CiPo - Specifications

Insertion Device - Electromagnetic Elliptical Wiggler

Spherical Grating Monochromator (SGM)

The beamline SGM monochromator covers the energy range 40 - 1000 eV, working in Padmore-type configuration and is equipped with a variable angle plane mirror and four different spherical gratings (G1 to G4), that cover the following energy ranges:

• G1 grating (1050 l/mm) from 440 to 1000 eV

• G2 grating (1050 l/mm) from 300 to 700 eV

• G3 grating (1050 l/mm) from 120 to 400 eV

• G4 grating (550 l/mm) from 40 to 140 eV

Grating #	Energy (eV)	Res. Power
G1	850	3400
G2	400	7600
G3	240	4400
G4	65	8100

Normal Incidence Monochromator (NIM)

The beamline NIM monochromator equipped with two different holographic gratings, covers the 5 - 35 eV energy range by means of two different gratings, as follows:

• Gold coated grating (2400 l/mm) from 10 to 35 eV

• Aluminum coated grating (1200 l/mm) from 5 to 15 eV

Circular Polarization

Measurements of the polarization were made using a multilayer polarimeter at several photon energies between 92 and 573 eV. The measured linear and circular polarization rates as a function of the horizontal deflection parameter (i.e. EEW horizontal current I_h) for wiggler mode are shown in the figures. At 92.5 eV a comparison  between undulator and wiggler mode of operation is reported. In the undulator case a maximum circular polarization rate close to unit can be obtained with equal vertical and horizontal deflection parameters (K_x=K_y), whereas in the wiggler case smaller values of the circular polarization rate are obtained due to the ratio K_x/K_y always less than unit. In both cases reversing the horizontal magnetic field direction results in a change of the helicity of the radiation as expected. The photon energy range below 40 eV is available with the characteristic discrete line spectrum emitted by an undulator.
The degree of circular polarization changes with photon energy in the range from 40% at 8.5 eV to 80% at 575 eV. Full circular polarization condition (90%) is achieved when the EEW works as a pure circular undulator, i.e. when the horizontal and vertical magnetic fields are equal. Under these conditions the available first harmonic lies in the photon energy range between 50 eV and 150 eV.

Switching Mode

Because of the specificity of the CiPo Beamline to measure the dichroic behavior of materials, it was very important to provide a mode of operation that allows to minimize uncertainty introduced in the dichroic spectra by the random errors of monochromator repositioning. This is especially required at the edges of absorption of materials, where rapid change in the signal intensity may introduce false dichroic signal when scanning sequential absorption spectra alternating the right- and left–hand status of polarization of the photon beam. Handness switching of circular polarization is often important in the case of  XMCD measurements in magnetic materials where the reversing of the magnetic field in not always reproducible, but it is crucial in the case of PECD in which the effect is very small.
The EEW could produce alternatively a right- and left-handed circularly polarized radiation at a frequency of 0.1 or 0.05 Hz operating in wiggler or ondulatror mode. A square waveform is generated to drive the horizontal current power supply allowing to switch between +260 A and -260 A, producing the change of the polarization handness. After a switching time, a definite polarization state remain in the plateau of the square wave, during this steady state period the measurement occur before changing to the new handness and starting a new set of measurements. The sequence may be repeated for several times until the desired signal to noise ratio is reached. The timing of the measured signals to the polarization state is controlled by a suitable reference status voltage level from the EEW power supply. The measured signal from the sample is normalized to the incident photon flux detected through the photocurrent emitted by the last mirror gold surface or by a photodiode.

End-Stations

The CiPo beamline guarantees to the users the possibility to perform several kind of experiments using four different type of end-stations. The users can also install their own end-stations after discussion and in agreement with beamline staff.

XMCD End-Station

The XMCD End-Station allows for absorption experiments under two different range of magnetic field, and presents the following specifications:

• Low Magnetic Field: up to 0.4 T by means of an electro-magnet

• High Magnetic Field: up to 4.0 T by means of a super-conducting magnet

• Helium cooled 5-degrees manipulator: down to 4°K from room temperature

The XMCD End-Station is also equipped with a preparation chamber for in-situ sample treatment, where the following instruments are available:

• LEED

• Sputtering Ion Gun

• Heatable 4-degrees manipulator for annealing and sample preparation (up to 600°C)

• Evaporators

• Quartz thickness monitor balance

 

UPS and XPS End-Station

The UPS and XPS End-Station allows for solid-state and surface photoemission experiments and presents the following specifications:

• Omicron 125: emispherical electron kinetic energy analyzer with 5 channeltrons

• UHV surface photoemission set-up

• Helium cooled 5-degrees manipulator: down to 100°K from room temperature

The UPS and XPS End-Station is also equipped with a preparation chamber for in-situ sample treatment, where the following instruments are available:

• LEED

• Sputtering Ion Gun

• Heatable 4-degrees manipulator for annealing and sample preparation (up to 600°C)

• Evaporators

• Quartz thickness monitor balance

PECD End-Station

The PECD End-Station allows for photoelectron circular dichroism experiments on chiral systems in the gas phase, and presents the following specifications:

• VSW 30: emispherical electron kinetic energy analyzer set at the magic angle (54.7°)

• Heatable needle for the inlet of the sample vapour pressure (up to 100°C)

• Differential pumping

OctoMass End-Station

The OctoMass End-Station allows for photoionization and photofragmentation mass-resolved experiments on molecular systems in the gas phase, and presents the following specifications:

• RF Octupolar Ion Trap: collect and guide the ions and fragments generated

• Extrel MAX4000: Quadrupolar Mass filter with 10 - 4000 m/z range

• Differential pumping