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Future colliders such as NLC and JLC will require a highly-polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly-doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 hour at 600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning., 11 pages, 3 figures, 1 table, contributed to 10th Workshop on Polarized Sources and Targets, Novosibirsk, Sept. 22-26, 2003, to be submitted to Nucl. Instrum. and Meth. A

X-band accelerator structures meeting the next linear collider design requirements have been found to suffer vacuum surface damage caused by rf breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. rf reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in rf structures. Particle contaminations found following clean autopsy of four rf-processed traveling wave structures have been catalogued and analyzed. Their influence on rf breakdown, as well as that of several other material-based properties, are discussed.

A high-gradient-doping technique is applied to strained polarized photocathodes. A 5.0– 7.5 nm p-type surface layer doped to 5×10 19 cm −3 is found sufficient to overcome the surface charge limit while maintaining high beam polarization. This technique can be employed to meet the charge requirements of the Next Linear Collider with a polarization approaching 80%.

Strong in-plane magnetic field pulses of 2--4.4 ps duration are used to study magnetization reversal in perpendicularly magnetized Co/Pt films. Ring domains, reminiscent of the field contour during exposure, are observed later with Kerr microscopy. Their radii represent switching fields which are in quantitative agreement with the coherent rotation model. The observation of intrinsic transition broadening is attributed to the existence of static and dynamic fluctuations of the magnetic anisotropy.

The deformation potentials a, b and d for GaAs have been determined from polarized photoluminescence measurements upon a set of epitaxially grown strained GaAs structures possessing varying levels of compressive biaxial lattice strain. X-ray diffraction measurements yield values for the degree of lattice strain while the polarized photoluminescence measurements permit a separate determination to be made of the heavy hole and light hole band energies. Correlation of these data allows for the determination of the deformation potentials within the context of the orbital-strain Hamiltonian.

The SLAC Quark Search Group has demonstrated successful operation of a low cost, high mass throughput Millikan apparatus designed to search for fractionally charged particles. About six million silicone oil drops were measured with no evidence of fractional charges. A second experiment is under construction with 100 times greater throughput which will utilize optimized search fluids.

An anisotropy in the quantum efficiency (QE) has been observed in photoemission from strained GaAs photocathodes excited by linearly polarized light. The wavelength dependence of the anisotropy is closely correlated with that of the electron-spin polarization. Based on a theoretical analysis, we show that the QE anisotropy is caused by an in-plane strain anisotropy arising from anisotropic strain relaxation. The QE anisotropy calculated from the in-plane strain anisotropy measured with X-ray diffraction and the measured QE anisotropy are in good agreement.

Spin-polarized electron photoemission has been studied for GaAs/GaAs$_{1-x}$P$_x$ strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.

We present a precise measurement of the left-right cross section asymmetry ([ital A][sub [ital L][ital R]]) for [ital Z] boson production by [ital e][sup +][ital e][sup [minus]] collisions. The measurement was performed at a center-of-mass energy of 91.26 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (63.0[plus minus]1.1)%. Using a sample of 49 392 [ital Z] decays, we measure [ital A][sub [ital L][ital R]] to be 0.1628[plus minus]0.0071(stat)[plus minus]0.0028(syst) which determines the effective weak mixing angle to be sin[sup 2][theta][sub [ital W]][sup eff]=0.2292[plus minus]0.0009(stat) [plus minus]0.0004(syst).

The polarization of photoemitted electrons from thin AlxGa1−xAs layers grown by molecular‐beam epitaxy has been studied as a function of Al concentration by varying x in steps of 0.05 from 0.0 to 0.15. As the fraction x is increased, the wavelength dependence of the polarization shifts toward shorter wavelengths, permitting wavelength tuning of the region of maximum polarization. A maximum electron polarization of 42%–43% is obtained for AlxGa1−xAs samples with x≥0.05 while the maximum polarization of GaAs (x=0) samples reaches 49%. To investigate the lower polarization of AlxGa1−xAs, additional samples have been studied, including a short‐period superlattice (GaAs)7 ‐ (AlAs)1 .

