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Video showing how a Quadrupole Mass Spectrometer works

Quadrupole Mass Spectrometers are one of the most widely used methods of Residual Gas Analysis used in vacuum technology. There is a very good description of how RGAs work and their anatomies the book, Understanding Modern Vacuum Technology. This animation is helpful to round out one’s understanding of how the gases are ionized and passed through the analyzer.

Gas is ionized, extracted from the ionization chamber and directed down the mass filter to a detector. The QMS consists of four parallel rods arranged in the form of a square. Each opposing rod pair is connected together electrically and a radio frequency (RF) voltage with a DC offset voltage is applied between one pair of rods and the other. Ions travel down the quadrupole between the rods. Only ions of a certain mass-to-charge ratio will reach the detector for a given ratio of voltages:

Schematic of a Quadrupole Mass SpectrometerJPG

Schematic of a Quadrupole Mass Spectrometer from Understanding Modern Vacuum Technology

Other ions have unstable trajectories and will collide with the rods. This permits selection of an ion with a particular M/z or allows the operator to scan for a range of M/z-values by continuously varying the applied voltage.

The Pfeiffer Quadrupole Mass Spectrometer video shows the two common ion detection schemes used, the Faraday cup and the electron multiplier. The Faraday cup is more robust and can operate at higher pressures while the electron multiplier is used for more UHV work as they amplify the ion signal in the device.

Understanding Modern Vacuum Technology, 2nd Ed discusses pressure measurement in detail and covers the history of partial pressure measurement and alternative methods used for residual gas analysis.

 

Normandale Community College offers Foundations of Vacuum Science course online

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I was asked by my friends at Normandale Community College to get the word out about an online vacuum technology class they are launching, Foundations of Vacuum Science. This class is designed to give the learner a background in the physical sciences needed for a solid foundation on which to learn vacuum technology.

Normandale Community College offers accredited vacuum and thin film technology courses and specializes in training the technicians that are in high demand in Minnesota. I featured Normandale in a recent post if you would like to learn more. They have an impressive faculty that is passionate about vacuum technology. I very much recommend their program.

Links to the course documents:

VACT1900_Spr2018_CourseSyllabus

VACT1900_InstructionsToRegisterAtNormandaleCC_RegisterStarID_1802Feb23

Spring2018_VACT1900_01OnlineClass_CoHortRegistrationForm_Rev01

 

Thoughts about the SpaceX Falcon Heavy Test Flight

I was going up to YouTube and found a video taken live during the launch of the SpaceX Falcon Heavy rocket. As a kid growing up in the 60s, we would always watch the rockets launch. We would even take time out of the school day to watch space events on one of the three TV stations that we had access to.

I must admit that I have not seen a live space launch, probably since 28 January, 1986. With launches up to the International Space Station being so routine and the busy work-a-day world, I have lost that boyhood infatuation with space travel.

Today, I find myself looking at the interest in manned space flight to Mars. I am seeing a younger generation leveraging the Baby Booomer generation’s technology and putting their hopes and energy into space travel. We have a great many talented young folks getting involved with space on an engineering level. It is actually fun to see these younger folks get excited about space and that is great because it gives us a drive to become strong in science and technology again.

When I look at a rocket or a space mission, I see a lot of engineering and technology that is supported by vacuum technology. I think of the systems used in the manufacturing and testing of space technology and how the Vacuum Industry has supported space science and exploration.

Launch of the SpaceX Falcon Heavy rocket

Launch of the SpaceX Falcon Heavy rocket

With mild interest, I started watching the video and although it was not live, I found myself getting caught up in the excitement. The SpaceX Falcon Heavy is quite a piece of engineering. It can put 63,800 kg (70 tons) of payload into low Earth orbit.using 27 SpaceX Merlin engines. Only the Saturn V from used in the Apollo program has lifted a heavier payload.

The second unique engineering feet that SpaceX has accomplished is the reuse of rocket boosters. The boosters and the center core return to Earth for refurbishment and reuse. This supports the SpaceX drive to vastly reduce the cost of space travel.

Falcon Heavy at Max Q, the time of the heaviest stress on the rocket.

Falcon Heavy at Max Q, the time of the heaviest stress on the rocket.

This mission was a test flight of the Falcon Heavy. For a test flight, a “mass simulator” is put in the rocket to simulate a real payload. Examples of “real payloads” might be a package of instruments, supplies for the International Space Station or sections of a space station. This mission had something a little more fun. It had a cherry red Tesla Roadster with a mannequin in a SpaceX space suite. Also on board was an archival package, a plaque with the names of the SpaceX employees and some Issac Asimov novels.

