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High-yield positron systems for linear colliders

Description: Linear colliders, such as the SLC, are among those accelerators for which a high-yield positron source operating at the repetition rate of the accelerator is desired. The SLC, having electron energies up to 50 GeV, presents the possibility of generating positron bunches with useful charge even exceeding that of the initial electron bunch. The exact positron yield to be obtained depends on the particular capture, transport and damping system employed. Using 31 GeV electrons impinging on a W-type converter phase-space at the target to the acceptance of the capture rf section, the SLC source is capable of producing, for every electron, up to two positrons within the acceptance of the positron damping ring. The design of this source and the performance of the positron system as built are described. Also, future prospects and limitations for high-yield positron systems are discussed. 11 refs., 5 figs., 3 tabs.
Date: April 1, 1989
Creator: Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

Notes on the IMACON 500 streak camera system

Description: The notes provided are intended to supplement the instruction manual for the IMACON 500 streak camera system. The notes cover the streak analyzer, instructions for timing the streak camera, and calibration. (LEW)
Date: January 31, 1985
Creator: Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

Summary of Polarized e-/e+ Source Presentations

Description: The development of polarized electron sources in the 1970s capable of generating beams for injection into electron accelerators has been a major enabling factor for spin physics with electrons during the past quarter century. These sources continue to be refined for higher polarization and better operability. Recent developments were presented at this workshop in both plenary sessions and in 2 separate parallel sessions. The ILC plans to utilize not only a polarized electron source but also a polarized positron source. The current state of two types of positron sources were presented. This paper is a brief summary of all of these presentations.
Date: November 28, 2007
Creator: Clendenin, J. E.
Partner: UNT Libraries Government Documents Department

Polarized electron sources

Description: Polarized electron sources for high energy accelerators took a significant step forward with the introduction of a new laser-driven photocathode source for the SLC in 1992. With an electron beam polarization of >80% and with {approximately}99% uptime during continuous operation, this source is a key factor in the success of the current SLC high-energy physics program. The SLC source performance is used to illustrate both the capabilities and the limitations of solid-state sources. The beam requirements for future colliders are similar to that of the SLC with the addition in most cases of multiple-bunch operation. A design for the next generation accelerator source that can improve the operational characteristics and at least minimize some of the inherent limitations of present sources is presented. Finally, the possibilities for producing highly polarized electron beams for high-duty-factor accelerators are discussed.
Date: May 1, 1995
Creator: Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

Beam parametr measurements for the SLAC linear collider

Description: A stable, closely-controlled, high-intensity, single-bunch beam will be required for the SLAC Linear Collider. The characteristics of short-pulse, low-intensity beams in the SLAC linac have been studied. A new, high-intensity thermionic gun, subharmonic buncher and S-band buncher/accelerator section were installed recently at SLAC. With these components, up to 10/sup 11/ electrons in a single S-band bunch are available for injection into the linac. the first 100-m accelerator sector has been modified to allow control of short-pulse beams by a model-driven computer program. Additional instrumentation, including a computerized energy analyzer and emittance monitor have been added at the end of the 100-m sector. The beam intensity, energy spectrum, emittance, charge distribution and the effect of wake fields in the first accelerator sector have been measured. The new source and beam control system are described and the most recent results of the beam parameter measurements are discussed.
Date: January 1, 1981
Creator: Clendenin, J.E.; Blocker, C. & Breidenbach, M.
Partner: UNT Libraries Government Documents Department

RF photoinjectors

Description: RF photoinjectors have been under intensive development for the past decade since they promise to be the high-brightness electron beam sources required for FELs. Progress has been sufficiently good to make optically switched RF photoinjectors attractive candidates as injectors for future colliders, especially those colliders which plan to use complex beam pulse structures. Although present RF photoinjectors will not today meet all the requirements of some collider designs, their potential capabilities seem greater as well as more versatile than conventional injectors. The present status and future goals of RF photoinjectors are compared. The principal problems remaining for achieving these goals while also providing high reliability for linacs during continuous, long-term operation are examined.
Date: August 1, 1996
Creator: Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

The high-gradient S-band linac for initial acceleration of the SLC (SLAC linear collider) intense positron bunch

