# Notes on ultra-high vacuum technique **URL:** \ **Category:** Materials & methods\ **Created:** [January 6, 2024, 5:21pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180 "2024-01-06T17:21:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [January 6, 2024, 5:21pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/1 "2024-01-06T17:21:10Z")
_this is intended to be a public wiki. Please feel free to edit!_ # ConFlat The mechanics of conflat are discussed in Lutkiewicz and Rathjen 2008 Flanges made from aluminium are also available, using hardened coatings on the knife-edges, which are exclusively usable with aluminum gaskets. This is sometimes used for the greater thermal capacity. Unless there is a seriously compelling reason to, I would suggest avoiding aluminum gaskets. In the case of aluminum . Copper gaskets have a work-hardening property that makes it retain a good seal preload even in the case of temperature fluctuations and baking. In some areas at our facility, equipment (cameras, lights, etc) may be mounted using brackets to the outside of flanges using the flange circle’s bolts or studs. This is convenient as it does not require. However, for the reasons discussed below, great care must be taken when modifying this kind of mount. The distance . groove grabber. Many . Metal-to-metal. leave some gap between the faces so any leaks can be re-sealed. dd gasket stays in the non-rounded punch face. ca The forces involved in bringing some flanges metal-to-metal may exceed the yield strength of stainless steel bolts. See () for more information on this topic. Reluctance to use anti-galling compounds for fear of contamination, seizing stainless fasteners is very common. Copper gasket clips gasket removal tool # Suppliers and manufacturers kimball physics # To add Vacuum hackers warning to samy > Bolts that show signs of deformation should be discarded. Some vacuum workers do not attempt to reuse 1.33" conflat flange screws because a significant number are distorted after one use. [https://www.mtm-inc.com/proper-torque-for-conflat-flange-bolts.html](https://www.mtm-inc.com/proper-torque-for-conflat-flange-bolts.html) Books The Physical Basis of Ultrahigh Vacuum, P.A. Redhead, J.P. Hobson, E.V. Kornelsen, American Vacuum Society Classics, American Institute of Physics, 1993 Foundations of Vacuum Science and Technology, Edited J.M. Lafferty, John Wiley & Sons, 1998 Handbook of Accelerator Physics and Engineering, A. W. Chao, M. Tigner, World Scientific, 1998 CAS CERN Accelerator School : Vacuum Technology, Edited : S. Turner. CERN 99-05, 19 August 1999 Handbuch Vakuumtechnik, M. Wutz et. al, Vieweg, Braunschweig/Wiesbaden, 2000 Journals: VACUUM Journal of Vacuum Science and Technology (A) Nuclear Instruments and Methods (Section A) [https://indico.cern.ch/event/414191/attachments/845420/1176230/a01443s3t3.pdf](https://indico.cern.ch/event/414191/attachments/845420/1176230/a01443s3t3.pdf) [http://www.ece.ualberta.ca/\~schmaus/vacf/index.html](http://www.ece.ualberta.ca/%5C~schmaus/vacf/index.html) Vacuum basics. [http://www.ece.ualberta.ca/\~schmaus/vacf/vacsys.html](http://www.ece.ualberta.ca/%5C~schmaus/vacf/vacsys.html) How to operate a diffusion pump. [http://www.vacuumlab.com/articles.htm](http://www.vacuumlab.com/articles.htm) More advanced vacuum information. [http://shop.store.yahoo.com/vacuumshopper/oils.html](http://shop.store.yahoo.com/vacuumshopper/oils.html) Rotary vane and diffusion pump oils. > Definition Pressure Boundaries > > mbar > > Low Vacuum LV 103 − 1 > Medium Vacuum MV 1 − 10−3 > High Vacuum HV 10−3 − 10−9 > Ultra High Vacuum UHV 10−9 − 10−12 > Extreme Vacuum XHV \< 10−12 > 2.1 Basic notions > 2.1.1 Ideal Gas Law > A rarefied gas which obeys to the ideal gas state equation can be defined as ideal. > Table 2.1 Degrees of vacuum and their pressure boundaries from Lafferty john o’hanlon a user’s guide to vacuum technology high vacuum technology, a practical guide vacuum engineering holkeboer, jones, pagano, and santler Varian vacuum training manual - Basic Vacuum Practice, Varian ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [March 21, 2024, 9:41pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/2 "2024-03-21T21:41:14Z")
> This event is > displayed in Figure 4.16. Shortly after the second sudden increase the QCM failed. > QCM’s are known to fail once too much mass is on the deposition surface. This was > expected to happen eventually. QCM failure is marked by a constant reading (flat > line). The behavior of the QCM before failure is consistent with the film fracturing. > As the film fractures, it delaminates from the surface of the QCM and causes sudden > jumps in the frequency reading (Westley et al. (1998); Pugh (2003)). [https://trace.tennessee.edu/cgi/viewcontent.cgi?article=2364&context=utk\_graddiss](https://trace.tennessee.edu/cgi/viewcontent.cgi?article=2364&context=utk_graddiss) ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [March 27, 2024, 8:43pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/3 "2024-03-27T20:43:52Z")
