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Overview of proton drivers for neutrino super beams and neutrino factories

Description: There has been a world-wide interest in Proton Drivers in the past decade. Numerous design proposals have been presented in Asia, Europe and North America, ranging from low energy rapid cycling synchrotrons, normal or superconducting linacs to high energy slow cycling synchrotrons and FFAGs. One thing in common is that all these machines provide MW beam power and are used primarily for neutrino experiments. This paper gives an overview of these activities. In the last section the author expresses his personal opinion on the future of this field.
Date: June 1, 2006
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

A Simple Transition-Free Lattice of an 8 GeV Proton Synchroton

Description: A transition-free lattice is a basic requirement of a high-intensity medium-energy (several GeV) proton synchrotron in order to eliminate beam losses during transition crossing. An 8 GeV synchrotron is proposed as a principal component in an alternative hybrid design of Project-X [1]. This machine would be housed in the Fermilab antiproton source enclosure replacing the present Debuncher. A simple doublet lattice with high transition gamma has been designed. It uses just one type of dipoles and one type of quadrupoles (QF and QD are of the same length). It has no transition crossing. It has a triangular shape with three zero dispersion straight sections, which can be used for injection, extraction, RF and collimators. The beta-functions and dispersion are low. This lattice has plenty of free space for correctors and diagnostic devices, as well as good optical properties including large dynamic aperture, weak dependence of lattice functions on amplitude and momentum deviation.
Date: May 1, 2009
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

High energy H- ion transport and stripping

Description: During the Proton Driver design study based on an 8 GeV superconducting RF H{sup -} linac, a major concern is the feasibility of transport and injection of high energy H{sup -} ions because the energy of H{sup -} beam would be an order of magnitude higher than the existing ones. This paper will focus on two key technical issues: (1) stripping losses during transport (including stripping by blackbody radiation, magnetic field and residual gases); (2) stripping efficiency of carbon foil during injection.
Date: May 1, 2005
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Negative transverse impedance

Description: Recently, measurements in the SPS show that the coherent tune shift in the horizontal direction has positive values whereas that in the vertical direction has negative ones. Thus the existence of negative transverse impedance gets confirmed in a real machine. This stimulates us to start a new round of systematic studies on this interesting phenomenon. The results obtained from our computer simulations are presented in this note. Our simulations demonstrate that the negative transverse impedance may appear when the rotational symmetry embedded in a discontinuity is broken, and that the geometries that we have studies may be the source of the positive horizontal tune shift measured in the SPS.
Date: June 12, 1989
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Emittance growth due to ground motions

Description: To evaluate the dynamic emittance growth due to ground motions for a synchrotron light source, a method using the so-called transfer function. This method assumes, among others, that the displacement of the magnetic elements is equal to that of the ground. In other words, the support effects are neglected. on the other hand, another reference proposes a normal-mode method to calculate the displacement magnification due to supports. It is then natural to combine the two methods together to get a more complete picture of the vibration - emittance growth problem.
Date: October 1, 1988
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

The method of boundary perturbation, and its application to wakefield calculations

Description: The boundary perturbation method, suggested by Zhang and (independently) by Chatard-Moulin, Cooper, and their colleagues, is employed to the wakefield calculations for geometrical discontinuities in accelerators. Results are compared with that obtained from the mesh calculations using TBCI. When the perturbation is small and the geometry is suitable for TBCI, agreement is good. Discrepancies observed in other cases are also discussed.
Date: December 31, 1990
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

3-D computer simulations of EM field sin the APS vacuum chamber. Part 2: Time-domain analysis

Description: Our simulations suggest that the strong peak around 4 GHz in the narrow gap observed in the measurements is generated by TE modes. Therefore, one should not worry about this peak insofar as the coupling impedance is concerned. On the other hand, some discrepancies between our simulations and the measurements are noticed and remain to be resolved.
Date: January 20, 1989
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Beam instability studies for the SSC

