摘要 :
Slow-position beams produced from negative-work-function solid-state moderators have found numerous applications in condensed matter physics. There are potential advantages in using low-energy primary electron beams for positron p...
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Slow-position beams produced from negative-work-function solid-state moderators have found numerous applications in condensed matter physics. There are potential advantages in using low-energy primary electron beams for positron production, including reduced radiation damage to single-crystal moderators and reduced activation of nearby components. The authors present numerical calculations of positron yields and other beam parameters for various target-moderator configurations using the Argonne Wakefield Accelerator (AWA) (1) and Advanced Photon Source (APS), (2) electron linacs, (3) as examples of sources for the primary electron beams. The status of experiments at these facilities is reviewed.
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The Advanced Photon Source (APS) linac beam position monitors can be used to monitor the position of a positron beam also containing electrons. To accomplish this task, both the signal at the bunching frequency of 2856 MHz and the...
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The Advanced Photon Source (APS) linac beam position monitors can be used to monitor the position of a positron beam also containing electrons. To accomplish this task, both the signal at the bunching frequency of 2856 MHz and the signal at 2 x 2856 MHz are acquired and processed for each stripline. The positron beam position is obtained by forming a linear combination of both 2856- and 5712-MHz signals for each stripline and then performing the standard difference over sum computation. The required linear combination of the 2856- and 5712-MHz signals depends on the electrical calibration of each stripline/cable combination. In this paper, the calibration constants for both 2856-MHz and 5712-MHz signals for each stripline are determined using a pure beam of electrons. The calibration constants are obtained by measuring the 2856- and 5712-MHz stripline signals at various electron beam currents and positions. Finally, the calibration constants measured using electrons are used to determine positron beam position for the mixed beam case.
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Topics covered in this issue include electrostatic channel guiding, research with channeling radiation, and high-intensity positron beams. Abstracts of individual items were prepared separately for the data base. (ERA citation 11:017063)
摘要 :
The Next Linear Collider (NLC) currently under investigation at SLAC requires a positron source with a flux of about 8.6 (times) 10(sup 13) particles per second, 14.4 times more than the SLC source. Based on the SLC experience, a ...
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The Next Linear Collider (NLC) currently under investigation at SLAC requires a positron source with a flux of about 8.6 (times) 10(sup 13) particles per second, 14.4 times more than the SLC source. Based on the SLC experience, a source for NLC is proposed that can be realized with present accelerator technology. It consists of a 7 GeV S-band electron linac, a solid moving target, a 1.8 GeV L-band positron accelerator and a pre-damping ring with a large acceptance. The pre-damping ring performs positron accumulation and the matching of the positron source emittance to the NLC main damping ring acceptance. The scheme and parameters of the NLC positron source are given and the expected source performance is computed.
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The yield of positrons as a function of drive beam energy for a K=1, planar undulator-based positron source is evaluated using the EGS4 simulation code. Raw yield, yield into a fixed phase space acceptance, and rms emittance of em...
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The yield of positrons as a function of drive beam energy for a K=1, planar undulator-based positron source is evaluated using the EGS4 simulation code. Raw yield, yield into a fixed phase space acceptance, and rms emittance of emitted positrons is calculated. For a fixed geometry, the yield varies as the square of the drive beam energy. A faster fall off at the low energy end is seen and is due to reduced emission of positrons produced with initially low energies (in the range of a few MeV).
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摘要 :
The NLC (Next Linear Collider, proposed) is optimized with respect to positron yield, target integrity, cooling, and shielding. Copper is proposed as a possible optimal choice.
摘要 :
The NLC (Next Linear Collider, proposed) is optimized with respect to positron yield, target integrity, cooling, and shielding. Copper is proposed as a possible optimal choice.
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Using an electromagnetic (EM) calorimeter and lead absorbers in the beam, the non-EM backgrounds (muons and hadrons) in the nominal 300 GeV e- and e+ beams were measured to be approximately 6 % and 37 % respectively.
