by Dr. John Weisend II, European Spallation Source ERIC, CSA chairman, john.weisend@esss.sen and M. E. Edgerton composer, professor of artistic
research in music, michael.edgerton@mhm.lu.se
He II or superfluid helium, which already plays an important role in the cooling of superconducting magnets and superconducting radiofrequency cavities, has now also inspired music. Composer Michael Edward Edgerton, a professor at Lund University’s Malmo Academy of Music in Sweden has written an innovative piece, “Der Rufer,” for a percussion quartet based on phenomena found in He II including: anisotropy, isotropy, quantum leap (bifurcation), mutual friction, superfluid turbulence, quantized vortices and second sound.
He II is a quantum mechanical phenomenon that can be modelled as two fluid components that flow independently of one another. For example, the normal fluid and superfluid components may flow in opposite directions and thus flow through each other (see Figure 1). In addition, the normal fluid component consists of fluctuations in the density of particle-like thermal excitations (rotons and phonons). These fluctuations may occur within regions in which particles are packed into either dense or sparse formations (see Figure 2). Since it has no viscosity, superfluid remains unaffected by fluctuations of N particle denseness. The propagation of thermal waves as a result of these fluctuations is known as second sound.
Figure 2. He II may present fluctuations of particle density, from tightly to loosely packed. Image: Michael Edgerton
How was He II represented in music?
In “Der Rufer,” Edgerton loosely modelled three ideas: a) independence of normal fluid and superfluid, b) fluctuations of particle density and c) dense vs sparse formations of N. In Figure 3, we see all principles in play: a) representing independence, both left and right excerpts show a single percussionist rubbing a hand-held cymbal in large arcs near the rim to produce a relatively high, strident pitch with periods of intermittent roughness. This gesture represents superfluid and is independent from the other percussionists. Simultaneously, the other percussionists represent normal fluid by producing iterative gestures on multiple percussion instruments. b) In He II, the overall density must remain constant. In both excerpts, the density of N varies slightly but overall remains perceptually self-similar within each local context. c) Lastly, second sound embodies dense to sparse formations of N. In the excerpt to the left, we see N is relatively tightly packed over a duration of three pulses, while the excerpt on the right features less activity over a longer time and may be said to embody a loosely-packed or sparse formation (see Figure 3).
The title, “Der Rufer”, refers to a sculpture in Bremen by Gerhard Marcks that refers to a Greek Herald from Homer’s Iliad. On the base of the sculpture is written:
Der Rufer von Gerhard Marcks (1889 –1981)
Der Rufer ist der Figur des Stentor nachempfunden, der mit gröherziger und ehernen Stimme so laut rief wie fünfzig Männer. (Homer, Ilias, 730 v. Chr.)
Der Rufer is modeled on the figure of the stentor (Herald, bard, or crier) who shouted as loudly as fifty men in a generous and brazen voice. (Homer, Iliad, 730 BC)
Die drei Meter hohe Bronzeskulptur wurde 1967 von Gerhard Marcks im Auftrag von Radio Bremen geschaffen. Am 25 November 2007 wurde der Rufer vor dem Neubau von Radio Bremen an der Weser aufgestellt.
The three-meter-high bronze sculpture was created in 1967 by Gerhard Marcks on behalf of Radio Bremen. On November 25, 2007, Der Rufer was placed in front of the new Radio Bremen building on the Weser river.
“Der Rufer” was written for the Bremer Schlagzeugensemble, directed by professor of Percussion at the Hochschule für Künste-Bremen, Olaf Tzschoppe. The premiere, scheduled for December 2020, was postponed due to COVID-19 and will now take place in October 2021 in Malmö, Sweden. Additional performances are being planned.
Figure 3. Tightly packed (left) and loosely packed (right). Image: Michael Edgerton
ESS, based on the world’s most powerful linear accelerator, is one of the largest users of He II in Europe. At ESS, He II cools the superconducting RF cavities that provide the bulk of acceleration for the proton accelerator that drives what will be the world’s brightest neutron source. Research using neutrons at ESS will enable scientific breakthroughs in a wide range of fields including: materials, health, energy, the environment and engineering. More information on ESS may be found here: europeanspallationsource.se. ■
CSA Archive 