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molecular physics

(6 points)5. Series 26. Year - S. series


  • Go to this site and download data gathered with a Langmuir probe from the tokamak COMPASS. Draw the volt-ampere characteristic and estimate the value of the floating potential.
  • Given the surface area of the probe ($A=6\;\mathrm{mm}^{2})$ and the composition of the plasma (deuterium), analyze the volt-ampere characteristic and determine the value of electron temperature and density.
  • Write a short ode describing the invention of the Langmuir probe.


(6 points)4. Series 26. Year - S. More tokamaks


  • Using the expression for the frequency of impacts from the last part of this series, derive a formula for the diffusion coefficient of classical diffusion and calculate its value for a typical plasma in a tokamak.
  • Derive a formula for the dependence of the fraction of captured particles on the ratio of the main and small plasma radius $r⁄R_{0}$.


(6 points)3. Series 26. Year - S. tokamak


  • Calculate the specific resistance of hydrogen plasma at temperature 1 keV. Compare your result with the resistance of common conductors.
  • Calculate the current necessary to create a sufficiently strong poloidal magnetic field in a tokamak with a major radius of 0.5 m. The toroidal field is created using a toroidal coil with 20 windings per meter. The current inside this coil is 40 kA. The magnitude of the poloidal field should be approximately 1/10 of the magnitude of the toroidal field.
  • Create a physical model of the field lines of the force field inside the tokamak, take a photo of it, and send it to us.

(6 points)2. Series 26. Year - S. drifting


  • What kind of drifts can we observe in a linear trap? Assume that the axis of the trap is horizontal. Will the drift caused by the gravitational force have a significant effect on the motion of a particle?
  • Derive a formula for the loss cone and draw an original picture illustrating the behavior of a particle in a linear trap.
  • Derive a formula for the drift caused by an electric field that is perpendicular to a magnetic field and that has a constant gradient parallel with the electric field. Discuss the the dependence of the particle trajectories on the magnitude of this gradient.

(6 points)1. Series 26. Year - S. series


  • Find out typical properties of a plasma present is the solar wind, in the center of a tokamak and in a low-pressure discharge and calculate the corresponding value of $λ_{D}$.
  • Derive an expression for the Debye length of plasma that consists of electrons at temperature $T_{e}$ and ions at temperature $T_{i}$. Do not assume that the ions are static.
  • Calculate the electrostatic potential of two infinite parallel conducting planes that are separated by a distance $d$. The potential on these planes is kept $φ=0$ and the space in between these planes is filled with a gas of particles with charge $q$ and concentration $n$.


3. Series 22. Year - 3. save helium

They have a new attraction in „Dolni Dvur“: Helium filled soap bubble, which are just levitating in the air. What is heavier? Helium in bubble or its wall?

Z maďarské přípravy na FO od Dalimila vybral Aleš.

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