Radiative properties of hot dense X-pinch

J Quanr

Pergamon

S

PROPERTIES

A P~Kuz,~ B A M

RoMANovA,?

BRYUNETKIN,~

N

Lebedev Physlcal Insmute

Tram/er Vol 51, No I/2, pp 291-302 1994 Copyright IS’ 1994 Elx\~erScmce Ltd

Primedm GreatBntam All nghlsrexned 0022407394 56 00 + 0 00

OF HOT DENSE G V

SKOBELEV,~ A

I Yu

and T A tP

Rodrar

00224073(93)EOO35-Q

RADIATIVE

V

Specrrosc

IVANENKOV,~ A YA

X-PINCH

R MINGALEEV,~

FAENOV,~ S YA

KHAKHALM,~

SHELKOVENKO~

Moscow and SNPO VNIIFTRI, 141570 Russia

Mendeleevo. Moscow

Region

Abstract-A

high lummoslty spectrometer wtth a sphencally bent mica crystal has been used to obtam H- and He-ltke spectra of Al and SI Ions In X-pinch plasma with hgh spectral (A/A1 c 3000) and spatial (C 30 pm) resolution The electron density (up to 2 10z4cn-‘) and the temperature (up to 950eV) In the “hot pomt” were measured by means of X-ray spectroscopy methods The estimates show, that the emlsslon of K-line radlatlon can be up to I .I, the power being IO9 W) The total energy emitted In the spectral regton S-lOO A IS about I kJ

INTRODUCTION

The development of methods for the creation and dlagnostlcs of hot dense plasma IS of great Interest to many topics of plasma mvestlgatlons ICF. mteractlon of Intense ultrashort laser pulses with matter, X-ray lasers On the other hand, for many apphed problems, for example opacity measurements, creation of mverslon m schemes with resonance photopumpmg or photoIonIzatIon. medical-blologcal mvestlgatlons, compact powerful sources of X-rays are needed To this point of view, the fast z-pmch m high-current dIodesI-’ IS a very prospectike physlcal ObJect In Ref 4. for example, It was shown that the spectral radiant intensity of the *‘hot point” emission IS IO’-IO6 W/A sr m the spectral region IO-100 8, It allows to consider this X-ray source as a possible one for pumpmg the active medium of shortwavelength lasers>’ and for other apphed problems An addItIona interest IS due to the fact, that many details of the “hot pornt” creation m fast z-pinches IS not clear yet To achieve ultrahigh plasma parameters and X-ray radlatlon charactenstlcs, the arrangement named “X-pmch”“‘” was Investigated m this work It IS necessary to remark, that some dlagnostlc tools (spectrometer with sphencally bent nuca crystal, Bragg-Fresnel lens) have a unique combmatlon of lummoslty, spectral and space resolution EXPERIMENTAL

SETUP

AND

THE

COMPLEX

OF

DIAGNOSTICS

A fast pulse storage-faclhty (FPS)” IS assembled as follows Marx generator-Intermediate capacitor-wngle formlng hne-vacuum diode Elements commumcatlon IS carned out by gas switch The energy storage of the formmg line at a charge voltage of 600 kV was 3 25 kJ The output current In the short-cIrcuIted regime exceeds 270 kA In expenments with a plasma load the diode current reaches 250 kA with pulse duration of about 100 nsec on a level 0 I The load of the vacuum diode are thm metal wires or dlelectrlc fibres, spanned m the IO-15 mm gap as shown on Fig 1 In this case, plasma compresslon with reaching high temperatures and densities IS m a fixed place---l e at the crossing of the wires-m contrast to the case of a smgle wire or hner The addltlon, due to the posslblhty of easy flow of matenal from the hot spot of the X-pinch, higher specific plasma parameters can be achieved than m the case of single wires Plasma processes were Investigated with the help of a number of dlagnostlc apparatus m different spectral ranges The pmch formmg processes were observed m vtslble and Infrared hght wth the help of a five-frame fast camera (Fig 2) and a YAG-laser (Fig 3) Vacuum ultravlolet (VUV)-radlatlon was recorded by vacuum X-ray diodes and spectrometers with a transmlsslon grating (Fig 4) ” 291

(a) Z, mm

(b) Z. mm

J

15

25 FIN 3 Shxbgraph

35

45

Image, ol pldsmd In the CAS ol tour-\\Ires

55 lad

1. nsec

Rad~auic

proprrtws

of hoI dense A -pmch

a

(a) A Z. mm

t

2 I

X-pmch Pd 30 pm

0

Pin hole grating d=lpm

025 pm

(b)

X-pmch SO,

D I

OVII.

