Institute of Plasma Physics and Laser Microfusion Warsaw, Poland Status and Prospect of MJ Plasma Focus Experiment by Marek Scholz Institute of Plasma

Institute of Plasma Physics and Laser MicrofusionWarsaw, Poland

Status and Prospect of MJ Plasma Focus Experiment

by

Marek Scholz

Institute of Plasma Physics and Laser Microfusion

Warsaw, Poland


Outline1. Introduction

– Goals of experiment

2. Time evolution of PF discharge for two kinds of electrodes correlated with neutron emission

– Visualization of the pinch dynamics and structure

3. Neutrons measurements

4. Summary - upgrade of PF-1000


Motivation

We can get easily high temperature plasma.

Unexpected high neutron yield is obtained.


Neutron yield Yn

254

TI

a

lPlYn

v

v4

DDnNP

Tc

IND 2

2

4

v

a 2a

Nn D

D

for keVT 9 47106,1 Ia

lYn


Scaling


Large PF device

PF – 3 (Moscov), Eb = 3 MJ, Ub= 20 kV;

Frascati (Program Euroatom), Eb = 1 MJ; Ub= 50 kV;

Poseidon (Stutgart), Eb = 750 kJ; Ub= 80 kV;

PF-1000 (Warsaw), Eb = 1 MJ; Ub= 40 kV


Scaling

EILL 202

1

0LL

EI 22EYn

Frascati (Program Euroatom), Eb = 1MJ; Ub= 50 kV;


Main QuestionsThis observed saturation in the Yn is caused by the incorrect formation of a proper plasma sheath due to many reasons (e.g. impurities, sheath instabilities)

orThere exists a fundamental threshold for saturation in the Yn

Mechanism of neutron production in large PF facilities


Poseidon (Stuttgart)

Typical neutron signal on Poseidon

• the compression phase (t<0)

• the quiescent phase (plasma expands to r 2rmin

• the instability phase (m=0)

• break-up of the plasma column caused by instability

Beam-Target !?


Anisotropy

;124

30

20

u

EQE d

n

v

190

00

0

Y

YA

ED(keV) 20 100 300

En(00) (MeV)

2.56 2.80 3.06


Goals of Experiment

Definition of the neutron emission characteristics (neutron anisotropy and spectra) from large PF facility;

Definition of the relation between the Yn and plasma sheath dynamics, with particular attention paid to structures appearing within the pinch column;

Definition of correlation between the neutron generation and other types of ionizing radiation produced within PF discharges, i.e. fast electrons, protons from DD reaction, soft and hard X-rays, etc


Apparatus


Generator PF-1000

the charging voltage - U0 = 20 - 40 kV,

the bank capacitance - C0 = 1.332 mF,

the bank energy - E0 = 266 - 1064 kJ,

the nominal inductance - L0 = 15 nH,

the quarter discharge time - T1/4 = 6 s,

the short-circuit current – ISC = 12 MA,

the characteristic resistance - R0 = 2.6 m,


ElectrodesCE diameter - 226 mm

OE diameter - 400 mm

OE consists 24 rods (diam. 32 mm)

length of electrode - 560 mm

length of insulator - 113 mm

CE diameter - 226 mm

OE diameter - 400 mm

OE consists 12 rods (diam. 80 mm)

length of electrode - 560 mm

length of insulator - 113 mm


Diagnostics

v2

DDnNP

254

TI

a

lPlYn

v

Silver Activation Counter

(anizotropy)

PMT

TOF (spectra T)

Rogovski coilFrame cameras;

Streak camera


Measurements of Current and Voltage

I(t)I(t)

dI/dtdI/dt

U(t)U(t)

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

I [M

A]

time [s]

i_rog i_rog i_rog i_rog

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8-1,6-1,4-1,2-1,0-0,8-0,6-0,4-0,20,00,20,40,60,81,01,21,41,61,82,0

dI/d

t

time [s]

di1/dt di1/dt di1/dt di1/dt

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5-5

0

5

10

15

20

25

30

35

U [k

V]

time [s]

u_col u_col u_col

Ub= 27 kV, Eb= 480 kJ,

p = 3,5 Torr

Y = 51010 - 31011


Compression, Pinch & Post-pinch

-170 ns -120 ns 0 ns 50ns 140 ns

Visible frames - exposure time 1 ns, window 589 nm


Compression, Pinch & Post-pinch

XUV frames - exposure time 2 ns, window 200-300 eV+above 600 eV


1.0 1.5 2.0 2.5

HardXrays

SoftXrays

PINdiode

Electrons

dIdt

Neu180deg

time [s]