Passenger seat view from the Tesla Roadster launched on the Falcon Heavy rocket.

Passenger seat view from the Tesla Roadster launched on the Falcon Heavy rocket.

Once the fairing was opened, the Roadster and Starman were exposed to space. The plan is to put them in orbit “for a billion years”. Yes, this is the actual view from the roadster in space.

Actual view of the Tesla Roadster and Starman dummy headed for their new Mars crossing orbit around the sun.

Actual view of the Tesla Roadster and Starman dummy headed for their new Mars crossing orbit around the sun.

Okay, this is some fun stuff. It certainly tickled my funny bone to see this non-serious mass simulator put into orbit. I think back on my baby boomer generation and wonder why they just couldn’t kick back an exhibit a little insouciance*.  But back then, space travel was real serious. After all, the Reds were watching.

MVac-D SpaceX Merlin engine pushing the Falcon Heavy payload into orbit.

MVac-D SpaceX Merlin engine pushing the Falcon Heavy payload into orbit.

 

 

*Insouciant
noun
1.
lack of care or concern; indifference.

The Webb Space Telescope Finishes Cryogenic Testing

Vacuum chambers come in many shapes and sizes, from small, hermitically sealed microelectronics to huge space systems test chambers to the 4km long LIGO chambers. On December 1st, the James Webb Space Telescope emerged from the large Chamber A test facility at Johnson Space Center, which is a great piece of vacuum technology.

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NASA’s James Webb Space Telescope sits inside Chamber A at NASA’s Johnson Space Center in Houston after having completed its cryogenic testing on Nov. 18, 2017. This marked the telescope’s final cryogenic testing, and it ensured the observatory is ready for the frigid, airless environment of space. Credits: NASA/Chris Gunn

The James Webb Space Telescope will be a large infrared telescope with a 6.5m primary mirror. The scheduled launch date is in the spring of 2019. It will be lifted on an Arian 5 rocket from French Guiana.

Before a space instrument is put into service, it must be rigorously tested in a space simulation chamber. NASA’s Johnson Space Center’s Chamber A was prepared. The vault-like, 40-foot diameter, 40-ton door was sealed shut on July 10, 2017, beginning the scheduled 100 days of cryogenic testing for NASA’s James Webb Space Telescope in Houston.

There are two important reasons that Webb needs to be tested in a space simulation chamber. First is that the telescope will be operating in a far orbit at cryogenic temperatures. Webb was designed so that the instrument will come to thermal and mechanical stability to known dimensions in the cold of deep space. Secondly, the infrared equipment must be tested in a cryogenic chamber because objects at room temperature emit infrared energy that would swamp the instruments, so putting the space telescope in a cryogenic chamber all but eliminates background infrared energy.

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Engineers watch as Chamber A’s colossal door closes at NASA’s Johnson Space Center in Houston.
Credits: NASA/Chris Gunn

The chamber evacuation sequence started on July 20, 2017. Engineers began to bring the chamber, the telescope and its science instruments down to cryogenic temperatures a process that took about 30 days. The cold gaseous helium shroud inside Chamber A is the innermost of two shrouds used to cool the Webb telescope down to the temperatures at which it will operate while in orbit. This shroud sits inside an outer liquid nitrogen shroud.  During cool down, Webb and its instruments transferred their heat to surrounding cold gaseous helium and liquid nitrogen shrouds. Liquid nitrogen reaches 77 Kelvin (minus 321 degrees Fahrenheit/minus 196 degrees Celsius), while the cold gaseous helium in the shroud gets as low as 11 Kelvin (minus 440 Fahrenheit/minus 262 Celsius).

Webb remained at “cryo-stable” temperatures for about another 30 days. The thermal sensors kept track of the temperature of the telescope, while the specialized camera systems monitored the physical position of Webb’s components as they moved during the cool down process. These tests included an important alignment check of Webb’s 18 primary mirror segments, to make sure all of the gold-plated, hexagonal segments acted like a single, monolithic mirror. This was the first time the telescope’s optics and its instruments were tested together, though the instruments had previously undergone cryogenic testing in a smaller chamber at Goddard.

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NASA’s James Webb Space Telescope cools to cryogenic temperatures by radiating heat through the surrounding vacuum, to the liquid nitrogen and cold gaseous helium shrouds. The outside dimensions of Chamber A are 19.8m (65ft) in diameter and 33.6m (120ft) in height. The chamber is equipped with staged roughing pumps, valved turbo molecular and cryo absorption pumps, and 20 K (-424 oF) helium refrigeration units. The high vacuum pumps speeds are rated at 2 x 107 liters/sec condensibles and 3 x 105 liters/sec noncondensables at 1 x 10-6 torr pressure.

