Double_t dphi = 15.;
Double_t twist = 10;
Double_t rmin = 0.;
Double_t rmax = 1.;
Double_t rtor = 5.;
Double_t local[3] = {rtor, 0., 0.};
Bool_t composite = kFALSE;

void spiral(Int_t nsegments=100)
{
   TGeoManager *geom = new TGeoManager("test", "spiral made of toruses");
   //--- define some materials
   TGeoMaterial *matVacuum = new TGeoMaterial("Vacuum", 0,0,0);
   TGeoMaterial *matPoly = new TGeoMaterial("Poly",0,0,0);
	
   //--- define some media
   TGeoMedium *Vacuum = new TGeoMedium("Vacuum",1, matVacuum);
   TGeoMedium *Plexi = new TGeoMedium ("Plexiglass",3,matPoly);

   //--- make the top container volume
   TGeoVolume *top = geom->MakeBox("TOP", Vacuum, 250, 250, 250);
   geom->SetTopVolume(top);
   TGeoTorus *tor = new TGeoTorus("tor",rtor,rmin,rmax,0,dphi);// The toroidal part
   TGeoVolume *guide;
   if (composite) {
   // Make a single composite shape
      TGeoUnion *bnode;
      TGeoShape *left, *right;
      TGeoMatrix *lmat, *rmat;
      left = tor;
      right = tor;
      lmat = gGeoIdentity;
      for (Int_t i=0; i<nsegments; i++) {
         rmat = MakeMatrix(i);
         bnode = new TGeoUnion(left, right, lmat, rmat);
         left = new TGeoCompositeShape("spiral", bnode);
      }   
      guide = new TGeoVolume("lguide1",left,Plexi);
      guide->SetLineColor(kRed);
   } else {
   // Make an assembly of segments
      TGeoVolumeAssembly *aguide = new TGeoVolumeAssembly("lguide2");
      guide = aguide;
      TGeoVolume *vtor = new TGeoVolume("tor", tor, Plexi);
      vtor->SetLineColor(kRed);
      aguide->AddNode(vtor, 0);
      for (Int_t i=0; i<nsegments; i++) {
         aguide->AddNode(vtor, i+1, MakeMatrix(i));
      }
   }            
   top->AddNode(guide,1, new TGeoRotation("",0,0,0));
   geom->CloseGeometry();
   top->Draw("ogl");
}   

TGeoMatrix *MakeMatrix(Int_t i)
{
   TGeoRotation rz;
   rz.RotateZ(dphi);
   TGeoRotation *ext = new TGeoRotation();
   TGeoRotation xr;
   Double_t dummy1[3],dummy2[3],trans[3];
   Double_t final[3];
   rz.LocalToMaster(local, final);
   for (Int_t j=0; j<i; j++) {
      ext->RotateY(twist);
      ext->RotateZ(dphi);
      xr = *ext;
      xr.MultiplyBy(&rz);
      // X^j, X*Rz computed
      ext->LocalToMaster(local, dummy1);
      xr.LocalToMaster(local, dummy2);
      for (Int_t k=0; k<3; k++) {
         trans[k] = final[k]  - dummy1[k];
         final[k] = dummy2[k] + trans[k];
      }
   }   
   
   TGeoCombiTrans *matrix = new
            TGeoCombiTrans(Form("tr%d",i),trans[0],trans[1],trans[2], ext);
   matrix->RegisterYourself();
   return matrix;
}