Measurements of ({sup 3}He,d) reactions can provide information on the proton widths of states that play a role in astrophysically important (p,{gamma}) reactions. We report on the first study of the ({sup 3}He,d) reaction in inverse kinematics with a {sup 56}Ni (T{sub 1/2}=6.1 d) ion beam. The Q-value resolution of {approx} keV achieved in this experiment was sufficient to separate the transitions populating the ground state and the 1/2{sup -}-5/2{sup -} doublet at E{sub x}{approx}1.1 MeV in {sup 57}Cu. Prospects for similar ({sup 3}He,d) experiments with improved energy resolution are also discussed.

The rapid cycling synchrotron of the intense pulsed neutron source at Argonne National Laboratory normally operates at an average beam current of 14 to 15 mu A, accelerating protons from 50 to 450 MeV 30 times per second. The beam current is limited by a single-bunch vertical instability that occurs in the later part of the 14 ms acceleration cycle. By analyzing turn-by-turn beam position monitor data, two cases of vertical beam centroid oscillations were discovered. The oscillations start from the tail of the bunch, build up, and develop toward the head of the bunch. The development stops near the bunch center and oscillations remain localized in the tail for a relatively long time (2-4 ms, 1-2 x 10(4) turns). This vertical instability is identified as the cause of the beam loss. We compared this instability with a head-tail instability that was purposely induced by switching off sextupole magnets. It appears that the observed vertical instability is different from the classical head-tail instability.

Measurements of ($^{3}\mathrm{He}$,$d$) reactions can provide information on the proton widths of states that play a role in astrophysically important ($p,\ensuremath{\gamma}$) reactions. We report on the first study of the ($^{3}\mathrm{He}$,$d$) reaction in inverse kinematics with a $^{56}\mathrm{Ni}$$ ({T}_{1/2}=6.1 \mathrm{d})$ ion beam. The $Q$-value resolution of $~$ keV achieved in this experiment was sufficient to separate the transitions populating the ground state and the $1/{2}^{\ensuremath{-}}\text{\ensuremath{-}}5/{2}^{\ensuremath{-}}$ doublet at ${E}_{x}~1.1$ MeV in $^{57}\mathrm{Cu}$. Prospects for similar ($^{3}\mathrm{He}$,$d$) experiments with improved energy resolution are also discussed.

Measurements of (He-3,d) reactions can provide information on the proton widths of states that play a role in astrophysically important (p,gamma) reactions. We report on the first study of the (He-3, d) reaction in inverse kinematics with a Ni-56 (T-1/2 = 6.1 d) ion beam. The Q-value resolution of similar to 700 keV achieved in this experiment was sufficient to separate the transitions populating the ground state and the 1/2(-)-5/2(-) doublet at E-x similar to 1.1 MeV in Cu-57. Prospects for similar (He-3,d) experiments with improved energy resolution are also discussed.

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.

The rapid cycling synchrotron (RCS) of the intense pulsed neutron source (IPNS) at ANL accelerates > 3.0 times 10 12 protons from 50 MeV to 450 MeV with 30-Hz repetition frequency. During the acceleration cycle, the rf frequency varies from 2.21 MHz to 5.14 MHz. Presently, the beam current is limited by a vertical instability. By analyzing turn-by-turn beam position monitor (BPM) data, large- amplitude mode 0 and mode 1 vertical beam centroid oscillations were observed in the later part of the acceleration cycle. The oscillations start in the tail of the bunch, build up, and remain localized in the tail half of the bunch. This vertical instability was compared with a head-tail instability that was intentionally induced in the RCS by adjusting the trim sextupoles. It appears that our vertical instability is not a classical head-tail instability [1]. More data analysis and experiments were performed to characterize the instability.

In the rapid cycling synchrotron (RCS), a single proton bunch (h=1) is accelerated from 50 MeV to 450 MeV in approximately 14.2 ms. The bunch experiences an instability shortly after injection (<1 ms). During the first millisecond, the beam is bunched but little acceleration takes place; therefore this period is similar to a storage ring mode of operation. Natural vertical oscillations (assumed to be tune lines) show the vertical tune to be rising toward the bare tune value, suggesting neutralization of space charge and a reduction of its detuning effects. Neutralization time near injection ranges from 250 mus - 500 mus, depending on the background gas pressure. Oscillations move from the LSB to the USB before disappearing. Tune measurements made with a recently installed ferrite- magnet pinger system show the horizontal chromaticity to be positive early but approaching zero later in the cycle; on the other hand, the vertical chromaticity is negative throughout the cycle. During pinger studies near injection, two vertical lines are observed. Neutralization of the beam space charge implies the generation of plasma in the beam volume early in the cycle which may then dissipate as the time-varying electric fields of the beam become stronger.