 

Systems testing continued and on Sept. 27, the engineers began to warm the chamber back to near room temperature, before pumping the air back into it and unsealing the door. This was done slowly and on the 18th of November, the chamber door was unsealed.

Measuring Gas Pressure with LASERs

I have just returned from the American Vacuum Society Symposium in Tampa, Florida. During the Vacuum Technology Division Sessions, we were updated on the NIST project to develop photonic based vacuum measurement standards. In order to introduce the topic, below is an excerpt from my book Understanding Modern Vacuum Technology, 2nd Ed.

As this work is being compiled, there is groundbreaking work being done at NIST in the Thermodynamics Group. This is in alignment with the “NIST on a Chip” program which has a goal of having reference standards based on quantum phenomena that can be scaled down to extremely small packages.

The pressure standards that are in use today are manometers that are evolutionary advances of the mercury barometer that Torricelli developed in 1643. While the principle behind the primary standards is simple, the manometers are operationally complex, requiring accurate determination of temperature, density, gravity, speed of sound, and ultimately column height. The manometers are large instruments (up to 3m tall) and contain up to 250kg of hazardous mercury. Mercury manometers are still used at eleven National Metrology Institutes, including NIST.

The NIST 13 kPa, 160 kPa and 360 kPa Ultrasonic Interferometer Manometers (UIMs) use ultrasound pulses to determine column heights with a resolution of 10 nm or a pressure resolution of 3.6 mPa and provide the world’s lowest pressure uncertainties. Once the instrument is set up, it takes about a minute to take a data point.

NIST mercury interferometer pressure standards.

Figure 4 45 10 kPa Ultrasonic Interferometer Manometer in the foreground and the 360 kPa UIM in the background. The 260 Pa UIM stands three meters tall and provides the nation with best-in-the-world capabilities for measuring absolute and differential pressure from 1 Pa to 360 kPa.

The goal is to replace the oil and mercury manometers with a standard that can be easily transported between national labs, researchers and industrial users. Once the photonic based standard is developed, NIST will be able to export a primary standard to an end user.

The photonic based method is to make vacuum and pressure measurements using Fabry–Pérot optical cavities to measure the interaction of light with a gas. This represents a disruption in pressure measurement technology and a way of realizing and disseminating the pascal, the SI unit of pressure.

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Figure 4‑46 A fixed length optical cavity realizes pressure by comparing the beat-frequency, f1-f2, as the pressure in gas cavity is increased while the vacuum in the reference cavity is held constant. This standard is simple (has no moving parts) and requires that the temperature of the cavity and molar index of the gas in the cavity is known from either measurements (for example nitrogen) or from theory (helium). (Hendricks, et al., 2015)

The basis of the optical technique is a Fabry–Pérot cavity, where two highly-reflecting mirrors face each other. Two Fabry–Pérot cavities built on a single low-expansion glass spacer, with one of the cavities serving as a vacuum reference. Figure 4‑46 shows a schematic for a dual Fabry–Pérot device. A laser shines in the end of one cavity and the transmitted light is detected at the other end, after bouncing back and forth inside the cavity multiple times (depending on reflectance of the mirror coatings). When the laser light entering the cavity has a wavelength such that an integer number of half wavelengths exactly fits between the two mirrors, a resonance occurs along with a detected signal intensity maximum at the detector, which is used in a stabilization feedback loop to lock the laser into resonance with the cavity.

The Fabry–Pérot cavity is used to determine the pressure by measuring the refractive index n or equivalently, the refractivity n-1. The first approximation, the refractivity of a gas is proportional to the number density of molecules

equation.GIF

first photonic sensor.JPG

 

Happy Birthday, AMAT

In 1967, I received a transistor radio for a birthday present. This was pretty whiz-bang for the day. It was great because I could listen to New York Yankee games in my room. Little did I know back in the 60s that a new company was being born in California that I would work for someday. I say with great confidence that the device you are reading this post on has chips that have been processed in our equipment.

I have gone from transistor radios, to boom boxes to, to SONY Walkmans, to PDP11s, to PCs to desktops, to laptops, to flip phones and now smart phones. The information age is just getting started. AMAT has been a big part of all these transitions.

On November 10, 2017, AMAT turned 50 years old.

