Sensors and Detectors — DU B.Sc. (Hons) Physics Previous Year Question Papers

Semester VIII-Semester (DSH paper) (a) Discuss th.e role of a plasma in thermonuclear fusion. (b) What is the electron plasma frequency? How does it differ fi.om the ion-plasma fie quency? . (c) What is solar plasma? State two phenomena associated with it -solar wind and coronal heating, and their relevance to space plasma physics. (d) A deuteron (md = 3.34xl0-27 kg) moves in a unifomi magnetic field 8 = 1.2 T with velocity, Vi = 4xl06 in/s pexpendicular to the field. Calculate its Lamor radius and cyclotron fie quency. (e) Is plasma a diamagnetic or paramagnetic medium? Justify your answer. ® A plasma slab has electron density, ne = 9X10]6 in-3. An electromagnetic wave of frequency f = 3 GHz is incident on it. Determine whether the wave propagates or is reflected. (g) Explain the operating principle of an ion thruster in rocket propulsion, and state one advantage it has over chemical rockets in terms of specific impulse. Q2)(a) State Saha's equation for the degree of ionization of a gas in themiodynamic equilibriuln. Identify each term. Using the equation, explain why a higher temperature leads to a greater degree of ionization at a constant density. (8) (b) A plasma has electron temperature, Te = 2 ev and electron density, ne = 5x 1017 in-3. (i) Calculate the Debye length (^D), (ii) Verify quasi-neutrality by checking that the plasma dimension L = 0.3 meter satisfies L >> ^D, and (iii) Calculate the plasma frequency (cope) (10) Q3) (a) Derive the expression for curvature drift of a charged particle moving along curved magnetic field lines. Show that in a eylindrical geometry, the curvature drift and grad- 8 drift act in the same direction. Explain the consequence of this combined drift for plasma confinement. (10) a) An electron is trapped in a magnetic mirror device with Bo = 0.15 T at the midplane and Bin = 1.8 T at the mirror throat. This electron has a total kinetic energy of 8 kev and a pitch angle, ou = 30° at the midplane. (i) Calculate the mirror ratio QM) (ii) Find the lossreone angle. (8) Q4) (a) If the electric field is 10 volt/in and the magnetic field is 1 Tesla what is the drift velocity of the guiding center? (6) a) Using physical arguments and schematic diagrams only, show that the electron plasma oscillations will not propagate in an infinite cold plasma. Explain the role of ious in these o s cil latious. (6) (c) Write a set of fluid equntious ofplasmas and their significance for electrostatic wave propagation in an urmagnetized plasma. (6) Q5) (a) Describe the motion of a charged particle in a uniform magnetic field. Show that the particle undergoes helical motion and derive expressions for (i) the gyroradius (rL) and (ii) the gyrofrequency (coc). Extend this analysis, if an electric field is applied transverse to the magnetic field. (10) a) What is plasma processing of materials? How does plasma processing differ from conventional chemical processes.? (4)