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Adaption of the BESSY I-3m normal incidence monochromators to the BESSY II source
Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
Adaption of the BESSY I-3m normal incidence monochromators to the BESSY II source G. Reichardt*, T. Noll, I. Packe, P. Rotter, J.-S. Schmidt, W. Gudat BESSY GmbH, Experimental Division, Albert-Einstein-Str. 15, D-12489 Berlin, Germany
Abstract The optical and mechanical lay-out of pre- and post-monochromator optics as well as calculated performance data of the 3m-normal incidence monochromators transferred from BESSY I to BESSY II will be presented. For the design, special emphasis was laid on high resolving power and small spot size at the experiment. # 2001 Elsevier Science B.V. All rights reserved. PACS: 07.85.Qe; 41.50.th; 42.15.Eq Keywords: Beamline design; Normal incidence monochromator; Focussing optics
1. Introduction Two 3m-normal incidence monochromators (3m-NIM) of large vertical and horizontal acceptance were in successful user operation at BESSY I for almost 15 years [1]. In order to accomplish the requests in the low energy spectral range, these two monochromators were selected to be transferred to BESSY II bending magnet frontends. At BESSY I the short distance of the first mirror to the source of only 3 m, allowed for a horizontal acceptance angle of up to 50 mrad with reasonable mirror sizes, results in a large flux at the experiment. With the minimum distance of 12.5 m at BESSY II this design is no longer feasible. Thus, a new optical *Corresponding author. Tel.: +49-30-6392-4983; fax: +4930-6392-4983. E-mail address: [email protected], [email protected] (G. Reichardt).
lay-out had to be elaborated, concentrating less on flux than on the benefits of the increased brilliance of the new source. Heatload on the first mirror was already an important problem at BESSY I, so we had to seriously concentrate on this problem for the BESSY II lay-out. Two design studies for the first mirror geometry were performed: A vertical deflecting first mirror, accepting the full 22 mrad (hor.) of a BESSY II frontend and alternatively a horizontally deflecting mirror of maximum 1 m length accepting only 8 mrad. The only technically feasible material for the vertical deflecting mirror was found to be aluminum with all its well-known disadvantages. In addition, calculations showed that only an intrinsic cooling scheme would be suitable to keep the thermal surface distortions below the critical values. The same analysis for the horizontally deflecting mirror revealed that the mirror can be produced in Silicon, water-based
0168-9002/01/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 0 3 5 7 - 6
G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
side cooling is sufficient and that for good resolving power (slit sizes 5100 mm) the same flux as with the large acceptance arrangement can be delivered at the experimental station.
2. Optical design The optical design is summarized in Fig. 1 and Table 1. 2.1. Pre-monochromator optics According to the results of our heatload studies we adopted the pre-monochromator optics to the horizontally deflecting M1-design. The first mirror M1 is a 1 m long toroid, producing a 1 : 1 intermediate vertical image and a 12.5 : 13.6 magnified horizontal image on the entrance slit. The M1 is made of Silicon and due to the small gracing incidence angle of 68 no additional coating is necessary, even if the surface is seriously oxidized. A suitable mirror chamber has been developed not only for this beamline, but as a BESSY-standard for all horizontally deflecting optical arrangements with mirrors longer than 500 mm. As with all new precision mirror chambers the mechanics is based on a BESSY-patented
459
cartesian 6-strut system [2] allowing for the adjustment of all 6 degrees of freedom. The second pre-monochromator mirror M2, a plane ellipse demagnifies the intermediate vertical image 10 : 1 onto the entrance slit. From the chosen deviation angle and the desired energy range this mirror considered to be made of uncoated quartz. For reasons of demagnification and slope error tolerance, the distance of the second mirror to the entrance slit is only 100 mm. This made it necessary to construct a completely new mirror chamber and entrance slit unit (Fig. 2). The new chamber was designed on the basis of a cartesian 6-strut system [2] allowing for an adjustment in all 6 degrees of freedom. The entrance slit mechanism is based on a parallelogram guide. It allows for a continuous variation of the slit size between 0 and 1000 mm. The slit blades are electrically insulated for measuring the photoemission current and hence provide an adjustment signal for the pre-monochromator optics. With this design the total intensity accepted from the bending magnet (5 mrad (v) 8 mrad (h)) can be transmitted through a 20 mm entrance slit. 2.2. Monochromator unit Despite the elimination of some known constructional shortcomings, the monochromator
Fig. 1. Optical lay-out of the 3 m-NIM beam lines at BESSY II.
