 15 (IMo – IMres)/50 - rw (currents in kA)
L + R = rw
Shot RT tmax Ip IMres rw ST L R
ohm ms MA kA Wb Wb Wb Wb
25091 0.584 57 1.482 10.1 6.92 2.17 4.45 2.47
25326 0.467 75 1.420 9.5 7.21 2.06 4.26 2.95
25329 0.42 82 1.373 9.5 7.28 1.99 4.12 3.16
Lstray = ST/Ip ~ 1.4 H
From experiments:
Stray inductance
* In case of no amper-turn compensation Lstray ~ 4 H
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
16
Varying the magnetizing current - Fixed transfer resistor: 0.42 ohm
KR ~ 2.1 @ RT = 0.42
From experiments:R scale about with Ip and depends on RT
R ~ KR Ip
If Ip in MA:
“Resistive” flux consumption
Shot IM0 tmax Ip IMres rw ST L R
kA ms MA kA Wb Wb Wb Wb
25360 38.2 75 1.294 9.3 6.69 1.98 3.88 2.81
25330 43.2 76 1.482 10.8 7.65 2.07 4.45 3.20
25334 46.1 70 1.606 11.8 8.06 2.23 4.82 3.24
25366 48.3 76 1.691 11.9 8.67 2.25 5.07 3.60
25367 50.0 78 1.770 12.0 8.98 2.42 5.31 3.67
KR ~ 1.6 @ RT = 0.58
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
17
What can be done?
= M0 - MF = ST + L + R
= 6 Ip (Ip in MA) @ RT = 0.58
= 6.5 Ip (Ip in MA) @ RT = 0.42
IM IFIRIconv
IF = 10.4 Ip/2 [kA] (Ip in MA)
RTIR = 50 Vp-p / RT
(Vp-p is the plasma loop voltage during the flat top)
IMF = IF + IR - IconvF
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
18
What we have done
Case 1 – Rise with RT and flat-top with converters
RT = 0.42 Vp-p = 20 V VR = 50 Vp-p = 1000 VIconv = 15 kA
Ip = 1.77 MA
Flat-top: 20 V & 220 ms 30 V & 150 ms
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
19
What can be done?
Case 2 – Rise with RT and flat-top with converters
RT = 0.58 Vp-p = 20 V VR = 50 Vp-p = 1000 VIconv = 15 kA
Ip = 1.92 MA
Flat-top: 20 V & 220 ms 30 V & 150 ms
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
20
What can be done?
Case 3 – Flat top converters with series configuration (8 kA & 60 V voltage loop) used to rise plasma current (R probably underestimated)
RT = 0.58 Vp-p = 60 V VR = 50 Vp-p = 3000 VIconv = 8 kA
Ip = 2.1 MA
Flat-top: 20 V & 50 ms
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
21
Open issues
Can the plasma current further increased with the present machine?
Decreasing the resistive flux consumptionR ~ 3.2 Vs @ 2 MA
With different setting-up from the constant (matched mode)L = ~ 6 Vs @ 2 MA and w=1.4
1 V s Ip = 0.17 MA
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
22
Conclusions
RFX performances agree completely with design assumptions
done almost 30 years ago
2 MA plasma current, according to the initial specification, can
be reached
Volt-second needed for plasma current rise and sustainment
experimentally derived from experimental data
Further current increasing saving volt-second with the
optimization of plasma setting-up
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
23
What can be done?
Case 4 – Doubling the flat top converters with series configuration (15 kA & 60 V voltage loop) used to rise plasma current (R probably underestimated)This case requires power supply improvements and other verifications on peak power from HV grid
RT = 0.58 Vp-p = 60 V VR = 50 Vp-p = 3000 VIconv = 15 kA
Ip = 2.38 MA
Flat-top: 20 V & 50 ms
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
24
RUN 1401
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
25
Shots with higher currents
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
26
0
5.0
10.0
15.0
20.0
25.0
30.0
13
24
31
32
44
13
24
51
32
46
13
24
81
32
49
13
25
01
32
51
13
25
21
32
54
13
25
51
32
56
13
25
71
32
58
13
26
01
32
61
Maximum (locking)
Uniform
Po
wer
den
sity
[M
W/m
2 ]
Pulse number
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
13
24
31
32
44
13
24
51
32
46
13
24
81
32
49
13
25
01
32
51
13
25
21
32
54
13
25
51
32
56
13
25
71
32
58
13
26
01
32
61
E_lock.E_unif.
En
erg
y [
MJ]
Pulse number
RFX - 1 MA campaign
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
27
68.5
69
69.5
70
70.5
71
71.5
0 50 100 150 200
Kcont=250 W/m^2 KKcont=70 W/m^2 KAdiabatic conditionIR Camera measurement
Tem
per
atur
e [°
C]
Time [sec]
RFX - 1 MA campaign
0
2040
6080
100120
140160180
0 1 2 3 4 5 6 7 8
Tem
per
atur
e [°
C]
Time [h]
16/12/'994/06/'99
R. Piovan “RFX-mod: what does ...” RFX 2009 Programme WorkshopPadova, 20-22 Jan 2009
28
RFX initial scientific objectives
1. Extent the investigations to higher currents to study the confinement properties of RFP type so that comparison with properties of large stellarators and tokamaks can be made
2. To study the temperature, beta and confinement time scale with minor radius and current over an extended range
3. To study the setting-up of stable RFP configurations to minimize energy losses and optimize the configuration. This includes studying the effects of density control using gas injection, the first wall condition and impurities including the use of limiters, the importance of field error, the role of wall stabilization and, at a later stage, of operating without a shell
4. To study the sustainment phase and investigate the density/curren behavior