Magnetic Field Mapping

 

To complete the field mapping of Superconducting Cyclotron on several million data points an automated Magnetic Field Measuring set up has been developed and used.
The precision engineered mechanical system is made of non-magnetic materials and comprises of a centrally supported arm, a carriage to carry the search coil, the mechanism to drive the carriage and the mechanism to turn the arm through precision angles. Critical electronic components e.g. two ‘Smart-Motors’ for servo-drive, the ultra high resolution Linear and the Angular Encoders were fitted into the Magnetic Field Mapping jig.
Several light and miniature Search-coils with 5000 turns of 46 SWG wire are constructed on Plexi-glass bobbin to be the best approximation to a point coil. The coil and a Digital Integrator combination is used to generate digital data proportional to the difference in the absolute field value between two points.
A PC based system is built to control and monitor movements of the field mapping gear and to control the electronic signal processing, data acquisition, calibration and preliminary analysis. More than 98000 data-points are mapped in a ‘SCAN’ lasting 3 hours without any human intervention.
A ‘Magnetic Field Mapping SERVER’ program, controls devices e.g. NMR Gauss-meter, Digital Integrator, Jig motors, collects and sends field data and status information to Console. The controller PC is placed in the Vault near the main magnet and the Console Client PC is placed at the main Control room. The controller PC and the operator’s Console PC are connected by an Ethernet Control LAN. The process of commissioning of the Magnetic Field Mapping system started with telescope-aided alignment of the search coil path and centre of jig with respect to the geometric structure of the magnet. Several total azimuthal ‘SCAN’s were undertaken and field data were generated. The analysis of such relative field distribution data gave insights into the jig centre alignment. Field data taking is continuing at prescribed ALPHA-BETA current combinations in order to investigate the Magnetic Field orientation and its various spatial distributions.

Position monitoring of SCC magnetic channels

The superconducting cyclotron comprises one active and eight passive magnetic channels to support proper beam extraction. The drive system of each channel uses a synchronous motor, which drives a lead mount. An absolute optical encoder, attached with the motor shaft through gears, works as a rotational sensor for the position monitoring. The developed microcontroller based module reads the encoder output, calculates position and then communicates to PC through RS485 multi-drop line.

Operation :

The designed microcontroller module calculates the absolute position, proportional to the encoder reading for multiple rotations of the encoder. The key feature of the instrument is to memorize the position reading before power off. The module monitors the power-good signal and stores the current reading in built-in EEPROM in case of power failure. The instrument has the ability to correct +/- half rotational error during power off. The module locally displays the absolute position in terms of linear displacement (in mm).

Specification :

Resolution                      : 8 bit per rotation (for M1 channel: ~ 6 micron with gear ratio 90/60)
Range                                       : +/- 128 encoder revolutions (for M1 channel: ~ +/- 7.5 inch)
Communication interface           : RS485 multi-drop (all instruments are in SLAVE mode)
Address selectability                 : 16 instruments (0 to 15) by DIP switch
Sensor used                    : 8 bit absolute optical encoder
Local display                            : 16x1 LCD module with backlit
Initial position calibration           : By hardware or software reset.

Scintillator Phase Probe

The development of an integrated miniaturized scintillator phase detector system has been initiated using available ASIC chip and integrated module. Collaborative efforts with Electronics Division and Nuclear Physics Division BARC have been planned for required design guidance and instrument facility to implement an integrated electronics solution for the scintillator phase detector system.

Specification of components:

Plastic Scintillator

• Base-Polyvinyl toluene
• Density-1.032
• H:C-1.1
• RI-1.58
• Rise Time-0.5ns
• Decay Time-1.4ns
• Pulse Width(FWHM)-1.2ns
• Wavelength of maximum emission-391nm
• Maximum count rate-1000pps

Time to Digital Converter (TDC)

• 8 channel with 120 ps resolution
• 60 ps HRM
• Multihit capability
• 40 MHz reference clock(max)
• Low current consumption
• PC interface

Fiber Optics

• Wavelength                    : Ultra Violet to Visible region
• Bundle Transmission       : More than 50% in  350nm –550nm region
• Fiber description             : Preferably Hard Silica Clad and pure undoped silica Core fiber
• Mode and Index              : Multimode graded Index    
• Numerical Aperture         : 0.48(minimum)
• Core Diameter                 : 200±5µm(max)
• Clad Diameter                 : 225±5µm(max)
• Buffer                             : No Buffer
• Configuration                  : Round to Round Bundle
• Active Bundle Diameter   : 1cm       
• Terminations                   : Round Ferrule to Round Ferrule
• Sheathing                        : Stainless Steel monocoil sheath
• Temperature                    : Ambient
• Length                            : 5.0 meters ± 55mm
• Resistant                        : Radiation Resistant