shot 3108

p = 3.00 TorrUb = 33.0 kV

Eb = 734.0 kJ

Imax = 1.66 MA

L1 = 77897

L2 = 66392

L3 = 47298

L4 = 78015

L5 = 31732

1.269 s 1.289 s 1.299 s


Density at 10.2 s

-50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0-30.0

-20.0

-10.0

0.0

10.0

20.0

30.0

1E+019 cm^-3

2E+019 cm^-3

3E+019 cm^-3

4E+019 cm^-3

5E+019 cm^-3

6E+019 cm^-3

7E+019 cm^-3

8E+019 cm^-3

9E+019 cm^-3


Visible streak-camera

4 cm

ns100 2000

implosion of the current sheath

first pinch developmentof instabilities

second pinchexplosion


Visible frames - exposure time 1 ns, window 589 nm

a-d implosion 2x105m/se minimum radius t=0c-g intense light - dense plasma, dense spherical structureg-p instabilitiesj-m second pinch m-n second explosion m-p second dense structure



a-c pinch ø 1-2 cm;d – first expansione-f - second pinchg-i explosion, dense structuredense spherical structure


Correlation of neutron signals with frames (first neutron pulse)

0

0,5

1

1,5

2

-100 0 100 200 300 400

[ns]

-50 ns 50 ns-30 ns -10 ns 0 ns 10 ns 30 ns

-10 ns-20 ns 30 ns -30 ns 0 ns

hard x-rays

neutron signal

onset of neutron pulse – zipper effect, beam-target decrease of neutrons – dense structure isotropic distribution


t1

t2

t2-t1=10ns





Calculated density st 72,5


Calculated temperature of ions

st 72,5


PM-355 detector

Aluminium foil

Small ion pinhole cameras equipped with PM-355 detectors were used to determine fusion-reaction proton emission sources.

To eliminate fast primary deuterons the detector samples used in the cameras were covered with 80 μm thick Al-foils..


Positioning of ion-pinhole cameras within the PF-1000 facility during measurements of fusion-produced protons.


Images of fusion-proton emitting areas, as obtained after etching of the PM-355 detectors irradiated during five successive discharges within the PF-1000 facility (operated at p0 = 4 Torr D2,

U0 = 31 kV).


Example of the image of the fusion-produced protons, as recorded upon the detector placed at 900 to the z-axis in the PF-1000 facility.


S2 S1 S0 S4 S5 S8

SC1

SC3 SC2

Activation silver counters: SC1(30o), SC2(60o), SC3(90o), SC5(150o)

Scintillator PMT detectors: S0(58.34m, 0o), S1(16.33m, 0o),

S2(7m, 0o), S4(7m, 180o), S5(17m, 180o), S8(58.34m, 180o)

2.27m

Collector

Copper electrode

7 m

16.33m

58.34 m

SC5


SHOT 6543

1,8x10-6 2,0x10-6 2,2x10-6 2,4x10-6 2,6x10-6 2,8x10-6 3,0x10-6

-3

-2

-1

0

volta

ge

time [s]

7m, 90o

7m, 0o

7m, 180o

1,0x10-6 2,0x10-6 3,0x10-6 4,0x10-6 5,0x10-6 6,0x10-6

-0,06

-0,03

0,00

0,03

volta

ge

time [s]

58m, 0o

58m, 180o

1,0x10-6 2,0x10-6 3,0x10-6 4,0x10-6 5,0x10-6 6,0x10-6

-0,18

-0,09

0,00

volta

ge

time [s]

84m, 0o

84m, 180o


0 1 2 3 4 5 6 7 8-8

-7

-6

-5

-4

-3

-2

-1

0

1

volta

ge

[V]

time [s]

S0 S8

2 3 4 5 6-8

-4

0

2,88 MeV

t = 4,76-(2,26 - 0,195) sVol

tage

[V]

time [s]

S0t = 4,62-(2,33 - 0,195) s

2,45 MeV

2 3 4 5

-8

-4

0

2,14 MeV

t = 5,02 - (2,33 - 0,195) s

volta

ge [V

]

time [s]

S8

SHOT 5566


Results of TOF measurements

Shot

number

Yn

L1(90o)

tn (0O)

[s]

tn (180O)

[s]

t=tn (180O) - tn (0O)

[s]

Eb [keV]

5544 2.03.1011 4.734 5.055 0.321 70.0

5566 1.49.1011 4.615 5.035 0.420 120

5569 1.76.1011 4.643 4.965 0.322 70.4

5575 1.92.1011 4.509 4.789 0.280 53.2

5592 1.34.1011 4.623 4.911 0.288 56.3

5605 2.28.1011 4.770 5.158 0.388 102

5620 1.14.1011 4.860 5.147 0.287 55.9

5649 1.55.1011 4.573 4.874 0.301 61.5


PF-1000, 1,8 MA,

Y 31011 n/shot,

E=480 kJ

A “historical” experimental scaling law for neutron yield as a function of the total dischargecurrent (assembled in 1975).