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G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
Table 1 Optical lay-out and description of the optical components Element source
Geometry
Description bending magnet DIP 03.1A
Distance
Deviation angle
M1
12500
1688 horizontal
F1
12500
M2
1000
ES
100
G
3000-t
AS
3000-t
M3
1500
Exp.
1500
Toroid, 1000 mm 60 mm, water-cooled Si-blank, R¼ 124 625 mm, r¼ 1306:6 mm, sR ¼ 0:500 , sr ¼ 500 Intermediate vertical focus
175.58 vertical
Plane ellipse, 130 mm 20 mm, quartz-blank, uncoated, a¼ 550 mm; b¼ 12:415 mm, x0 ¼ 450:118 mm, sm ¼ 200 , ss ¼ 1000 0–1000 mm continuous
4.58 vertical
Glass-blank, 1150 mm, R¼ 3000 mm, sR 50:400 G1 : 2400 l/mm, lopt ¼ 80 nm, Pt-coated G2 : 600 l/mm, lblaze ¼ 150 nm, Al/MgF2-coated 0–2000 mm continuous
1558 horizontal
Toroid, 100 mm 80 mm, ULE-blank, Ni-coated, R¼ 6825 mm, r¼ 324:7 mm, sR ¼ 200 , sr ¼ 2:700 Spot size typ. 50 400 mm2
itself remained unchanged. It contains two in vacuum interchangeable gratings with 2400 l/mm and 600 l/mm. Rotation and translation of the grating are performed according to the operation principle of an off-Rowland-circle normal incidence monochromator [3] in-vacuum by linear feedthroughs and stepping motors. Due to imperfections of the mechanics and slope errors of the gratings a resolving power of 20.000 at max is expected.
2.3. Post-monochromator optics
Fig. 2. Mirror positioning mechanism for pre-monochromator mirror M2 and entrance slit. The positioning mechanism is based on the patented cartesian 6-strut design. The entrance slit is only 100 mm away from the center of M2.
Vertically a 1 : 1 image of the exit slit is focussed in the experiment by means of a horizontally deflecting toroidal refocusing mirror. Due to the sagittal focusing properties of the spherical grating the horizontal focus size is slightly wavelength dependent. The radius of the toroid M3 was chosen to produce the best spot for a photon energy of 15 eV in combination with the 2400 l/mm grating. The mirror chamber for the M3 is also
G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
461
constructed on the basis of the cartesian 6-strut scheme [2].
3. Performance data
The spot size at the experiment is slightly energy dependent for photon energies below 15 eV (see lower part of Fig. 3). Above 15 eV the horizontal spot size is 400 mm, vertically a 1 : 1 image of the exit slit is obtained. Fig. 3 shows the calculated resolving power and flux values for the 2400 l/mm grating and 50 mm entrance and exit slits. For these monochromator settings typical values for resolving power E=DE and flux F of 10.000 and 1011 photons/s 100 mA 0.1% BW, respectively, are expected. As characteristic for spherical grating monochromators the resolving power decreases with 1=E. Due to the use of two p-reflections the degree of linear polarization is not as high as with the old BESSY I set-up. Nevertheless, by means of remote-controlled water-cooled aperture blades in front of the first mirror and by sacrificing 50% of the flux it is possible to increase the degree of linear polarization to over 80%. In addition circular polarization of some 80% is feasible by simply setting the aperture blades for the selection of off-plane radiation.
Fig. 3. Performance data as calculated for the 2400 l/mm grating and 50 mm slit sizes. The slope error for the grating was set to 0.3 arcsec rms.
increased brilliance of the BESSY II source by an improved resolving power and flux density at the experiment.
4. Conclusion
References
Two old and field-tested 3 m-normal incidence monochromators, which were almost 15 years in operation at BESSY I will be equipped with new pre- and post-monochromator optics for the installation at BESSY II bending magnets. Although due to lower horizontal acceptance the total flux at BESSY II will be less than at BESSY I, these monochromators will benefit from the
[1] G. Reichardt, VUV-fluoreszenspektroskopische Untersuchung quasi-gebundener Rotationsniveaus im Elektronengrundzustand des Wasserstoffmolek.uls nach rotationsselektiver Anregung mit Synchrotronstrahlung, Shaker, 1994. [2] T. Noll et al., Six-Strut Arrangement for cartesian Movements of Mirrors, Nucl. Instr. and Meth. A 467–468 (2001), these proceedings. [3] J. Samson, Techniques of Vacuum Ultra Violet Spectroscopy, Wiley, New York, 1967.
