Better error messaging with read_beam. (#761)

* Update Tao doc.

* Better error messaging with read_beam.

bmad/code/type_ele.f90

@@ -86,7 +86,7 @@ subroutine type_ele (ele, type_zero_attrib, type_mat6, type_taylor, twiss_out, t
 integer, optional, intent(out) :: n_lines
 integer ia, im, i1, ig, i, j, n, is, ix, iw, ix2_attrib, iv, ic, nl2, l_status, a_type, default_val
 integer nl, nt, n_term, n_att, attrib_type, n_char, iy, particle, ix_pole_max, lb(2), ub(2)
-integer id1, id2, id3, ne, na
+integer id1, id2, id3, ne, na, nn
 
 real(rp) coef, val, L_mis(3), S_mis(3,3) 
 real(rp) a(0:n_pole_maxx), b(0:n_pole_maxx)
@@ -955,8 +955,25 @@ subroutine type_ele (ele, type_zero_attrib, type_mat6, type_taylor, twiss_out, t
  enddo
 
  if (has_it) then
+
+ nn = 10
+ na = 12
+ nt = 12
+
+ do im = 1, ele%n_lord
+ lord => pointer_to_lord (ele, im, ctl)
+ nn = max(nn, len_trim(lord%name)+2)
+ select case (lord%lord_status)
+ case (super_lord$, multipass_lord$, girder_lord$)
+ case default
+ na = max(na, len_trim(ctl%attribute)+2)
+ if (.not. lord%is_on) nt = 18
+ end select
+ enddo
+
+ str1 = ''
  nl=nl+1; li(nl) = 'Controller Lord(s):'
- nl=nl+1; li(nl) = ' Index Name Attribute Lord_Type Expression'
+ nl=nl+1; write (li(nl), '(9a)') ' Index Name', str1(:nn-4), 'Attribute', str1(:na-9), 'Lord_Type', str1(:nt-9), 'Expression'
 
  do im = 1, ele%n_lord
  lord => pointer_to_lord (ele, im, ctl)
@@ -975,13 +992,13 @@ subroutine type_ele (ele, type_zero_attrib, type_mat6, type_taylor, twiss_out, t
  call split_expression_string (knots_to_string(lord%control%x_knot, ctl%y_knot), 70, 5, li2)
  endif
  a_name = ctl%attribute
- if (lord%lord_status == overlay_lord$ .and. .not. lord%is_on) str1 = 'Overlay [IS_ON = F]'
+ if (.not. lord%is_on) str1 = trim(str1) // ' [Is off]'
  end select
 
  if (nl+size(li2)+100 > size(li)) call re_allocate (li, nl+size(li2)+100)
- nl=nl+1; write (li(nl), '(i8, 3x, a32, a18, 2x, a21, a)') lord%ix_ele, lord%name, a_name, str1, trim(li2(1))
+ nl=nl+1; write (li(nl), '(i8, 3x, 4a)') lord%ix_ele, lord%name(:nn), a_name(:na), str1(:nt), trim(li2(1))
  do j = 2, size(li2)
- nl=nl+1; li(nl) = ''; li(nl)(84:) = trim(li2(j))
+ nl=nl+1; li(nl) = ''; li(nl)(17+nn+na+nt:) = trim(li2(j))
  enddo
  enddo
  endif

bmad/doc/charged-tracking.tex

@@ -329,7 +329,7 @@ \section{BeamBeam Tracking}
 end of any tracking so that the longitudinal starting point and ending point are identical. The
 longitudinal $s$--position of the \vn{BeamBeam} element is at the center of the strong bunch. For
 example, with \vn{n_slice} = 2 and with a solenoid field, the calculation would proceed as follows:
-\begin{enumerate}
+\begin{enumerate}[topsep=-0.2ex,itemsep=-0.0ex]
  \item 
 Start with the particle longitudinally at the \vn{beambeam} element (which is considered to have
 zero longitudinal length) in laboratory coordinates (\sref{s:coords.3}).
@@ -367,6 +367,38 @@ \section{BeamBeam Tracking}
  %
 \end{enumerate}
 
+There is an energy kick due to the motion of the strong beam. This is similar to the gravatational
+slingshot in orbital mechanics. The energy kick is simply calculated using conservation of
+4-momentum of the tracked particle and the strong beam where the mass of the strong beam is assumed
+to be large compared to the mass of the tracked particle.\footnote
+ {
+This assumption breaks down if a tracked particle is deflected due to a single scattering event with
+a particle of the strong beam. But particle-particle scattering is outside of the assumption of a
+strong beam that is unaffected by the weak beam.
+ }
+After a little bit of algebra. The energy kick $dE_w$ to lowest order in the angle of the weak
+particle with respect to the axis defined by the of motion of the strong beam is
+\begin{equation}
+ dE_w = \frac{c \, P_w}{2 \, (1/\beta_w + 1/\beta_s)} \, \left( \theta_{w2}^2 - \theta_{w1}^2 \right)
+\end{equation}
+where $P_w$ is the momentum of the weak particle, $\beta_w$ and $\beta_s$ are the weak and strong
+beam velocities, and $\theta_{w1}$ and $\theta_{w2}$ are angles of the weak particle trajectory with
+respect to the strong beam motion before and after the interaction. Converting to phase space
+coordinates, the momentum kick $dp_z$ is
+\begin{equation}
+ dp_z = \frac{1}{2 \, \beta_w \, (1/\beta_w + 1/\beta_s) \, (1 + p_z)} 
+ \left( dp_x \, (dp_x - 2p_{x1}) + dp_y \, (dp_y - 2p_{y1}) \right)
+\end{equation}
+where $dp_x$ and $dp_y$ are the transverse kicks and $p_{x1}$ and $p_{y1}$ are the initial phase
+space momenta.
+
+There is an added term to the energy kick when the strong beam's cross-section is changing due to
+the hourglass effect.
+
+
+
+\newpage
+
 %---------------------------------------------------------------------------------
 %---------------------------------------------------------------------------------
 \section{Bend: Exact Body Tracking with k1 = 0}