1 saw   1.1 \documentclass{chowto}
 2           
 3           \title{A Brief Description of the Hall C Beamline}
 4           \howtotype{reference}
 5           \author{Chen Yan}
 6           \category{beamline}
 7           %\maintainer{Chen Yan}
 8           \date{April 15, 2003}
 9           
10           \begin{document}
11           
12           \begin{abstract}
13           
14           Fundamental Hall C beamline optics, configuration and the major functions
15           is described.
16           
17           \end{abstract}
18           
19           \section{Conceptual Beamline Optics}
20           
21           \subsection{Separation Section}
22 saw   1.1 
23           Hall C beamline starts from the Lambertson magnet (match point) after
24           the recombiner section. Usually, one places the original source there.
25           The Lambertson dipole and the following 1 meter BN dipole plus three
26           quads (3C01,02, and 03) between them form the first 3.2 degree separation 
27           from the straight orbit. An achromatic imaging (R16 = R26 = 0) is obtained
28           at the end of this section.
29           
30           \subsection{The First Match SectionSecond Section}
31           
32           The next four quads (3C04, 05, 06, and 07) transport the beam achromatically
33           and give a double waist in front of Hall C 34.3 degree arc.
34           
35           \subsection{Arc Section}
36           
37           The arc section consists of 8 3 meter dipole magnets and 8 qudas. It provides
38           34.3$^{\circ}$ bending angle and an achromatic imaging. Like the general achromat,
39           at the mid-point 3C12, beam has a double waist and large dispersion about
40           4 cm/${\%}$. At the end of the arc, the beam is recombined achromatically
41           at 3C17.
42           
43 saw   1.1 \subsection{The second match section}
44           
45           After Hall C arc, the final three quads (3C18, 19, and 20A)provide adequate 
46           focusing property on either Hall C target or G$_{0}$ target. The beam size 
47           adjustment is done by varying them.
48           
49           \subsection{Chicane}
50           
51           Two Chicane dipole magnets (B$_{E}$ and B$_{Z}$) are located downstream
52           the second match section. The function of chicane is to generate additional
53           bending power in vertical plane to compensate the beam vertical offset caused
54           by 3 tesla Hermholtz coils suround polarized target.
55           \section{Major Function of Hall C Beamline}
56           
57           \subsection{Optics Decoupling}
58           
59           There are three double focusing locations along Hall C beamline. At each
60           double focusing point, the beam forgets its former behavior, therefore,
61           the beam optics tune at each section is decoubled with the previous.
62           Any local disturpancy cannot be transfered to the next section. This 
63           is the major requirement of optics tune in order to provide high
64 saw   1.1 reliability and reproducibility.
65           
66           \subsection{Achromat}
67           
68           During experiments, users want not only to have a well-focused beam on the
69           target, but also to have the beam spot size and the incident angle are
70           independent to beam momentum change, is defined as a term "double 
71           achromatic focusing", i.e. R${16}$ = R${26}$ = 0. This function is executed
72           mainly by Hall C $34.3^{\circ}$ arc achromat.
73           
74           \subsection{Compatible optics for Moeller and beam energy measurement}
75           
76           Some users want to have continuous beam transportation when the Moeller
77           polarimeter is on. The 3 tesla Helmholtz coils give axial field only.
78           It doesn't effect the global beamline optics. The two Moeller quads
79           have certain few percent effect on the downstream optics. With fine
80           adjustment of 3C18, 19, and 20A, the effect can be reduced and a set of 
81           compromising tuning parameters can be found.\\
82           
83           A new energy measurement optics will be verified in 2003 by CASA. The idea
84           is to use the first half of achromat (dispersive section) to determine the 
85 saw   1.1 absolute beam energy and to use the second half achromat recombining beam
86           achromatically. If this is doable, the Hall C beamline transporation optics
87           will be greatly simplified by applying only optics model. The impact of
88           such modification is to make beam energy measurement on-line, no optics
89           alternation is necessary.    
90           
91           \end{document}

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