ÿþ<HTML> <HEAD> <TITLE> A Stroll Through the PEP Tunnel </TITLE> </HEAD> <BODY> <A NAME="#top"></A> <center> <h1> A Stroll Through the PEP Tunnel at SLAC<br> September 15, 2006 </h1> </center> <p> Firstoff, it might be a good idea to take a look at the <a href="http://www.slac.stanford.edu/accel/pepii/ring/regions.html">PEP-II regions</a>. I started my stroll in interaction region 2 (IR-2). <p> <center> <img src="peptour/southbabar.jpg"><br> The southern side of BaBar - notice the beam injecting in the center. <p> <img src="peptour/just_in_tunnel.jpg"><br> ... and the view just inside the PEP tunnel. <p> <img src="peptour/pep_region_2.jpg"><br> Southward down the PEP tunnel away from IR-2. <p> </center>The beams of electrons and positrons and electrons are steered around PEP-II by magnets. Unlike charges in electricty no magnetic monopoles exist in nature, the simplest structure is a dipole. Charged particles have their tragectories bent by magnetic fields, so magnetic dipoles, quadrapoles, etc. can be used to steer them. Here are a few early examples: <center> <p> <img src="peptour/dipole1.jpg"><br> A dipole. Notice the beampipe passing through the center. <p> <img src="peptour/quadrapole1.jpg"><br> A quadrapole. <p> <img src="peptour/quadrapole1a.jpg"><br> This one was made in China. <p> <img src="peptour/quadrapole2.jpg"><br> Another quadrapole. <p> <img src="peptour/dipole2.jpg"><br> A bigger dipole. <p> <img src="peptour/pep_region_2_further.jpg"><br> Another view further down the tunnel. <p> <img src="peptour/ler_her.jpg"><br> There are two separate beams which collide in IR-2, a high energy electron one and a low energy positron one. The low energy ring (LER) is at 3.1 GeV whereas the high energy one (HER) is at 9 GeV. The LER is located above the HER in the PEP tunnel as shown in this photograph. <p> <img src="peptour/dipole3.jpg"><br> Being higher in energy, the HER beam needs somewhat larger dipoles like this one to steer it. <p> <img src="peptour/sextapole1.jpg"><br> A sextapole. <P> <p> <img src="peptour/permitted-access.jpg"> <p> </center> As I snuck further into the tunnel, not sure if I was really allowed to be there, I decided my goal (and cover story) would be that I wated to seen an octople magnet since there weren't any right near IR-2. The PEP ring is currently under "permitted access" during the shutdown which means that there oughtn't to be any hazardous radiation, so I wasn't concerned about any danger, just stepping on the annoying safety bureaucracies toes. For example, for the LST installation we have to work under the detector where it is very dusty. It would be nice to wear a simple dust mask in such a situation, however, this requires training and medical lung capacity tests. Not having weeks to set up such things we decided to forgo the masks and deal with black boogers and a little dust in our lungs. Just an example of how the safety bureaucracy makes the place more dangerous. Trying to look official with my camera, none of the techs I encountered questioned my presense though. <i>L'audace, toujour l'audace.</i> <center> <p> <img src="peptour/back_toward_ir2.jpg"><br> A view back toward IR-2. For some reason there is alwayss drippy water in HEP facilities. <p> <img src="peptour/4magnets.jpg"><br> A dipole, sextapole, quadrapole and dipole aligned in tandem to steer the beam. <p> <img src="peptour/monument_survey.jpg"><br> Survey markers were placed periodically in the floor of the PEP tunnel. <p> </center>The PEP tunnel was laced with graffiti:<center> <p> <img src="peptour/graffiti1.jpg"><br> <p> <img src="peptour/graffiti2.jpg"><br> <p> <img src="peptour/graffiti3.jpg"><br> <p> <img src="peptour/ir4-1.jpg"><br> IR-4 is a smaller scale replica of IR-2, but without the detector. Had the government deigned to fund them, several experimental detectors could have taken data on collisions at various points around the ring simultaneously. The LEP ring at CERN operated this way in the 90's and the LHC (built in the old LEP ring) will also run several detectors at once. <p> <img src="peptour/ir4-2.jpg"><br> Note that the HER and LER rings pass in IR-4 at slightly different radii soas to facilite steering them into collision had a detector been built here. Also the concrete curtain wall remains in place to left. <p> <img src="peptour/graffiti4.jpg"><br> Apparently there was some rare zealousness to prevent graffiti in this region. <p> <img src="peptour/rf.jpg"><br> An RF power device for creating the electomagnetic wave the electrons surf on. (The one for the positrons is identical). <p> <img src="peptour/firemaybe1.jpg"><br> Run 5b ended due to a fire which I think was either here <p> <img src="peptour/firemaybe2.jpg"><br> or here (but I'm not really sure). <p> <img src="peptour/exit.jpg"><br> Several places along the tunnel are exits like this one off to the left. <p> <img src="peptour/air_shaft.jpg"> <img src="peptour/exit_shielding.jpg"><br> Shafts allow airflow from the surface, and radiation shielding protects some exits in sensitive areas. <p> <img src="peptour/toward_ir6.jpg"><br> A view down the tunnel into IR-6. <p> <img src="peptour/ir6.jpg"><br> Inside IR-6. <p> <img src="peptour/sextapole2.jpg"><br> Another kind of sextapole, but still no sign of the elusive octopole. <p> <img src="peptour/poster1.jpg"> <img src="peptour/poster2.jpg"> <img src="peptour/poster3.jpg"><br> Posters on the wall in the PEP tunnel. (One day I need to learn not to be such a retard with the flash). <p> <img src="peptour/ir8.jpg"><br> IR-8<br> The concrete wall in the center shields large spare pieces of beampipe which are stored just inside the curtain wall. <p> <img src="peptour/away_ir8.jpg"><br> Still further down the tunnel to go... <p> <img src="peptour/ler_beamdump.jpg"><br> The LER beamdump ... I didn't linger. <p> <img src="peptour/ler_injector.jpg"><br> Looking down from the end of the LINAC toward the LER and HER in the PEP ring. The beampipe in the foreground is the LER injector. Positrons are accelerated down the LINAC and the injected into the LER until it is full. When the LER and HER are full, then the magnets near IR-2 are tuned so that collisions take place inside BaBar. <p> <img src="peptour/region10.jpg"><br> More ring to go until one reaches the HER injector. <p> <img src="peptour/spring.jpg"><br> A spring in the wall. <p> <img src="peptour/her_injector.jpg"><br> The HER injector. <p> <img src="peptour/graffiti5.jpg"><br> I decided to leave my own little bit of graffiti in the tunnel as well. <p> <img src="peptour/octopole.jpg"><br> Almost back to IR-2 I finally encountered one of the elusive octopoles. <p> <img src="peptour/almost_ir2.jpg"><br> IR-2 is up ahead. <p> <img src="peptour/tools.jpg"><br> Tools for surgery on PEP-II. <p> <img src="peptour/sob.jpg"><br> Ah, the welcome sight of the DIRC on the north side of BaBar means I've completed all ? miles of the ring! <p> </center> <p> <!-- links back to an anchor in this document. --> Return to the <A HREF="#top">top</A>,<Br> <a href="accelerators.html">More about accelerators</a>, or<br> Back to my <a href="../index.html">homepage</a>. <HR> <!-- ------------------------------------------------------------- --> <H5>Last " on 15 September 2006 by <a href="mailto: bradley@wogsland.org"> Bradley James Wogsland </a>.</H5> </BODY> </HTML>