Establish a bag stickering procedure to ensure that non-vacuum-cleaned parts do not get mixed in with vacuum cleaned parts, like this: ![PXL_20250109_175517637](http://forum.0xdbfb7.com/uploads/default/original/1X/7f4bff9da6acb20d47b1648857eb943cab27d8f2.jpeg) [https://www.hmark.com/product/clean-label/](https://www.hmark.com/product/clean-label/) like surgeon stickers. ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [April 16, 2024, 2:31am UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/4 "2024-04-16T02:31:05Z")
![dfb988c1-d3ea-486b-88c5-2cc01f7de238](http://forum.0xdbfb7.com/uploads/default/original/1X/0fd70d4d2ce2976c30f92f43421f291c12381e13.png) > **[A Survey of Ionization Vacuum Gages and Their Performance Characteristics](https://books.google.ca/books?hl=en&lr=&id=4dY15HrPcpoC&oi=fnd&pg=PA8&dq=%22activated%2Balumina%22%2B%22silicone%2Boil%22%2B%22diffusion%2Bpump%22%2B%22backstreaming%22&ots=Uc3gzHtdwm&sig=RHUhQqI9PZYJuveBRSLPSO6B3Pc#v=onepage&q=%22activated%20alumina%22%20&f=false)** > > The design of various types of ionization gages is outlined, with particular attention to the design elements important to performance.The performance and the many factors affecting the performance of the various \* gages are reviewed.Methods of... ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [April 16, 2024, 2:38am UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/5 "2024-04-16T02:38:36Z")
> At the 1st International Vacuum Congress (IVC) in 1947 Nottingham suggested that the limit to > the lowest measurable pressure was not caused by the pumps, but by an X-ray effect in the IG: he > proposed that soft X-rays, produced by electrons impinging on the anode, released photoelectrons > from the ion collector; this photocurrent was indistinguishable in the measuring circuit from the > current due to positive ions arriving at the ion collector. This hypothesis was soon confirmed by > Bayard and Alpert [3] who reduced the size of the ion collector from a large cylinder surrounding the > other electrodes to a fine wire on the axis of a grid anode. This elegant solution reduced the lowest > measurable pressure by a factor of 100 and is still the most common design in today’s commercial IG: > the Bayard–Alpert gauge or just BA gauge. > > When the X-ray limit was pushed down in this manner, another component to the background > current became evident. Electrons hitting the anode may ionize molecules adsorbed on the surface > with a subsequent release (Fig. 12). Ions generated in this manner cannot easily be distinguished from > those generated in the gas phase. Since a grid structure of a BA gauge has a surface area of about > 10 cm2 > the amount of adsorbed molecules can be rather high (1016). Therefore it is important that the > grid structure be very clean. Two measures are usually taken to cure this problem: the grid is cleaned > by electron bombardment after the gauge had been exposed to high pressures or the atmosphere, and > the electron current to the anode should not be too small during operation so that the gauge is > continuously ‘self-cleaning’. > **[p145.pdf](https://cds.cern.ch/record/1046855/files/p145.pdf)** > > 1326.59 KB ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [October 29, 2024, 7:58pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/6 "2024-10-29T19:58:40Z")
I’ve just come across a paper that’s really tickled me - [https://www.osti.gov/servlets/purl/555564](https://www.osti.gov/servlets/purl/555564) This paper presents a _timeshared rough vacuum system_. I don’t know if it would be practical to implement this anywhere around here, and probably folks around here are already aware that this is possible, but I found it a pretty nifty concept.The key is that modern turbopumps can tolerate a much higher foreline pressure than the base pressure that a good scroll pump can achieve (~10 torr \>\> ~100 mTorr).In this paper, they connect the forelines of **4 sample load-lock chambers and 5 beamline turbopumps to a single scroll pump** via two valves. They also add a “ballast tank” made out of a big chunk of PVC pipe. They add a TCG to the ballast tank with the setpoints configured such that, essentially, the scroll pump only turns on when the pressure rises above 1.5 Torr. The results are that they only actually need to run the pump at total of 4 hours per month. > “The large ballast volume, combined with the low leakage rate of the beamlines and sample chambers and the high foreline pressure tolerance, permitted only occasional pumping of the ballast volume, greatly reducing the operating time of the scroll