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ARDA/Groups/Accelerator Structures/Research

Dr. Juwen W. Wang (Group Leader)

Designing, engineering and testing accelerator structures for future linear colliders operating under extremely high gradient conditions with superior properties in higher modes suppression. The activities span theory, simulation, fabrication technology, microwave characterization and high power experiments.

Designing, engineering and commissioning injectors including bunching and accelerator structures, RF system, focusing magnet system, diagnostics and instrumentation. Activities span simulation of particles acceleration, loading and emittance, as well as system integration, beam operation and experimental measurements.


Dr. Roger M. Jones

My research is concerned with accelerating multiple bunches of charged particle beams to 1 TeV or more for future advanced linear colliders. Unless measures are taken to prevent it, the beam will enter a BBU (Beam Break Up) instability regime in which it will be resonantly driven into the walls of the accelerator and at 1 TeV with ~1010 electrons per bunch the beam would readily burn a hole through the wall of the accelerator. The beam is kept precisely focused and BBU is prevented from occurring by ensuring the wakefield generated by the energetic beam is damped by two orders of magnitude.   This damping is effected by two techniques: firstly, by tapering the dimensions of the cells such that the cell modes do not add coherently and the overall wakefield is forced to decay with a Gaussian distribution and secondly, by coupling out the wake to 4 attached manifolds which run along the outer shell of the linac.

My work has entailed damping this wakefield and tracking the progress of the beam through simulations of the emittance growth that occurs down 10km or so of the proposed advanced linac.  Additional activities have been on the beam diagnostics applications of the manifold.  Recent work has also been concerned with damping the wake in high phase advance traveling wave accelerator structures, machine alignment tolerances imposed due to wakefield control and, on a scattering wave method to measure the wakefield via a wire measurement technique.

This work has entailed a collaboration between KEK in Tsukuba, Japan and Fermilab in Batavia, Il., USA, both of which, together with SLAC, have opted for an X-band accelerating structure design. At SLAC I work closely with Roger Miller, Norman Kroll, Tor Raubenheimer, Gennady Stupakov and Zenghai Li.


Professor Roger H. Miller

My position as senior advisor in ARDA gives me license to kibitz on all sorts of activities related to high power RF, microwave measurements, standing and traveling wave accelerator structures, injectors (like CERNS Injector test facility, CTF3), high power beam operation (e.g., the beam for E158), and occasionally in areas in which I am really an amateur, such as lattices. The one area in which I am currently much more than a kibitzer is in designing an NLC X-band accelerator structure which suppresses the effects of the long range dipole wakefields by 2 orders of magnitude. 

I have been heavily involved with the group led by Juwen Wang to develop Gaussian detuned, manifold damped traveling wave structures. We have also looked a little at detuning and damping standing wave structures, and Gaussian detuned, locally damped traveling weave structures.  In this work I have worked closely with Norman Kroll, Roger Jones, and Zenghai Li. This work is a collaboration with KEK and Fermilab.


Dr. Nicoleta Baboi

I have started to investigate a coaxial wire method to measure the kick factors and synchronous frequency of the dipole bands of the NLC accelerating structures.  The coaxial wire technique allows the measurement on a test bench, without need for a particle beam, of wake fields of charged particles in accelerating structures. For this method, a wire is passed through the structure to be measured. There are two main possibilities: either simulate the wake field of a bunch with a very short current pulse on the wire (time domain measurement), or measure the transmission through the structure as function of frequency and deduce the properties of modes and pass-bands (frequency domain measurement). The dipole modes have the main contribution on the beam dynamics in the NLC main linac. In order to measure the first two dipole pass-bands of the NLC accelerating structures, adapting sections are being build that insure a good match over at least 2.5 GHz.  Higher dipole pass-bands will be measured as well.


Professor Norman M. Kroll (UCSD & SLAC P/T)

In the past I have consulted at SLAC on a weekly basis and this has entailed visiting SLAC for three days each week.  During this time I have contributed to work at ARDA and ARDB.   My main area of work in this department has been on damping the transverse wakefield in the design of a manifold damped accelerating structure known as a DDS (Damped Detuned Structure) and on RF component design. Last year, during my last visit to SLAC I suffered a broken back and since then I have been recovering at my home in San Diego. I have continued to collaborate remotely on a limited basis. Specific ARD-A collaboration has been with Roger Jones on interpretation of structure simulations and on developing equivalent circuit representations.  I have also consulted with Daryl Sprehn on separating overlapping resonances in network analyzer studies of klystron output structures.  My UCSD collaborations have been with the Schultz group on properties, simulations, and potential applications of negative index (or "left handed") meta-materials and on interpretation of rf measurements on a 5 cell photonic band gap cavity fabricated by the SLAC ARD-B Department.


Dr. Gordon Bowdon

As mechanical engineer in the structures group my responsibilities include designing and testing all accelerators structures that are being built within this group. This work has entailed all DDS (Damped Detuned Structures), high phase advance accelerator structures and associated RF components.

Last modified on Thursday, 14-Oct-2004 15:18:18 PDT 

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