Accelerator Physics at the Universität Siegen

15 000 Particle accelerators worldwide … but how do they work?!

When the pioneers of the field developed the first accelerators more than 70 years ago their motivation was nuclear and particle physics.  Probably they did not fully appreciated that such machines would become the enabling technology for an amazingly wide spectrum of applications of great relevance for modern-day society.  Of course most people know of huge accelerators such as the LHC and XFEL, but this is only the tip of the iceberg!  Over 15,000 accelerators are in operation in fields ranging from cancer therapy to port security to the analysis of proteins with synchrotron light.  New ideas are continuously being hatched, such as accelerators for transmutation of nuclear waste to solve our radioactive-waste-storage problem. 

Particle accelerators are machines of contrast.  Their size and “quick facts” can be daunting: km long rings, GW beam power, MV/m electric fields and beam travel distances equivalent to the run Earth - Pluto.  At the same time sub-mm beam sizes with pulse lengths as short as 50 fs must be handled, steered and timed precisely to guarantee success.  “Particle accelerator physics” thus consists of many disciplines from theoretical beam dynamics, to RF systems, to ultra-high vacuum technology, to lasers, to superconductivity to …  All these systems must be understood and interface perfectly for the machine as a whole to work.

Accelerator physics education

Not surprisingly, the demand for accelerator experts is enormous, far outpacing the number of scientists being educated in the field.  An important aspect of the activities in the Institute for SRF Science and Technology is therefore to educate the next generation of accelerator physicists.  For this reason GISRF’s Institute Head Jens Knobloch holds a joint appointment as Professor of Accelerator Physics at Universität Siegen.

Students and young scientists from Universität Siegen and Berlin Universities are given the opportunity for hands-on research in the Institute by completing Bachelor, Masters and Ph.D. thesis.  In addition, two classes are offered at Univesität Siegen, geared towards advanced Bachelor and Master students which provide the theoretical background for thesis work.

Winter Semester: Introduction to Accelerator Physics

This two-week course introduces students to the main concepts of accelerator physics.  We will start from basic beam dynamics topics: how to accelerate beams and keep them focused in the accelerator chambers, how to maintain stable acceleration, and some of the mechanisms by which the beam motion can become unstable.  We then focus on the electron storage ring.  Here synchrotron radiation plays an important role and beams are naturally damped to a very small size and divergence, critical for many applications, such as synchrotron radiation sources.
The course combines lectures and experiments both in the lab and at an accelerator to illustrate the main concepts taught in the classes.  We visit several accelerators in Berlin during the second half of the course, including the Metrology Light Source of the PTB, the Eye-Tumor Proton Therapy Center and the BESSY II Synchrotron Light Source.

The course comprises 15 lectures (1 ½ hours each)

Lecture 1: Introduction – Why accelerators, main components, accelerator applications
Lecture 2: The Accelerator Zoo – A gallop through the different types of accelerators
Lecture 3: RF acceleration Part 1 – Waveguides
Lecture 4: RF acceleration Part 2 – RF cavities
Lecture 5: Energy and Phase Stability I – Keeping the beam in lock-step with the RF field
Lecture 6: Guiding the beam – Magnets for accelerators
Lecture 7: Transverse beam dynamics I – Single particle motion in an accelerator
Lecture 8: Transverse beam dynamics II – Particle ensemble motion
Lecture 9: Transverse beam dynamics III – What happens when the particle energy deviates from the design energy
Lecture 10: Periodic systems – Beam dynamics in a ring
Lecture 11: Chromatic effects – Impact of energy dependent beam focusing
Lecture 12: Injection and bumps – How do we get the beam into the accelerator?
Lecture 13: Energy and Phase Stability II – Lecture 5 revisited for storage rings
Lecture 14: Synchrotron radiation – The bane and boon of electron storage rings
Lecture 15: Radiation effects – How does synchrotron radiation determine the beam’s equilibrium parameters

Summer Semester: Superconducting RF Systems

In the second (1 week) class we examine in detail one of the enabling technologies for modern next-generation accelerators: Superconducting Radio-Frequency (SRF) Systems.  Many present-day accelerators still employ copper normal-conducting (NRF) accelerating units.  This course analyzes the limitations of such systems and illustrates that power dissipation in copper cavities can be such a severe handicap that many new accelerator applications cannot be realized with conventional copper technology.  In detail we look at SRF as an alternative and why it offers so many advantages that go far beyond the idea of “just saving some electrical power.”   During the course of the week we also look at the basics of superconductivity, what materials can be used for SRF cavities, how they are produced and what other systems are needed to actually operate SRF cavities in an accelerator.  An important aspect of the class is the simulation lab that accompanies the lectures which illustrates in depth the concepts.

The course comprises seven lectures (1 ½ hours each)

Lecture 1: Limits of normal-conducting systems – The problem with the power dissipation
Lecture 2: Enter superconductivity – Physics or a Miracle?
Lecture 3: RF losses in superconductors – Why superconducting cavities actually dissipate power
Lecture 4: Anomalous losses in RF superconductors I – All the things that can go wrong in SRF cavities (residual losses and multipacting)
Lecture 5: Anomalous losses in RF superconductors – All the things that can go wrong in SRF cavities (thermal breakdown and field emission)
Lecture 6: Cavity production – The birth of an SRF cavity
Lecture 7: Auxiliary systems – And now for the rest of the story … What else is needed to run an SRF cavity in an accelerator