Adaption of the BESSY I-3m normal incidence monochromators to the BESSY II source G. Reichardt*, T. Noll, I. Packe, P. Rotter, J.-S. Schmidt, W. Gudat BESSY GmbH, Experimental Division, Albert-Einstein-Str. 15, D-12489 Berlin, Germany
Abstract The optical and mechanical lay-out of pre- and post-monochromator optics as well as calculated performance data of the 3m-normal incidence monochromators transferred from BESSY I to BESSY II will be presented. For the design, special emphasis was laid on high resolving power and small spot size at the experiment. # 2001 Elsevier Science B.V. All rights reserved. PACS: 07.85.Qe; 41.50.th; 42.15.Eq Keywords: Beamline design; Normal incidence monochromator; Focussing optics
1. Introduction Two 3m-normal incidence monochromators (3m-NIM) of large vertical and horizontal acceptance were in successful user operation at BESSY I for almost 15 years [1]. In order to accomplish the requests in the low energy spectral range, these two monochromators were selected to be transferred to BESSY II bending magnet frontends. At BESSY I the short distance of the first mirror to the source of only 3 m, allowed for a horizontal acceptance angle of up to 50 mrad with reasonable mirror sizes, results in a large flux at the experiment. With the minimum distance of 12.5 m at BESSY II this design is no longer feasible. Thus, a new optical *Corresponding author. Tel.: +49-30-6392-4983; fax: +4930-6392-4983. E-mail address: [email protected], [email protected] (G. Reichardt).
lay-out had to be elaborated, concentrating less on flux than on the benefits of the increased brilliance of the new source. Heatload on the first mirror was already an important problem at BESSY I, so we had to seriously concentrate on this problem for the BESSY II lay-out. Two design studies for the first mirror geometry were performed: A vertical deflecting first mirror, accepting the full 22 mrad (hor.) of a BESSY II frontend and alternatively a horizontally deflecting mirror of maximum 1 m length accepting only 8 mrad. The only technically feasible material for the vertical deflecting mirror was found to be aluminum with all its well-known disadvantages. In addition, calculations showed that only an intrinsic cooling scheme would be suitable to keep the thermal surface distortions below the critical values. The same analysis for the horizontally deflecting mirror revealed that the mirror can be produced in Silicon, water-based
0168-9002/01/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 0 3 5 7 - 6
G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
side cooling is sufficient and that for good resolving power (slit sizes 5100 mm) the same flux as with the large acceptance arrangement can be delivered at the experimental station.
2. Optical design The optical design is summarized in Fig. 1 and Table 1. 2.1. Pre-monochromator optics According to the results of our heatload studies we adopted the pre-monochromator optics to the horizontally deflecting M1-design. The first mirror M1 is a 1 m long toroid, producing a 1 : 1 intermediate vertical image and a 12.5 : 13.6 magnified horizontal image on the entrance slit. The M1 is made of Silicon and due to the small gracing incidence angle of 68 no additional coating is necessary, even if the surface is seriously oxidized. A suitable mirror chamber has been developed not only for this beamline, but as a BESSY-standard for all horizontally deflecting optical arrangements with mirrors longer than 500 mm. As with all new precision mirror chambers the mechanics is based on a BESSY-patented
459
cartesian 6-strut system [2] allowing for the adjustment of all 6 degrees of freedom. The second pre-monochromator mirror M2, a plane ellipse demagnifies the intermediate vertical image 10 : 1 onto the entrance slit. From the chosen deviation angle and the desired energy range this mirror considered to be made of uncoated quartz. For reasons of demagnification and slope error tolerance, the distance of the second mirror to the entrance slit is only 100 mm. This made it necessary to construct a completely new mirror chamber and entrance slit unit (Fig. 2). The new chamber was designed on the basis of a cartesian 6-strut system [2] allowing for an adjustment in all 6 degrees of freedom. The entrance slit mechanism is based on a parallelogram guide. It allows for a continuous variation of the slit size between 0 and 1000 mm. The slit blades are electrically insulated for measuring the photoemission current and hence provide an adjustment signal for the pre-monochromator optics. With this design the total intensity accepted from the bending magnet (5 mrad (v) 8 mrad (h)) can be transmitted through a 20 mm entrance slit. 2.2. Monochromator unit Despite the elimination of some known constructional shortcomings, the monochromator
Fig. 1. Optical lay-out of the 3 m-NIM beam lines at BESSY II.
