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<div class="moz-cite-prefix">For the Harp: it is both; we want high
peak current to get a large signal. Since the readout is sampled
at 60 Hz, there is no need for beam when not reading the Harp.
This will reduce the heat load on the Harp wire (and on the fork
if beam is mis-steered, which is usually the case when trying a
Hap scan). We can run CW on Harp, usually with same limit on
average current as peak current, but it is too risky especially if
there is a chance of hitting the fork.<br>
<br>
For the YAG, it is the average current. When the issue is heat
damage, then it is the average that is relevant. The time response
of the YAG is very fast (~80 ns); the camera has to capture the
light at the right time - not sure how these cameras work (?).
There should be enough light and at the right time for the camera.
We will find out when we run nC bunches on viewers.<br>
<br>
Yours,<br>
Riad.<br>
<br>
<br>
On 06/22/2018 09:50 AM, Fay Hannon wrote:<br>
</div>
<blockquote type="cite"
cite="mid:004101d40a2f$ea0a47f0$be1ed7d0$@jlab.org">
<pre wrap="">Just so I understand is it average or peak current on the diagnostics which
drives the duty factor? Or is it both?
Thanks
Fay
-----Original Message-----
From: Tgun <a class="moz-txt-link-rfc2396E" href="mailto:tgun-bounces@jlab.org"><tgun-bounces@jlab.org></a> On Behalf Of Riad Suleiman
Sent: Friday, June 22, 2018 9:36 AM
To: <a class="moz-txt-link-abbreviated" href="mailto:tgun@jlab.org">tgun@jlab.org</a>
Subject: Re: [Tgun] GTS Photogun Beam Structure
For the micro structure, we started at 374.25 MHz but will change to 499 MHz
later this summer to test a TE011 cavity. The micro structure repetition
rate can vary - but must match any RF components on beamline.
When we switch to the high power laser to generate nC bunches, we will run
at 1-20 Hz with a single micro bunch of about 50 ps. At this time, we have
to resolve any issues related to diagnostics.
Riad.
On 06/22/2018 09:25 AM, Matt Poelker wrote:
</pre>
<blockquote type="cite">
<pre wrap="">But you don't mind that the tgun will pulse at a different rep rate,
right?
On 6/22/2018 9:22 AM, Riad Suleiman wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hello,
These are the GTS beam structures used with the photogun:
1. CW Beam for high current runs: Micro structure of 374.25 MHz, 50 ps.
2. Tune Beam for Harp: Macro structure of 60 Hz, 250 us. The nominal
average beam current during a harp scan is 100 nA. This gives a peak
current during the 250 us of about 0.1*1/(60*0.000250) = 6.7 uA.
3. Viewer Limited Beam for Viewers (YAG): Macro structure of 60 Hz, 4
us. The nominal average beam current on viewer is 2 nA. This gives a
peak current during the 4 us of about 0.002*1/(60*0.000004) = 8.3 uA.
Notes:
1. We use a Beam Sync signal that goes to the laser table to generate
the beam macro structure. This signal also goes to the harp to
trigger the readout. Another copy goes to the camera of the third
viewer. Of the three viewers, only the third one has a camera with an
external trigger. We are planning to run at 10 Hz this summer and
will find out if there is any issues related to running at
frequencies other than 60 Hz.
2. The Harp ADC records only one sample at approximately the middle
point of the 250 us beam pulse. Thus, reducing the width of the Tune
Beam may require other changes to Harp readout.
Yours,
Riad.
</pre>
</blockquote>
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</pre>
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<p><br>
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