Description: Although short lengths of S-band standing-wave, disk-loaded waveguide have been successfully RF-processed to accelerating gradients equivalent to about 175 MeV/m in a traveling-wave structure, the 20 MeV/m gradient of the SLC 50 GeV linac has been the highest gradient S-band accelerator in operation. However, the 1.5 m traveling-wave constant impedance capture section for the SLC positron source, operating with a dedicated 60 MW klystron, is now routinely accelerating single-bunch beams of more than 7 /times/ 10/sup 10/ e/sup +//pulse at rates of up to 60 Hz with an accelerating gradient section are described. 11 refs., 1 fig. 1 tab.
Date: August 1, 1989
Creator: Clendenin, J.E.; Ecklund, S.D. & Hoag, H.A.
Partner: UNT Libraries Government Documents Department

Timing jitter measurements at the SLC electron source

Description: The SLC thermionic gun and electron source produce a beam of up to 15 /times/ 10/sup 10/ /sub e//minus/ in a single S-band bunch. A 170 keV, 2 ns FWHM pulse out of the gun is compressed by means of two subharmonic buncher cavities followed by an S-band buncher and a standard SLAC accelerating section. Ceramic gaps in the beam pipe at the output of the gun allow a measure of the beam intensity and timing. A measurement at these gaps of the timing jitter, with a resolution of <10 ps, is described. 3 refs., 5 figs.
Date: March 1, 1989
Creator: Sodja, J.; Browne, M.J. & Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

Solid state high power amplifier for driving the SLC injector klystron

Description: The SLC injector klystron rf drive is now provided by a recently developed solid-state amplifier. The high gain of the amplifier permits the use of a fast low-power electronic phase shifter. Thus the SLC computer control system can be used to shift the phase of the high-power rf rapidly during the fill time of the injector accelerator section. These rapid phase shifts are used to introduce a phase-energy relationship in the accelerated electron pulse in conjunction with the operation of the injector bunch compressor. The amplifier, the method of controlling the rf phase, and the operational characteristics of the system are described. 5 refs., 4 figs.
Date: March 1, 1985
Creator: Judkins, J.G.; Clendenin, J.E. & Schwarz, H.D.
Partner: UNT Libraries Government Documents Department

Polarized electronic sources for future e{sup +}/e{sup {minus}} linear colliders

Description: Polarized electron beams will play a crucial role in maximizing the physics potential for future e{sup +}/e{sup {minus}} linear colliders. We will review the SLC polarized electron source (PES), present a design for a conventional PES for the Next Linear Collider (NLC), and discuss the physics issues of a polarized RF gun.
Date: May 1, 1997
Creator: Tang, H.; Alley, R.K. & Clendenin, J.E.
Partner: UNT Libraries Government Documents Department

Nonintercepting emittance monitor

Description: A nonintercepting emittance monitor is a helpful device for measuring and improving particle beams in accelerators and storage rings as it allows continuous monitoring of the beam's distribution in phase space, and perhaps closed loop computer control of the distributions. Stripline position monitors are being investigated for use as nonintercepting emittance monitors for a beam focused by a FODO array in the first 100 meters of our linear accelerator. The technique described here uses the signal from the four stripline probes of a single position monitor to measure the quadrupole mode of the wall current in the beam pipe. This current is a function of the quadrupole moment of the beam, sigma/sup 2//sub x/ - sigma/sup 2//sub y/. In general, six independent measurements of the quadrupole moment are necessary to determine the beam emittance. This technique is dependent on the characteristically large variations of sigma/sup 2//sub x/ - sigma/sup 2//sub y/ in a FODO array. It will not work in a focusing system where the beam is round at each focusing element.
Date: August 1, 1983
Creator: Miller, R.H.; Clendenin, J.E.; James, M.B. & Sheppard, J.C.
Partner: UNT Libraries Government Documents Department

Energy matching of 1. 2 GeV positron beam to the SLC (Stanford Linear Collider) damping ring

