Return-Path: Received: from dlhc15.jlab.org (ccs16.jlab.org [129.57.35.75]) by ccs17.jlab.org (8.12.11/8.12.11) with ESMTP id jB7Gue9H027136; Wed, 7 Dec 2005 11:56:40 -0500 (EST) Received: from localhost (mack@localhost) by dlhc15.jlab.org (8.12.9/8.12.8) with ESMTP id jB7GueG9011520; Wed, 7 Dec 2005 11:56:40 -0500 Date: Wed, 7 Dec 2005 11:56:39 -0500 (EST) From: Dave Mack To: Mark Jones cc: Dave Mack Subject: Re: BCMs during Gen01 and RSS In-Reply-To: <43970436.8070908@jlab.org> Message-ID: References: <43970436.8070908@jlab.org> MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="964813088-383508212-1133971332=:11434" Content-ID: Content-Length: 5285 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. Send mail to mime@docserver.cac.washington.edu for more info. --964813088-383508212-1133971332=:11434 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Content-ID: Mark, Between the dial setting and changing some resistors with a soldering iron, I set the gains as high as they would go. Accuracy? The short answer is, 5% systematic. Based on the residuals in hclog 41520, I'd say there was also an error in the calibration of about +-0.2 nA point to point. (Perhaps the latter is helpful for determining your fitted pedestal uncertainty. Marco was always concerned about that.) The long story: At these low currents, the Unser monitor is pure noise, so I needed a different technique: * Plan A: It would have been possible to bootstrap an absolute calibration with RF sources if I could have calibrated the BCM's for a brief time with 25 microA of beam. It would have been a headache to get it right, but 1-2% would have been possible. Unfortunately, the Basel SEM prevented us from going to higher currents. So on to Plan B. * Plan B: We used the 5 MeV Faraday cup in the injector. (see attached test plan) Sinclair designed it and it's not very good for precision work. The "cup" is actually an inverted cone made of Copper which isn't ideal for 5 MeV electrons since they have a tendency to bounce off high Z materials. I do check to make sure the operators have centered the beam in the cup; you can change the current a few percent just by moving the beam around a little. I also turn off the other halls and make sure that beam transport appears to be clean. (Obviously, we're screwed if we scrape somewhere.) The new Keithley ammeter that they use to read out the current was probably good to 10**-4 absolute, but the limiting errors are the unmodelled charge collection inefficiency of the Faraday cup assuming the beam is properly centered (+-several percent). I assign a 5% absolute uncertainty and sleep very well at nite. Of course, when Arun Saha uses the same technique he assigns a 0.1% error and probably sleeps just as well! regards, Dave p.s. If we ever need to do better than 5% for the polarized target program, give me 6 months