We present the first measurement of the left-right cross section asymmetry (${\mathit{A}}_{\mathit{L}\mathit{R}}$) for Z boson production by ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4\ifmmode\pm\else\textpm\fi{}0.6)%. Using a sample of 10 224 Z decays, we measure ${\mathit{A}}_{\mathit{L}\mathit{R}}$ to be 0.100\ifmmode\pm\else\textpm\fi{}0.044(stat)\ifmmode\pm\else\textpm\fi{}0.004(syst), which determines the effective weak mixing angle to be ${\mathrm{sin}}^{2}$${\mathrm{\ensuremath{\theta}}}_{\mathit{W}}^{\mathit{e}\mathit{f}\mathit{f}}$=0.2378 \ifmmode\pm\else\textpm\fi{}0.0056(stat)\ifmmode\pm\else\textpm\fi{}0.0005(syst).

Spin-polarized electron photoemission has been investigated for strained GaAs epitaxially grown on a GaAs{sub 1{minus}{ital x}}P{sub {ital x}} buffer. The lattice-mismatched heterostructure results in a highly strained epitaxial layer and significant enhancement of electron-spin polarization is observed. The effect of epitaxial layer strain is studied for a variety of samples with epitaxial-layer thicknesses varying from 0.1 to 0.3 {mu}m and the phosphorus concentration {ital x} varying from 0.21 to 0.28. Electron-spin polarization as high as 90% has been observed. The 0.3-{mu}m-thick sample, well in excess of theoretical estimates for the critical thickness for pseudomorphic growth, reaches an electron-spin polarization of 80%, demonstrating a significant persistence of lattice strain.

Electron-spin polarization in excess of 70% has been observed in photoemission from a 0.1-\ensuremath{\mu}m-thick epitaxial layer of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As with x\ensuremath{\approxeq}0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9% lattice mismatch. The electron polarization and the quantum efficiency have been measured as a function of the excitation photon energy from 1.25 to 2.0 eV. A significant enhancement of the electron polarization occurs in the vicinity of 1.33 eV where the expected strain-induced level splitting permits optical excitation of a single-band transition.

Superconducting rf surface resistance measurements were made on oxidized Nb cavities that had been warmed for a few minutes to temperatures between 250 and 300° C. Warmed oxide layers were further studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy and secondary electron emission yield measurements. Warming usually reduced the temperature-dependent (BCS) part of the surface resistance by 10–20% while, for warming temperatures near 300° C, the low-temperature residual surface resistance increased by as much as 70 nΩ. Surface spectroscopy measurements showed that, at temperatures between 200 and 250° C, the oxide layer was chemically altered but remained surface-segregated; between 250 and 300° C, however, surface oxygen dissolved into the Nb bulk. Changes in the BCS resistance were consistent with a model based on a shortening of the electron mean free path by oxygen that had diffused into the Nb metal and based on the theoretical dependence of BCS resistance on electron mean free path. No specific cause for the increased residual resistance could be positively identified, although oxygen-induced surface roughening is a possibility.

The GaAsP/GaAs superlattice (SL) structure has been widely recognized as the most efficient spin polarized electron source with 90% maximum polarization and more than 1% quantum efficiency. The main spin depolarization mechanisms in these structures are: interband absorption smearing due to band-edge fluctuations, hole scattering between the heavy hole (HH) and light hole (LH) states that causes a broadening of the LH band, spin precession due to an effective magnetic field generated by the lack of crystal inversion symmetry and spin orbit coupling.

The main advantage of superlattice (SL) structures as spin polarized electron emitters is the ability to provide a large splitting between the heavy hole (HH) and light hole (LH) valence bands (VB) over a large active thickness compared to single strained layers. Two important depolarization mechanisms in these structures are the scattering effects during the transit of the electrons in the active region and the depolarization that takes place in the band bending region (BBR) near the surface. In this paper, we systematically study the effects of the electron mobility and transit time by using an InAlGaAs/GaAs SL with a flat conduction band (CB). Initial results by the SPTU-SLAC collaboration using such structures grown by the Ioffe Institute showed polarization and quantum yield (QE) of 92% and 0.2% respectively. We report measurements using similar structures grown by SVT Associates. The results (polarization up to 90%) are also compared with simulations.