Description: Positrons collected at the SLC positron source are transported over a 2-km path at 220 MeV to be reinjected into the linac for acceleration to 1.2 GeV, the energy of the emittance damping ring. Since the positron bunch length is a significant fraction of a cycle of the linac-accelerating RF, the energy spread at 1.2 GeV is considerably larger than the acceptance of the linac-to-ring (LTR) transport system. Making use of the large pathlength difference at the beginning of the LTR due to this energy spread, a standard SLAC 3-m accelerating section has been installed in the LTR to match the longitudinal phase space of the positron beam to the acceptance of the damping ring. The design of the matching system is described, and a comparison of operating results within simulations is presented. 5 refs., 4 figs., 1 tab.
Date: August 1, 1989
Creator: Clendenin, J.E.; Helm, R.H.; Jobe, R.K.; Kulikov, A. & Sheppard, J.C.
Partner: UNT Libraries Government Documents Department

Real time bunch length measurements in the SLC linac

Description: The longitudinal charge distribution of bunches accelerated in the Stanford Linear Collider (SLC) linac will strongly affect the performance of the Collider. Bunch lengths are chosen in a balance between the deleterious effects of longitudinal and transverse wakefields. The former impacts on the beam energy spread whereas the latter is important to the transverse emittance. Two bunch length measurement ports have been installed in the SLC linac: one in the injector region and one after the emittance damping ring to linac reinjection point. These ports utilize a fused quartz Cerenkov radiator in conjunction with an electrooptic streak camera to permit real time monitoring of single s-band buckets with a resolution of several picoseconds. The design of the radiators and light collection optics is discussed with an emphasis on those issues important to high resolution. Experimental results are presented. 7 refs., 4 figs.
Date: February 1, 1985
Creator: Sheppard, J.C.; Clendenin, J.E.; James, M.B.; Miller, R.H. & Ross, M.C.
Partner: UNT Libraries Government Documents Department

Single-bunch beams for BC-75

Description: On June 8, 1983, a beam consisting of a single S-band bunch was transported through the linac into the beam switchyard (BSY) and analyzed in the C-line (Beamline 27) at 30 GeV. The C-line toroid 2712 measured an intensity of approximately 2 x 10/sup 9/e/sup -//pulse. The exact intensity was uncertain due to the limited response time of the toroid for fast, single-bunch beams. However, the linear Q intensity monitors (Lin Q) showed the transmission of the beam through the linac between Sectors 2 and 30 to be fairly flat with an intensity of 3 x 10/sup 9/e/sup -//pulse in the final 19 sectors. The CID Faraday cup, which is located adjacent to the Gun Lin Q, was used to check the calibration of the Lin Q.
Date: June 1, 1983
Creator: Sodja, J.; Clendenin, J.E.; Erickson, R.A. & Miller, R.H.
Partner: UNT Libraries Government Documents Department

RF Gun Photo-Emission Model for Metal Cathodes Including Time Dependent Emission

Description: The quantum efficiency from a metal cathode is strongly dependent on the field at the cathode due to the Schottky effect. Since the field is time dependent the quantum efficiency is also time dependent. Thus the laser pulse shape used to generate electrons in a photocathode rf gun is not the same as the electron bunch shape. In addition since the thermal emittance and quantum efficiency are related, the thermal emittance is also time dependent.
Date: February 24, 2006
Creator: Schmerge, J.F.; Clendenin, J.E.; Dowell, D.H.; Gierman, S.M. & /SLAC
Partner: UNT Libraries Government Documents Department

Emittance calculations for the Stanford Linear Collider injector

Description: A series of measurements have been performed to determine the emittance of the high intensity, single bunch beam that is to be injected into the Stanford Linear Collider. On-line computer programs were used to control the Linac for the purpose of data acquisition and to fit the data to a model in order to deduce the beam emittance. This paper will describe the method of emittance calculation and present some of the measurement results.
Date: March 1, 1983
Creator: Sheppard, J.C.; Clendenin, J.E.; Helm, R.H.; Lee, M.J.; Miller, R.H. & Blocker, C.A.
Partner: UNT Libraries Government Documents Department

