Front-end and beamline activity of Indus-2 :

(a) Front-end

A typical bending magnet front-end has many components like (1) beam collimator (2) photon beam position monitor (3) Photon beam absorber (4) fixed mask (5) Safety shutter/beam shutter (6) beryllium window (7) vacuum hardware and (8) Electronics and interlock.

All the above components except beryllium windows & vacuum hardware were designed and fabricated in-house. The water cooling arrangement for all the components has been designed in such a way that there is no water to vacuum joint and hence any accidental leakage of water in vacuum system is avoided. These components have been tested for heat load using high power CO₂ laser. The tests were carried at in air and at laser power of 1.6 kW. The water flow was maintained at ~4 to 5 lpm. Using a thermocouple the temperature was monitored. In the steady state the temperature of the copper block was recorded as 50⁰C which is about 20⁰C above ambient. It may be noted that the tests were carried   at a power level 3 times expected in Indus-2. Photon beam position monitor to measure the average position of the X-ray beam has been developed and tested in Indus-1 and 8 KeV X-rays. It consists of two staggered blades which are water cooled. They are movable in vertical direction so that, if need be, they can be withdrawn from the photon beam path.

Typical components which are developed are shown in figure 2.
 

                                 Figure 2 : Front End Components

To achieve an ultra high vacuum in the entire front-end, baking of the vacuum vessels and tubes is necessary. A 8 channel baking controller system has been designed and fabricated. ECIL make control unit SP4806C is modified to have a remote operation via RS485 link. An auto ranging electrometer is being developed having a current measurement range of 10 pA-1mA. This will be  used in beam  position monitor. The main characteristics of electrometer are : current range 10 A-1mA, four conversion ranges 1nA/10V, 100nA/10V, 10µA/10V and 1`mA/10V.

 

The proposed control scheme for the front-end will be based on VME having 68040/68000 Motorola processor and various VME I/O cards. The scheme is shown in figure 3.. A complete control scheme is divided in to three layers. Layer-1 will be main controlling layer. It will read signals distributed along the front-end and will generate control signals. Here one

 

 

 

 

 

 

 

 

 

 

 

 

 

                                    Figure 3: Control Scheme for the Front End
 

21-slot VME crate (68K CPU) will serve 2/3 front-ends. This crate will be located just outside the shielding wall. It is planned to put one PC for each VME crate having RS232 serial interface. On layer-2, VME crate (68040 CPU) will act as supervisory layer, however one can give command to control any of front-end. It will be connected to layer-1 by profibus. Layer-2 will be connected to layer-3 (PC) by Ethernet. From here status of each front-end can be displayed on network which can be accessed from anywhere with a password. A graphical user interface will be made in Labview.

 

(b) X-ray diffraction beamline

A high- resolution powder diffraction beamline on Indus-2 is being constructed. Detailed designs of the beamline as well as the experimental station have been done. The beamline has been designed primarily for 5T superconducting wavelength shifter (WLS) source. Care has been taken in the design that the beamline could be installed on a bending magnet source without any alteration in the beamline hardware in the first phase , when the WLS source is not available. Depending upon the requirements of the planned experiments, the beamline can be operated in high flux, high-energy resolution, moderate angular resolution (Mode A) or moderate flux, high-energy resolution, moderate angular resolution (Mode C) modes. Also, high angular resolution mode (mode B) can be selected. At 10keV, expected energy resolution (E/DE) is 12,000 in mode A, 17,000 in mode B and 1000 in mode C. The corresponding flux (Photons/sec/100mA) is 3 x 10⁹ in mode A, 3 x 10⁹ in mode B and 4 x 10⁹ in mode C. The beam size is 0.7 x 0.2 mm²  in mode A, 0.7 x 0.8 mm² in mode B and 0.7 x 0.2 mm² in mode C. The beam size is independent of photon energy. It is possible to operate the beamline in so many modes because we have opted for bendable pre and post mirrors.  A double crystal monochromator with 3:1 saggitally focusing second crystal, has been used as the dispersing element. The optical lay out of the beamline has been shown in Figure 4. Performance of the beamline ( in the photon energy range of 5-25keV) in all the above modes of operation for WLS as well as bending magnet sources has been calculated using ray tracing program ‘Ray’. Thermal deformation due to heat load on the optical elements (pre-mirror and the first crystal of the double crystal monochromator) have been taken into account, as calculated using finite element software ‘Ansys’. Figure 5 shows the ray tracing result for 10 keV photons.
 

 

                        Figure 4 : Optical Layout of  X-Ray Diffraction Beamline
 

The experimental station will consist of a six circle diffractometer. Four main circles are in the incident beam while two circles are in the scattered beam, and contains the analyzer crystal. The experimental station sits on a stand with five degrees of freedom for sample adjustments. The 2q resolution of 0.15⁰ mode A), 0.02⁰ (mode B) and 0.15⁰ (mode C) will be achieved in the set up. Scintillation counter as well as area x-ray detectors will be used.
 

                         

Figure 5: Ray Tracing Result for 10 KeV Photons