pump” The advantages are: - No vibration 99.4% of the time. - The scroll pump essentially never needs the otherwise annual tip seal service.Of course, lots of disadvantages; a few obvious ones might be loss of redundancy and separation of systems, contamination from one region could propagate into another. The foreline pressures are allowed to rise, so I’d guess the base pressures in the turbopumped regions would be higher. Also, the vacuum load / leak rate from all the chambers needs to be sufficiently low for this to even be achievable. coworkers raised some important operational concerns; how often are coupled chambers vented if there’s a leak, could be catastrophic across many systems - would want lots of automatic isolation valves in lots of places * * * I’m told this technique is used on some Phillips TEMs. * * * Two such systems in use here at work, both on upstream / mono tanks - big foreline tanks. Say scrolls have lasted decades. * * * ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [December 4, 2024, 4:53pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/7 "2024-12-04T16:53:36Z")
Scroll pumps produce a lot of Teflon tip seal dust. When there is no purge gas and the system is not vented often, this can accumulate in the scroll. This dust can also be found a few tens of centimeters up the foreline. Counterintuitively, there can also be a fair amount of _moisture_ in the centimeters after the foreline. I’ve seen a filter kit (add mcmaster-carr unit #) used to prevent this dust from ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [January 21, 2025, 10:23pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/9 "2025-01-21T22:23:36Z")
put plastic hose type here ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [January 21, 2025, 10:51pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/10 "2025-01-21T22:51:08Z")
I’ve needed to spec out some bog-standard low-conductance valves - something you’d use for roughing or vent line applications. targets were: - direct-acting solenoid (not pneumatic). This excludes a lot of good options that you’ll usually find under the keyword “inline poppet valves” and limits the conductance / port sizes that you can expect. - elastomer seat is fine (don’t need all-metal) - but still with some sensible pedigree for high vacuum (something I’m comfortable sticking on the side of a UHV chamber - basically, not something that looks like it came from Tractor Supply) - as commodity as possible - not necessarily dirt-cheap, but something that I know I can get 10 of without waiting a year lead-time, and where I trust can get replacements for years Maybe I wasn’t looking in the right places, but I really didn’t find all that many options - especially from the big names in vacuum - and I’d be interested to hear what other folks use. But here’s what I came up with: - SMC Automation XSA series (distributor: Motion Canada). 1/4" or 3/8" Swagelok or VCR ports. ~$400 USD. They ship from Japan IIRC. - Pfeiffer Mini-inline valves, DVI 205 or DVI 005 - low 4 digits each. - LDS Vacuum’s low conductance offerings ([NW25 Low Conductance Solenoid High Vacuum Valve \ (LCSV-NW25)](https://www.ldsvacuumshopper.com/nwlowco.html)) - $300. - Agilent’s “Electromagnetic Block Valves” - $500. - Via this RBD Instruments blog post ([AVC solenoid replacement procedure | RBD TechSpot](https://www.rbdinstruments.com/blog/avc-solenoid-replacement-procedure/)): Warden Fluid Dynamics T062\* (distributor: “SunSource”) Honorable mention to Burkert (distributor: Tameson); you can buy some of their valves vacuum-clean, e.g. 151389. ~$500 USD. ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [February 4, 2025, 4:47pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/11 "2025-02-04T16:47:55Z")
[https://emvogil-3.mit.edu/~weiss/LIGO\_beamtube\_baseline/LIGO\_beamtube\_summary\_and\_baseline.pdf](https://emvogil-3.mit.edu/~weiss/LIGO_beamtube_baseline/LIGO_beamtube_summary_and_baseline.pdf) ![Screenshot 2025-02-04 10.47.36 AM](http://forum.0xdbfb7.com/uploads/default/original/1X/7518aff4cba1f9c85361c0a1ec1b9192cf2ad689.png) ![Screenshot 2025-02-04 10.48.09 AM](http://forum.0xdbfb7.com/uploads/default/original/1X/caa61b4a4b6c20eff03237486abbbe89c8682beb.png) ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [February 5, 2025, 8:41pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/12 "2025-02-05T20:41:15Z")