Isochronous 180 degree turns for the SLC positron system

Description: The design of the compact, achromatic, second order isochronous 180{degrees} turn for the SLC positron transport system will be described. Design criteria require an energy range of 200{plus minus}20 MeV, energy acceptance of {plus minus}5%, transverse admittance of 25{pi} mm-mr, and minimal lengthening of the 3 to 4 mm (rms) positron bunch. The devices had to fit within a maximum height or width of about 10 ft. Optics specifications and theoretical performance are presented and compared to experimental results based on streak camera measurements of bunch length immediately after the first isochronous turn (200 MeV) and positron beam energy spread after S-band acceleration to 1.15 GeV. 5 refs., 7 figs.
Date: May 1, 1991
Creator: Helm, R.H.; Clendenin, J.E.; Ecklund, S.D.; Kulikov, A.V. & Pitthan, R.
Partner: UNT Libraries Government Documents Department

Multi-channel pulser for the SLC thermionic electron source

Description: A new pulser developed for the SLC thermionic gun has been operational since September 1984. It consists of two planar triode amplifiers with a common output triode driving the gun cathode to produce two independent pulses of up to 9A with a 3 nsec FWHM pulse width. Three long-pulse amplifiers are also connected to the cathode to produce pulses with widths controllable between 100 nsec and 1.6 ..mu..sec. Each amplifier has independent timing and amplitude control through a fiber optic link to the high voltage plane of the gun cathode-grid structure. The pulser and its operating characteristics are described. 15 refs., 3 figs.
Date: January 1, 1985
Creator: Browne, M.J.; Clendenin, J.E.; Corredoura, P.L.; Jobe, R.K.; Koontz, R.F. & Sodja, J.
Partner: UNT Libraries Government Documents Department

Update on the high-current injector for the Stanford Linear collider

Description: The high current injector has become operational. There are two crucial areas where improvements must be made to meet collider specifications: while the injector can produce up to 10/sup 11/ e/sup -/ in a single S-band bucket, initially much of this charge was captured in a low energy tail and was this not suitable for transport through the accelerator and injection into the damping ring. Pulse to pulse position jitter has been observed, resulting in transverse wake field which increases beam emittance. The problems described above contribute to substantial current loss during transport from the injector (40 MeV) to the SLC damping ring (1.2 GeV). Experimental studies are continuing with the aim of understanding and improving beam characteristics including bunch length, pulse to pulse stability and emittance. The present status of these studies is reported.
Date: March 1, 1983
Creator: James, M.B.; Clendenin, J.E.; Ecklund, S.D.; Miller, R.H.; Sheppard, J.C.; Sinclair, C.K. et al.
Partner: UNT Libraries Government Documents Department

Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons

Description: The GaAsP/GaAs strained superlattice photocathode structure has proven to be a significant advance for polarized electron sources operating with high peak currents per microbunch and relatively low duty factor. This is the characteristic type of operation for SLAC and is also planned for the ILC. This superlattice structure was studied at SLAC [1], and an optimum variation was chosen for the final stage of E-158, a high-energy parity violating experiment at SLAC. Following E-158, the polarized source was maintained on standby with the cathode being re-cesiated about once a week while a thermionic gun, which is installed in parallel with the polarized gun, supplied the linac electron beams. However, in the summer of 2005, while the thermionic gun was disabled, the polarized electron source was again used to provide electron beams for the linac. The performance of the photocathode 24 months after its only activation is described and factors making this possible are discussed.
Date: February 27, 2006
Creator: Brachmann, A.; Clendenin, J.E.; Maruyama, T.; Garwin, E.L.; Ioakemidi, K.; Prescott, C.Y. et al.
Partner: UNT Libraries Government Documents Department

The S-Band 1.6 Cell RF Gun Correlated Energy Spread Dependence on pi and 0 Mode Relative Amplitude

Description: The {pi} mode or accelerating mode in a 1.6 cell rf gun is normally the only mode considered in rf gun simulations. However, due to the finite Q there is a small but measurable 0 mode present even at steady state. The {pi} mode by definition has a 180{sup o} phase shift between cells but this phase shift for the total field is several degrees different. This results in a correlated energy spread exiting the gun. A comparison of simulation and experiment will be shown.
Date: February 24, 2006
Creator: Schmerge, J.F.; Castro, J.; Clendenin, J.E.; Dowell, D.H.; Gierman, S.M.; Loos, H. et al.
Partner: UNT Libraries Government Documents Department

