subroutine cellimp(wtp,dwtp)
c---apply impulse of duration dwtp (in degrees) due to linac cell.
c---if dwtp is larger than dwtmax, set dwtp = dwtmax.
c----------------------------------------------------------------------
      save
c
      include 'param_sz.h'
      include 'cfldscom.h'
      include 'constcom.h'
      include 'misccom.h'
      include 'outcom.h'
      include 'pcordcom.h'
      include 'tstepcom.h'
      include 'syscom.h'
      include 'ucom.h'
c
      common/back/bmax,byz0,byzs,pzowmin,pzowmax,iback
c--------------------------------------------------------------------------
c*
      data cp/1./
      ne=rne
      if(iback.eq.1) call byfield(dwtp)  
      nc=el(6,ne)
      ph=wtp*radian*cellfreq(nc)/freq
      if(ph.eq.phold)go to 10
      sp=sin(ph)
      cp=cos(ph)
      phold=ph
   10 continue
      dwtmax=el(7,ne)
      if(dwtp.gt.dwtmax)dwtp=dwtmax
      con=dwtp*dcon/erest
      zc=z+hcll(nc)-zloc(ne)
      if (el(8,ne).gt.0.) zc=zc-hcll(nc)
      rsq=x**2+y**2
      if (rsq.gt.0.)then
      r=sqrt(rsq)
      else
      r=0.
      endif
      call cfield(r,zc,nc,ez,er,bt)
      s=sp*el(10,ne)+cp*el(9,ne)
      ezsauv=ez*el(10,ne)
      if(el(8,ne).eq.-2.) ezsauv=-ezsauv
      ez=el(5,ne)*ez*s
      dbgz=ez*con
      if((ip.eq.999).and.(r.eq.0.))
     1write(nimp,*) z,zc,ezsauv,ez*1.e02
      if(rsq.eq.0.)go to 20
c     bt component of rf magnetic field
c     bz beta_z
c     br beta_r
      bz=bgz/gamma
      c=cp*el(10,ne)-sp*el(9,ne)
      fr=el(5,ne)*(er*s-bz*bt*c)
      br=sqrt(bgx**2+bgy**2)/gamma
c      dbgz=dbgz+con*el(5,ne)*br*c   !!!
      dbgz=dbgz+con*el(5,ne)*br*bt*c
      dbgr=fr*con
      dbgx=dbgr*x/r
      dbgy=dbgr*y/r
      bgx=bgx+dbgx
      bgy=bgy+dbgy
   20 continue
      bgz=bgz+dbgz
      gamma=sqrt(1.+bgx**2+bgy**2+bgz**2)
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*