Measurements of Current and Voltage

I(t)I(t)

dI/dtdI/dt

U(t)U(t)

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

I [M

A]

time [s]

i_rog i_rog i_rog i_rog

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8-1,6-1,4-1,2-1,0-0,8-0,6-0,4-0,20,00,20,40,60,81,01,21,41,61,82,0

dI/d

t

time [s]

di1/dt di1/dt di1/dt di1/dt

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5-5

0

5

10

15

20

25

30

35

U [k

V]

time [s]

u_col u_col u_col

Ub= 27 kV, Eb= 480 kJ,

p = 3,5 Torr

Y = 51010 - 31011


-8,0x10-6-6,0x10-6-4,0x10-6-2,0x10-6 0,0 2,0x10-64,0x10-66,0x10-68,0x10-61,0x10-5

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

Y A

xis

Titl

e

time [s]

4,0x10-7 6,0x10-7 8,0x10-7 1,0x10-6 1,2x10-6 1,4x10-6 1,6x10-6 1,8x10-6 2,0x10-6

-1,0

-0,5

0,0

Y A

xis

Titl

e

time [s]

8m, 0o

8m, 90o

8m, 180o

SHOT 6543


PF-1000, 1,8 MA,

Y 31011 n/shot,

E=480 kJ

A “historical” experimental scaling law for neutron yield as a function of the total dischargecurrent (assembled in 1975).

PF-1000, 1,95 MA,

Y 61011 n/shot,

E=550 kJ


Question for future

Determination of parameters of the dense plasma structure in the head of the pinch

role of outflow role of disipation procesess of magnetic

field energy into a pinch plasma naturenature of neutron generation of neutron generation

Correct neutron measurements

Measurements of a current flowing in a pinch


Diagnostics

v4

DDnNP

254

TI

a

lPlYn

v

Activation Measurements

(anizotropy !!)

Method of calibration!

PMT

TOF (spectra Ti)

Current probesInterferometry !!;

Streak cameraSoft X-ray Measurements

(D+Ar or D+Kr)


Interferometry for PF-1000

Laser output specyfication

Max. Pulse energy, mJ

At 1053 nm 1000

At 527 nm 450

At 351 nm 320

At 263 nm 160

Pulse duration at 1053 nm (FWHM) < 1 ns

Optical pulse jitter +/-1 ns

Beam divergence at 1053 nm (ful angle @ 1/e2) < 0.25 mrad

Beam diametr 12 mm

Mach-Zenhder

16 frames, 60 ns between frames


5 00 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0

Sonda scyntylacyjna prod. ACS

Obudowa licznika scyntylacyjnego-wersja 08


Cut view of MCNP geometry of PF-1000 facility.

Cathode

AnodeNeutron source(Pinch)

Concrete hall structure

Chamber

X

IV

J I

V II

III

Detector Z


RSF ( Response Scaling Factor) as a function of detector angular position.

RSF =Response( 2.5 MeV source) / Response( Am-Be source).

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

RSF

0 31 50 90 150

Detector angular position [deg]


Thermal neutron flux as a function of detector position calculated for point 2.5 MeV neutron source located on ‘Z’ axis and distanced 0.1,

0.2, 0.5, 2, 4, 6 and 8 cm from the anode

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

0 20 40 60 80 100 120 140

Detector angular position [deg]

Neu

tro

n f

lux

[n/c

m2]

0.01cm 2cm4cm 6cm

8cm 0.02cm0.05cm


Idea of the method

Fast neutron interactions

(n,n’) tch 10-12 s

(n,), (n,n’), (n,2n)

(n,p), (n,), (n,)T1/2 s

n

r

A

MNY A

aA

MNF A

TA eaA

MNA 10

dEEE


Procedure of calibration

n

r

s

n

K

EES ,

exp

exp

TA eANMa

A

1/0

Calibration source with defined S1.

2. MCNP modelling including:

defined calibration source;

all masses surrounding the source;all masses surrounding the source;

defined samplesdefined samples

s

n

K

EES

cal

cal ,

3. MCNP modelling including:

DD neutron source (plasma) Yn;

all masses surrounding the source;all masses surrounding the source;

defined samplesdefined samples

s

n

K

EEY

DD

DDn ,

Documents

Institute of Plasma Physics and Laser Microfusion Warsaw, Poland Status and Prospect of MJ Plasma Focus Experiment by Marek Scholz Institute of Plasma