Papers by Mark Middendorf
arXiv (Cornell University), Oct 30, 2022
2022 23rd International Vacuum Electronics Conference (IVEC)
AIP Conference Proceedings, 1993
Physical Review A, 1994
ABSTRACT Absolute doubly differential cross sections for electron emission are presented for 0.5-... more ABSTRACT Absolute doubly differential cross sections for electron emission are presented for 0.5-MeV/u multicharged ion-atom collisions. The collision systems investigated are Bq+, Cq+ (q=2-5) and Oq+, Fq+ (q=3-6) projectiles impacting on helium and Cq+ (q=2-5) ions impacting on neon and argon targets. Laboratory electron emission angles between 10° and 60° were studied. Under the assumption that the cross sections scale with the square of an effective projectile charge, Zeff(ε,theta), the scaling was investigated as a function of emitted electron velocity and angle. For distant collisions (low-energy electron emission), we find that Zeff(ε,theta)>q for small q. For the highest values of q investigated, Zeff(ε,theta) was found to be smaller than the net projectile charge q. The effective projectile charges may be subject to a systematic underestimation since they were determined by referencing the partially stripped ion impact data to fully stripped boron, rather than proton, impact cross sections. In the binary-encounter region, the present data confirm previously observed features-namely that the emission increases as q decreases. For the helium target, the qualitative behavior is roughly in accordance with predictions by Schulz and Olson [J. Phys. B 24, 3409 (1991)]. Neon and argon targets also demonstrate these features, but less dramatically than helium.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Aug 9, 2022
High-power waveguide dampers have been designed and prototyped for the Short-Pulse X-ray (SPX) ca... more High-power waveguide dampers have been designed and prototyped for the Short-Pulse X-ray (SPX) cavities at the Advanced Photon Source. The cavities will operate at 2.815 GHz and utilize the TM110 dipole mode. As a result, higher-order (HOM) and lower-order mode (LOM) in-vacuum dampers have been designed to satisfy the demanding broadband damping requirements in the APS storage ring. The SPX
2007 IEEE Particle Accelerator Conference (PAC), 2007
2007 IEEE Particle Accelerator Conference (PAC), 2007
2007 IEEE Particle Accelerator Conference (PAC), 2007
The short pulse x-ray (SPX) part of the Advanced Photon Source (APS) Upgrade is an effort to enha... more The short pulse x-ray (SPX) part of the Advanced Photon Source (APS) Upgrade is an effort to enhance timeresolved experiments on a few-ps scale at the APS. The goal of SPX is the generation of short pulses of x-rays for pump-probe time-resolved capability using superconducting rf (SRF) deflecting cavities. These cavities will create a correlation between longitudinal position in the electron bunch and vertical momentum. The light produced by this bunch can be passed through a slit to produce a pulse of light much shorter (1-2 ps instead of 100 ps) than the bunch length at reduced flux. An SPX cavity has been tested with a helium vessel and tuner as have the integration and operation of many systems designed for SPX cryomodule in-ring operation. These systems include an APSconstructed 5-kW, 2.815-GHz amplifier, a digital low-level rf controller system designed and fabricated in collaboration with LBNL, a cavity tuner, and instrumentation systems designed for the existing APS infrastructure. Cavity performance and subsystem performance will be reported and discussed in this paper.
First beam test with the low output-impedance second harmonic cavity (LOI), was performed in Apri... more First beam test with the low output-impedance second harmonic cavity (LOI), was performed in April, 2011 using the ISIS synchrotron at 2.1×10 protons per pulse, which corresponds to the circulating beam current of 2.3~5.2A. The LOI was proven to be stable under such a high intensity beam. The output impedance of LOI was derived from the beam induced voltage across the cavity gap, resulting in 35ohm at 3.4MHz, which agrees well with the measurement by the network analyzer. Issues on the present LOI system and a plan for further beam experiments are also described.
A very low output-impedance (~35 ohms) second-harmonic cavity system is being developed for high ... more A very low output-impedance (~35 ohms) second-harmonic cavity system is being developed for high intensity proton accelerators [1]. The final amplifier is comprised of a grounded cathode scheme with a feedback loop from anode to grid. Due to the Miller effect, the grid voltage waveform is seriously distorted even if only a few percent of sub-harmonic or higher harmonic are mixed in the driver current. Such distortion is much enhanced by the beam loading. In order to eliminate the effect of this distortion upon the phase detector used to achieve precise cavity tuning, a swept bandpass filter was applied to the grid voltage at the phase detector input. Filter design details and the result of high power tests are reported.
2007 IEEE Particle Accelerator Conference (PAC), 2007
Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366), 1999
The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) delivers 450-MeV protons... more The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) delivers 450-MeV protons in 70 ns pulses at 30 Hz to a heavy-metal target producing spallation neutrons for material science research. The average current extracted from the RCS is 15 µA with a peak intensity of 10 Amps. The large circulating currents in the RCS generate oscillations in the bunch which are presently controlled by modulating the phase of the two rf cavities. By adding second harmonic (SH) rf, the bunch length can be increased reducing the peak current. Simulations suggest that a 20-40 percent increase in extracted current should be achievable. The simulation program allows for phasing between fundamental and SH rf voltages. Initial studies to optimize phase indicate the need to maximize bucket area early in the acceleration cycle, whereas bunching factor is more significant later in the cycle.
A wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron ... more A wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron has been developed by the collaboration between Argonne National Laboratory (US), KEK (Japan) and Rutherford Appleton Laboratory (UK). The system has less than ...
In the ISIS facility at Rutherford Appleton Laboratory (RAL) in the UK, a second target station p... more In the ISIS facility at Rutherford Appleton Laboratory (RAL) in the UK, a second target station project is under construction. Four 2nd harmonic RF cavities will be installed in the ISIS synchrotron to increase the trapping efficiency, and to mitigate the space charge ...
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)
U.S. Department of Energy Office of Scientific and Technical Information - OSTI OAI, Jul 19, 2022
This paper reports the results of high gradient testing of the two C-band (5.712 GHz) normal cond... more This paper reports the results of high gradient testing of the two C-band (5.712 GHz) normal conducting β=0.5 accelerating cavities. The first cavity was made of copper and the second was made of copper-silver alloy with 0.085% silver concentration. The tests were conducted at the C-Band Engineering Research Facility of New Mexico (CERF-NM) located at Los Alamos National Laboratory. Both cavities achieved gradients more than 200 MeV/m and surface electric fields more than 300 MV/m. The breakdown rates were mapped as functions of peak surface fields. The gradients and peak surface fields observed in the copper-silver cavity were about 20% higher than those in the pure copper cavity with the same breakdown rate. It was concluded that the dominant breakdown mechanism in these cavities was not the pulse heating but the breakdown due to very high surface electric fields.
This poster will report the results of high gradient testing of the two proton β=0.5 C-band accel... more This poster will report the results of high gradient testing of the two proton β=0.5 C-band accelerating cavities. The cavities for proton acceleration were fabricated at SLAC and tested at high gradient C-band accelerator test stand at LANL. One cavity was made of copper, and the second was made of a copper-silver alloy. LANL test stand was constructed around a 50 MW, 5.712 GHz Canon klystron and is capable to provide power for conditioning single cell accelerating cavities for operation at surface electric fields up to 300 MV/m. These β=0.5 C-band cavities were the first two cavities tested on LANL C-band test stand. The presentation will report achieved gradients, breakdown probabilities, and other characteristics measured during the high power operation.
Uploads
Papers by Mark Middendorf