Georg Hoffstaetter de Torquat



Physics of Beams; Accelerator Technology

Research Focus

The Physics of Beams is the study of accelerated beams as a special state of matter. It has many applications in particle accelerators, spectrometers, electron microscopes, and lithographic devices. These instruments have become so complex that an empirical approach to properties of the particle beams is by no means sufficient and a detailed theoretical understanding is necessary. Historically it has proved fruitful that studies in beam physics have been performed in the context of projects that developed or built one of these instruments, and I have worked on several such projects. Since 2020, I am working on the largest accelerator that the US is currently designing and constructing, the Electron Ion Collider  (EIC) at Brookhaven National Laboratory (BNL). It adds a high-energy polarized electron beam to the Relativistic Heavy Ion Collider (RHIC), the only collider with polarized beam. From 2016 to 2020, I was in charge of building CBETA in a collaboration with BNL; it is a new kind of accelerator at Cornell’s Wilson Laboratory and has become the world’s first 4-turn Energy Recovery Linac (ERL) where the energy of a spent beam is re-used to accelerate new beam. CBETA is also a prototyping facility for parts of a EIC. My group has constructed many technical components needed for such accelerators and designed a large-scale hard X-ray light source based on an ERL. Before arriving at Cornell, I worked on the 4 mile circular accelerator HERA in Hamburg, where I contributed to the understanding of the non-linear dynamics and long term stability of the stored particles, of polarization dynamics, and of space charge forces acting from one particle beam to another. What was learned has been published as a book by Springer, High Energy Polarized Proton Beams, a modern view. The particle beams in all these accelerators have interesting nonlinear beam dynamics, multi bunch instabilities, space charge within a tightly focused beam, the creation of synchrotron light, and the back-reaction of coherently emitted light on the beam. Charged particle accelerators have become an essential tool in today's investigation of all types of materials, from airplane wings to cell membranes and from pollutants in leaves to matter under earth-core pressures. Technical components that have been developed at Cornell for these applications are now being used in the development of LCLS-II, a new x-ray laser at SLAC. My group also had industrial collaborations with ASML, a company for industrial lithography of computer chips, with the Lighthouse project on the production of medical isotopes, and with RI on on superconducting accelerators for storage rings.

Accelerator Technology describes the technology used to accelerate large currents of tightly focused beams to high energies.  These beams are then used to study elementary particles, to produce synchrotron light for analysis in biophysics, in crystallography, in surface physics, or in the material sciences, for cancer therapy, and for a variety of other applications. Studies with synchrotron light are currently performed by CHESS at Cornell. The technology involved in accelerators is very rich and I am currently mostly interested in the technology required for the Electron Ion Collider, including components that are tested by CBETA.  These particles are produced in a photo cathode electron gun that involves a very complex system of lasers. Subsequently they are accelerated in a high-power superconducting radio-frequency (SRF) linac that has been constructed in my group. This system holds world records in beam brightness and in current through an SRF linac. A second SRF linac was constructed that couples only little RF power to the beam, because it is optimized for ERLs where the power is supplied by a decelerating beam. This complete accelerating system from the electron source through the ERL linac and its permanent magnet return loop recovered the beam’s energy for the firs time in June 2019 and became the world’s first 4-turn SRF ERL in 2020.  With 4-different beam energies in one beam pipe simultaneously, this is first-of-its kind technology.

Graduate Students

Lucy Lin (Machine Learning for large accelerator operations) Jonathan Unger (Dynamic Aperture in the rings of the EIC) Matthew Signorelli (Polarization in the EIC) Ningdong Wang (Beam dynamics in the ERL of the EIC hadron cooler) Eiad Hamwi (Polarized protons in RHIC and the EIC)


Group meetings:

Tuesdays and Fridays 12:30pm in PSB 470

Further information can be obtained by contacting research associates at Wilson Laboratory and at

Graduate and undergraduate students interested in beam physics and the application of particle accelerators are encouraged to join this group. There are many opportunities for student involvement.


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