The primary purpose of the Fermilab Recycler Ring Transverse Digital Damper System is to prevent instabilities due to high phase space densities of the cooled antiproton beam. The system was designed to facilitate Beam Transfer Function measurements using a signal analyzer connected to auxiliary system ports for timing and diagnostic purposes. The Digital Damper System has the capability for both open and closed loop measurements. The Beam Transfer Function provides direct measurement of the machine impedance, and beam and lattice parameters such as betatron tune and chromaticity. An overview of the technique is presented along with analysis and results from open and closed loop measurements in the Fermilab Recycler Ring.
We present a simulation study to characterize the stability region of the Fermilab (FNAL) Recycler in the context of secondary emission yield (SEY). Interactions between electrons and beam pipe material can produce electron clouds that jeopardize beam stability in certain focusing configurations. Such an instability was documented in the Recycler, and the work presented here reflects improvements to better understand that finding. We incorporated the Furman-Pivi Model into a PyECLOUD analysis, and we determined the instability threshold given various bunch lengths, intensities, SEY magnitudes,…
Simple model of electron cloud is developed in the paper to explain e-cloud instability of bunched proton beam in the Fermilab Recycler. The cloud is presented as an immobile snake in strong vertical magnetic field. The instability is treated as an amplification of the bunch injection errors from the batch head to its tail. Nonlinearity of the e-cloud field is taken into account. Results of calculations are compared with experimental data demonstrating good correlation.
A means for non-invasive measurement of transverse and longitudinal characteristics of bunched beams in synchrotrons has been developed based on high sensitivity slotted waveguide pickups. The pickups allow for bandwidths exceeding hundreds of MHz while maintaining good beam sensitivity characteristics. Wide bandwidth is essential to allow bunch-by-bunch measurements by means of a fast gate. The Schottky detector system is installed and successfully commissioned in the Fermilab Tevatron, Recycler and CERN LHC synchrotrons. Measurement capabilities include tune, chromaticity, and momentum sprea…
Theoretical analysis of e-cloud instability in the Fermilab Recycler is represented in the paper. The e-cloud in strong magnetic field is treated as a set of immovable snakes each being initiated by some proton bunch. It is shown that the instability arises because of injection errors of the bunches which increase in time and from bunch to bunch along the batch being amplified by the e-cloud electric field. The particular attention is given to nonlinear additions to the cloud field. It is shown that the nonlinearity is the main factor which restricts growth of the bunch amplitude. Possible rol…
Fermilab's Recycler ring was used as a storage ring for accumulation and subsequent manipulations of 8-GeV antiprotons destined for the Tevatron collider. To satisfy these missions, a unique electron cooling system was designed, developed and successfully implemented. The most important features that distinguish the Recycler cooler from other existing electron coolers are its relativistic energy (it employs a 4.3 MeV, 0.1 A DC electron beam), a weak continuous longitudinal magnetic field in the cooling section (~100 G), and lumped focusing elsewhere. With the termination of the collider operat…
An electron cloud instability might limit the intensity in the Fermilab Recycler after the PIP-II upgrade. A multibunch instability typically develops in the horizontal plane within a hundred turns and, in certain conditions, leads to beam loss. Recent studies have indicated that the instability is caused by an electron cloud, trapped in the Recycler index dipole magnets. We developed an analytical model of an electron cloud driven instability with the electrons trapped in combined function dipoles. The resulting instability growth rate of about 30 revolutions is consistent with experimental o…
The transfer line for beam extraction from the Recycler ring to P1 line provides a way to deliver 8 GeV kinetic energy protons from the Booster to the Delivery ring, via the Recycler, using existing beam transport lines, and without the need for new civil construction. It was designed in 2012. The kicker magnets at RR520 and the lambertson magnet at RR522 in the RR were installed in 2014 Summer Shutdown, the elements of RR to P1 Stub (permanent quads, trim quads, correctors, BPMs, the toroid at 703 and vertical bending dipole at V703 (ADCW) were installed in 2015 Summer Shutdown. On Tuesday, J…
