P. Limon

Bio: P. Limon is an academic researcher. The author has contributed to research in topics: Particle accelerator & Vacuum tube. The author has an hindex of 1, co-authored 3 publications receiving 11 citations.

Synchrotron radiation issues in the VLHC

Abstract: Fermilab and other DOE high energy physics laboratories are studying the possibility of a Very Large Hadron Collider (VLHC) for operation in the post-LHC era. The current VLHC design foresees a 2-staged approach, where the second stage (referred to as VLHC-2) has a proton energy up to 100 TeV at a peak luminosity of 2/sup ./10/sup 34/ cm/sup -2/ sec/sup -1/. The protons are guided through a large 233 km circumference ring with 10 T bending magnets using Nb/sub 3/Sn superconductor at 5 K. The synchrotron radiation (SR) power emitted by the beam in such a machine is /spl sim/5 W/m/beam. However, other VLHC scenarios with smaller rings and higher luminosity result in SR power levels exceeding this value, reaching 10 or even 20 W/m/beam. Intercepting and removing this power in a cryogenic environment is a major challenge. In this paper a discussion of SR in the VLHC-2, and various approaches to the issue, are presented.

Synchrotron radiation and beam tube vacuum in a Very Large Hadron Collider, Stage 1 and Stage 2 VLHC

Abstract: SYNCHROTRON RADIATION AND BEAM TUBE VACUUM IN A VERY LARGE HADRON COLLIDER, STAGE 1 AND STAGE 2 VLHC ℵ M. Pivi * , W.C. Turner, LBNL, Berkeley, CA 94720, USA P. Bauer and P. Limon, FNAL, Batavia, IL 60510 USA Abstract Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime [1]. We discuss the beam tube vacuum in the low field Stage 1 and Stage 2 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. In Stage 2, the ~100 o K beam screen, or liner, illuminated by the synchrotron radiation, is inserted into the magnet cold bore. Cryo-pumping is provided by the cold bore kept at 4.2 o K, through slots covering the beam screen surface. Possible beam conditioning scenarios are presented for reaching design intensity, both for Stage 1 and 2. The most important results are summarized in this paper. pumping speed for CH 4 is then S eff ~2.2 l/s-m [2]. We will define the beam-gas scattering lifetime to be negligible when τ g >5 τ L , with τ L = τ pp /2 = 46.5 hrs. Once τ g = 5 τ L =232 hrs is fixed, we estimate the average beam tube gas pressure for each gas species taken separately, with the results given in the second column of Table 2. From Table 2, we can see that the CO scattering equivalent tube pressure should be less than 0.33 nTorr to reach τ g >5 τ L . Table 1.VLHC parameters for the low field Stage 1, the high field Stage 2, and related synchrotron radiation parameters. Parameter Beam energy Dipole field Circumference Bunch population Total beam current Luminosity Beam pipe semi-axis Beam pipe temperat. IP pp collision lifetime Critical photon energy Photon flux SR power per meter Symbol E, TeV B, T C, km N b I, mA L, cm s a,b cm o T, K τ pp , hrs E c , eV Γ ph/s-m P', W/m 1 INTRODUCTION In the present report the required pumping speed, a possible beam current conditioning scenario, and the beam-gas scattering lifetime are discussed for Stage 1 and Stage 2 VLHC. A self-consistent calculation is performed assuming that the beam lifetime depends on the beam tube vacuum gas pressure and on the pp collision rate at two interaction points (IPs). The vacuum tube pressure, and therefore the beam-gas scattering lifetime, is a function of the beam intensity. The parameters necessary for evaluating the beam tube vacuum in the two VLHC stages are shown in Tables 1. In Table 1, τ pp represents the proton lifetime determined by pp collisions at two IPs at the design luminosity, with the p-p total cross section assumed to be σ pp =137 mb at 40 TeV c.m. and σ pp =178 mb at 175 TeV cm. Stage 1 2.5 x 10 10 1 x 10 34 0.9 x 1.4 7.9 x 10 Stage 2 7.5 x 10 9 2 x 10 34 1.0 x 1.5 1.2 x 10 Table 2: Numerical bounds on beam tube pressure Stage 1, ambient room temperature equivalent pressure. gas H 2 CH 4 H 2 O CO CO 2 P j [at τ g =5τ L ] (nTorr) P j [at 0.1W/m] (nTorr) 2 VACUUM SYSTEM FOR THE STAGE 1 VLHC In the low field Stage 1 VLHC, we will consider a distributed NEG strip plus lumped ion or cryo pump system for pumping methane, in a pumping antechamber connected to the beam tube with long slots. We assume lumped ion pumps, with pumping speed S=30 l/s, are connected to the pumping antechamber at an axial interval of L=22.5meters. The effective cylindrical diameter of the antechamber is 8.3cm. The pumping speed of the lumped ion pumps will be conductance limited by the beam tube and the antechamber, and the effective We estimate the beam tube pressure that would result in a scattered beam power of 0.1 W/m, results for each gas species are given in the third column of Table 2, where we can see that the pressure limiting factor is given by beam- gas scattering particle loss rather than the power loss. 2.1 Photodesorption in Stage 1 The inverse power dependence of the photodesorption yield on the photon dose implies the so called conditioning effect, or the decreasing photodesorption yield due to the removal of gas molecules from the near surface oxide layer with continued exposure to photons. The photodesorption coefficients are key parameters for the Supported by the US DOE under contract DE-AC03-76SF00098. mpivi@lbl.gov