The RF Design of an HOM Polarized RF Gun for the ILC

Description: The ILC requires a polarized electron beam. While a highly polarized beam can be produced by a GaAs-type cathode in a DC gun of the type currently in use at SLAC, JLAB and elsewhere, the ILC injector system can be simplified and made more efficient if a GaAs-type cathode can be combined with a low emittance RF gun. Since this type of cathode is known to be extremely sensitive to vacuum contamination including back bombardment by electrons and ions, any successful polarized RF gun must have a significantly improved operating vacuum compared to existing RF guns. We present a new RF design for an L-Band normal conducting (NC) RF gun for the ILC polarized electron source. This design incorporates a higher order mode (HOM) structure, whose chief virtue in this application is an improved conductance for vacuum pumping on the cathode. Computer simulation models have been used to optimize the RF parameters with two principal goals: first to minimize the required RF power; second to reduce the peak surface field relative to the field at the cathode in order to suppress field emitted electron bombardment. The beam properties have been simulated initially using PARMELA. Vacuum and other practical issues for implementing this design are discussed.
Date: November 15, 2006
Creator: Wang, J.W.; Clendenin, J.E.; Colby, E.R.; Miller, R.A.; /SLAC; Lewellen, J.W. et al.
Partner: UNT Libraries Government Documents Department

Transport Mechanisms in Polarized Semiconductor Photocathodes

Description: We investigated the effect of an accelerating field on the spin polarization of photogenerated electrons in a 100nm thick GaAs based photocathode active region. By decreasing the transport time of the electrons and the number of scattering events that cause depolarization, we expected to increase the polarization as was indicated by Monte Carlo simulations of the scattering and transport time statistics of the electrons. A tungsten (W) grid was deposited on the cathode surface to provide a uniform voltage distribution across the cathode surface. The metal grid formed a Schottky contact with the semiconductor surface. The bias voltage was primarily dropped at the metal semiconductor interface region, which is the cathode active region. For positive surface bias, the accelerating voltage not only increased the polarization, but it also enhanced the quantum efficiency of the photocathode. Preliminary results verify the bias effect on both quantum efficiency and polarization by a factor of 1.8 and 1% respectively.
Date: December 18, 2006
Creator: Ioakeimidi, K.; Brachmann, A.; Clendenin, J.E.; Garwin, E.L.; Kirby, R.E.; Maruyama, T. et al.
Partner: UNT Libraries Government Documents Department

Low Emittance Guns for the ILC Polarized Electron Beam

Description: Polarized electron beams generated by DC guns are routinely available at several accelerators including JLAB, Mainz and SLAC. These guns operate with a cathode bias on the order of -100 kV. To minimize space charge effects, relatively long bunches are generated at the gun and then compressed longitudinally external to the gun just before and during initial acceleration. For linear colliders, this compression is accomplished using a combination of rf bunchers. For the basic design of the International Linear Collider (ILC), a 120 kV DC photocathode gun is used to produce a series of nanosecond bunches that are each compressed by two sub-harmonic bunchers (SHBs) followed by an L-band buncher and capture section. The longitudinal bunching process results in a significantly higher emittance than produced by the gun alone. While high-energy experiments using polarized beams are not generally sensitive to the source emittance, there are several benefits to a lower source emittance including a simpler more efficient injector system and a lower radiation load during transport especially at bends as at the damping ring. For the ILC, the SHBs could be eliminated if the voltage of the gun is raised sufficiently. Simulations using the General Particle Tracer (GPT) package indicate that a cathode bias voltage of {ge}200 kV should allow both SHBs to be operated at 433 or even 650 MHz, while {ge}500 kV would be required to eliminate the SHBs altogether. Simulations can be used to determine the minimum emittance possible if the injector is designed for a given increased voltage. A possible alternative to the DC gun is an rf gun. Emittance compensation, routinely used with rf guns, is discussed for higher-voltage DC guns.
Date: December 1, 2006
Creator: Clendenin, J.E.; Brachmann, A.; Ioakeimidi, K.; Kirby, R.E.; Maruyama, T.; Miller, R.H. et al.
Partner: UNT Libraries Government Documents Department