Description: Beam instability studies of the Superconducting Super Collider (SSC) during the period 1989--1993 are briefly reviewed in this paper. Various topics are covered: single bunch and multi-bunch, single beam and beam-beam, parasitic heating and active feedback, etc. Although the SSC will not be built, many of the results obtained from these studies remain as useful references to the accelerator community.
Date: September 1, 1994
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Acccelerator Physics Issues of a Very Large Hadron Collider

Description: A Very Large Hadron Collider (VLHC) was proposed for the post-LHC future. This paper gives a quick survey of a number of accelerator physics issues based on the information obtained from a parameter spreadsheet SSP. The main technical challenges to build such a machine appear to be: the large number of events per crossing (in hundreds), enormous beam stored energy (equivalent to tens tons of TNT), ground motion (which is particularly harmful when the synchrotron frequency is in the sub-Hertz range), small dynamic aperture (due to long filling time), fast growth of the resistive wall instability (in a fraction of one turn), low threshold of the single bunch transverse instability (due to big machine size), strong synchrotron radiation (at a level close to the LEP) and short radiation damage lifetime, etc. Possible solutions to some of these problems will also be discussed.
Date: June 1, 1997
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Impedance Scaling and Impedance Control

Description: When a machine becomes really large, such as the Very Large Hadron Collider (VLHC), of which the circumference could reach the order of megameters, beam instability could be an essential bottleneck. This paper studies the scaling of the instability threshold vs. machine size when the coupling impedance scales in a ``normal`` way. It is shown that the beam would be intrinsically unstable for the VLHC. As a possible solution to this problem, it is proposed to introduce local impedance inserts for controlling the machine impedance. In the longitudinal plane, this could be done by using a heavily detuned rf cavity (e.g., a biconical structure), which could provide large imaginary impedance with the right sign (i.e., inductive or capacitive) while keeping the real part small. In the transverse direction, a carefully designed variation of the cross section of a beam pipe could generate negative impedance that would partially compensate the transverse impedance in one plane.
Date: June 1, 1997
Creator: Chou, W. & Griffin, J.
Partner: UNT Libraries Government Documents Department

3-D computer simulations of EM fields in the APS vacuum chamber: Part 1, Frequency-domain analysis

Description: The vacuum chamber proposed for the storage ring of the 7-GeV Advanced Photon Source (APS) basically consists of two parts: the beam chamber and the antechamber, connected to each other by a narrow gap. A sector of 1-meter-long chamber with dosed end plates, to which are attached the 1-inch-diameter beampipes centered at the beam chamber, has been built for experimental purposes. The 3-D code MAFIA has been used to simulate the frequency-domain behaviors of EM fields in this setup. The results are summarized in this note and are compared with that previously obtained from 2-D simulations and that from network analyzer measurements. They are in general agreement. A parallel analysis in the time-domain is reported in a separate note. The method of our simulations can be briefly described as follows. The 1-inch diameter beampipes are terminated by conducting walls at a length of 2 cm. The whole geometry can thus be considered as a cavity. The lowest RF modes of this geometry are computed using MAFIA. The eigenfrequencies of these modes are a direct output of the eigenvalue solver E3, whereas the type of each mode is determined by employing the postprocessor P3. The mesh sizes are chosen such that they are small enough for computations in the frequency region in which we are interested (the sampling theorem), while the total number of mesh points is still well within the range that our computer system can cope with.
Date: September 4, 1990
Creator: Chou, W. & Bridges, J.
Partner: UNT Libraries Government Documents Department

