How to improve performance of Quiescence Search?

Question

Thanks to information provided by a previous answer I added a quiescence search to the end of my negamax search to ensure I am not left with a piece hanging. I think it works however it takes a very long time, how can I change the code to speed it up? Here is my code: (C#)

private float quiescenceSearch(Board board,float alpha, float beta)
{
    qCount++;
    //Evaluation without captures
    float stand_pat = Evaluate(board);
    if (stand_pat >= beta) return beta;
    if (stand_pat > alpha) alpha = stand_pat;
    Move[] legalMoves = board.GetLegalMoves();
    foreach (Move move in legalMoves)
    {
        board.MakeMove(move);
        if (move.IsCapture||board.IsInCheck())
        {
            float eval = -quiescenceSearch(board, -beta, -alpha);
            board.UndoMove(move);
            if (eval >= beta) return eval;
            if (eval < alpha) alpha = eval;
        }
        else    board.UndoMove(move);
    }
    return alpha;
}

Answer 1

One thing you can do if your quiescence search is taking too long (more than 90% of your total search time) is limit the maximum depth of the quiescence search. This can be done the same way you would limit a normal search. Another unrelated tip that doesn't make much of a difference: for your eval function you can return a result in centipawns or millipawns so you can use an int for eval instead.