Rad resistant Coax (RG58 specifically) - Page 1
Forum section: electronics / general

author: slimbobaggins
author_rank: Newbie
timestamp: May 20, 2016, 04:47:50 pm
content: Hey folks,This topic (IMO) didn't seem to gel in any other subforum, so if the mods think it needs to be moved, please do so as you see fit.Anyhow, at my job we use high voltage RG58 to power ion pumps, and they're getting dosed pretty good. We're upgrading all of the multiconductor cables to rad-resistant stuff, but don't yet have a good option for the coax.We may not need to upgrade the coax, as the multiconductor stuff is by far more susceptible to damage, but we're starting to look at what our options might be if we have to go that way. The existing coax we use is custom made stuff by an Italian company, that is already supposed to be somewhat rad tolerant. The specific manufacturer's name I'm not sure.I don't necessarily need to stick to RG58, but the high voltage connectors on our devices are designed for RG-58, so whatever I use has to be adaptable to RG58, and the cable and connectors/ adapters have to be available with a 10 kV rating.Estimated worst case dose at the source was about 10 Mrad over 700 hr of run time. If I assume it's all gamma, and the dosimeter was about an inch from the source, and my cables are about 3ft away, then my crappy math tells me the dose rate is about 10.95 rem/ hr.We've already ordered kapton multiconductor from one manufacturer, but they don't offer RG58. We're going to talk to a few more companies, but I figured I'd post this here, in case anyone has any experience, and already has a solution they use.

author: uncle_bob
author_rank: Unknown
timestamp: May 20, 2016, 04:56:53 pm
content: HiLooks like:http://www.allectra.com/index.php/en/2012-02-19-11-23-10/radiation-resistant-kapton-insulated-wiresMakes stuff that is mighty close. I'd at least contact them and see.Bob

author: slimbobaggins
author_rank: Newbie
timestamp: May 20, 2016, 06:02:04 pm
content: Quote from: uncle_bob on May 20, 2016, 04:56:53 pmWow thanks. I hadn't come across that vendor. You made it too easy.

author: uncle_bob
author_rank: Unknown
timestamp: May 20, 2016, 06:49:35 pm
content: Quote from: slimbobaggins on May 20, 2016, 06:02:04 pmHiWe use them for vacuum stuff. I knew they had radiation as one of the specs, it just never has mattered to us.Bob

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 20, 2016, 10:28:17 pm
content: FYI, there's no such thing as "RG-58 but not". RG-58 specifies the construction, so you can't have something "RG-58-like" that's magically more rad-hard than whatever polyethylene can take. (Which, I'm guessing, ends up stiff and hard after some dosing (think PEX tubing), and brittle and cracked after more? And probably burned and conductive after still more? That's a *lot* of nastiness you've got there...)So if you're searching, probably do something more general, like "50 ohm coax, >70% braid, 7mm o.d., solid copper core". I mean, not actually in quotes, but searching for stuff that meets those parameters.Tim

author: slimbobaggins
author_rank: Newbie
timestamp: May 21, 2016, 01:07:44 am
content: Quote from: T3sl4co1l on May 20, 2016, 10:28:17 pmYou are correct, it's not true RG-58, but I refer to it as such because the vendors from which we have purchased the cable that we use now (Times Microwave, and the Italian company) noted it as RG-58 in the PO, so the moniker has stuck in our "in house" terminology.You're correct, in that the center conductor and jacket harden and brittle and ultimately crack, it's fun stuff.

author: TimFox
author_rank: Super Contributor
timestamp: May 23, 2016, 08:41:02 pm
content: I'm not sure about available rad-hard dielectrics for commercial coax, but be sure to avoid teflon. It is very radiation sensitive, and will turn to charcoal given enough dose. I once saw a linear accelerator x-ray generator where someone had re-wired the non-coax stuff with teflon-insulated wire (which is normally a premium option) and the wire "blackened and turned into coal" (to quote an old song).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 23, 2016, 09:37:11 pm
content: On a narrowly related subject(?), I recall that:At my college, the Physics department had a small accelerator built up. People who don't know about this sort of stuff, will be impressed to hear it was powered by a 15 HP Van de Graaf generator (making up to 500kV at maybe 10mA?). At the time I saw it, they were working with it gun-positive, i.e., getting protons out of it (by ionizing hydrogen or water molecules in the electron-gun section, and accelerating the now-bare protons down the accelerator tube).What brings this to mind is, the detector. At the cathode, they had a Teflon film followed by a gamma ray spectrometer. Sure, you'll get bremmstrahlung (i.e., continuum x-rays) from protons impacting stuff, but what's special about Teflon is, fluorine has a nuclear resonance around 500keV where it can absorb a proton (fusion!), and something something happens, and decay, with characteristic energies and particles that definitely aren't bremsstrahlung.The same probably isn't true of electrons or gammas or other radiation, but this same result might actually be present if you have hydrogen impurities in your vacuum system!Tim

author: slimbobaggins
author_rank: Newbie
timestamp: May 24, 2016, 03:50:25 pm
content: Quote from: TimFox on May 23, 2016, 08:41:02 pmYep we used to use teflon way back, before we went to the current stuff. The teflon cause all sorts of issues.I did check with Allectra, and unfortunately their coax is RG-174 sized, so it's a no-go. I can't get compatible connectors to adapt from that to the connectors on the hardware.In the end we might just end up making jumpers out of current cable, and then change them every 6 months as preventative maintenance.Quote from: T3sl4co1l on May 23, 2016, 09:37:11 pmThat is pretty interesting stuff. I didn't know Van de Graaf generators were used as guns. Truth be told though, I'm not familiar with our gun here, so for all I know, it could be the same.