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The presence of trapped ions in electron storage rings has caused significant degradation in machine performance. The best known way to prevent the ion trapping is to leave a gap in the electron bunch train. The topic of this pape...
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The presence of trapped ions in electron storage rings has caused significant degradation in machine performance. The best known way to prevent the ion trapping is to leave a gap in the electron bunch train. The topic of this paper is the dynamics of ions in the field of the bunch train with uneven bunch filling. We consider High Energy Ring (HER) of the PEP-II B-factory. In the first section we summarize mechanisms of the ion production. Then the transverse and longitudinal dynamics are analyzed for a beam with and without gap. After that, the effect of the ions is considered separating all ions in the ring in several groups depending on their transverse and longitudinal stability. The main effects of the ions are the tune shift and the tune spread of the betatron oscillations of the electrons. The tune spread is produced by bunch to bunch variation of the electric field of ions and by nonlinearity of the field. It is shown that the main contribution to the shift and spread of the betatron tune of the beam is caused by two groups of ions: one-turn ions and trapped ions. One-turn ions are the ions generated during the last passage of the bunch train. Trapped ions are the ions with stable transverse and longitudinal motion. In the last section we discuss shortly related problems of parameters of the clearing electrodes, injection scenario, and collective effects. Clearing electrodes should be located at the defocusing in x-plane quadrupole magnets. An electric DC field of value 1.0 kv/cm will be enough to prevent the ion trapping process. During the injection, it is recommended to fill the bucket with the design number of the particles per bunch N(sub B) before going to the next bucket. In addition, it is recommended to have the sequential filling of the ring, i.e. the filling from one bucket to the next sequentially. It was shown that ions will not be trapped at the location of the interaction point. The reason for this is that the current of the positron beam is twice as large as the current of the electron beam, while the transverse sizes of both the electron and positron beams are equal at the IP. It is shown that the linear ion's oscillations can not result in the longitudinal coupled beam instabilities.
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摘要 :
The presence of trapped ions in electron storage rings has caused significant degradation in machine performance. The best known way to prevent the ion trapping is to leave a gap in the electron bunch train. The topic of this pape...
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The presence of trapped ions in electron storage rings has caused significant degradation in machine performance. The best known way to prevent the ion trapping is to leave a gap in the electron bunch train. The topic of this paper is the dynamics of ions in the field of the bunch train with uneven bunch filling. We consider High Energy Ring (HER) of the PEP-II B-factory. In the first section we summarize mechanisms of the ion production. Then the transverse and longitudinal dynamics are analyzed for a beam with and without gap. After that, the effect of the ions is considered separating all ions in the ring in several groups depending on their transverse and longitudinal stability. The main effects of the ions are the tune shift and the tune spread of the betatron oscillations of the electrons. The tune spread is produced by bunch to bunch variation of the electric field of ions and by nonlinearity of the field. It is shown that the main contribution to the shift and spread of the betatron tune of the beam is caused by two groups of ions: one-turn ions and trapped ions. One-turn ions are the ions generated during the last passage of the bunch train. Trapped ions are the ions with stable transverse and longitudinal motion. In the last section we discuss shortly related problems of parameters of the clearing electrodes, injection scenario, and collective effects. Clearing electrodes should be located at the defocusing in x-plane quadrupole magnets. An electric DC field of value 1.0 kv/cm will be enough to prevent the ion trapping process. During the injection, it is recommended to fill the bucket with the design number of the particles per bunch N(sub B) before going to the next bucket. In addition, it is recommended to have the sequential filling of the ring, i.e. the filling from one bucket to the next sequentially. It was shown that ions will not be trapped at the location of the interaction point. The reason for this is that the current of the positron beam is twice as large as the current of the electron beam, while the transverse sizes of both the electron and positron beams are equal at the IP. It is shown that the linear ion's oscillations can not result in the longitudinal coupled beam instabilities.
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