For NOvA and future experiments requiring high intensity proton beams, Fermilab is in the process of upgrading the existing accelerator complex for increased proton production. One such improvement is to reduce the Main Injector cycle time, by performing slip stacking, previously done in the Main Injector, in the now repurposed Recycler Ring. Recycler slip stacking requires two new RF cavities operating at slightly different frequencies (df = 1260Hz). These are copper, coaxial, quarter wave cavities with R/Q =13 ohms. They operate at a peak gap voltage of 150 kV with 150 kW peak drive power (6…
At the end of its operations in 2011, the Fermilab antiproton production complex consisted of a sophisticated target system, three 8-GeV storage rings (namely the Debuncher, the Accumulator and the Recycler), 25 independent multi-GHz stochastic cooling systems, the world's only relativistic electron cooling system and a team of technical experts equal to none. The accelerator complex at Fermilab supported a broad physics program including the Tevatron Collider Run II, neutrino experiments using 8-GeV and 120-GeV proton beams, as well as a test beam facility and other fixed target experiments u…
Transverse instabilities of the antiproton beam have been observed in the Recycler ring soon after its commissioning. After installation of transverse dampers, the threshold for the instability limit increased significantly but the instability is still found to limit the brightness of the antiprotons extracted from the Recycler for Tevatron shots. In this paper, we describe observations of the instabilities during the extraction process as well as during dedicated studies. The measured instability threshold phase density agrees with the prediction of the rigid beam model within a factor of 2. …
For NOvA and future experiments requiring high intensity proton beams, Fermilab is in the process of upgrading the existing accelerator complex for increased proton production. One such improvement is to reduce the Main Injector cycle time, by performing slip stacking, previously done in the Main Injector, in the now repurposed Recycler Ring. Recycler slip stacking requires new tuneable RF cavities, discussed separately in these proceedings. These are quarter wave cavities resonant at 52.809 MHz with a 10 kHz tuning range. The 10 kHz range is achieved by use of a tuner which has an electrical …
The extraction bucket position in the Fermilab Booster is controlled with a cogging process that involves the comparison of the Booster RF count and the Recycler Ring revolution marker. A one RF bucket jitter in the extraction bucket position results from the variability of the process that phase matches the Booster to the Recycler. However, the new slow phase lock process used to lock the frequency and phase of the Booster RF to the Recycler RF has been made digital and programmable and has been modified to correct the extraction notch position. The beam loss at the Recycler injection has bee…
In order to achieve higher luminosities in Run II a separate antiproton storage ring was built in the Main Injector tunnel. To reduce both construction and operations costs permanent magnets were used. This paper discusses the design criterion and specifications, including temperature dependence, longitudinal uniformity, and adjusting of the higher harmonics of the magnets. The design tolerances for a storage ring are more stringent than for a single pass beam line. The difference between the measured and ideal central field for each magnet was held to better than 0.1%. The temperature stabili…
In era of NOvA operation, it is planned to slip-stack six on six Booster proton batches in the Recycler ring for a total intensity of 5 1013 protons/cycle. During the slip-stacking, the chromaticities are required to be jumped from (-2,-2) to (-20,-20). However, they can only be adjusted to (-12,-12) from (-2,-2) using existing 2 families of powered sextupoles. On the other hand, the presently designed Recycler lattice for Nova replaces the 30 straight section with 8 D-D half FODO cells . We use 3 quads in a half-cell to obtain the working point under the limit of the feasible quad strength, a…
The Recycler Electron Cooler (REC) was the first cooler working at a relativistic energy (gamma = 9.5). It was successfully developed in 1995-2004 and was in operation at Fermilab in 2005-2011, providing cooling of antiprotons in the Recycler ring. After introducing the physics of electron cooling and the REC system, this paper describes measurements carried out to tune the electron beam and optimize its cooling properties. In particular, we discuss the cooling strategy adopted for maximizing the collider integrated luminosity.
