source: PSPA/madxPSPA/doc/usrguide/Introduction/bv_flag.html @ 430

Last change on this file since 430 was 430, checked in by touze, 11 years ago

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1<head>
2<TITLE>BV flag in the Beam command</TITLE>
3<!-- Changed by: Thys Risselada 29-Mar-2009 -->
4</head>
5<!BODY BGCOLOR="#eeeeee">
6<HR>
7
8<center>
9EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
10<IMG SRC="http://cern.ch/madx/icons/mx7_25.gif" align=right>
11<H2>Effect of the bv flag in MAD-X</H2>
12</center>
13<p>
14<h4></b>
15When reversing the direction ("V") of a particle in a magnetic field ("B")
16while keeping its charge constant, the resulting force V * B changes sign.
17This is equivalent to flipping the field, but not the direction.
18<p>
19For practical reasons the properties of all elements of the LHC are defined in the MADX input as if
20they apply to a clockwise proton beam ("LHC beam 1"). This allows a single definition for elements
21traversed by both beams. Their effects on a beam with identical particle charge but running in the
22opposite direction ("LHC beam 2") must then be reversed inside the program.
23<p>
24In MADX this may be taken into account by setting the value of the <b>BV</b> attribute in the
25<b>Beam</b> commands. In the case of LHC beam 1 <b>(clockwise)</b> and beam 2 <b>(counter-clockwise)</b>,
26treated in MADX both as clockwise proton beams, the Beam commands must look as follows:
27<b><pre>
28   Beam, sequence=lhcb1, particle=proton, pc=450, bv=+1;
29   Beam, sequence=lhcb2, particle=proton, pc=450, bv=-1;
30</pre></b>
31
32</h4>
33
34<p><br><br><br>
35<address>
36<a href="http://www.cern.ch/Frank.Schmidt/frs_sign.html">frs</a>, March 29, 2009
37</address>
38</body>
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