Also on this date, the AMAT-VSE deal closed in 2011.

Torricelli used to hang with Galileo?

Every once in a while, I find a really interesting piece of vacuum technology history. This APS article provides additional insight into Torricelli and his work. We have been using Torricelli’s barometers as pressure reference standards for the best part of 400 years. This piece is taken from the American Physical Society News Letter October 2017, Vol 21, no. 9 in full, unedited as APS directs below. It is my hope that you become aware of the APS News resource and maybe you also will find something that interests you there.
APS News 

This Month in Physics History

October, 1644: Torricelli Demonstrates the Existence of a Vacuum

Elegant physics experiment; enduring practical invention

 

Evangelista Torricelli 

Evangelista Torricelli

Ed. Note: This month’s column was written by guest author Richard Williams.

Evangelista Torricelli, born of a humble family, eventually rose to the top of the Italian intellectual community. He led Italy, and then the world beyond, to resolve a two-thousand-year-old philosophical debate about vacuum and the nature of space. He did this by performing and understanding a single elegant physics experiment. The apparatus he used was also a practical invention–the mercury barometer.

Torricelli was born at Faenza, Italy on October 15, 1608. “Left fatherless at an early age” he was sent to Rome for his education. His achievements there brought him to the attention of Galileo in Florence. He came there and lived with Galileo. Galileo was preoccupied with a problem of Tuscan well diggers who were frustrated in their attempts to raise water more than about ten meters with lift pumps. When they tried to raise it higher, the water separated from the pump plunger and would go no farther. Could this be due to a vacuum forming under the plunger? They asked Galileo why the water could not be pumped higher. He considered the problem seriously, but died in 1642 with it still unresolved.

Then, in 1644, Torricelli took up the problem. After some study of earlier experiments he did one of his own. The apparatus was a glass tube about a meter long, sealed at one end. He filled it with mercury, covered the open end, and inverted it over a dish of mercury. This was not as easy as it sounds today. Glass tubes at the time were fragile and hard to come by. They often broke when filled with a kilogram of mercury. But with the help of a skilled assistant the experiment was done. The mercury in the tube fell and stabilized at a level about 76 centimeters above the level in the dish. Torricelli surmised correctly that the mercury rose in the tube because of the weight of the atmosphere pressing down on the mercury in the dish, and that the space above the mercury column was a vacuum. It was the first time that a vacuum had been created in the laboratory, and understood as such.

The concept of a vacuum had been contentious since antiquity. Both Plato and Aristotle thought the existence of a vacuum to be impossible, against Nature. In medieval Europe, this was summed up by the expression: “Nature abhors a vacuum.” To discuss a vacuum became heretical and dangerous.

The word “vacuum” first appeared in the English language in 1550, introduced by Thomas Cranmer, the Archbishop of Canterbury, who composed the Book of Common Prayer, the central document of the Church of England. The phrase he used, as part of a theological argument, is cited in the Oxford English Dictionary:  “Naturall reason abhorreth vacuum, that is to say, that there should be any emptye place, wherein no substance shoulde be.” This was the sanctioned view, but, with the accession of the Catholic Queen Mary in 1553, the winds of orthodoxy shifted. Cranmer was convicted of heresy in 1555, and was burned at the stake the following year.

Torricelli’s achievement brought the concept of vacuum from the dialectics of antiquity into experimental physics. Mindful of the contention around the idea of vacuum, he did not make his experiment public at first, but disclosed it only in letters to a friend, Michelangelo Ricci. In October, 1644, the French scientist Marin Mersenne visited Torricelli, who repeated the experiment for him and gave him copies of the letters to Ricci. Mersenne took these to Blaise Pascal and others in France, disclosing Torricelli’s work publicly for the first time.

Pascal immediately understood the meaning of the experiment, and repeated it in 1646. He believed that the atmospheric pressure should decrease with altitude, and engaged a relative and some friends to carry a barometer up a mountain in the south of France. They found the anticipated decrease of pressure with altitude, laying the foundation for the science of meteorology.

Pascal understood the pressure to be equal to the weight of the atmosphere per unit area. He combined this with the surface area of the earth and calculated the total mass of the atmosphere. His result differed by less than 30% from the currently accepted value as cited in The Handbook of Chemistry and Physics. About the calculation, Pascal noted that “a child who knows addition and subtraction could do it,” a strong endorsement of the French school system.

