Combine sugar, water and lemon juice in heavy large saucepan. Stir over low heat until sugar dissolves. Increase heat and bring to boil. Add rhubarb. Simmer until rhubarb is tender, about 10 minutes. Transfer mixture to processor and puree until smooth. Stir in corn syrup. Refrigerate mixture until cold, about 1 hour.
Transfer rhubarb mixture to ice cream maker and process according to the manufacturer’s instructions. Freeze. (Can be prepared 3 days ahead. Keep frozen.)