PAC2013 - List of Authors (Spickermann, T.)

Paper	Title	Page
TUPAC19	Experimental Verification of Dipole Edge Focusing in Linear Model by Operating in the Weak Focusing Regime at the Los Alamos Proton Storage Ring	490
	J.S. Kolski, D.B. Barlow, R.J. Macek, T. Spickermann LANL, Los Alamos, New Mexico, USA
	Linear optics models are important for the operation of circular accelerators because of their ability to predict lattice functions, primarily betatron amplitude functions and tunes. The accuracy of the model’s prediction is dependent on how well the real machine’s focusing lattice is known and represented. While quadrupoles may be mapped magnetically and their focusing properties well understood, the focusing effect due to dipole edge fields is less certain. For rings with rectangular dipoles like the Proton Storage Ring (PSR) at Los Alamos National Laboratory, the dipole edge focusing can be a significant contributor to the vertical focusing. Most accelerator modeling codes, like MAD and AT, use the K. Brown formulation and can lead to errors ~10% in the model’s betatron tune prediction. Here we discuss particle tracking through simulated dipole fields, including edge effects, with TOSCA 3D to obtain the focal lengths of the edge focusing. We verify model focal lengths by operating the PSR in the weak focusing regime (without vertically focusing quadrupoles) and show that the model predicts the betatron amplitude functions and tunes even in this unusual operating condition.

TUPAC20	Coherent Space Charge Tune Shift Measurements in the Los Alamos Proton Storage Ring	493
	J.S. Kolski, R.J. Macek, T. Spickermann LANL, Los Alamos, New Mexico, USA
	The coherent space charge tune shift describes the average frequency shift experienced by particles due to the force of the beam’s image charge and is proportional to the instantaneous beam current. For long beam pulses like the 290 ns long accumulated beam bunch in the Los Alamos Proton Storage Ring, we can observe the change in the coherent space charge tune shift longitudinally along the pulse. We measure an asymmetric tune distribution about the bunch center even though the beam current profile is symmetric about the peak intensity. We also observe the tune shift to vary with turn during a store. Quality measurements of the coherent space charge tune shift may provide a unique handle on interesting physics including wake field effects and electron cloud buildup. We digitize beam signals from a beam position monitor, stack the digitized vector turn-by-turn, and fit the tune for each slice (0.5 ns digitization bin) along the pulse after a single-turn vertical kick. We compare the difference between the measured and theoretical tune shifts and infer a charge neutralization, which we relate to the electron cloud density along the pulse and buildup in turn number.

Paper

Title

Page

Experimental Verification of Dipole Edge Focusing in Linear Model by Operating in the Weak Focusing Regime at the Los Alamos Proton Storage Ring

490

J.S. Kolski, D.B. Barlow, R.J. Macek, T. Spickermann
LANL, Los Alamos, New Mexico, USA

Linear optics models are important for the operation of circular accelerators because of their ability to predict lattice functions, primarily betatron amplitude functions and tunes. The accuracy of the model’s prediction is dependent on how well the real machine’s focusing lattice is known and represented. While quadrupoles may be mapped magnetically and their focusing properties well understood, the focusing effect due to dipole edge fields is less certain. For rings with rectangular dipoles like the Proton Storage Ring (PSR) at Los Alamos National Laboratory, the dipole edge focusing can be a significant contributor to the vertical focusing. Most accelerator modeling codes, like MAD and AT, use the K. Brown formulation and can lead to errors ~10% in the model’s betatron tune prediction. Here we discuss particle tracking through simulated dipole fields, including edge effects, with TOSCA 3D to obtain the focal lengths of the edge focusing. We verify model focal lengths by operating the PSR in the weak focusing regime (without vertically focusing quadrupoles) and show that the model predicts the betatron amplitude functions and tunes even in this unusual operating condition.

TUPAC20

Coherent Space Charge Tune Shift Measurements in the Los Alamos Proton Storage Ring

493

J.S. Kolski, R.J. Macek, T. Spickermann
LANL, Los Alamos, New Mexico, USA

The coherent space charge tune shift describes the average frequency shift experienced by particles due to the force of the beam’s image charge and is proportional to the instantaneous beam current. For long beam pulses like the 290 ns long accumulated beam bunch in the Los Alamos Proton Storage Ring, we can observe the change in the coherent space charge tune shift longitudinally along the pulse. We measure an asymmetric tune distribution about the bunch center even though the beam current profile is symmetric about the peak intensity. We also observe the tune shift to vary with turn during a store. Quality measurements of the coherent space charge tune shift may provide a unique handle on interesting physics including wake field effects and electron cloud buildup. We digitize beam signals from a beam position monitor, stack the digitized vector turn-by-turn, and fit the tune for each slice (0.5 ns digitization bin) along the pulse after a single-turn vertical kick. We compare the difference between the measured and theoretical tune shifts and infer a charge neutralization, which we relate to the electron cloud density along the pulse and buildup in turn number.