Impedance studies: Part 1, A composition rule

Description: The impedances and the loss factors experienced by a particle beam that circulates in the APS storage ring play an essential role in the studies of the beam instability problem. Due to a large variety of structures in the ring, the computation of these parameters amounts to enormous work. During the last months, this was tackled numerically by invoking the MAFIA family, a set of codes developed mainly at DESY. The results are to be reported in several LS notes. This note is the first part and will discuss a composition rule that we observed in our calculations. The composition rule can be stated as follows. For a complicated structure, one may decompose it into simple components and compose these components to form new structures. Under certain conditions, the old and the new structures will give the same loss factors. This rule is in analogy to and an extension of the law of addition of resistances in sequence in the conventional circuit theory. We will discuss two examples to illustrate this rule.
Date: July 1, 1988
Creator: Chou, W. & Jin, Y.
Partner: UNT Libraries Government Documents Department

Emittance growth in a storage ring due to ground motion

Description: For a synchrotron light source designed for a small natural emittance, ground motion could lead to a non-negligible growth in emittance. When the ground motion is of the plane-wave type, one can study this dynamical process analytically by employing a method that combines the previously developed transfer function technique with a normal mode analysis that takes into account the magnification of the motion due to magnet supports. The explicit relationship between the amplitudes of the ground vibration and the emittance growth as a function of the vibration frequency is presented. Numerical examples are included. 3 refs., 3 figs., 1 tab.
Date: January 1, 1989
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

Fast beam stacking using rf barriers

Description: Two barrier RF systems were fabricated, tested and installed in the Fermilab Main Injector. Each can provide 8 kV rectangular pulses (the RF barriers) at 90 kHz. When a stationary barrier is combined with a moving barrier, injected beams from the Booster can be continuously deflected, folded and stacked in the Main Injector, which leads to doubling of the beam intensity. This paper gives a report on the beam experiment using this novel technology.
Date: June 1, 2007
Creator: Chou, W.; Capista, D.; Griffin, J.; Ng, K.-Y.; Wildman, D. & /Fermilab
Partner: UNT Libraries Government Documents Department

Induction barrier RF and applications in Main Injector

Description: Two induction barrier rf systems have been designed and fabricated at Fermilab and installed in the Main Injector. They use the nanocrystal magnetic alloy called Finemet for the cavities and high voltage fast MOSFET switches for the modulators. Each system delivers {+-}10 kV square pulses at 90 kHz. They have been used for adiabatic beam stacking (beam compression), machine acceptance measurement and gap cleaning in the injection area for magnet protection, and will be tested for fast beam stacking for doubling the proton flux on the NuMI production target. The systems work reliably and cost much less than a resistive barrier rf system. Comparison with a similar system built at KEK reveals many similarities and also some important differences. This work is partially funded by the US-Japan collaborative agreement.
Date: July 1, 2006
Creator: Chou, W.; Wildman, D.; /Fermilab; Takagi, A. & /KEK, Tsukuba
Partner: UNT Libraries Government Documents Department

Report on Workshop on Future Directions for Accelerator R&D at Fermilab

Description: Accelerator R&D has played a crucial role in enabling scientific discovery in the past century and will continue to play this role in the years to come. In the U.S., the Office of High Energy Physics of DOE's Office of Science is developing a plan for national accelerator R&D stewardship. Fermilab undertakes accelerator research, design, and development focused on superconducting radio-frequency (RF), superconducting magnet, beam cooling, and high intensity proton technologies. In addition, the Lab pursues comprehensive integrated theoretical concepts and simulations of complete future facilities on both the energy and intensity frontiers. At present, Fermilab (1) supplies integrated design concept and technology development for a multi-MW proton source (Project X) to support world-leading programs in long baseline neutrino and rare processes experiments; (2) plays a leading role in the development of ionization cooling technologies required for muon storage ring facilities at the energy (multi-TeV Muon Collider) and intensity (Neutrino Factory) frontiers, and supplies integrated design concepts for these facilities; and (3) carries out a program of advanced accelerator R&D (AARD) in the field of high quality beam sources, and novel beam manipulation techniques.
Date: September 1, 2009
Creator: Shiltsev, V.; Church, M.; Spentzouris, P.; Chou, W. & /Fermilab
Partner: UNT Libraries Government Documents Department