The Rapid Cycling Synchrotron (RCS) of the Intense Pulsed Neutron Source (IPNS) at ANL accelerates > 3.0 times 10 12 protons from 50 MeV to 450 MeV with 30-Hz repetition frequency. During each acceleration cycle, the RF varies from 2.21 MHz to 5.14 MHz. In order to improve capture efficiency, we varied the injection timing and the early RF voltage profiles. The experimental results are compared with simulation results obtained with the 1-D tracking code, CAPTURE. This allowed us to optimize injection time and the RF voltage profile for better capture efficiency. An optimized injection time and RF voltage profile was found that resulted in raising the capture efficiency from 85.1% to 88.6%. These studies have now also been expanded to include second harmonic RF during the capture and initial acceleration cycle in the RCS.

Continuing with the work started two years ago, the technique of using a two-beamlet model to measure beam size is presented[1]. Beam signals are detected on terminated 50-Ω, stripline BPMs located in the transport line between the 50 MeV linac and rapid cycling synchrotron. Each BPM is constructed with four striplines: top, bottom, left and right. Using a fastsampling oscilloscope to compare the signals from opposite strip lines allows one to determine beam size assuming a two beamlet model. Measurements made with the two-beamlet approach are compared with other standard profile diagnostics such as wire-scanners, segmented Faraday cups, and scintillators. Advantages of the two-beamlet method are that it is non intrusive and does not require the presence of a background gas necessary for an IPM. Disadvantages of the technique are that it does not provide a detailed profile and the longitudinal beam pulse length must be short relative to the stripline length.

Pinger magnets for measuring horizontal and vertical tunes in the IPNS RCS have been constructed and installed. Reference horizontal tune data was collected using the extraction kicker magnets in December 2005. More recent data collected at the end of February 2006 with the dedicated pinger magnets confirms December measurements and provided simultaneous vertical tune information. Chromaticity variation with sextupole field strength is examined in an effort to optimize tune profiles.

Continuing with the work started two years ago, the technique of using a two-beamlet model to measure beam size is presented(1). Beam signals are detected on terminated 50-Ω, stripline BPMs located in the transport line between the 50 MeV linac and rapid cycling synchrotron. Each BPM is constructed with four striplines: top, bottom, left and right. Using a fast- sampling oscilloscope to compare the signals from opposite strip lines allows one to determine beam size assuming a two beamlet model. Measurements made with the two-beamlet approach are compared with other standard profile diagnostics such as wire-scanners, segmented Faraday cups, and scintillators. Advantages of the two-beamlet method are that it is non intrusive and does not require the presence of a background gas necessary for an IPM. Disadvantages of the technique are that it does not provide a detailed profile and the longitudinal beam pulse length must be short relative to the stripline length.

The Rapid Cycling Synchrotron (RCS) at IPNS is a sixperiod combined function synchrotron with a magnet structure of D00FDF0 which was commissioned and demonstrated operation up to 1x10 protons/pulse in 1979[1]. Operation was intermittent over the next couple years during which the extraction was changed to provide beam to the present IPNS target. Initial attempts to increase the charge/pulse in 1981 were limited by a headtail instability that had a threshold just under 1x10 protons/pulse. Tune measurements revealed that the horizontal chromaticity became slightly positive near the end of the acceleration cycle. The trim-sextupole power supplies were changed from dc to programmable to adjust the chromaticity, allowing an intensity increase to 2x10 protons/pulse[2]. Limited experiments of adding 2harmonic rf to spread the bunch longitudinally were performed in early 1983 and it was proposed to add a 3 rf cavity to improve beam handling as a route to higher charge per pulse[3]. Between 1983 and 1985, improvements to control loops[4] and the introduction of a cavity-to-cavity phase modulation (PM) or “scrambler” to broaden the bunch longitudinally[5] provided another intensity increase to slightly greater than 3x10 protons per pulse. Funding problems prevented development of a third rf cavity and the “scrambler” proved a low-cost cure to the instability threshold at 2x10 protons/pulse. Thus by 1985, the RCS had reached its original design goal of operating at 3x10 protons pulse. Funding constraints indefinitely postponed further attempts to get closer to the RCS’s space charge limit for a uniformly distributed beam of 5.6 x10 protons/pulse. Funding for U.S. DOE user facilities improved in the late 1990's and operational imperatives at IPNS changed from year-to-year survival to ensuring operation for the indefinite future with ever-increasing scientific capabilities. Neutron-scattering instrument improvements offered the most cost-effective route to significant gains, several of which have achieved data-rate increases of more than a factor of ten through adding detectors, neutron guides and other enhancements. For the accelerator system the goals were more modest, increase beam-on-target by increasing operating time (to ~ 30 weeks/year) and increase protons/pulse while maintaining or improving reliability. Initially, the emphasis had to be on updating or replacing those subsystems that were becoming obsolete (spares no longer available or nearing end-of-life) and controlling losses so that operating hours could increase without increasing the activation of components. Calculations[6] showed that improving synchrotron rf system capabilities could reduce beam losses, and had the further advantage of providing redundancy to improve reliability. Thus, fifteen years after the original proposal, work started on a third rf system[7] for the RCS. More recently, improvements in diagnostics and better computer modeling have let us take a more detailed look at what limits the charge-per-pulse in the RCS and begin studies to increase the threshold current of the instability.