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.

Strained‐superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important.

The ILC project will be the next large high energy physics tool that will use polarized electrons (and positrons). For this machine spin physics will play an important role. The polarized electron source design is based on electron injectors built for the Stanford Linear Collider (polarized) and Tesla Test Facility (un‐polarized). The ILC polarized electron source will provide a 5GeV spin polarized electron beam for injection into the ILC damping ring. Although most ILC machine parameters have been achieved by the SLC or TTF source, features of both must be integrated into one design. The bunch train structure presents unique challenges to the source laser drive system. A suitable laser system has not yet been demonstrated and is part of the ongoing R&D program for ILC at SLAC. Furthermore, ILC injector R&D incorporates photocathode development, increasing available polarization, and improving operational properties in gun vacuum systems. Another important area of research and development is advancing the design of DC and RF electron gun technology for polarized sources. This presentation presents the current status of the design and outlines aspects of the relevant R&D program carried out within the ILC community.

We investigated the effect of an accelerating field on the spin polarization of photo‐generated 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% respecti...

Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile. Preliminary measurements have been carried out on bulk and thin film GaAs. As expected, the yield change far from the bandgap is quite large for bulk material. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case.

The SLC polarized electron source (PES) can meet the expected requirements of the International Linear Collider (ILC) for polarization, charge and lifetime. However, experience with newer and successful PES designs at JLAB, Mainz, Nagoya and elsewhere can be incorporated into a first-generation ILC source that will emphasize reliability and stability without compromising the photocathode performance. The long pulse train for the ILC may introduce new challenges for the PES, and in addition more reliable and stable operation of the PES may be achievable if appropriate R&D is carried out for higher voltage operation and for a simpler load-lock system. The outline of the R&D program currently taking shape at SLAC and elsewhere is discussed. The principal components of the proposed ILC PES, including the laser system necessary for operational tests, are described.

Future electron-positron linear colliders require a highly polarized electron beam with a pulse structure that depends primarily on whether the acceleration utilizes warm or superconducting rf structures. The International Linear Collider (ILC) will use cold structures for the main linac. It is shown that a dc-biased polarized photoelectron source such as successfully used for the SLC can meet the charge requirements for the ILC micropulse with a polarization approaching 90%., 4 pages, 2 tables, contributed to SPIN04 Symposium (Trieste)

This report summarizes results of recent upgrades to SLAC's polarized source drive laser system. A Q-switching system has been incorporated into the flashlamp-pumped Ti:Sapphire laser system. The Q-switched laser provides energies up to 5 mJ for a 200 ns long pulse. Slow Q-switching provides control over length and shape of the laser pulse. A peak current of > 5.5 A has been demonstrated using a GaAs photocathode illuminated by this laser system.

Atomic hydrogen cleaning followed by heat cleaning at 450$^\circ$C was used to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs cathodes, higher than the results obtained using conventional 600$^\circ$C heat cleaning. The low-temperature cleaning technique was successfully applied to thin, strained GaAs cathodes used for producing highly polarized electrons. No depolarization was observed even when the optimum cleaning time of about 30 seconds was extended by a factor of 100.

X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer vacuum surface damage caused by radio frequency (RF) breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. RF reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in RF structures. Particle contaminations found following clean autopsy of four RF-processed travelling wave structures, have been catalogued and analyzed. Their influence on RF breakdown, as well as that of several other material-based properties, will be discussed.

Single strained, medium‐doped (5×1018 /cm3) GaAs photocathodes show the surface charge limit (SCL). The SCL poses a serious problem for operation of polarized electron sources at future linear colliders such as the NLC/JLC. A high‐gradient‐doping technique has been applied to address this problem. A 5 –7.5 nm p‐type surface layer doped to 5×1019/cm3 is found sufficient to overcome the SCL, while maintaining high beam polarization. This technique can be employed to meet the charge requirements of the NLC with a polarization approaching 80%.

