Using Server.MapPath() inside a static field in ASP.NET MVC

I'm building an ASP.NET MVC site where I'm using Lucene.Net for search queries. I asked a question here about how to properly structure Lucene.Net usage in an ASP.NET MVC application and was told that the best method is to declare the my IndexWriter as public static, so that it can be re-used.

Here is some code that is at the top of my SearchController:

public static string IndexLocation = Server.MapPath("~/lucene");
public static Lucene.Net.Analysis.Standard.StandardAnalyzer analyzer = new Lucene.Net.Analysis.Standard.StandardAnalyzer();
public static IndexWriter writer = new IndexWriter(IndexLocation,analyzer);

As writer is static, IndexLocation must also be static. Thus, the compiler is giving me the following error for Server.MapPath():

An object reference is required for the non-static field, method, or property 'System.Web.Mvc.Controller.Server.get'

Is there a way of using Server.MapPath() or something similar from a static field? How can I fix this error?