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Title: Absolute beam emittance measurements at RHIC using ionization profile monitors

Abstract

In the past, comparisons between emittance measurements obtained using ionization profile monitors, Vernier scans (using as input the measured rates from the zero degree counters, or ZDCs), the polarimeters and the Schottky detectors evidenced significant variations of up to 100%. In this report we present studies of the RHIC ionization profile monitors (IPMs). After identifying and correcting for two systematic instrumental errors in the beam size measurements, we present experimental results showing that the remaining dominant error in beam emittance measurements at RHIC using the IPMs was imprecise knowledge of the local beta functions. After removal of the systematic errors and implementation of measured beta functions, precise emittance measurements result. Also, consistency between the emittances measured by the IPMs and those derived from the ZDCs was demonstrated.

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Collider-Accelerator Dept.
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States). Relativistic Heavy Ion Collider (RHIC)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1154892
Report Number(s):
BNL-105970-2014-IR; BNL-C-A/AP/522
R&D Project: KBCH139; KB0202011; TRN: US1500116
DOE Contract Number:
AC02-98CH10886
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; BROOKHAVEN RHIC; IONIZATION CHAMBERS; BEAM EMITTANCE; DATA COVARIANCES; COMPARATIVE EVALUATIONS; FUNCTIONS; ACCURACY; POLARIMETERS; BEAM PROFILES; BEAM MONITORS; relativistic heavy ion collider

Citation Formats

Minty, M., Connolly, R, Liu, C., Summers, T., and Tepikian, S. Absolute beam emittance measurements at RHIC using ionization profile monitors. United States: N. p., 2014. Web. doi:10.2172/1154892.
Minty, M., Connolly, R, Liu, C., Summers, T., & Tepikian, S. Absolute beam emittance measurements at RHIC using ionization profile monitors. United States. doi:10.2172/1154892.
Minty, M., Connolly, R, Liu, C., Summers, T., and Tepikian, S. Fri . "Absolute beam emittance measurements at RHIC using ionization profile monitors". United States. doi:10.2172/1154892. https://www.osti.gov/servlets/purl/1154892.
@article{osti_1154892,
title = {Absolute beam emittance measurements at RHIC using ionization profile monitors},
author = {Minty, M. and Connolly, R and Liu, C. and Summers, T. and Tepikian, S.},
abstractNote = {In the past, comparisons between emittance measurements obtained using ionization profile monitors, Vernier scans (using as input the measured rates from the zero degree counters, or ZDCs), the polarimeters and the Schottky detectors evidenced significant variations of up to 100%. In this report we present studies of the RHIC ionization profile monitors (IPMs). After identifying and correcting for two systematic instrumental errors in the beam size measurements, we present experimental results showing that the remaining dominant error in beam emittance measurements at RHIC using the IPMs was imprecise knowledge of the local beta functions. After removal of the systematic errors and implementation of measured beta functions, precise emittance measurements result. Also, consistency between the emittances measured by the IPMs and those derived from the ZDCs was demonstrated.},
doi = {10.2172/1154892},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Aug 15 00:00:00 EDT 2014},
month = {Fri Aug 15 00:00:00 EDT 2014}
}

Technical Report:

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  • Measurements of the normalized emittance of the beam produced by the Advanced Test Accelerator (ATA) injector yielded values near 0.4 Radian-Centimeters at currents up to 10 kAmps. The instrument was also used to obtain beam-current-density profiles in two dimensions at the entrance mask of the instrument.
  • One way of measuring the profile of CEBAF`s low emittance and high power beam is to use the Optical Transition Radiation (OTR) emitted from a thin foil surface when the electron beam passes through it. We present the design of a monitor using the forward OTR emitted from a 0.25 {mu}m carbon foil. We believe that the monitor will resolve three main issues: (i) whether the max temperature of the foil stays below the melting point, (ii) whether the beam loss remains below 0. 5%, in order not to trigger the machine protection system, and (iii) whether the monitor resolutionmore » (unlike that of synchrotron radiation monitors) is better than the product {lambda}{gamma}. It seems that the most serious limitation for CEBAF is the beam loss due to beam scattering. We present results from Keil`s theory and simulations from the computer code GEANT as well as measurements with Al foils with a 45 MeV electron beam. We also present a measurement of a 3.2 GeV beam profile that is much smaller than {lambda}{gamma}, supporting Rule & Fiorito`s calculations of the OTR resolution limit due to diffraction.« less
  • Ultra-low emittance (tens of nm) beams can be generated in a plasma accelerator using ionization injection of electrons into a wakefield. An all-optical method of beam generation uses two laser pulses of different colors. A long-wavelength drive laser pulse (with a large ponderomotive force and small peak electric field) is used to excite a large wakefield without fully ionizing a gas, and a short-wavelength injection laser pulse (with a small ponderomotive force and large peak electric field), co-propagating and delayed with respect to the pump laser, to ionize a fraction of the remaining bound electrons at a trapped wake phase,more » generating an electron beam that is accelerated in the wake. The trapping condition, the ionized electron distribution, and the trapped bunch dynamics are discussed. Expressions for the beam transverse emittance, parallel and orthogonal to the ionization laser polarization, are presented. An example is shown using a 10-micron CO 2 laser to drive the wake and a frequency-doubled Ti:Al 2O 3 laser for ionization injection.« less
  • Four ionization profile monitors (IPMs) are in RHIC to measure vertical and horizontal beam profiles in the two rings. These work by measuring the distribution of electrons produced by beam ionization of residual gas. During the last two years both the collection accuracy and signal/noise ratio have been improved. An electron source is mounted across the beam pipe from the collector to monitor microchannel plate (MCP) aging and the signal electrons are gated to reduce MCP aging and to allow charge replenishment between single-turn measurements. Software changes permit simultaneous measurements of any number of individual bunches in the ring. Thismore » has been used to measure emittance growth rates on six bunches of varying intensities in a single store. Also the software supports FFT analysis of turn-by-turn profiles of a single bunch at injection to detect dipole and quadrupole oscillations.« less