truncated multivariate gaussian distribution with support on an 2-norm (euclidean) ball of parametrized radius

Where can I find information about the analytic expression of a truncated multivariate gaussian probability distribution with support on an 2-norm (euclidean) ball of parametrized radius? What other alternative multivariate distribution exist where the form is parametrized by, among other parameters, the variance (it's supposed that the covariance matrix is spherical,i.i., depends only on one parameter) and the support of this function ( parametrized by the radius of an 2-norm euclidean ball with the center determent by the means vector)

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You may find answers to this question (2d case) useful. –  Sasha Mar 3 '13 at 14:11