<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Hi Michael,<div class=""><br class=""></div><div class="">Here at Berkeley we are looking at the idea similar to the BPM pickup. This could be done with a quadrupole cavity or in theory with a non-resonant pickup (e.g. striplines, pixels). The problem in the latter case is signal-noise ratio but if we are still evaluating if it is doable with the existing hardware. There is a company in San Diego that makes quadrupole cavities β itβs a spinoff from an R&D done at SLAC. The caveat is that a single cavity does not measure the beam size (ie. <x^2+y^2>) β you measure quadrupole modes, which are <x^2-y^2> and <xy>. But this may be good enough for a constraint on the beam size asymmetries, especially since <x^2> would dominate due to synchrotron emission in the bends. SLAC guys did publish a paper that claims that one could measure the full emittance of the beam with 6 quadrupole cavities positioned at different betatron phases. </div><div class=""><br class=""></div><div class="">The other option that could potentially work is to have a sufficiently pixelated synchrotron light monitor, and de-correlate variations in energy from it. Silicon pixel sensors would get fried quickly, but one could consider diamond sensor technology that is just being developed for high-luminosity colliders. </div><div class=""><br class=""></div><div class="">Yury<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Apr 30, 2019, at 1:16 PM, Michael Tiefenback <<a href="mailto:tiefen@jlab.org" class="">tiefen@jlab.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div id="divtagdefaultwrapper" dir="ltr" style="caret-color: rgb(0, 0, 0); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class=""><div style="margin-top: 0px; margin-bottom: 0px;" class="">Valeri Lebedev was considering using such an imaging device here many years ago, adapted from proton ring practice. The reason he dropped the idea was the strong ionization of background gas by VUV Synchrotron Radiation. He concluded that the background would be unworkably large. This may or may not be so, depending upon how close the device is to the final dipole, and how much or little S.R. is generated in the focusing fields of quadrupoles.</div><div style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></div><div style="margin-top: 0px; margin-bottom: 0px;" class=""><span class="">In that ionization detector imaging, I think that a transverse magnetic field was desirable to preserve the spatial structure, the electrons being low-energy and "tied" to the field lines. In such a way, it was possible to keep the phosphor somewhat distant from the beam while preserving optical fidelity.</span><br class=""></div><div style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></div><div style="margin-top: 0px; margin-bottom: 0px;" class="">Alternate 1) Optical Transition Radiation is quite prompt. One might be able to use this on an occasionally inserted target, although not for the continuous monitoring supported by the ionization detector.</div><div style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></div><div style="margin-top: 0px; margin-bottom: 0px;" class="">Alternate 2) Another alternative might be placement of a wire array (say, eight BPM-ish pickups) on a 1 cm radius circle and routing the signals out on coax into one of the nonlinear-processing devices to obtain estimates of beam size. We've toyed with such an idea, but the size of the BPMs we have is large. I expected the aspect ratio to suppress the achievable resolution. But if such an array could be placed close to the beam, possibly as an adjunct to a "halo target," it might work out well.<br class=""></div><div class=""><br class=""></div><div class="">This seems to me to be a potentially workable path. I included the whole "moller" group in reply, as Jay included them in his suggestion.</div><div class=""><br class=""></div><div class="">Michael Tiefenback<br class=""></div><br class=""><div style="" class=""><hr tabindex="-1" style="display: inline-block; width: 1018.21875px;" class=""><div id="divRplyFwdMsg" dir="ltr" class=""><font face="Calibri, sans-serif" style="font-size: 11pt;" class=""><b class="">From:</b><span class="Apple-converted-space"> </span>Jay Benesch <<a href="mailto:benesch@jlab.org" class="">benesch@jlab.org</a>><br class=""><b class="">Sent:</b><span class="Apple-converted-space"> </span>Tuesday, April 30, 2019 2:30 PM<br class=""><b class="">To:</b><span class="Apple-converted-space"> </span><a href="mailto:moller@jlab.org" class="">moller@jlab.org</a><br class=""><b class="">Cc:</b><span class="Apple-converted-space"> </span>Michael Tiefenback<br class=""><b class="">Subject:</b><span class="Apple-converted-space"> </span>Noninvasive LHC transverse beam size measurement