The Fermilab Booster is a fast ramping (15Hz) synchrotron which accelerates protons from 400MeV to 8GeV. During commissioning of a transverse digital damper system, it was shown that the damper could provide a measurement of the machine tune throughout the cycle by exciting just 1 of the 84 bunches with minimal impact on the machine operation. The algorithms used to make the measurement have been incorporated into the damper FPGA firmware allowing for real-time tune monitoring of all Booster cycles.
The Main Injector (MI) was commissioned using data acquisition systems developed for the Fermilab Main Ring in the 1980s. New VME-based instrumentation was commissioned in 2006 for beam loss monitors (BLM)[2], which provided a more systematic study of the machine and improved displays of routine operation. However, current projects are demanding more data and at a faster rate from this aging hardware. One such project, Real-time Edge AI for Distributed Systems (READS), requires the high-frequency, low-latency collection of synchronized BLM readings from around the approximately two-mile accele…
The brightness of the antiproton beam in Fermilab's 8 GeV Recycler ring is limited by a transverse instability. This instability has occurred during the extraction process to the Tevatron for large stacks of antiprotons even with dampers in operation. This paper describes observed features of the instability, introduces the threshold phase density to characterize the beam stability, and finds the results to be in agreement with a resistive wall instability model. Effective exclusion of the longitudinal tails from Landau damping by decreasing the depth of the RF potential well is observed to lo…
The Recycler Ring at Fermilab uses a barrier rf system for all of its rf manipulations. In this paper, I will give an overview of historical perspective on barrier rf systems, the longitudinal beam dynamics issues, aspects of rf linearization to produce long flat bunches and methods used for emittance measurements of the beam in the RR barrier rf buckets. Current rf manipulation schemes used for antiproton beam stacking and longitudinal momentum mining of the RR beam for the Tevatron collider operation are explained along with their importance in spectacular success of the Tevatron luminosity …
During Nova operations it is planned to run the Fermilab Recycler in a 12 batch slip stacking mode. In preparation for this, measurements of the tune during a six batch injection and then as the beam is slipped by changing the RF frequency, but without a 7th injection, have been carried out in the Main Injector. The coherent tune shifts due to the changing beam intensity were measured and compared well with the theoretically expected tune shift. The tune shifts due to changing RF frequency, required for slip stacking, also compare well with the linear theory, although some nonlinear affects ar…
The Fermilab Proton Improvement Plan II, or PIP-II, would enable the world's most intense high-energy neutrino beam and would help scientists search for rare particle physics processes. The PIP-II goal is to deliver 1.2 MW of proton beam power from the Fermilab Main Injector, over the energy range 60 - 120 GeV, at the start of operation of the LBNF/DUNE program. PIP-II provides a variety of upgrade paths to higher beam power from the Main Injector, as demanded by the neutrino science program and as recommended by the 2014 P5 report. Delivering more than 2 MW to the LBNF target in the future wi…
The latest generation of IPMs installed in the Fermilab Main Injector and Recycler incorporate a 1 kG permanent magnet, a newly designed high-gain, rad-tolerant preamp, and a control grid to moderate the charge that is allowed to arrive on the anode pick-up strips. The control grid is intended to select a single Booster batch measurement per turn. Initially it is being used to allow for a faster turn-on of a single, high-intensity cycle in either machine. The expectation is that this will extend the Micro Channel Plate lifetime, which is the high-cost consumable in the measurement system. We d…
Antiprotons in Fermilab's Recycler ring are cooled by a 4.3 MeV, 0.1 - 0.5 A DC electron beam (as well as by a stochastic cooling system). The unique combination of the relativistic energy (γ = 9.49), an Ampere - range DC beam, and a relatively weak focusing makes the cooling efficiency particularly sensitive to ion neutralization. A capability to clear ions was recently implemented by way of interrupting the electron beam for 1-30 \mus with a repetition rate of up to 40 Hz. The cooling properties of the electron beam were analyzed with drag rate measurements and showed that accumulated ions s…
Electron cloud can lead to a fast instability in intense proton and positron beams in circular accelerators. In the Fermilab Recycler the electron cloud is confined within its combined function magnets. We show that the field of combined function magnets traps the electron cloud, present the results of analytical estimates of trapping, and compare them to numerical simulations of electron cloud formation. The electron cloud is located at the beam center and up to 1% of the particles can be trapped by the magnetic field. Since the process of electron cloud build-up is exponential, once trapped …
I describe a new scheme for selectively isolating high density low longitudinal emittance beam particles in a storage ring from the rest of the beam without emittance dilution. I discuss the general principle of the method, called longitudinal momentum mining, beam dynamics simulations and results of beam experiments. Multi-particle beam dynamics simulations applied to the Fermilab 8 GeV Recycler (a storage ring) convincingly validate the concepts and feasibility of the method, which I have demonstrated with beam experiments in the Recycler. The method presented here is the first of its kind.
