D. Horan

A 50-MeV mm-wave electron linear accelerator system for production of tunable short wavelength synchrotron radiation

The Advanced Photon Source (APS) at Argonne in collaboration with the University of Illinois at Chicago and the University of Wisconsin at Madison is developing a new millimeter wavelength, 50-MeV electron linear accelerator system for production of coherent tunable wavelength synchroton radiation. Modern micromachining techniques based on deep etch x-ray lithography, LIGA (Lithografie, Galvanoforming, Abformung), capable of producing high-aspect ratio structures are being considered for the fabrication of the accelerating components.<<ETX>>

The IPNS second harmonic RF upgrade

The intense pulsed neutron source (IPNS) rapid cycling synchrotron (RCS) is used to accelerate protons from 50 MeV to 450 MeV, at a repetition rate of 30 Hz. The original ring design included two identical rf systems, each consisting of an accelerating cavity, cavity bias supply, power amplifiers and low-level analog electronics. The original cavities are located 180 degrees apart in the ring and provide a total peak accelerating voltage of ~21 kV over the 2.21-MHz to 5.14-MHz revolution frequency sweep. A third rf system has been constructed and installed in the RCS. The third rf system is capable of operating at the fundamental revolution frequency for the entire acceleration cycle, providing an additional peak accelerating voltage of up to ~11 kV, or at the second harmonic of the revolution frequency for the first ~4 ms of the acceleration cycle, providing an additional peak voltage of up to ~11 kV for bunch shape control. We describe here the hardware implementation and operation to date of the third rf cavity in the second harmonic mode.

An overview of the APS 352-MHz RF systems

The Advanced Photon Source (APS) is a 7-GeV full energy positron storage ring for generating synchrotron radiation with an injector. The booster synchrotron RF system consists of a single 1-MW klystron which drives four five-cell cavities at 352 MHz. The storage ring cavities consist of four groups of four single cells powered by two 1-MW klystrons for 100-mA operation. An overview of the operation of the APS 352-MHz RF systems is presented.

Reconfigurable high-power RF system in the APS

The 352-MHz high-power system for the Advanced Photon Source (APS) storage ring and booster synchrotron has been configured to allow two to four klystrons to power the storage ring and one klystron to power the booster. A quadrature hybrid combines two klystron outputs with two 45/spl deg/ phase shifters at each output of the hybrid for proper phasing at the storage ring cavities for the selected mode. The phase shifters in the hybrid outputs and three waveguide switches are used to choose an operation mode in any one of twelve possible configurations using three to five klystrons to power the storage ring and booster. The system can be configured to use one klystron as the power source of a test station.

Phase loop bandwidth measurements on the Advanced Photon Source 352-MHz RF systems

Phase loop bandwidth tests were performed on the Advanced Photon Source storage ring 352-MHz RF systems. These measurements were made using the HP3563A Control Systems Analyzer, with the RF systems running at 30 kilowatts into each of the storage ring cavities, without stored beam. An electronic phase shifter was used to inject approximately 14 degrees of stimulated phase shift into the low-level RF system, which produced measurable response voltage in the feedback loops without upsetting normal RF system operation. With the PID (proportional-integral-differential) amplifier settings at the values used during accelerator operation, the measurement data revealed that the 3-dB response for the cavity sum and klystron power-phase loops is approximately 7 kHz and 45 kHz, respectively, with the cavities the primary bandwidth-limiting factor in the cavity-sum loop. Data were taken at various PID settings until the loops became unstable. Crosstalk between the two phase loops was measured.

A divide-down RF source generation system for the Advanced Photon Source

A divide-down RF source system has been designed and built at Argonne National Laboratory to provide harmonically-related and phase-locked RF source signals between the APS 352-MHz storage ring and booster synchrotron RF systems and the 9.77-MHz and 117-MHz positron accumulator ring RF systems. The design provides rapid switching capability back to individual RF synthesizers for each one. The system also contains a digital bucket phase shifter for injection bucket selection. Input 352-MHz RF from a master synthesizer is supplied to a VXI-based ECL divider board which produces 117-MHz and 9.77-MHz square-wave outputs. These outputs are passed through low-pass filters to produce pure signals at the required fundamental frequencies. These signals, plus signals at the same frequencies from independent synthesizers, are fed to an interface chassis where source selection is made via local/remote control of coaxial relays. This chassis also produces buffered outputs at each frequency for monitoring and synchronization of ancillary equipment.

