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{\large {\bf Beam Tests}}\\[2mm]
Trials with $^{24}$Mg at the ANU}}\\[7mm]
\makebox[2.5cm][l]{Author:} P.H. Regan \& D.C. Weisser\\[2mm]
\makebox[2.5cm][l]{Date:} 14 May 1993\\[2mm]
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\begin{center}
{\large\bf $^{24}$Mg Beam Test for CHARISSA}
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\vspace{0.5cm}

\begin{center}
{P.H. Regan and D. Weisser}
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\vspace{0.5cm}

The experiments proposed by the CHARISSA collaboration require the 
14UD to produce relatively large current yields ($\sim$5pnA on target)
of $^{24}$Mg at a beam energy of 170 MeV.
$^{24}$Mg beams are accelerated through the tandem as a hydride with 
with the hydrogen being introduced as NH$_4$ gas in the ion source.
This results is beam species of $^{24}$MH, $^{24}$MH$_2$ and $^{24}$MH$_3$
being created.
In order to test which were the most favourable setting for the various
parameters (eg. single stripping or double stripping, which hydride to use
etc.) four days of beams test (including machine conditioning) were performed 
over the period 19-22 April 1993 using both standard and reflected geometry 
magnesium cones.

The three charge/terminal voltage combinations resulting in 170 MeV beams that  
were investigated are given in the table.

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\begin{center}
\begin{tabular}{|c|c|c|}\hline
Stripping  &  Q$_1$,Q$_2$   & V$_T$ (MV) \\ \hline
Double     &  8$^+$, 11$^+$ & 15.48      \\ 
Double     &  9$^+$, 11$^+$ & 15.01      \\ 
Single     &  10$^+$        & 15.44      \\ \hline 
\end{tabular}
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The initial tests used a reverse geometry $^{24}$Mg cone which yielded
very small currents ($\sim$5 enA) at the low energy cup.
As much as 40 enA was observed after 24 hours operation but no further 
increase was obtained.
The full tests (beam through the machine) were performed using
the standard geometry cone.
The table below shows the currents in enA, of the three species 
(A=25, 26 and 27) at the low energy cup with time. 
The number in brackets is the field setting of the anaylsing magnet 
(in gauss) for that particular species. 

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\begin{tabular}{|c|c|c|c|}\hline
Time         &  $^{24}$Mg+H & $^{24}$Mg+H$_2$ & $^{24}$Mg+H$_3$ \\ 
             &  (3470)      &  (3537)         &  (3607)        \\ \hline
12.35        &  50          &  60             & 14             \\ 
13.45        &  50          &  20             & 35             \\ 
15.15        &  78          &  30             & 38             \\ 
15.35        &  105         &  40             & 80             \\ 
17.05        &  200         &  37             & 240            \\ \hline 
\end{tabular}
\end{center}
\vspace{0.2cm}

The following table shows the parameters for the A=25 and 27 beams
for 8$^+$/11$^+$ at 15.48 MV.
All currents are given in eNa.

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\begin{tabular}{|c|c|c|c|c|c|}\hline
Time  & A   & LE   & Tank  & HE  & Stop  \\ \hline
11.05 & 27  & 150  & 110   & 540 & 40    \\ \hline
11.25 & 25  & 125  & 90    & 500 & 40 \\ 
14.20 & 25  & 135  & 100   & 600 & 50 \\ 
16.05 & 25  & 165  & 120   & 600 & 60 \\ \hline
\end{tabular}
\end{center}
\vspace{0.2cm}

The 9$^+$/11$^+$ charge states at 15.17 MV and the singly stripped 10$^+$ at 
15.44 MV were both found to produce only approximately one third of the 
8$^+$/11$^+$ 170 MeV yield at the stop.
These ratios were found to be in line with the predictions of the code STRIP.
The initial cone hole diameter was measured to be approximately 1mm rising to
1.4mm by the end of the test.

In conclusion, the favored configuration of double stripping (8$^+$/11$^+$) at 
15.48 MV resulted in acceptible currents of $^{24}$Mg ($\geq$5pNa) at the 
stop.
Either the tri-hydride or mon-hydride molecules can be used from the ion source
to give the required current yields assuming a standard geometry cone  used.


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