Sl11 grating

A - IO

,

VIII

0

I x I mm

d=lpm

100 FIN 4 Transmlsslon gratmg (a) tungsten gratmg period

XUV I pm

50

0

50

100

A. A

spectra of the A’-pmch plasma III the spectral region 5-lOO A dlamerer 25pm (b) gold grating. penod I pm sht 0 I x I mm

Soft X-ray radlatlon was mbestlgated by pin-hole cameras, sclntlllatlon detectors. various types of crystal spectrometers (with plane and curbed crystals according to the Johann scheme, and with spherrcally bent crystals) and a Bragg-Fresnel lens I3 Because of Its very high luminosity a spectrometer with a spherlcally bent crystal” allowed the observation of spectra of multicharged plasma Ions with high spectral and spatial resolution not only In the “hot pomt” area but also at some distance (up to several mm) from It

DISCUSSION X -pulclr

I101 plusma

jomtng

OF

RESULTS

OBT4lNED

mi~estrgmtrotis

The maln stages of the pinch fonmng process are shown on the photos obtamed with the help of multl-frames EOC On Fig 2(a) the development of a double-wire X-pinch (W, diameter of 8 i(m) IS shoHn The evpansron \elocltl of the lummous area reaches Its peak after 30 nsec from current appearance and dbout IO cm ,usec along the axis and 2 cm,psec transversely These values gl\e the lower estlmdtlon of the real velocity of evpanston (only the sufficiently hot parts of the p&ma radiate) Up to 50 nsec cold external plasma layers absorb the radlatton from the central Photos of the d-wires i-pinch e\ploslon are shown on Fig 2(b) Here maximal luminous area expansion \elocitles reach I 5 IO‘msec in longltudlnal dIrectIon dnd 0 3 IO’msec In trdnskersdl one Preserved metal wire frames ha\e been well seen up to 100 nsec and pass the current for pinch m cross Comparison with discharge through a single mire show3 that Increase of per unit length load mass lncredses esploslon process penod of time Analogous picture IS observed dt photos obtained Local

wclth the help of laser radiation hot points” are well seen on the pin-hole photos (see Fig 5) Hard X-raj

asvmmetq

can

be r\plalned bq action on plasma of electron beam being generated In mini-diode This substdntiates d\alldblllty ofcold plasmd stream charactenstlcal radiation lines on spectiogrdms (see Fig 5) So ulth the help of the X-pinch It IS possible to create locahzed point-like X-rdq sources of short duration of about IO nsec The materldl of the wire determines the dlmenslon of the plasma (between 5 and 200pm) and the spectral range of the emlsslon Estimdtions of the plasma compression Here carried out on the basis of the radiating hot point model ’ It orlglndtes In the radlatlie

collapse Idea that has been put forward

for the plasma focus

and the micro-pinch “I’ According to this Idea the e\olutlon of a .I’-pinch single hot point” IS as follows metal electrical explosion pldsmd expansion and lummosit] of skm been observed on Its background have InstabIlIty near cross point as a result Hot plasma flows along the system axis during the first stage ( - IO nsec) dnd Increases the magnetic compression Its result IS cumulation of shoch wd\e on the a\ls and Its subsequent pmch surface exposure changes the balance of magnetic and thermdl pressure But heating now not only favours expansion but also increase3 repeated lonlzatlon and radlatlon (In continuous spectrum-bremsstrahlung and recomblnatlon radiation) While current exceeds some cntlcal value (Pease-Bragmnsku current m correspondence \ilth

the lonlzatlon

multlpllclt])

the second compression appears m which radiation

losses are of

great significance Here radiation from the most Inner layers cdn unlock that sufficiently increase expansion \eloclt!, ( -0 I nsec) Calculations of the plasma elpdnslon of the Y-pinch dre d rather complicated tush That IS \\h> model calculations of d Z-pinch configuration were cdrned out Computdtions for d single dlumlnlum wcIre with a diameter of IOk~rn show that In our case the conditions for the appearance