At high field levels, field emission losses in superconducting cavities have an adverse effect in both reducing the otherwise extremely high Q > 10^9, and the magnetic breakdown field bringing it well below the critical magnetic field of the superconductor. The two effects may well be related as field enhancing whiskers responsible for the field emission losses can be driven normal thus reducing the magnetic breakdown field. Both the beneficial and deleterious effects of anodizing the inner surface of superconducting cavities are discussed and analyzed., 6 pages

The SLAC high-gradient-doped MOCVD-grown GaAs cathode presently in use consists of a strained GaAs low-doped layer (with a small admixture of P) capped by a few nanometers of highly Zn-doped GaAs, which is heat-cleaned at relatively high temperature and then activated by Cs/NF{sub 3} co-deposition. The high-gradient-doped structure solves the problem of the surface charge limit that the previously-used SLAC cathodes had, and this preparation procedure has produced satisfactory results. However, the preparation procedure has a few weaknesses that prevent cathodes from achieving the ultimate desired performance. The peak polarization is limited to 80% due to strain relaxation in the relatively thick strained layers. Also dopant loss causes the surface charge limit effect to reappear after multiple high-temperature heat-cleanings. In this paper, we will discuss recent progress made at SLAC that addresses these limitations, including using the MBE growth technique with Be doping and using the superlattice structure. In addition, to reduce the heat-cleaning temperature, an atomic hydrogen cleaning technique is explored.

Electron spin polarization in excess of 70% has been observed in photoemission from a 0.1- mu m-thick epitaxial layer of In/sub x/Ga/sub 1-x/As, with x approximately=0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9% lattice mismatch, as confirmed by X-ray diffractometer measurements of the lattice parameter. The electron polarization and the quantum efficiency have been measured as a function of the excitation photon energy from 1.25 to 2.0 eV. A significant enhancement of the electron polarization occurs in the vicinity of 1.33 eV, where the expected strain-induced level splitting permits optical excitation of a single band transition. Measurements made on a control sample of 1.14- mu m thickness, significantly larger than the critical thickness for pseudomorphic strain, show no polarization enhancement. >

The authors describe the design of the ultra-high vacuum system for the beam-line from the 160 kV polarized electron gun to the linac injector in the Stanford Linear Collider (SLC). The polarized electron source is a GaAS photocathode, requiring 10/sup -11/ Torr-range pressure for adequate quantum efficiency and longevity. The photocathode is illuminated by 3 ns-long laser pulses. Photocathode maintenance and improvements require occasional substitution of guns with rapid restoration of UHV conditions. Differential pumping is crucial since the pressure in the injector is more than 10 times greater than the photocathode can tolerate and since electron-stimulated gas desorption from beam loss in excess of 0.1% of the 20 nC pulses may poison the photocathode. The design for the transport line contains a differential pumping region isolated by a pair of valves. Exchange of guns requires venting only this isolated region, which can be restored to UHV rapidly by baking. The differential pumping is performed by nonevaporable getters and an ion pump. >

A set of thin GaAs p-type negative electron affinity (NEA) photocathodes have been used to measure the yield of photoemitted electrons at high intensity excitation. The active layer thickness is 100 nm and the p-type doping ranges from 5\times10^{18} cm^{-3} to 5\times10^{19} cm^{-3} for a set of four samples. The results show that the surface escape probability is a linear function of the NEA energy. The surface photovoltage effect on photoemission is found to diminish to zero at a doping level of 5\times10^{19} cm^{-3}. The experimental results are shown to be in good agreement with calculations using a charge limit model based on surface photovoltage kinetics that assume a constant electron energy relaxation rate in the band bending region., LaTeX RevTeX 11 pages, 6 figures

The doping concentration dependence of the charge limit phenomenon is studied using a set of thin unstrained GaAs. The p-type doping concentration ranges from 5×1018 cm−3 to 5×1019 cm−3. The surface photovoltage effect on photoemission is found to diminish rapidly with increasing doping concentration. The doping concentration effect on electron polarization is studied using high surface doped strained GaAs. The charge enhancement is explored using a direct, lateral surface charge sink in the form of a metallic grid overlaid on the surface.

