C# MSChart如何更改系列虚线之间的间距

我有一个带有虚线的系列，由以下内容组成：

tmpChart.Series["function"].BorderDashStyle = ChartDashStyle.Dash;

---

但是我怎样才能改变破折号之间的间距呢

这里有一个小的变通方法来处理alpha部分：

    private void SetChartTransparency(Chart chart, string Seriesname)
    {
        bool setTransparent = true;
        int numberOfPoints = 3;          
        chart.ApplyPaletteColors();
        foreach (DataPoint point in chart.Series[Seriesname].Points)
        {
            if (setTransparent)
                point.Color = Color.FromArgb(0, point.Color);
            else
                point.Color = Color.FromArgb(255, point.Color);
            numberOfPoints = numberOfPoints - 1;
            if (numberOfPoints == 0)
            {
                numberOfPoints = 3;
                setTransparent = !setTransparent;
            }         
        }     
    }