EXPERIMENTAL STUDY OF EM RADIATION FROM THE FASTER-

THAN-LIGHT VACUUM MACROSCOPIC SOURCE

A. V. Bessarab, S.P. Martynenko, N.A. Prudkoi, A.V. Soldatov*, V.A. Terekhin

Russian Federal Nuclear Center –All-Russian Research Institute of Experimental Physics

RFNC-VNIIEF

Schemes of EMP generation

B dP/dt (Lcx) or d2P/dt2 (Lcx); P e; Be; R (Le)-1 ne

-1/2; ne JX.

B-field; P-dipole moment per unit area; e , ne -electron energy and density;

x ,R-X-ray and EMP pulse duration; JX-X-ray intensity; L-target dimensions

Z

X=0 V>C

nEMP

X-ray wave frontsX-rays

TargetElectronEmissionPhotocurrent

IonisingRadiation EMP

n

Vacuum Chamber

anode

cathode

d

Scheme of the EMP generation in case an infiniteconductive target (N.J. Carron and C.L.Longmire,1976)

Scheme of EMP device(Yu.N.Lasarev, P.V.Petrov, 1994)

Research equipment: “echo-less” vacuum chamber 1950 2994 mm vacuum system P110-4 Torr high voltage power supply system Umax=100 kV optical scheme of input laser

radiation E1900 J, E2300 J, =1.315 m, 0.50.3 ns Q101415 W/cm2

Experimental setup for EMP research on “Iskra-5” laser facility

Experimental set-up

FC3

5 GHz

5 GHz

Vacuum chamber

Radio absorber

Faraday cup

Magnetic sensorTarget

Modeling device

The chamber was supplied with a diagnostic system for measurements of current parameters, and parameters of incident X-ray and investigated EMP

rise time of accelerated electron current sensors was 75 ps rise time of field sensor was 40 ps.

X-rays parameters

X-ray spectrum of Au target

0,5 1,0 1,50

5

10

15

20

XRD Transmittig grating Planck spectrum with T=85 eV

J*sr

-1*k

eV-1

Energy, keV

X-ray pulse time-shape

-2 0 2 4 6 8 10

0,0

0,2

0,4

0,6

0,8

1,0

h>4 eV

0.51.35 ns

h0.45 keV0.97 ns

Laser Pulse

f0.26 ns

0.50.64 ns

I, ar

b.un

.

t, ns

Radiating unit design (plane diode)

cathode

grid anode

dielectric bracketof cathode

bracket of anode

Faraday cup

eCiL

sC

1 6 .5 m m

5 . 0

m m

14

mm

10

mm

D e s ig n o f a c c e l e r a t e d e l e c t r o n c u r r e n t s e n s o r

r a d i o - f r e q u e n c y c a b l e

h o u s i n g

d i a p h r a g m

g r a p h i t e c o l l e c t o r

i n s u l a t o r m e t a l s h i e l d

S e n s o r g e o m e t r ya n d e q u iv a le n t e l e c t r i c c i r c u i t

C a l ib r a t io n b ys c a t t e r o m e t r y m e th o d

M e a s u r e m e n t s e tu p : - g e n e r a to r - U m a x1 1 V

0 . 5

4 3 p ss a m p l in g o s c i l l o s c o p e b a n d w id th > 1 2 G H z

C a l c u la t e d s t e p r e s p o n s e o f F a r a d e y C u p

0 , 0 0 , 5 1 , 00 , 0

0 , 5

1 , 0

1 , 5

resp

on

se,

no

rm.u

n.

t i m e , n s

R is e t im e o f e l e c t r o n c u r r e n t s e n s o r r = 7 3 p s

Anode electron current vs emission current

Anode current density vs emission current density

v E capac.Ez

eB

e

v

Mesh

Cathode

Emission front

EMP

e

Faradey cup

Laser PlasmaX-ray Sourse

X-ray

Plastic’s Shield(Protect part of capacitor’sarea from X-ray irradiation)

1E-3 0.01 0.1 1

cathode (emission) current Is, arb.un.

curr

ent d

ensi

ty, A

/cm

2

0

1

2

3

4

5

6

7

8

9

10Ecapac =40 kV/cm ICL =13.2 A/cm2

Ecapac =53 kV/cm ICL =23.5 A/cm2

Nonlinear mode

opened cathod

protected cathod

Linear mode

Anode electron current vs emission current (cont.)

0.001 0.010 0.100 1.0000

2

4

6

8

10

Ecapc

=53 kV/cm ICL

=23.5 A/cm2

Ecapc

=40 kV/cm ICL

=13.2 A/cm2

Linear mode

Nonlinear mode

anod

e cu

rent

den

sity

, A/c

m2

cathode (emission) curent Is, arb.un.

e

e

e ee

e

eee

Plastic's Shield(Protect part of capacitor's area from X-ray irradiation)

Faradey Cup

Laser PlasmaX-ray Sourse

X-ray

e

e

e

v E capac.Ez

eB

e

v

Mesh

Cathode

e

e

e

e

ee

Emission front

EMP

e

Anode current density vs emission current density

protected cathod

opened cathod

Accelerated electron current density Iz vs emission current density

0.001 0.010 0.100 1.0000

2

4

6

8

10

Ecapc

=53 kV/cm ICL

=23.5 A/cm2

Ecapc

=40 kV/cm ICL

=13.2 A/cm2

Linear mode

Nonlinear mode

anod

e cu

rent

den

sity

, A/c

m2

cathode (emission) curent Is, arb.un.