Synchrotron radiation and beam tube vacuum in a Very Large Hadron Collider, Stage 1 and Stage 2 VLHC

Abstract: Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime. We discuss the beam tube vacuum in the low field Stage 1 and Stage 2 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. In Stage 2, the 100 K beam screen, or liner, illuminated by the synchrotron radiation, is inserted into the magnet cold bore. Cryo-pumping is provided by the cold bore kept at 4.2 K, through slots covering the beam screen surface. Possible beam conditioning scenarios are presented for reaching design intensity, both for Stage 1 and 2. The most important results are summarized in this paper.

Future expectations, limits and operational issues for high field superconducting accelerator dipole magnets*

Abstract: Energy upgrades of existing accelerators require the use of the highest field magnets available. Steady improvement in the application of Nb3Sn technology has been made over the last several years and it can now be considered a viable material for practical high field accelerator magnets. This paper presents a brief review of current work in this area and in particular discusses recent results from the LBNL High Field Dipole R&D Program and how they might apply to future accelerator magnet capabilities. A projection of limits and expectations for practical applications over the next 10 – 15 years will be discussed along with some of the operational issues associated with high field magnets.

Post-LHC accelerator magnets

Abstract: The design and practicality of future accelerators, such as hadron colliders and neutrino factories being considered to supercede the LHC, will depend greatly on the choice of superconducting magnets. Various possibilities will be reviewed and discussed, taking into account recent progress and projected improvements in magnet design and conductor development along with the recommendations from the 2001 Snowmass workshop.

VLHC accelerator physics

Abstract: A six-month design study for a future high energy hadron collider was initiated by the Fermilab director in October 2000. The request was to study a staged approach where a large circumference tunnel is built that initially would house a low field ({approx}2 T) collider with center-of-mass energy greater than 30 TeV and a peak (initial) luminosity of 10{sup 34} cm{sup -2}s{sup -1}. The tunnel was to be scoped, however, to support a future upgrade to a center-of-mass energy greater than 150 TeV with a peak luminosity of 2 x 10{sup 34} cm{sup -2} sec{sup -1} using high field ({approx} 10 T) superconducting magnet technology. In a collaboration with Brookhaven National Laboratory and Lawrence Berkeley National Laboratory, a report of the Design Study was produced by Fermilab in June 2001. 1 The Design Study focused on a Stage 1, 20 x 20 TeV collider using a 2-in-1 transmission line magnet and leads to a Stage 2, 87.5 x 87.5 TeV collider using 10 T Nb{sub 3}Sn magnet technology. The article that follows is a compilation of accelerator physics designs and computational results which contributed to the Design Study. Many of the parameters found in this report evolved during the study, and thus slight differences between this text and the Design Study report can be found. The present text, however, presents the major accelerator physics issues of the Very Large Hadron Collider as examined by the Design Study collaboration and provides a basis for discussion and further studies of VLHC accelerator parameters and design philosophies.

Report on the First VLHC Photon Stop Cryogenic Design Experiment

Abstract: As part of Fermilab’s study of a Very Large Hadron Collider (VLHC), a water‐cooled photon stop was proposed as a device to intercept the synchrotron radiation emitted by the high‐energy proton beams in the high‐field superconducting magnets with minimal plug‐cooling power. Photon stops are radiation absorbers operating at room temperature that protrude into the beam tube at the end of each bending magnet to scrape the synchrotron light emitted by the beam one magnet up‐stream. Among the technological challenges regarding photon stops is their cryo‐design. The photon stop is water‐cooled and operates in a cryogenic environment. A careful cryo‐design is therefore essential to enable operation at minimum heat transfer between the room temperature sections and the cryogenic parts. A photon stop cryo‐design was developed and a prototype was built. This paper presents the results of the cryogenic experiments conducted on the first VLHC photon‐stop prototype.