# PEEK vacuum compatibility Haru over at the the Hackers said he had issues with PEEK at UHV, even after baking at 200 C. [https://cr4.globalspec.com/thread/79137/Cleaning-PEEK-to-UHV-Standards](https://cr4.globalspec.com/thread/79137/Cleaning-PEEK-to-UHV-Standards) > Thanks for all the suggestions. I think we’ve pretty much decided on a wash in alcohol, several stages of demin water ultrasonic & a vacuum bake at below the glass temperature for PEEK, around 100°C. > The PEEK parts did not give any problems. > Our systems are working at 10^-9 or 10^-10 Torr & have been in use for over a year with out any problems. As mentioned before, these systems are continuously pumped so any outgassing might not be noticed. ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [February 5, 2025, 8:44pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/13 "2025-02-05T20:44:52Z")
UHV process traveller for LIGO > **[E0900008\_QPDupgrade\_kit.pdf](https://dcc.ligo.org/public/0000/E0900008/001/E0900008_QPDupgrade_kit.pdf)** > > 40.71 KB Wrap & Tag vacuum clean parts per E960022-A E960022-v24 has bagging and labelling description ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [February 6, 2025, 3:16pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/14 "2025-02-06T15:16:57Z")
> **[TRIUMF%20UHV%20Cleaning%20&%20Assembly%20%20Procedure.pdf](https://titan.triumf.ca/intern/documents/TRIUMF%20UHV%20Cleaning%20&%20Assembly%20%20Procedure.pdf)** > > 13.13 KB ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [March 17, 2025, 1:50am UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/15 "2025-03-17T01:50:54Z")
![Screenshot from 2022-08-10 10-09-07](http://forum.0xdbfb7.com/uploads/default/original/1X/ba69f7b295736f772c3ddc07c0e7b579c9389dec.png) ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [March 17, 2025, 2:19am UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/16 "2025-03-17T02:19:41Z")
![Capture6988965](http://forum.0xdbfb7.com/uploads/default/original/1X/6d74801f7433a352faeeabeea556f49efead4afe.png) ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [May 9, 2025, 8:57pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/17 "2025-05-09T20:57:36Z")
When you think of ion gauge filament burnout, I’ve thought about this in the context of chemistry (tungsten oxidation) or poisoning. However, there’s another failure mechanism that can occur even with an inert gas and a chemically unreactive noble-metal filament: thermal shock. ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [July 22, 2025, 3:40pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/18 "2025-07-22T15:40:40Z")
[https://link-springer-com.cyber.usask.ca/chapter/10.1007/978-3-540-74433-7\_2](https://link-springer-com.cyber.usask.ca/chapter/10.1007/978-3-540-74433-7_2) Baker and Staniforth (1968) [1-19] presented an article, “The development of an adsorption foreline trap suitable for quick cycling vacuum systems.” “By using 5–10 mm diameter activated alumina balls in an inline column geometry trap the adsorption of water vapor during pumping was reduced to a minimum. With this material and trap design unlimited repeat pumpdown cycles to less than 100 millitorr were possible on a typical 116 liter volume chamber. The pump-down time in this case was extended from 3.5 minutes without the trap to 6.5 minutes with the trap.” ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [July 22, 2025, 3:42pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/19 "2025-07-22T15:42:10Z")
![dfb988c1-d3ea-486b-88c5-2cc01f7de238](http://forum.0xdbfb7.com/uploads/default/original/1X/ec8d661d8408ab12c30b9966929683508d95f4f5.png) > **[A Survey of Ionization Vacuum Gages and Their Performance Characteristics](https://books.google.ca/books?hl=en&lr=&id=4dY15HrPcpoC&oi=fnd&pg=PA8&dq=%22activate%5B%E2%80%A6%5Dckstreaming%22&ots=Uc3gzHtdwm&sig=RHUhQqI9PZYJuveBRSLPSO6B3Pc)** > > The design of various types of ionization gages is outlined, with particular attention to the design elements important to performance. The performance and the many factors affecting the performance of the various gages are reviewed. Methods of... ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [July 22, 2025, 9:59pm UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/20 "2025-07-22T21:59:11Z")
mcmaster-carr 5077T143 fpm seal ---
**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\ **Post date:** [October 1, 2025, 11:06am UTC](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180/21 "2025-10-01T11:06:48Z")
> In the last years, efforts have > been undertaken to develop a ‘cold’ turbo pump, operating at cryogenic (e.g. 77 K) temperatures > [15]. In this case, the gas density is being increased what should lead to a higher pumping speed at > given pump size. Unfortunately, this development was never successful, mainly for two reasons: > Firstly, the magnetic levitation at this low temperature never worked probably and, secondly, it could > be shown that the thermal-creep effect, that leads to a flow against the pumping direction due to a > thermal gradient, overcompensates the advantage of the low operational temperature [16]. > Novel vacuum pumping concepts for fusion power plants [Next page](http://forum.0xdbfb7.com/t/notes-on-ultra-high-vacuum-technique/180.md?page=2)