Ultrafast magnetic field pulses as short as 2 picoseconds are able to reverse the magnetization in thin, in-plane, magnetized cobalt films. The field pulses are applied in the plane of the film, and their direction encompasses all angles with the magnetization. At a right angle to the magnetization, maximum torque is exerted on the spins. In this geometry, a precessional magnetization reversal can be triggered by fields as small as 184 kiloamperes per meter. Applications in future ultrafast magnetic recording schemes can be foreseen.

A method for measuring the flux of atomic oxygen utilizing a silver film on a quartz‐crystal deposition rate monitor is described. Measuring the initial oxidation rate of the silver, which is proportional to the atomic oxygen flux, determines a lower limit on the atomic oxygen flux. This method is more direct than measuring the conductance of the silver film, has an intrinsic flux detection range of 1013–1017 atoms/cm2 s, and is reversible by exposing the sensor to an atomic hydrogen flux.

The anomalous part of the gyromagnetic ratio, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC% vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz% ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb% L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe% pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam% aaeaqbaaGcbaaceaGaa8xyaiaa-1dadaWcaaqaaiabigdaXaqaaiab% ikdaYaaacqGGOaakcqWGNbWzcqGHsislcqaIYaGmcqGGPaqkaaa!4351! $$a = \frac{1}{2}(g - 2)$$ of the muon has been measured by determining the precession θ= aω0-Bt for 100 MeV/c muons as a function of storage timet in a known static magnetic field of the formB=B 0(1+ay+by2+cy3+dy4). The result is aexp = (1162±5)·10-6 compared with the theoretical value ath=α/2π+0.76α2/π2=1165·10−6. This agreement shows that the muon obeys standard quantum electrodynamics down to distances ∼ 0.1 fermi. Details are given of the methods used to store muons for ∼ 103 turns in the field, and of measuring techniques and precautions necessary to achieve the final accuracy. Some of the methods of orbit analysis, magnet construction shimming and measurement, polarization analysis, and digital timing electronics may be of more general interest.

We present the first measurement of the left-right cross-section asymmetry (ALR) in Z-boson production observed at the SLAC Linear Collider. In 1992 the SLD detector recorded 10 224 Z events produced by the collision of longitudinally polarized electrons with an unpolarized positron beam at a center-of-mass energy of 91.55 GeV. The average electron beam polarization during the run was (22.4 ± 0.6)%. We measure ALR to be 0.100 ± 0.0440 (stat.) ±0.004 (syst.), which determines the effective weak mixing angle to be $\sin^2\theta_W^{\rm {eff}} = 0.2378\pm 0.0056\, ({\rm stat.})\pm 0.0005\, ({\rm syst.})$.

We have measured parity violating asymmetries in the inelastic scattering of longitudinally polarized electrons from deuterium and hydrogen. For deuterium near Q2 = 1.6 (GeV/c)2 the asymmetry is (−9.5 × 10−5)Q2 with statistical and systematic uncertainties each about 10%.

The Ginzburg–Landau–Lifshitz (GLL) equation, which describes the time dependence of spin precesssion in an external magnetic field1 relates the minimal field required to reverse the magnetization at fixed pulse length to the anisotropy field of the sample.23 We have systematically varied this parameter between 1.3 and about 5.0 T in a series of perpendicularly magnetized Co/Pt multilayer films and studied the magnetization reversal in picosecond in plane field pulses. Such pulses of several Tesla field strength and ultrashort duration were obtained in the final focus test beam section of the Stanford Linear Accelerator Center. The resulting magnetization pattern, which is reminiscent of the field during exposure, is subsequently analyzed with Kerr microscopy2 (see Fig. 1). As a prominent feature, we observe a beam field related switching radius from up to down magnetization which we compare to the theoretically expected field within the GLL formalism.