of He- and H-like

Ions exist

The computed

Lalues for T, and w, were T,, 1 -IO0 e\

z. mm 3 2 I 0/

A. mm E KeV Fig

0 043

““I4 I

35

40

45

3

5 Plnholc nnagc (al dnd \-XI\

qwctrd

th) of the k pmch (palladwm

\c~res dlanwsr

3ljcmI

h.Ij

Radlauve propertles of hot dense X-pmch

295

n, 2 6 102?crnm3. and the expenmental ones were T, ‘c 400 eV, n, 1: 5 10” crnm3’ ” The calculated pmch radius IS about IO pm, the resistance IS about I R The estimate of the apphed pmch voltage (‘c 100 kV) IS consistent with the data from the bremsstrahlung radiation from the anode where the quantum energy reaches 60 keV (an electron beam IS generated durmg pmch decay) Resistance was observed expenmentally as well as beam generanon, Just analogous process are observed in case of X-pinch Energy estlmatlons showed that the K-hne radiation output can reach about 0 l-10 J (2 1 GW of power) Kmetlc energy of the pinch and magnetic field power have values of the same magmtude The plasma stream carries about 0 1 mg of matenal that corresponds to about 0 5 J m energy Photorecombmatlon radiation output of the prnch exceeds 1 J, but Its power IS on the level of IGW The total radiation energy m the wavelength range from 5 to 100 8, IS about I kJ The dtagnostlcs of X-pmch plasmas

For the measurement of plasma parameters we used X-ray spectroscopic methods The plasma emlsslon spectra have been recorded on film, and the spectrographs used allowed spatial resolution for one coordinate I, I e the anode-cathode dIrectIon All spectrograms are integrals of the plasma radiation over both time and two spatial coordmates normal to z-axis The integral character of the spectra IS most crucial for plasma regions close to the X-pmch “hot pomt”, where plasma parameter gradients are very large In this case, the spectrograph sums as well the plasma radlatlon at the moments of both “hot pomt” creation and decay as It Integrates over the transverse expansion of the plasma source with very small (< IO pm) mltlal dimension This effect IS less crucial for plasma regions far from the “hot point”, because (I) there the plasma IS more homogeneous m transverse du-ectlon and (2) m this case, as well as the case of flat target laser-produced plasma. the spatial coordmate z IS approximately equivalent to some temporal stage of plasma expansion For this reason. to diagnose a “hot point” plasma one must use spectral lines which are weakly excited m the decaying plasma I e , when the plasma temperature IS sharply decreased (For example. the transltlons from autolomzmg levels of multiply charged Ions may be used ) For such lines the lntensmes observed correspond mainly to the moment when the “hot pomt” plasma has maximum values of temperature and density X-pmch “hot potnr” parameters determtnatron The plasma electron density measurements were carned out by means of relative mtensltles of dlelectromc satelhtes to resonance lines of the H-like Ions Al XIII and SI XIV The ratio of the sum of tnplet satellites 2~’ 3P + Is2p ‘P and 2s2p ‘P + 1.~2~‘S mtensltles to the singlet satellite 2~’ ‘D -, ls2p ‘P, intensity was used It follows from the calculations” (see also Refs 19-22), that this ratio depends only very slightly on plasma temperature and IS determined mainly by the electron density Figures 6-10 show the densltograms of plasma emlsslon spectra obtained with the help of a spherical mica and a flat CsAP crystal spectrograph Figures &9 correspond to wire explosions of glass fibres and Fig IO to that of alummlum The density was derived by comparison of the expenmental intensity ratlo value with the calculations of Ref 18. the results are shown m Fig I I The plasma electron temperature measurements were carned out by means of the mtenslty ratlo of the dlelectromc satellite 2p ’ ID,--ls2p ‘P, to the H-like resonance line 23The values of T, obtamed are also presented m Fig I I It can be seen from Fig I I that although the “hot point” plasma parameters m different spots are not the same, the typical values are in the range T, 2: (550-950)eV and N, z (3 lo”-2 IO’“) cm-’ This means that the x-pmch “hot pomt” plasma at present possesses probably highest Internal energy concentration laboratory mstallatlons Plasma parameters for the decay stage of the “hot potnts” In order to Investigate the spectra radiated by plasma regions at some distance from the “hot pomt”. we employed a flat CsAP crystal spectrograph This spectrograph covers a range sufficient to observe the series of the lsnp ‘P, + 1s * ‘S, transitions (n = 5-9) In the He-like alummium Ion Both the spectra obtamed m our expenments and the X-ray pinhole camera results are presented m Fig 12 The spatial dlstnbutlon along the z-axis (anode-cathode axls) of some He-like Al XII spectral hnes IS shown m Fig 13 To denve the plasma parameters, Intensity ratios were compared with

