Thursday, Sept. 3, 2015
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Today's New Announcements

"Ask Me About ReadyTalk" booth in atrium today

Lecture: "The Life of a Honeybee" on Sept. 9

Python Programming Basics scheduled for Oct. 14, 15, 16

Python Programming Advanced on Dec. 9, 10, 11

School's Day Out - Sept. 4

Bible exploration group starting new study called "Live Justly" - Sept. 8

Pilates registration due Sept. 8

September AEM meeting date change to Sept. 14

Fermilab Lecture Series: Visualizing the Future of Biomedicine - Sept. 18

Fermilab Arts Series: 10,000 Maniacs - Sept. 26

Workshop on Future Linear Colliders - register by Sept. 28

Fermilab Prairie Plant Survey

New line dancing class

Pine Street road closing

Fermilab Board Game Guild

Walk 2 Run on Thursdays

English country dancing at Kuhn Barn

Scottish country dancing moves to Kuhn Barn Tuesdays evenings after Labor Day

International folk dancing returns to Kuhn Barn Thursday evenings after Labor Day


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In Brief

Much ado about neutrinos during Neutrino Action Week

Deputy Director Chris Mossey (right) listens to a presentation at the LBNF/DUNE risk assessment workshop. Photo: Reidar Hahn
David Vardiman of the South Dakota Science and Technology Authority presents at the LBNF/DUNE risk assessment workshop. Photo: Reidar Hahn
Coffee breaks are the perfect time to get amped about neutrinos. Photo: Reidar Hahn
Scientists chat about DUNE. Photo: Reidar Hahn
Scientists learn about the synergies between the Fermilab Short-Baseline Neutrino program and DUNE. Photo: Reidar Hahn
DUNE co-spokesperson Mark Thomson takes in a talk. Photo: Reidar Hahn

Neutrino Action Week at Fermilab is in full swing. On Monday and Tuesday, Fermilab hosted the LBNF/DUNE far-site risk workshop and the SBND-DUNE workshop on Wednesday. Wednesday also kicked off the three-and-a-half day DUNE collaboration meeting.

Learn more about the meetings in the Aug. 31 issue of Fermilab Today.

In Brief

IARC room naming contest winner and new OPTT contest

Name this Office of Partnerships and Technology Transfer meeting room.

Aaron Sauers, OPTT, is the winner of the recent contest to name a conference room in the IARC Office, Technical and Education Building. The new name of the conference room is the Floating Point.

Now you have a second chance to name a room in the IARC building. This time the subject is the meeting room for the Office of Partnerships and Technology Transfer. See the picture above.

The OPTT mission is to enable high-impact partnerships with outside institutions, so the name should be related to invention, innovation, commercialization or partnerships.

The contest is open to Fermilab badge holders. The deadline for submissions is Wednesday, Sept. 30. The winner will be announced shortly afterward.

Email your submissions to Dawn Staszak, and enter "OPTT conference room naming contest" in the subject line.

Photo of the Day

Main Ring scene

Main Ring, outdoor, nature, clouds, sky, Main Ring Pond
If you take a walk along the gravel path inside the Main Ring, you may encounter this quaint gazebo. Photo: Valery Stanley, WDRS
In the News

How quantum symmetry makes solid matter possible

From Forbes, Aug. 25, 2015

Physicists are forever dividing the universe into two classes of things — ordinary matter and dark matter, quarks and leptons, conductors and insulators. Some of these definitions are just matters of convenience, but others are fundamental to the structure of the universe. One of the most fundamental splits is that between the particles known as bosons and those known as fermions. This is a difference that seems arcane and arbitrary when you first encounter it, but it turns out to be of critical importance. In fact, life as we know it would be impossible were it not for the difference between bosons and fermions, as you can't have solid objects without it.

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Physics in a Nutshell

Resonant cavities for the acceleration of charged particles

In an accelerating cavity, electric and magnetic fields are set up as shown here to accelerate a particle beam from one side to the other.