Fermilab Booster synchrotron requires an intensity upgrade from 4.5x1012 to 6.5x1012 protons per pulse as a part of Fermilabs Proton Improvement Plan-II (PIP-II). One of the factors which may limit the high-intensity performance is the fast transverse instabilities caused by electron cloud effects. According to the experience in the Recycler, the electron cloud gradually builds up over multiple turns in the combined function magnets and can reach final intensities orders of magnitude greater than in a pure dipole. Since the Booster synchrotron also incorporates combined function magnets, it is…
The development of magnetic cogging is part of the Fermilab Booster upgrade within the Proton Improvement Plan (PIP). The Booster is going to send 2.25E17 protons/hour which is almost double the present flux, 1.4E17 protons/hour to the Main Injector (MI) and Recycler (RR). The extraction kicker gap has to synchronize to the MI and RR injection bucket in order to avoid a beam loss at the rising edge of the extraction and injection kickers. Magnetic cogging is able to control the revolution frequency and the position of the gap using the magnetic field from dipole correctors while radial positio…
One of the factors which may limit the intensity in the Fermilab Recycler is a fast transverse instability. It develops within a hundred turns and, in certain conditions, may lead to a beam loss. The high rate of the instability suggest that its cause is electron cloud. We studied the phenomena by observing the dynamics of stable and unstable beam, simulating numerically the build-up of the electron cloud, and developed an analytical model of an electron cloud driven instability with the electrons trapped in combined function di-poles. We found that beam motion can be stabilized by a clearing …
Currently, Fermilab Booster accelerates ~4.5E12 protons per pulse (ppp) in 81 bunches from 400 MeV to 8 GeV at 15 Hz to provide beam to multiple HEP experiments and is being upgraded to handle higher beam intensity >6.7E12 ppp at a repetition rate of 20 Hz. In the current mode of operation, we control longitudinal coupled bunch instabilities (LCBI) using combination of passive and active dampers. The issues with LCBI are expected to worsen at higher beam intensities. Here, we would like to investigate at what time in the beam cycle a particular mode is going to originate and how much it contri…
In this Letter, I report on a novel scheme for beam stacking without any beam emittance dilution using a barrier rf system in synchrotrons. The general principle of the scheme called longitudinal phase-space coating, validation of the concept via multi-particle beam dynamics simulations applied to the Fermilab Recycler, and its experimental demonstration are presented. In addition, it has been shown and illustrated that the rf gymnastics involved in this scheme can be used in measuring the incoherent synchrotron tune spectrum of the beam in barrier buckets and in producing a clean hollow beam …
Our objective will be to integrate ML into Fermilab accelerator operations and furthermore provide an accessible framework which can also be used by a broad range of other accelerator systems with dynamic tuning needs. We will develop of real-time accelerator control using embedded ML on-chip hardware and fast communication between distributed systems in this proposal. We will demonstrate this technology for the Mu2e experiment by increasing the overall duty factor and uptime of the experiment through two synergistic projects. First, we will use deep reinforcement learning techniques to improv…