The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 3.2×10E12protons from 50 MeV to 450 MeV in a single bunch (h=1) at 30 Hz. The rf frequency varies from 2.21 MHz to 5.14 MHz during the 14.2 ms acceleration interval. To maintain stability of the bunch, phase modulation is introduced to the rf at approximately twice the synchrotron frequency (synchrotron tune is 0.0014). This phase modulation causes a parametric quadrupole oscillation to develop in the bunch, and as this occurs, the bunch spectrum shows a significant increase in high frequency content. Without phase modulation, the beam experiences an instability which results in the loss of a large fraction of the charge 2-4 ms prior to extraction. It is unclear if the stability imparted to the beam by phase modulation comes from the quadrupole oscillation or from the high frequency excitation. A longitudinal tracking code has been modified to include amplitude and phase modulation of the bunch. The numerical analysis is used to compare growth rates with those observed in the machine. The results of this analysis will be important as we introduce second harmonic rf with a new third cavity in the RCS later in 2005.

The Energy Spread and Energy Monitor (ESEM) is an on-line, non-intrusive diagnostic used to characterize the output beam from the 200-MHz, 50-MeV IPNS linac. The energy spread is determined from a 3-size, longitudinal emittance measurement; whereas the energy is derived from time of flight (TOF) analysis. Signals are detected on 50-ohm, stripline beam position monitors (BPMs) terminated in their characteristic impedance. Each BPM is constructed with four striplines: top, bottom, left and right. The ESEM signals are taken from the bottom stripline in four separate BPM locations in the 50-MeV transport line between the linac and the synchrotron. Deterministic linac noise is sampled before and after the 70-microsecond macropulse. The noise phasor is vectorially subtracted from the beam signal. Noise subtraction is required at several frequencies, especially the fundamental and fifth harmonics (200 MHz and 1 GHz). It is also necessary to correct for attenuation and dispersion in the co-axial signal cables. Presently, the analysis assumes a single particle distribution to determine energy and energy spread. Work is on-going to allow for more realistic longitudinal distributions to be included in the analysis.

In the process of accelerating protons from 50 to 450 MeV at 30 Hz, low-energy electrons are generated within the IPNS RCS vacuum chamber. Electrons from background gas stripping are detected using an Ionization Profile Monitor (IPM) to generate integrated, horizontal charge distributions of the single-harmonic bunch during acceleration. Recently, a Retarding Field Analyzer (RFA) was installed in the RCS to look for evidence of beam-induced multipacting by measuring the electrons ejected by the space charge of the beam. A wide-band, high-gain transimpedance amplifier has been built to observe time structure in the electron signal detected with the RFA. Though a noisy power supply prevented full I-V characteristics from being obtained, interesting features are observed; especially, after the period of phase modulation between the rf cavities that is deliberately introduced during the cycle. The phase modulation generates a longitudinal quadrupole oscillation in the bunch, which is believed to enhance beam stability. Preliminary results indicate that electron multipacting is not significant in the RCS. The effects of background gas neutralization are considered and details of the RFA measurements are presented.

The Kicker system (1-2) is used to extract beam from the Rapid Cycling Synchrotron (RCS). The Kicker consists of four identical pulse circuits, each providing over 3.8 kA to each magnet winding. The magnet length is restricted to the space between vacuum bellows attached to the ring magnets. This leaves 0.89m for the magnet. To keep the voltage low the magnet conductor is broke up into 4, ¼-turn magnet windings. Each pulse circuit consists of a Pulse Forming Network (PFN) that is charged to 50 KV. The PFN is discharged through a thyratron into a 6.3-ohm transmission line to one of the magnet windings. Our system has always had marginal rise time of around 100 ns. Although the thyratron switching time is much faster than this, losses in the transmission lines cause the slower response. By using ferrite to make a fast switch between the transmission lines and the magnet, the rise time in the magnet can be reduced. To make a fast ferrite switch, the saturation point must carefully be chosen. Parameters related to choosing the proper ferrite to provide fast saturation, at the correct current will be discussed.

The Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 50 MeV protons to 450 MeV 30 times per second for spallation neutron production. Average current from the RCS has recently exceeded 16 muA with peak instantaneous current approaching 15 A. The RCS makes efficient use of 21 kV of RIF accelerating voltage and uses phase-modulation between the two rf cavities to damp vertical instabilities. Split-ring electrodes in the ring suggest an anomalous tune shift that increases with time in the acceleration cycle. Based on a background gas pressure of 1 muTorr, the neutralization time for the beam is approximately 0.5 ms at injection suggesting the beam becomes fully neutralized relatively quickly in the cycle. Over-neutralization of the beam can lead to a positive tune shift that is presumably incoherent. Studies are underway to characterize the ionization within the RCS using the existing Profile and Position System (PAPS) and a newly installed Retarding Field Analyzer (RFA). Also a newly installed fast, deep-memory digitizing oscilloscope allows the entire history of a single acceleration cycle to be recorded from all four components of the split ring electrodes simultaneously at a rate of 250 MS/s.