A 10‐GeV, 5‐MW proton source for a muon‐muon collider

The performance parameters of a proton source which produces the required flux of muons for a 2‐TeV on 2‐TeV muon collider are: a beam energy of 10 GeV, a repetition rate of 30 Hz, two bunches per pulse with 5×1013 protons per bunch, and an rms bunch length of 3 nsec (1). Aside from the bunch length requirement, these parameters are identical to those of a 5‐MW proton source for a spallation neutron source based on a 10‐GeV rapid cycling synchrotron (RCS) (2). The 10‐GeV synchrotron uses a 2‐GeV accelerator system as its injector, and the 2‐GeV RCS is an extension of a feasibility study for a 1‐MW spallation source described elsewhere (3–9). A study for the 5‐MW spallation source was performed for ANL site‐specific geometrical requirements. Details are presented for a site‐independent proton source suitable for the muon collider utilizing the results of the 5‐MW spallation source study.

Feasibility study of a 1-MW pulsed spallation source

A feasibility study of a 1-MW pulsed spallation source based on a rapidly cycling proton synchrotron (RCS) has been completed. The facility consists of a 400-MeV H/sup -/ linac, a 30-Hz RCS that accelerates the 400-MeV beam to 2 GeV, and two neutron-generating target stations. The design time-averaged current of the accelerator system is 0.5 mA, and is equivalent to 1.04/spl times/10/sup 14/ protons per pulse. The linac system consists of an H/sup -/ ion source, a 2-MeV RFQ, a 70-MeV DTL and a 330-MeV CCL. Transverse phase space painting to achieve a Kapchinskij-Vladimirskij (K-V) distribution of the injected particles is accomplished by the charge exchange injection and programming of the closed orbit during the injection. The synchrotron lattice uses FODO cells of 90/spl deg/ phase advance. Dispersion-free straight sections are obtained by using a missing magnet scheme. Synchrotron magnets are powered by a dual-frequency resonance circuit that excites the magnets at a 20-Hz rate and de-excites them at a 60-Hz rate, resulting an effective rate of 30 Hz, and reducing the required rf power by 1/3. Details of the study are presented.

352-MHz klystron performance at the Advanced Photon Source

The general performance of the Advanced Photon Source (APS) 352-MHz/1-MW continuous wave (CW) klystrons is discussed. The original seven-klystron inventory at the Advanced Photon Source has been in operation since 1995 with good results. Five tubes are presently in accelerator operation, with two tubes as spares. The overall performance of the tubes has been very good. Two tubes were removed from service due to intolerable operational problems: one suffered collector heat damage and was subsequently rebuilt and placed back in service; the other developed a suspected high-voltage (HV) leakage path between the mod-anode terminal and body. One tube has a history of high 3rd to 5th harmonic power production and is presently kept as a spare. Several of the tubes have experienced damage to the oil-tank HV connectors due to over-tightening of the bayonet clamps, and one tube had high leakage current in an ion pump that gave a false indication of bad vacuum.

A 1- to 5-MW, RCS-based, short-pulse spallation neutron source

Two accelerator configurations, the linac/compressor ring scheme and the linac/RCS scheme, are commonly used to provide the proton beam power for a short-pulse spallation neutron source. In one configuration, a full-power linac provides the beam power and a compressor ring shortens the pulse length from 1-ms down to 1 /spl mu/s. In the other, rapid cycling synchrotrons (RCSs) provide the beam power and also shorten the pulse length. A feasibility study of a staged approach to a 5-MW proton source utilizing RCS technology, allowing intermediate operation at 1 MW, was performed at ANL and is presented in this paper. This study is complementary to a study in progress at ORNL based on a linac and an accumulator ring. Our 1-MW facility consists of a 400-MeV injector linac that delivers 0.5-mA time-averaged current, a synchrotron that accelerates the beam to 2 GeV at a 30-Hz rate, and two neutron-generating target stations. In the second phase, the 2-GeV beam is accelerated to 10 GeV by a larger RCS, increasing the facility beam power to 5 MW.