The time dependences of the electron current density Iz and emission current density in linear mode

0 1 2

0

1

2

3

cathode (emission)current

accelerated electroncurrent density

curr

ent d

ensi

ty, A

/cm

2

time, ns

The time dependences of the electron current density Iz and emission current

density in nonlinear mode (with space charge limitation)

0 1 2 3 4

0.0

0.2

0.4

0.6

0.8

1.0

emission (cathode)currentf0.3 ns

accelerated electroncurrent densityf0.14 ns

curr

ent

dens

ity,

no

rmal

ized

time, ns

-800 -600 -400 -200 0 200 400 600 800-8

-6

-4

-2

0

section #1 measured analytics code-1D code-2D

J, A

/cm

2

, ps

• Anode current

Comparison of Experimental & Theoretical Results

The spectrum of electrons, accelerated in a gap of the capacitor.Measurement was executed with the help of electron spectrometer that operates

according to a principle of 180 deviation of electrons in a constant magnetic field

20 40 60 80

0

2

4

6

8

U=80 kV

ele

ctro

n d

en

sity

, d

Ne/(

dE

*dS

),

10

8 ele

ctro

n/(

keV

*cm

2 )

energy, keV

Electrons accelerated in the diode had energy from 30 up to 60 keV though the voltage 80 kV was applied

The time dependence of the electron current density Iz (FC1) for the voltage U changing

across the capacitor

1 2 3 4

-1.6

-1.2

-0.8

-0.4

0.0

0.4

U=80 kV0.50.3 ns

U=60 kVns

U=30 kV0.50.41 ns

ano

de

curr

ent

den

sity

, A

/cm

2

time, ns

Electron current density Iz vs voltage U changing across the capacitor

20 30 40 50 60 70 80 900

2

4

6

8

10

illuminatedfull surface

local illumination

vphc

vphc

anod

e cu

rent

den

sity

, A/c

m2

voltage, kV

With increase in a voltage duration of curent pulse decreases

It was found out that the character of emission current dependence of the accelerated electron current depended on whether the diode was irradiated in a local manner or X-ray front passed along the whole of the cathode surface

EM sensorsDesign of magnetic field sensor

(Spiegel R.О., Booth C.A., Bronaugh E.L., 1983)

metal support

polyethylene shell

radio-frequency connector

semi-winding

coaxial cable

1 cm

Calibration field table simulator

conic monopole

calibrated sensor

Metallic base

Calibration setup: step-generator - Umax5 V, 0.1-0.930 ps

sampling oscilloscope bandwidth >12 GHz

Design of capacitor antenna (King R.W.R., 1983)

metal support

polyethylene shell

radio-frequency connector

conic monopole

Step response of field sensor

0 200 400 600 800 1000

0,0

0,2

0,4

0,6

0,8

1,0

1,2

calibrationfield

sensorresponse

resp

onse

, nor

m.u

n.

time, ps

Rise time of field sensor r<40 ps

Radiation zones diagram

1-chamber walls, 2- X-ray source, 3 - X-ray source mirror image, 4 – diode, 5 – edge rays, 6 – wave zone boundary, 7 – laser axis

Time shape of magnetic field for different direction

0 1 2 3-3

-2

-1

0

Imax2.7 A/cm2

0.35 ns

0.11 ns

anod

e cu

rent

den

sity

, A/c

m2

time, ns

0 1 2 3 4

-150

-100

-50

0

50

100

mag

netic

fie

ld in

tens

ity H

y, A

/m

time, ns

MS3 MS2 MS1

MS3 MS1

Target

Modeling device

MS2

The time dependence of electron current densityat the nearby edge of anode

It was experimentally established that radiation of the faster-than-light EMP source has a directed character

Time shape of magnetic field for different target location

0.0 1.0 2.0 3.0 4.0 5.0

-1.0

-0.5

0.0

0.5

1.0

1.5

mag

netic

fie

ld in

tens

ity H

y, n

orm

al.

time, ns

MS3 MS2 MS1

MS3 MS1

Target

Modeling device

MS1MS3 MS2MS2

Target

Modeling device

Target over modeling deviceTarget shifted (faster-than-light mode)

0 1 2 3 4 5

-1.0

-0.5

0.0

mag

netic

fie

ld in

tens

ity H

y, n

orm

al.

time, ns

MS3 MS2 MS1

At normal strike of the model device by X-ray the preferential direction of radiation was absent

The time dependence of the magnetic field HY (MS3 direction) for

the different diode voltage U

0.0 1.0 2.0 3.0 4.0 5.0-150

-100

-50

0

50

U=80 kV 0.5=0.38 ns

U=60 kV 0.5=0.46 ns

U=30 kV 0.5=0.63 ns

mag

neti

c fi

eld

inte

nsit

y, А

/m

Time, ns

The dependence of the magnetic field amplitude HY (MS3 direction) for the different diode voltage

U

20 30 40 50 60 70 800

50

100

150

200

250

Al-cathode Al-cathode Ni-cathode

S=510 cm2

Imax5.1 A/cm2 (U=80 kV)

S=1440 cm2

Imax5.0 A/cm2 (U=80 kV)

Am

plitu

de o

f mag

netic

fiel

d in

tens

ity p

ulse

, A/m

Voltage, kV

With growth of the applied voltage the first phase EMP as well as current pulse is shortened It was shown that the amplitude of the first phase of EMP changed approximately as U It was found out that increase of diode square led to approximately proportionally increase of the field

amplitude

Comparison of Experimental & Theoretical Results

Conclusions

• EMP from faster-than-light source was studied experimentally

• Direct-like EM radiation pattern was found

• EM pulse with ~ 100 kV/m amplitude and ~ 250 ps rise-time at distance of 3 m from source was detected (diode voltage is 80 kV)

• EMP amplitude dependence on diode voltage is stronger than linear

• Diode current decreasing due to diode electromagnetic insulation was proved experimentally