In previous columns I have discussed some of the more interesting aspects of accelerating charged particles to high energies, but I have necessarily omitted important details. For example, my last column discussed phase stability and transition using an oscillating electric field, yet I gave no details for how such fields are produced.

Recall that substantial electric fields are required to accelerate charged particles to high energies. Early in our discussions we ruled out batteries and large electrostatic generators as viable ways to achieve energies at the MeV or higher scale. The most viable solution for achieving GeV energies is to arrange for the beam to pass through a substantial accelerating field many times. Even so, the problem remains difficult. For example, we cannot naively drill beam holes in two plates, install the plates in an accelerator, connect an AC voltage across the plates and hope to accelerate a proton beam with enough moxie to create serious a neutrino beam. Instead we must take a page from the radio engineering manual and make use of resonant cavities.

A resonant cavity allows us to set up a radio-frequency (RF) standing wave inside it with significant voltage and minimal power loss. The first figure (above) shows an example of a cavity with electric and magnetic field lines that result from exciting the cavity with an RF source. Both fields oscillate sinusoidally, reversing direction during each cycle as shown in the second figure (below). The bunched beam is present in the cavity only when the electric field is oriented to provide an acceleration. The oscillations make it possible for the standing wave to reach substantial potentials. By stringing cavities together, we can achieve on more than a million volts for each pass of the beam around the accelerator.

In order for the resonant cavities to be effective for accelerating particles, they must match the frequency of the beam bunches. This works well when the beam bunches arrive with a constant frequency. However, this is not always the case in an accelerator ring, especially when protons are being accelerated. For example, as the protons accelerate, their speed increases until they approach the velocity of light. This means the frequency of their arrival in the cavity increases during the early part of the acceleration cycle. For Fermilab's 8-GeV Booster and Main Injector accelerators, the increase in frequency is substantial enough that running the resonant cavities at a constant frequency would not work.

One way to change the frequency of a resonant cavity is to change its shape and size. However, this is not very practical since the change must occur during the acceleration cycle. One can imagine mechanical solutions involving moving parts, or a large, radiation-resistant, gorilla trained to deform the cavities at just the right time.

Fortunately, there is a better solution. It comes in the form of a ferrite-loaded transmission line that is attached to the accelerating cavity. The resonant frequency of the accelerating cavity changes when a current passes through the transmission line. The current changes the magnetic properties of the ferrite, changing the resonant frequency. Adjusting this bias current during acceleration allows the frequency of the RF cavity to follow the beam frequency. An example of a tuner coupled to a cavity is shown in the third figure (below).

As you can see, creating high-energy beams requires accelerator scientists to overcome many subtleties. We know it is worth the effort when we see the look on a young experimenter's face the first time she or he is finally convinced that there truly are neutrinos.

Roger Dixon

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The acceleration of a particle beam is timed so that it arrives inside an accelerating cavity when the electric field inside it is at its peak (point A). That way, the electric field can push it forward and toward the next cavity. The particle beam's acceleration is also timed so that the beam is in between cavities when the cavities' electric field is at its lowest point (point B). Thus the beam idles in between pushes from one cavity to the next.
A tuner helps adjust the accelerating frequency of a cavity by adjusting the current transmitted to it. This allows the accelerating cavity to follow the frequency of the beam's arrival in the cavity.
In the News

Space station dark-matter experiment hits a glitch

From Nature, Sept. 2, 2015

The operators of a US$2-billion dark-matter experiment aboard the International Space Station are striving to figure out how to keep three crucial cooling pumps working after the failure of a fourth last year. The glitch raises the most serious concerns yet about whether the Alpha Magnetic Spectrometer (AMS), which probes cosmic rays for signs of dark matter being annihilated in deep space, will last until the space station's planned retirement in 2024. Originally designed for a three-year mission, the AMS is in its fourth year with nine to go.

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