Torricelli’s apparatus was the first mercury barometer. Minor improvements were later made to increase the precision of the readings, but the basic design remained unchanged. In meteorological stations around the world it served as the reference standard for measuring atmospheric pressure for more than three centuries, perhaps a record time for an instrument to be used with the same design. Finally, in 1977, the US National Weather Service announced that the mercury barometer would be replaced as the reference standard by a recently developed piezoelectric quartz crystal pressure transducer.

Torricelli stood at the nexus where, with a single elegant experiment, vacuum and the nature of space, defined in philosophical terms for two thousand years, gave way to the modern view, defined by experimental physics. In the twentieth century, physicists went far beyond this. They found, not an “emptye place, wherein no substance shoulde be,” but rather a vacuum filled with wonders: electromagnetic radiation, including that from the last gasp of the Big Bang; a sea of virtual particle-antiparticle pairs; a space bent out of shape by gravitational warping–all unimaginable to earlier physicists.

Following his work on the barometer, Torricelli did research in mathematics and physics. His formula for the efflux of a liquid from a small orifice in a container is still known as Torricelli’s Theorem. He died in Florence in 1647, at the age of thirty nine. A commemorative statue of him was erected in Faenza in 1864.

©1995 – 2017, AMERICAN PHYSICAL SOCIETY

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: Alan Chodos

Rainer Weiss, Barry Garish and Kip Thorn share Nobel Prize in Physics

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2017 with one half to Rainer Weiss, LIGO/VIRGO Collaborationand, and the other half jointly to Barry C. Barish, LIGO/VIRGO Collaboration, and Kip S. Thorne, LIGO/VIRGO Collaboration, “for decisive contributions to the LIGO detector and the observation of gravitational waves”

In this YouTube video, the work by Weiss et. al. is describe and also there is a live feed from the US to Switzerland where Dr. Weiss speaks to the Academy and the Swiss press. It is a very informative exchange.

LIGO interferometer

Description of the LIGO Interferometer from Royal Swedish Academy Popular Science Background article.

The vacuum systems for LIGO are quite significant. But today everyone is focused on the physics. The gravitational waves detected are generated by some of the most violent events ever conceived by humans, yet the detection of gravitational waves is quite a challenge. These space-time distortions are on the order of 1/10,000th of the diameter of an atomic nucleus.

Congratulations to the LIGO and VIRGO teams for winning this prize. This is a very exciting time for cosmology.

MKS Semiconductor and Process Technology Handbook

MKS Instruments just released a new handbook that describes many of the basic design structures and processes for semiconductors. The first section has articles describing the basic transistor structures for the devices being built today including planar and 3D structures. It starts off with a discussion of the simple P-N junction and goes right up through the transistor technologies up to the cutting edge 3D FinFET structure. It has definitions of all of the common diode and transistors.

MKS Handbook.jpg

Click the image to go to the MKS Semiconductor Devices and Process Technology ebook download page.

The handbook goes into the silicon, dielectric and interconnect materials used and their fabrication methods. It has a wealth of information of the process sequence from raw wafer to finished product.

The second section of the handbook includes vacuum technology; some vacuum basics, pump information, gauging and components. MKS has a wealth of vacuum metrology solutions and the majority are mentioned in the handbook. What is very helpful is that the articles show how all of the MKS technology solutions can be used together as subsystems within a larger system.

If you work in a section of the industry and would like to be introduced to other processes in the industry, then I would encourage you to check this out. It will give you a good encyclopedia level education in semiconductors as well as see all of the MKS technology solutions.

In other news, in case you missed it, the second edition of Understanding Modern Vacuum Technology is available. There is a discount available for readers of this blog.

The Second Edition of Understanding Modern Vacuum Technology is Now Available!

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Cover art for the book Understanding Modern Vacuum Technology, 2nd Edition 

The second edition of Understanding Modern Vacuum Technology is now available! This book contains all the information found in the first book PLUS information that is not found in any other book to date.

What’s new? There is information on the cutting edge technology being done at NIST to develop new quantum based pressure standards. This is so new that the project is moving from the concept and feasibility phase to developing the standards that will replace the mercury manometers that are the primary standards used today.

There is an extensive section describing the Granville-Phillips VQM™  (Vacuum Quality Monitor). This is a revolutionary method for measuring the gas composition in a high vacuum system based on ion trap technology.

The second edition contains an introduction to leaks and their detection.

There are now knowledge check questions at the end of each chapter.

The book is available through Amazon.com and Amazon’s European websites including Amazon.co.uk, Amazon.de, Amazon.fr, Amazon.it, and Amazon.es. For larger quantities, it is recommended to order from the Understanding Modern Vacuum Technology book store.