using inelastic beam-gas interactions</font><div class=""> </div></div><div class="BodyFragment"><font size="2" class=""><span style="font-size: 11pt;" class=""><div class="PlainText"><a href="https://gcc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fjournals.aps.org%2Fprab%2Fabstract%2F10.1103%2FPhysRevAccelBeams.22.042801&data=02%7C01%7Cmoller%40jlab.org%7C11b60a14f8be481df1c008d6cdc33a38%7Cb4d7ee1f4fb34f0690372b5b522042ab%7C1%7C0%7C636922635710545858&sdata=ASFDvThUfuJo%2FvNTADfcMxunhY7suk%2F7ToygfJ8aqQc%3D&reserved=0" originalSrc="https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.22.042801" shash="WusPbUGLDyknJfA/J6vmnG/etoVuiqHnbLozMBgTGfv+OSENa5HFyWFGD9aDuxybOFEAn/dMVwk4dKshXIwdCzlkmKG7aE/VRfHO+KLRycLIKmqsfdol62UeU77cgQiNEa0O6+6R6KY4/tsadj728hbxpynB6PASC29fVmPe4So=" originalsrc="https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.22.042801" shash="SyhxC93mvfsmyjGtZMFhgp4fQTYGihl/wD2LnwtYGl0psY78OXlN9uMeIV9OHKXKFyL7zADGUl7HN/MKfEouLJLWbEmhoLnt3bvmC35KhuiodmZRdUsmVHm1bwWnsEMca9RFQUHxLXl4cjsbeMPHaMCWjlF2ospcnjFSS/7ZtEc=" id="LPlnk533276" class="OWAAutoLink" previewremoved="true">https://gcc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fjournals.aps.org%2Fprab%2Fabstract%2F10.1103%2FPhysRevAccelBeams.22.042801&data=02%7C01%7Ctiefen%40jlab.org%7C0a8294e5122a4d6c5f7108d6cd99fef4%7Cb4d7ee1f4fb34f0690372b5b522042ab%7C1%7C0%7C636922458627310032&sdata=Q0rqTs0MSVeIOD%2BFYt2xj8kXrFKsdpPMn3o8dWWt580%3D&reserved=0</a><br class=""><br class="">Noninvasive LHC transverse beam size measurement using inelastic<span class="Apple-converted-space"> </span><br class="">beam-gas interactions<br class="">A. Alexopoulos et al. (The BGV Collaboration)<br class="">Phys. Rev. Accel. Beams 22, 042801 β Published 11 April 2019<br class=""><br class="">The beam-gas vertex (BGV) detector is an innovative instrument measuring<span class="Apple-converted-space"> </span><br class="">noninvasively the transverse beam size in the Large Hadron Collider<span class="Apple-converted-space"> </span><br class="">(LHC) using reconstructed tracks from beam-gas interactions. The BGV<span class="Apple-converted-space"> </span><br class="">detector was installed in 2016 as part of the R&D for the<span class="Apple-converted-space"> </span><br class="">High-Luminosity LHC project. It allows beam size measurements throughout<span class="Apple-converted-space"> </span><br class="">the LHC acceleration cycle with high-intensity physics beams. A<span class="Apple-converted-space"> </span><br class="">precision better than 2% with an integration time of less than 30 s is<span class="Apple-converted-space"> </span><br class="">obtained on the average beam size measured, while the transverse size of<span class="Apple-converted-space"> </span><br class="">individual proton bunches is measured with a resolution of 5% within 5<span class="Apple-converted-space"> </span><br class="">min. Particles emerging from beam-gas interactions in a specially<span class="Apple-converted-space"> </span><br class="">developed gas volume along the beam direction are recorded by two<span class="Apple-converted-space"> </span><br class="">tracking stations made of scintillating fibers. A scintillator trigger<span class="Apple-converted-space"> </span><br class="">system selects, on-line, events with tracks originating from the<span class="Apple-converted-space"> </span><br class="">interaction region. All the detector elements are located outside the<span class="Apple-converted-space"> </span><br class="">beam vacuum pipe to simplify the design and minimize interference with<span class="Apple-converted-space"> </span><br class="">the accelerated particle beam. The beam size measurement results<span class="Apple-converted-space"> </span><br class="">presented here are based on the correlation between tracks originating<span class="Apple-converted-space"> </span><br class="">from the same beam-gas interaction vertex.<br class=""><br class="">------------------<br class="">Seems like it should be easy (i.e. several dissertations) to extend this<span class="Apple-converted-space"> </span><br class="">to measuring electrons at 11 GeV, 249 MHz, helicity correlated, to 10ppm<span class="Apple-converted-space"> </span><br class="">desired by MOLLER. Nice reference list.<br class=""></div></span></font></div></div></div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Moller mailing list</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="mailto:Moller@jlab.org" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">Moller@jlab.org</a><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="https://mailman.jlab.org/mailman/listinfo/moller" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://mailman.jlab.org/mailman/listinfo/moller</a></div></blockquote></div><br class=""></div></body></html>