Efficiency and lifetime of carbon foils

Description: Charge-exchange injection by means of carbon foils is a widely used method in accelerators. This paper discusses two critical issues concerning the use of carbon foils: efficiency and lifetime. An energy scaling of stripping efficiency was suggested and compared with measurements. Several factors that determine the foil lifetime--energy deposition, heating, stress and buckling--were studied by using the simulation codes MARS and ANSYS.
Date: November 1, 2006
Creator: Chou, W.; /Fermilab; Kostin, M.; /Michigan State U., NSCL; Tang, Z. & /Fermilab
Partner: UNT Libraries Government Documents Department

Summary of sessions B and F: High intensity linacs and frontend & proton drivers

Description: This paper summarizes the sessions B&F of the 33rd ICFA Advanced Beam Dynamics Workshop on High Intensity & High Brightness Hadron Beams held in Bensheim, Germany. It covers high intensity linacs, front ends and proton driver topics.
Date: January 1, 2005
Creator: Ferdinand, R.; /Saclay; Chou, W.; /Fermilab; Galambos, J. & Ridge, /Oak
Partner: UNT Libraries Government Documents Department

BPERM version 3.0: A 2-D wakepotential/impedance code

Description: BPERM 3.0 is an improved version of a previous release. The main purpose of this version is to make it more user friendly. Following a simple 1-2-3 procedure, one obtains both text and graphical output of the wakepotential and impedance for a given geometry. The calculation is based on a boundary perturbation method, which is significantly faster than numerical simulations. It is accurate when the discontinuities are small. In particular, it works well for tapered structures. 5 refs., 3 figs.
Date: October 1, 1996
Creator: Barts, T. & Chou, W.
Partner: UNT Libraries Government Documents Department

Summary report on transverse emittance preservation

Description: During the past years, significant progress has been made in understanding the beam transverse emittance blow-up and its preservation. However, one often finds him-/herself ignorant when he/she tries to explain what was observed in an existing machine or to predict what will happen in a machine under design. There are a number of such examples given in this report. Some of them are even fundamental. These are the challenges. But they are also the directions leading to new achievements. The workshop gladly acknowledged them and promised to work on them.
Date: December 1, 1997
Creator: Chou, W. & Vos, L.
Partner: UNT Libraries Government Documents Department

REPORT OF THE SNOWMASS M6 WORKING GROUP ON HIGH INTENSITY PROTON SOURCES.

Description: The M6 working group had more than 40 active participants (listed in Section 4). During the three weeks at Snowmass, there were about 50 presentations, covering a wide range of topics associated with high intensity proton sources. The talks are listed in Section 5. This group also had joint sessions with a number of other working groups, including E1 (Neutrino Factories and Muon Colliders), E5 (Fixed-Target Experiments), M1 (Muon Based Systems), T4 (Particle Sources), T5 (Beam dynamics), T7 (High Performance Computing) and T9 (Diagnostics). The M6 group performed a survey of the beam parameters of existing and proposed high intensity proton sources, in particular, of the proton drivers. The results are listed in Table 1. These parameters are compared with the requirements of high-energy physics users of secondary beams in Working Groups E1 and E5. According to the consensus reached in the E1 and E5 groups, the U.S. HEP program requires an intense proton source, a 1-4 MW Proton Driver, by the end of this decade.
Date: August 14, 2001
Creator: CHOU,W. & WEI,J.
Partner: UNT Libraries Government Documents Department

Dynamic aperture studies during collisions in the LHC

Description: The dynamic aperture during collisions in the LHC is mainly determined by the beam-beam interactions and by multipole errors of the high gradient quadrupoles in the interaction regions. The computer code JJIP has been modified to accommodate the LHC lattice configuration and parameters and is employed in this study. Simulations over a range of machine parameters are carried out, and results of preliminary investigation are presented.
Date: June 1, 1997
Creator: Chou, W., Ritson, D.
Partner: UNT Libraries Government Documents Department