A Monte Carlo model solving only in velocity space is proposed to investigate a low recycling scrape-off layer (SOL) plasma. In the model, the effects of Coulomb collisions are accurately described by a non-linear Monte Carlo collision operator; a conductive heat flux into the SOL is effectively modelled via randomly exchanging the source particles and the SOL particles; secondary electrons are included. A steady state SOL plasma, which satisfies the particle and energy balances and the neutrality constraint, is determined in terms of the total particle and heat fluxes across the separatrix, the edge plasma temperature, the secondary electron emission coefficient and the SOL size. The model gives gross features of the SOL, such a~ plasma temperatures and densities, the total sheath potential drop and the sheath energy transmission factor. Simulations neglecting unlike collisions are performed. It is found that the potential drop and the electron energy transmission factor in collisional SOL plasmas are in close agreement with theoretical predictions. The present model primarily provides useful information about collisionless SOL plasmas that is difficult to obtain analytically.

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We propose a quantum nondemolition measurement of the photon-number distribution for a two-mode cavity field. In the scheme two sequences of two-level atoms interact dispersively with the respective cavity modes and resonantly with two classical fields, and then are detected continually. The Geld finally reduces to a two-mode Fock state. The probability of collapsing to a given Fock state is determined by the initial photon-number distribution. The scheme can be easily generalized to a field with N modes.

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