notice and I'll get Arne to build us a re-entrant 5 MeV Faraday cup. Or give me a year's notice and we can make an insertable low power Faraday cup for Hall C. But I definitely need more than the 24 hours notice I got from Joe Mitchell. On Wed, 7 Dec 2005, Mark Jones wrote: > Dave, > For the BCMs during Gen01 and RSS was there some change to > get down to 100 nA range or just a lowering of the gain to 1. What would > say the accuracy of the BCM is at the 100nA level? > > Thanks, > Mark > --964813088-383508212-1133971332=:11434 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII; NAME="gen01_bcmcal.txt" Content-Transfer-Encoding: BASE64 Content-ID: Content-Description: Content-Disposition: ATTACHMENT; FILENAME="gen01_bcmcal.txt" CQ0KDQoJCQkJCQkJMTAvMjgvMjAwMQ0KDQoJCUdlbjAxIEZBUkFEQVkgQ1VQ IEJDTSBDQUxJQlJBVElPTiBQUk9DRURVUkUgDQoJCS0tLS0tLS0tLS0tLS0t LS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0NCg0KdGltZSBlc3RpbWF0 ZTogMSBob3VyDQoNCjEuIFR1cm4gSGFsbCBBIGFuZCBIYWxsIEIgbGFzZXJz IG9mZi4NCg0KMi4gQ2hlY2sgbWFjaGluZSBhcGVyYXR1cmVzIHdpdGggMzAg SHogc3lzdGVtLiBSZWNvcmQgdGhlIHZvbHRhZ2VzIGluIHRoZSBlbG9nLg0K QmFjayBvdXQgdGhlIDMwIEh6IHN5c3RlbS4gDQoNCiAgICBJZiB0aGUgYXBl cmF0dXJlcyBhcmUgdG9vIHRpZ2h0IChpZSwgPCAzIHZvbHRzKSwgdHJ5IHRv IG1ha2UgaXQgYmV0dGVyDQp3aXRoaW4gc29tZSByZWFzb25hYmxlIHRpbWUg bGltaXQuIE90aGVyd2lzZSwgQUJPUlQuIA0KDQogICAgIEluIHRoZSBmb2xs b3dpbmcsIHRoZSBIYWxsIEMgYmVhbSBjdXJyZW50IG11c3QgYmUgc3RhYmxl IHRvIGJldHRlciB0aGFuDQo1JSBmb3IgbWludXRlcyBhdCBhIHRpbWUuIA0K DQozLiBTZXQgdXAgbm9taW5hbCAxMDAgbkEgYmVhbSB0byBIYWxsIEMuDQoN CjQuIFN0ZWVyIGJlYW0gdG8gdGhlIGluamVjdG9yIDUgTWVWIEZhcmFkYXkg Y3VwLiBUcnkgdG8gY2VudGVyIHVwIHRoZSBiZWFtIA0KKGllLCBtYXhpbWl6 ZSB0aGUgcmVzcG9uc2UpIHRvIGEgMSUgZmxhdC10b3AuIA0KDQoJICAgSWYg dGhlIGJlYW0gY3VycmVudCBpc24ndCBzdGFibGUgd2l0aGluIDUlIG92ZXIg NSBtaW51dGVzLCB0cnkNCnRvIGltcHJvdmUgdGhpbmdzLiBPdGhlcndpc2Us IEFCT1JULiANCg0KNS4gU3RyaXAgY2hhcnQgdGhlIEZhcmFkYXkgQ3VwIGFu ZCB0aGUgSGFsbCBDIEJDTTEgYW5kIEJDTTIuIE91ciBwdXJwb3NlIGlzDQp0 byBjYWxpYnJhdGUgQkNNMSBhbmQgQkNNMiBhZ2FpbnN0IHRoZSBGYXJhZGF5 IEN1cC4gDQoNCjYuIENhbGwgSGFsbCBDIGFuZCB0ZWxsIHRoZW0gdG8gc3Rh cnQgYSBydW4gd2l0aCBtb3N0IG9mIHRoZSBkYXRhIHByZXNjYWxlZCANCmF3 YXkuDQoNCjcuIFBlcmZvcm0gdGhlIGZvbGxvd2luZyBvcGVyYXRpb25zLCB1 c2luZyAzMCBzZWNvbmRzIHBlciBpbnRlcnZhbCAoaWYgdGhlcmUncw0KYW4g UkYgdHJpcCB0aGVuIHdhaXQgZm9yIGJlYW0gY3VycmVudCB0byBzdGFiaWxp emUsIHRoZW4gY29udGludWUpOg0KCQkgICAgIA0KCQkJCSAgICBGYXJhZGF5 IEN1cCBTdGF0dXMNCiAgIEJlYW0gQ3VycmVudCAobm9taW5hbCkJSW4JT3V0 CUluCU91dA0KDQogICA1MCBuQQkJCQ0KDQogICA3NSBuQQ0KDQogICAxMDAg bkENCg0KICAgMTI1IG5BDQoNCiAgIDE1MCBuQQ0KDQo4LiBJbXBvcnRhbnQ6 IGVsb2cgdGhlIHN0cmlwIGNoYXJ0IG9mIHRoZSBGYXJhZGF5IGN1cCBjdXJy ZW50Lg0KDQoNCjkuIEJhY2sgb3V0IChpZSwgcmVzdG9yZSBpbmplY3RvciBz dGVlcmluZywgbGFzZXJzLCBhbmQgc2xpdHMgdG8gcHJldmlvdXMgDQp2YWx1 ZXMpDQoNCg0KICAgVGhhbmtzISENCg0KCURhdmUgTWFjaw0KDQoNCg0KDQo= --964813088-383508212-1133971332=:11434--