The magnetic reversal mechanism in perpendicularly oriented, premagnetized Co based thin film alloys, induced by ultra short magnetic field exposure of a few picoseconds duration has been studied. Field pulses with a magnitude of several thousand Tesla were generated by the 50 GeV final focus electron beam at the Stanford Linear Accelerator Center (SLAC). Characteristic remanent domain patterns are observed in these films long after field exposure using polar Kerr microscopy. Complete reversal of the magnetization is found to occur during a single spin precession event of 6.0 ps duration where the inplane‐field amplitude is greater or equal to the macroscopically determined perpendicular anisotropy field. Further, a wide transition range, dividing the reversed and nonreversed regions is observed which is broken into a quasi periodic stripe domain structure with stripe‐width 0.3 μm. As a main result of this experimental study we find that magnetization reversal on this time scale is solely governed by the intrinsic effective field, i.e., anisotropy‐ and demagnetization‐field contributions, rather then by complex curling and buckling mechanisms. Unique insight into fundamental spin reversal mechanisms and their ultimate speed in thin magnetic recording films is provided by these experiments.

Vacuum requirements for electron storage rings are most demanding to fulfill, due to the presence of gas desorption caused by large quantities of synchrotron radiation, the very limited area accessible for pumping ports, the need for 10-9 torr pressures in the ring, and for pressures a decade lower in the interaction regions. Design features of a wide variety of distributed ion sublimation pumps (DIP) developed at SLAC to meet these requirements will be discussed, as well as NEG (non-evaporable getter) pumps tested for use in the Large Electron Positron Collider at CERN. Application of DIP to much higher pressures in electron damping rings for the Stanford Linear Collider will be discussed.

Thin (

Valence band x-ray photoelectron spectra from Fe(100) have been measured as a function of temperature to above the Curie temperature, Tc. The room temperature data can be reconciled with the theoretical one-particle density of states (DOS). At T = 1.034Tc, the data do not resemble the paramgnetic DOS of Fe as calculated in the disordered-local-moment limit.

During 4 years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO 2 on the PC's during running at LN 2 temperatures. Such PC's can be rejuvenated by warming to 90 K, i.e. above the CO 2 desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during in situ heat cleaning prior to activation. In this mode, As is preferentially evaporated from the GaAs, leaving a Ga 2 O 3 layer on the surface. This effect has been studied by AES sputter profiling which indicates that the substantial thickness of the oxide layer blocks photoemission. These PC's may only be recovered by chemically removing the oxide layer. A third mode which is not as well characterized appears for thin Ga oxide layers. Properties of these PC's include reduced emission and the presence of a cutoff bias level. Such PC's are also not recoverable in situ .

Low secondary electron emission yield (1–1.3), low radio‐frequency (rf) loss films are of interest as coatings for alumina ceramic high power klystron windows. Very thin (15–50 A) Ti and TiN layers have been previously used with success in klystron tubes operating at lower power levels (

We have developed a new technique to produce diamondlike carbon films in an rf system with water‐cooled electrodes. Hydrocarbon gas is leaked into the experimental chamber through the upper electrode which is a Pyrex cylinder inside a coil forming an rf oven. The gas (CH4) undergoes ionization/dissociation in one rf field, within an axial magnetic field. A circular water‐cooled electrode supports the substrate to be coated, and is powered from a second rf generator, developing a negative self‐bias on the substrate. Thus dissociation and ion production at the upper electrode and ion acceleration by the lower electrode could be separately controlled to optimize the film properties. It is shown that low stress, highly dense carbon films can be deposited by this method. Information is also given on bulk and surface properties as well as modification of these properties by the deposition conditions.

Secondary electron yield measurements before and after Ar ion sputter cleaning were made on Nb and Nb compounds of interest for rf superconducting cavities. Total secondary electron yields (σ) for primary energies 20–1500 eV were measured for solid Nb (σmax=1.3 at 300 eV), anodized Nb2O5 (σmax=1.2 at 300 eV), and powders of Nb(σmax=1.0 at 400 eV), NbO (σmax=0.9 at 400 eV), NbO2 (σmax=1.0 at 400 eV), Nb2O5 (σmax=0.95 at 400 eV), NbC(σmax=0.8 at 400 eV), and NbN (σmax=0.8 at 500 eV). Determinations were made for Auger elemental sensitivities, and the relationship between Auger peak heights and oxide stoichiometry is discussed. The sputter etch rate of anodized Nb2O5 was measured by depth profiling anodic coatings of known thickness.