460
G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
Table 1 Optical lay-out and description of the optical components Element source
Geometry
Description bending magnet DIP 03.1A
Distance
Deviation angle
M1
12500
1688 horizontal
F1
12500
M2
1000
ES
100
G
3000-t
AS
3000-t
M3
1500
Exp.
1500
Toroid, 1000 mm 60 mm, water-cooled Si-blank, R¼ 124 625 mm, r¼ 1306:6 mm, sR ¼ 0:500 , sr ¼ 500 Intermediate vertical focus
175.58 vertical
Plane ellipse, 130 mm 20 mm, quartz-blank, uncoated, a¼ 550 mm; b¼ 12:415 mm, x0 ¼ 450:118 mm, sm ¼ 200 , ss ¼ 1000 0–1000 mm continuous
4.58 vertical
Glass-blank, 1150 mm, R¼ 3000 mm, sR 50:400 G1 : 2400 l/mm, lopt ¼ 80 nm, Pt-coated G2 : 600 l/mm, lblaze ¼ 150 nm, Al/MgF2-coated 0–2000 mm continuous
1558 horizontal
Toroid, 100 mm 80 mm, ULE-blank, Ni-coated, R¼ 6825 mm, r¼ 324:7 mm, sR ¼ 200 , sr ¼ 2:700 Spot size typ. 50 400 mm2
itself remained unchanged. It contains two in vacuum interchangeable gratings with 2400 l/mm and 600 l/mm. Rotation and translation of the grating are performed according to the operation principle of an off-Rowland-circle normal incidence monochromator [3] in-vacuum by linear feedthroughs and stepping motors. Due to imperfections of the mechanics and slope errors of the gratings a resolving power of 20.000 at max is expected.
2.3. Post-monochromator optics
Fig. 2. Mirror positioning mechanism for pre-monochromator mirror M2 and entrance slit. The positioning mechanism is based on the patented cartesian 6-strut design. The entrance slit is only 100 mm away from the center of M2.
Vertically a 1 : 1 image of the exit slit is focussed in the experiment by means of a horizontally deflecting toroidal refocusing mirror. Due to the sagittal focusing properties of the spherical grating the horizontal focus size is slightly wavelength dependent. The radius of the toroid M3 was chosen to produce the best spot for a photon energy of 15 eV in combination with the 2400 l/mm grating. The mirror chamber for the M3 is also
G. Reichardt et al. / Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 458–461
461
constructed on the basis of the cartesian 6-strut scheme [2].
3. Performance data
The spot size at the experiment is slightly energy dependent for photon energies below 15 eV (see lower part of Fig. 3). Above 15 eV the horizontal spot size is 400 mm, vertically a 1 : 1 image of the exit slit is obtained. Fig. 3 shows the calculated resolving power and flux values for the 2400 l/mm grating and 50 mm entrance and exit slits. For these monochromator settings typical values for resolving power E=DE and flux F of 10.000 and 1011 photons/s 100 mA 0.1% BW, respectively, are expected. As characteristic for spherical grating monochromators the resolving power decreases with 1=E. Due to the use of two p-reflections the degree of linear polarization is not as high as with the old BESSY I set-up. Nevertheless, by means of remote-controlled water-cooled aperture blades in front of the first mirror and by sacrificing 50% of the flux it is possible to increase the degree of linear polarization to over 80%. In addition circular polarization of some 80% is feasible by simply setting the aperture blades for the selection of off-plane radiation.
Fig. 3. Performance data as calculated for the 2400 l/mm grating and 50 mm slit sizes. The slope error for the grating was set to 0.3 arcsec rms.
increased brilliance of the BESSY II source by an improved resolving power and flux density at the experiment.
4. Conclusion
References
Two old and field-tested 3 m-normal incidence monochromators, which were almost 15 years in operation at BESSY I will be equipped with new pre- and post-monochromator optics for the installation at BESSY II bending magnets. Although due to lower horizontal acceptance the total flux at BESSY II will be less than at BESSY I, these monochromators will benefit from the
[1] G. Reichardt, VUV-fluoreszenspektroskopische Untersuchung quasi-gebundener Rotationsniveaus im Elektronengrundzustand des Wasserstoffmolek.uls nach rotationsselektiver Anregung mit Synchrotronstrahlung, Shaker, 1994. [2] T. Noll et al., Six-Strut Arrangement for cartesian Movements of Mirrors, Nucl. Instr. and Meth. A 467–468 (2001), these proceedings. [3] J. Samson, Techniques of Vacuum Ultra Violet Spectroscopy, Wiley, New York, 1967.