S A

296

PIKUZ et al

510: X-pmch SI XI\

At

=

u UUJ A

-t-t-

=

AA 0 004 4

It

a

A,

I

I III 6 IS

6 20

b 25

A. A FIN 8 Fig 69

Densltogram traces of plasma spectra near the resonance hne L\, of hbdrogenllke SI XIV recorded at different condltlons of an explosion of glass ulre> In ,I -pinch configuratlon

Ion

Radlatlve

propertles

of hot

dense A’-pmch

297

X-pinch Al XIII

0 1 mm

U

71

72

73

I.. 8, FIN

IO

Densltogram of the enusslon spectrum of the plasma near the resonance hne Ly, hydrogenhke Al XIII Ion, obtamed by means of a CsAP flat-crystal spectrometer

of the

numeric results calculated In quaslstatmnary apprownatmn for a radlatlve-collrsronal plasma kmetlc model m Ref 24 The theoretlcal results are presented m Fig 14 for two hmltmg cases (I) when the excited levels of the Al XII Ion are populated only by excltatlon from Its ground state (iamzmg UCs&&y-state plasma] and (2) when these levels are populated only by recombmatron of H-like Al XIII Ion (recombmmg plasma) We can conclude from the comparison of expenmental and theoretical mtenslty ratios that at sLale i5 rm,mb-r~ig ~vQ~s&~ dlsOTllZaUOTl

I 1024

-

c

T

*-f-

‘&

1

+t+ I

;u 1023 t 600

800

1000

Te. eV Fig

osai- 51c-_-r

II

Parameters

of X-pmch

hot pomt plasmas measured m expenments alummlum (0) thm-wrre explosions

with

glass (m)

and

plasma) In this case the Intenslt) rdtlos menttoned depend onI1 slIghtI> on plasnw temperature and can be used for plasma densIt> determmatton (see Fig I-4) The Lalues of ,\; ohtdlned bj this method are shown In Table I for the region 1: 12 300 jlrn It should be noted that the recombtnlng character ot the plasma state III this spatial region was also confirmed bq the ln\crslon of bomc

I \Sp ‘P,

41 XII level\ (for example the 1x6~ ‘P, and 1.57~ ‘P, lebels populartons are greater one) \\hlch are observed burel) on spectrograms presented III Fig I2 Tlw obstvwttwt o/ L-spew lro o/ hrtl tom In our experiments ue also obser\cd multlpli charged NI Jnd Cu Ions rxclted III the X-pinch plasma Ewmples

thJn

spectrograms

spectra

dre presented

111Fig

I5

The densltograms

of Cu plasma

emlsston

L-spcctrd ot’ ol‘ obt,unrd

(4

I 23

23

0 06

0 008

3p

II

9 rlll

3 0 Eo.keV 0 06 &mm

AIXIII

8

7

I r6p

I

I

I

Is2

ls5p I

AIXII

III

the

Radtattve

properttes of hot dense X-pmch

(b)

6

5 95

6 05

615

5 95

ld

6 05

615

18,

Fig IZ (a) Pinhole Images of the exploston of an Al wre recorded with different cut-off energy E, of the filters and dtfferent diameter A of the holes (a) enuwon spectrum of the Al-plasma obtained wtth a sphertLall\ curled mica crbstal at the tarlow levels the emtsston reductton (b. c) (b) densttograms of Al plasma spectra at the dlfterent distances from the hot spot

Al X-pmch

I

I

I

I

I

I

2

I

0

1

2

2. mm anode FIR

I3

The spatial dlstrtbutton

_

cathode

along the anodecathode axis of the intensity of some He-hke spectra lines

Al XII

s

300

4

PIKL'Zet dl

_*+

I

‘\

_-’

--

--__

\ II

a::’

-___ -.

:;;-= -.

\

*._ -______-----

-.__ --

--__

--__--

FIN II The dependence ot reldtne mlensltle> 01 He-Ike AI XII ion spectral llneb reld[l\e lnlenllrlcs on plasma electron density calculated lor r, = Xi8 e\’ 1-j and 7, = 1-I-l r\ I~ -I Upper Indese> WC and exe correspond to the cases uhcrs the level> are onI4 populared LX recombtnatlon or ewuuon procews respectl\el\

Table

I The electron plasmd densIt) In regions Idr lrom

-1

Z (mm) Ye km -

’I

7 IO’

-I IO”

’

-I 5-l

3 IO”

I6

10’9

I

hot po~nl -0

-I

2 5

7 Iill”

2 6

I()‘”

X-pmch

G-4

2, mm

Hot point

0 1

NI XIX

I) placed al : = (JI

O’,

0 81

I 1

1 7 (0”

