Characteristic Impedance Measurement of Pickup Panel made up with a Suitable Dielectric Material, and Surface Resistivity (Automation) for large RPC electrodes Manoj Kumar Singh Department of Physics Banaras Hindu University Varanasi

1  Introduction to RPC Detector  Charge pick-up strip panel  Measurement of Characteristic Impedance of pick-up panel  Surface Resistivity & its measurement  Future outlook  Summary  AcknowledgementContents

Resistive Plate Chamber (RPC) Detector 2  Gas mixture typically of Argon, Freon (R134a) and Isobutane.  Localized charge produced due to the passage of ionizing radiation through the gas volume, induces charge on appropriate read out strips.  Introduced in 1981 by R. Santonico and R. Cardarelli.  Rugged and low-cost gas detector and extensively used for the detection of charged particles.  Time resolution < 2ns & position resolution few tens of µm.  Electrodes (Glass / Bakelite) surface are coated with conductive paint. Electrodes Pickup strips 2 mm thick spacer Graphite coating on the outer surfaces of glass

3 Two Important part of RPC Pick-up strip panel  Pick-up strip panel Surface resistivity of electrodes  Surface resistivity of electrodes

4 Pick-up Strip Panel Fire proof  Fire proof  Water proof  Flexible  Light weight  Cost effective  Characteristic Impedance match with external circuitry  Locally Available Requirements on dielectric material to be used for making the Pick-up strip panel for the underground laboratories such as INO (India Based Neutrino Observatory) [Polycarbonate] [Ceramic Foam]

7 Making of Pick-up strip panel We have studied several dielectric materials of which we found ONLY TWO are close to our requirements  Ceramic Fiber  Ceramic Foam  Fireproof  Flexible  Light weight  Moisture proof  Thickness 2-3mm  Hard to keep strips and back sheet stick

5 Characteristic Impedance  The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections.  It depend on the geometry and materials of the transmission line and for a uniform transmission line it is independent of its length.  It is purely a function of the capacitance and inductance distributed along the line's length, and would exist even if the dielectric were perfect (infinite parallel resistance) and the wires superconducting (zero series resistance).

6 Signal Reflection  A signal in a cable is the sum of original signal and reflected signal traveling in the opposite direction.  If the reflection of the signal lap with the original, it will cause distortion of the signal.  Reflections occur when signals travel through two cables of different impedances, and occur at the boundary interface of the two cables.  Signal reflection and distortion can be avoided between cables by matching their impedances to each other.  The NIM1 standard requires that all input and output device impedances and cables impedances be 50 ohms.  But there are times when two cables or devices of two different impedances need to be interconnected to each other. When this need arises, the principle of termination is used.  Termination can be done either in series or in parallel or a combination of both. Pulse – Large reflection (incorrect termination impedance) Pulse – Virtually no reflection (close matching of termination impedance)

Characteristic Impedance Measurement 8 Below circuit is used To measure the CI of Pick-up strip

9  Waveform of an open circuit  At 48.5Ω for honeycomb based pick-up panel  At 48.5Ω for Ceramic foam of thickness 4.0cm Characteristic Impedance Measurement  At 48.5Ω for Ceramic Foam of thickness 5.0cm  To remove the reflection completely we have to vary the thickness of Dielectric material.

Automated Surface Resistivity Measurement  The electrical resistance that exists between two parallel electrodes in contact through the surface.  The Ratio of DC voltage drop per unit length of the electrode to current per unit width.  The quality of coating will affects the distribution of HV very seriously.  Automated Scheme is important for the large number of measurements.  We require a suitable automated device to measure its surface resistivity with good accuracy and in less time.

11 Methods to Measure the Surface resistivity Method 1  44 jigs of size ( 30 cm X 30 cm) attached by a plastic sheet.  Individual ohmmeters will be used for each jig.  Readings of all jigs collected simultaneously.  Time taken to record all the measurements would be about 3.47 days. Finally Conducting Foam will replace Cu-bars

12 Method 2  Use two motors, of them one motor will be for the motion along Y-axis and another one will be used along z-axis.  Less number of ohmmeters will be required ~ 6.  Fully automated method by using data interfacing technique.  Calculated time for the resistivity measurement with six jigs (30cm x 30cm) and 60 RPM motor (5 mm shaft diameter) ~3 days. Methods to Measure the Surface resistivity

13 Method 3  Use two motors for the X and Y axis movement on aluminum bars. Third motor for up and down movement of Jig.  Only one conductive foam jig and an ohmmeter requires.  Movement could be controlled through PC using motor controller kit.  This would be fully automated method by using data acquisition system.  Total time taken will be ~20 days  Calibration of RPC can also be done Methods to Measure the Surface resistivity

14 Prototype 50 cm x 50 cm Fabrication  Aluminum bars  Belts  Wheel  Connecting wires  One DC (12V/DC/10RPM) motor and two DC (12V/DC/60RPM)  Switches  Motor Bee Controller Kit  A conductive foam jig of (6x5 cm) size We focused on third method for the prototyping.

15 Data Flow and Motor Control DAQ USB Adopter PC Motor Bee Controller USB Adopter

16 Data View

17 Future works Our next aim is: To operate the movement of jig using motor controller kit with PC Circuit Diagram  Two motors (12 V/DC/60RPM) are attached with one motor bee for movement along x and y axis of the jig.  One motor (12V/DC/10RPM) is attached with second motor bee in same manner for up and down movement of the jig.

18 Summary  Ceramic foam seems to be good dielectric material for the use in making pick-up strip panel.  To measure the quality of coating & value of surface resistivity of electrodes, and calibration of RPC detector at large scale, we can use the suggested method to control the motion of jig along three coordinates with three motors.  This measurement can be precisely completed in a short period of time.

Acknowledgement  Deeply thankful to Shri Ravindra Raghunath Shinde, Prof. B. Satyanarayana, my friends Abhishek Kumar, Shivangi Shree and N. MariMuthu for helping me.  I am also grateful to the DST, New Delhi for providing financial support and INO Collaboration for providing me a challenging atmosphere to do good work for our country.

Thank You!