imaging X-ray mirrors having both very small and large apertures of various types ... only a few pieces of this type of optics were manufactured in the en- tire world, the cost of one system being several hundred thousands US dollars /I/. Taking into ... ca method already applied with success in astronomical X-ray optics. /2,3/.
JOURNAL DE PHYSIQUE Colloque C1, Supplement au n03, Tome 49, mars 1988
THE POSSIBILITIES OF THE USE OF REPLICA X-RAY IMAGING MIRRORS IN PLASMA DIAGNOSTICS
R. HUDEC, B. V A L N ~ E E K ,L. S V ~ T E K " ,V. LANDA* and H. FIEDOROWICZ* *
Astronomical Institute of the Czechoslovak Academy of Sciences, 0nd;e jov, Czechoslovakia "~nstitutefor Material Research, Praha, Czechoslovakia * * Institute for Plasma Physics and Laser Microfusion, Warszawa, Poland
ABSTRACT The replica technology based on galvanoplastics offers the unique possibility of manufacturing of precise light-weight and low-cost imaging X-ray mirrors having both very small and large apertures of various types (paraboloid-hyperboloid, paraboloid-paraboloid, elipsoid-hyperboloid). Some of the further advantages such as the wide use of X-ray microscopic systems and the possibility to built large arrays of identical optical systems for simultaneous multispectral analysis are discussed together with the presentation of some examples of the manufactured mirrors. The first preliminary results are also presented. INTRODUCTION One o f the most important tasks in laboratory nuclear fusion experiments is the investigation of hot plasma in soft X-rays. Apart from experiments with a pinhole camera-with limited resolution and effective area-this task can be accomplished mainly by uslng microscopis X-ray optics. The development and the production of such optical systems are, however, extremely dxfficult and demanding, since it i s necessary to treat the inside cavity nearly 1 cm in diameter with the highest accuracy-surface roughness must not exceed a few nm. That is why only a few pieces of this type of optics were manufactured in the entire world, the cost of one system being several hundred thousands US dollars /I/. Taking into account the final distance of the source, these systems were of the elipsoid-hyperboloid type. The extreme difficulty of execution, however, and the price constitute the main limitations to a broader application of these X-ray microscopes. The problem can be efficiently solved thanks to the galvanoplastics replica method already applied with success in astronomical X-ray optics / 2 , 3 / . This solution has two main advantages, namely it is not necessary to grind / polish the cavity of a very small diameter-it is sufficient to treat the rfegatlve i.e. outside surface. Second, i t is possible to derive up to 10 precise replicas from one master. Altogether 50 grazing incidence replica mirrors were produced this way since 1970, with apertures between 1.7 and 24 cm and grazing angles between 5 arcmin. and 5 degrees. 'Nickel or gold metal layers served a s reflecting surfaces. THE X-RAY MICROSCOPIC SYSTEMS Until now, two X-ray microscopic optical systems for mapping of hot X-ray plasmas were developed. The main parameters of the paraboloid-paraboloid ( P P ) and elipsoid-hyperboloid (EH) systems are summarized in Table 1.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988147
JOURNAL DE PHYSIQUE
C1-232
Tab1 e 1: Czechoslovak microscopic X-ray optics program Type Magnificance Object distance(mm) Image distance(rnm) Grazing angle(deg) Working range(nm) Aperture at midplane(mm) Lengt of each surface(mm) Outside diameter(mm) Material of reflecting surface Number of systems already produced Number of systems to be produced in near future
Figure 1:
PP 1x
300 300
1 5 20 25 28 Ni 12
7 N
6
X-ray microscopic replica system
of EH type
Figure 2: X-ray microscopic replica system of PP type.
THE PROPERTIES The replica X-ray mirrors were tested both in optical and X-ray wavelenghts /4,5/. Both bigger ( astrophysical ) and smaller ( laboratory plasma ) m i r r ~ r swere tested. The X-ray optical properties, measured mainly at the wavelenght of 0.83 n m , can be summarized a s follows: 1. The reflectivity reaches up to 90% of the calculated value, being nearly 0.60 for one or 0.36 for two reflections at grazing angle of lo at 0.83 nm. The effective area of the microscopic mirrors represents nearly 4 mm2 for both PP and EH systems. 2. The X-ray scattering is generally low and corresponds to the typical microroughness of the reflecting surface of 2 n m , which is essentialy the same a s the roughness of masters used for replication process. 3. The imaging properties are characterized by FWHM ( full width of half maximum) and HPR ( half power radius ) parameters of order of 0.5-1 arcmin or better. 4 . The imaging properties of the mirrors does not show strong decrease over a field of view of 1 deg. in diameter. 5. The degradation of imaging parameters due to the replication process is generally l o w , lying below 5 to 10% between the replica N and N+1. More quantitative results on the properties of the mirrors as well as on their dependence on the off axis angle are in detail given elsewhere /4,5/. POSSIBLE APPLICATIONS FOR THE STUDY OF LABORATORY PLASMA First test microscopic mirrors were already tested also directly at the facilities for laser-produced plasmas at the Institute for Plasma Physics and Laser Microfusion , Warsaw, and at the Lebedev Physical Institute, Moscow. The first obtained experience indicate the replica mirrors are well suited for further imaging and spectroscopic experiments with laboratory plasmas the angular resolution being 3 0 arcsec. or better and the useful field of view of 30 arcmin at least.
CONCLUSIONS The advantages of the use of the replica X-ray grazing incidence mirrors in laboratory olasma e x ~ e r i m e n t scan be summarized as follows : 1. Unlike all the thin steamed lavers used most freouentlv. the aalvanoplastically applied nickel lsyer i s highly resistant'to enviromental influences and to effects of nuclear fusion. 2. If needed, it can be washed off without any serious degradation in a superpure ultrasound cleaner ( unlike vacuum steamed layers) 3. The production of numerous low-cost mirrors enables the wide use of X-ray imaging systems in laboratory plasma fusion equipments. 4. The multispectral simultaneously operating cameras with several optical paths can be constructed enabling the multifilter spectral analysis of obtained images.