I()”

5-1 I()‘”

Radlarlve

properues

ol hoI dense X -pmch

301

X-pmch

Z. mm I

0

j

Fig

I5

I

I

11

I2

The spectrogram3

of NI (a) and Cu (b) plasma

region A c 12 5-12 9 A are shoun In Fig 16 It can be seen from Fig I6 that spectral by a hot pomt” plasma are strongly asjmmetrlc In our oplmon. this effect self-absorption of the spectral lines In the dense plasma

hnes emltted caused by

IS

In conclusion we re\lewed the mean results of our present Inkestlgatlons The explosion of thm \\lres In the gap of a high-current diode In “A’-pinch” geometry results m an x-ray source of umque bnghtness The comparison of numerical slmulatlons alth the evperlmental obserbatlons shows, that the radiating hot point” model. based on the radiation collapse conceptlon. describes sufficiently well the process of the hot point” evolution The spectroscopic arrangement that has been used In the experiment. has unique luminosity, spectral and spatial resolution The ultrahigh values of the plasma parameters measured m our experiments allo\\ the statement that this object has a unique energy density

12 5

12 h

12 7

I? 8

I2 9

?.A

FIN

16 The densltograms

of Cu plasma spectra emltted by spallal barlow from the hot pomr

regions at different distances

302

s A

Plhuz

er al

REFERENCES I 2 3 4 5 6

7 8 9 IO II I2 I3 I4 I5 I6 I7 I8 I9 20 21 22 23

24

S M Zaharov, G V Ivanenkov, 4 A Kolomenskql et al, F/s Plu~~~,r~9, 469 (1983) (In RussIan) S M Zaharov, G V Ibanenkov. A A Kolomenskyl et al FIS P/u:m~ 13, 206 (1987) (In Russldn) A Bartmk et al. FE Pfasm~ 16, 1482 (1990) (m Ruwan) B A Bryunetkrn, A Ya Faenok. S A Plkuz, and I Yu Shobele\ Laser Purtrtie Beam 10 (I9921 (m press) R C Elton, X-ray Lasers, Academic, Boston, MA (1990) E FIII et al. Izu Acud Scl USSR 55, 794 ( 1991) J Nllsen, Opt Lett 15, 798 (1990), Izr Acad SCI USSR 55, 782 (1991) S M Zaharov, G V Ivanenkov, A A Kolomenskyl et al Pu’mu 17ZhTF 8, 1060 (1982) (In Russian) G V Ivanenkov, A N Lebedev, and S A Plkuz. P IV Lebedel Phts hst Preprrtrt No 2 IO M ( 1989) N QI, D A Hammer, D H Kalantar et al, JQSRT44, 519 (1990) G V Ivanenkov, A R Mmgaleev, S A Plkuz et al. P N Lebeder HIJS Itrsr Preprm No 50. M (1992) (m Russlan) B A Bryunetkm, G V Ivanenkov, S A Plkuz et al. Pu’ma 17ZhTF 17, I6 (1991) (m Russidn) Yu A Agafonov. B A Bryunetkm. A I Erko et al Pu’ma L’ ZhTF 18, 56 (1992) (In Russian) B A Bryunetkm. G V Ivanenkov, S A Plkuz et al PIS nw 1 ZhTF 17. 24 (1991) (m Ruswn) V V Vlhreb and K G Gureev ZhTFI, 2264 (1978) (m Russlan) V V Vlhreb. V V Ivanot, and K N Kosheleb. FIN- PIUS~II 8, I21 I (1982) (In Russldn) A Ya Faenov, S Ya Hahalrn, A A Kolomenskyl et al J Phls D 18. 1337 (1985) A V Vmogradok and I Yu Skobelek Pu’mu 1’ ZhETF 27. 97 (1978) (In Russian) J G Lunney and J F Seely, I%JS Rep Lerr 16, 342 (1981) J F Seely, R H Dixon, and R C Elton Phls Rer, -I 23, I437 (1981) I Yu Skobelev and S Ya Hahalm. Opr SpeXtrosX 59, 22 (1985) (In Russidn) P S Antslferov. K N Koshelev V I Krauz et al FIS Pluwl 16. 1319 (1990) (In Rumdn) V A Bolko, A Ya Faenol. S A Plkuz and U I Safrono\a Mm Vor R -Isrr SOC 181, 107 (1977) I Yu Skobeleb, S Ya Hahalm and S I Ydkovlenko Pm I VIIFTRI 4. hl ( 1986) (In RussIan)