Progress at SLAC on high-power rf pulse compression

Rf pulse compression is a technique for augmenting the peak power output of a klystron (typically 50--100 MW) to obtain the high peak power required to drive a linear collider at a high accelerating gradient (typically 200 MW/m is required for a gradient of 100 MV/m). The SLED pulse compression system, with a power gain of about 2.6, has been operational on the SLAC linac for more than a decade. Recently, a binary pulse-compression system with a power gain of about 5.2 has been tested up to an output power of 120 MW. Further high-power tests are in progress. Our current effort is focused on prototyping a so-called SLED-II pulse-compression system with a power gain of four. Over-moded TE[sub 01]-mode circular waveguide components, some with novel technical features, are used to reduce losses at the 11.4-GHz operating frequency

Flow shear suppression of turbulence using externally driven ion Bernstein and Alfven waves

The utilization of externally-launched radio-frequency waves as a means of active confinement control through the generation of sheared poloidal flows is explored. For low-frequency waves, kinetic Alfven waves are proposed, and are shown to drive sheared E {times} B flows as a result of the radial variation in the electromagnetic Reynolds stress. In the high frequency regime, ion Bernstein waves are considered, and shown to generate sheared poloidal rotation through the ponderomotive force. In either case, it is shown that modest amounts of absorbed power ({approximately} few 100 kW) are required to suppress turbulence in a region of several cm radial width. 9 refs

Very close pairs of quasi-stellar objects

It is pointed out that there are now known four very close pairs of QSOs with separations > 5 arcsec and very different redshifts. Several estimates of the probability that they are accidental configurations range between 10"-"7 and 3.5 x 10"-"3. We conclude either than this is further evidence that QSOs have significant non-cosmological redshift components, or that the pairs must be explained by gravitational lensing. (orig.)Available from TIB Hannover: RR 4697(916) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Top quark pair production at threshold: complete next-to-next-to-leading order relativistic corrections

The complete next-to-next-to-leading order (i.e. O(#upsilon#"2), O(#upsilon##alpha#_s) and O(#alpha#_s"2)) relativistic corrections to the total photon mediated tt production cross section at threshold are presented in the framework of nonrelativistic quantum chromodynamics. The results are obtained using semi-analytic methods and ''direct matching''. The size of the next-to-next-to-leading order relativistic corrections is found to be comparable to the size of the next-to-leading order ones. (orig.)29 refs.Available from TIB Hannover: RA 2999(98-008) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A three-gap klystron output cavity at X-band

A high-power X-band klystron employing a double-gap output cavity has been operating at SLAC. Multi-gap output circuits have lower surface gradients at the interaction gaps than single-gap ones but are prone to self-oscillate due to negative loading and trapped higher-order modes. In the double-gap circuit design, considerable attention had been directed to deal with these stability problems. The performance of the present tube appears to be limited by gap breakdown and beam interception particularly at long pulses. A three-gap output cavity is currently under development to further reduce the gap surface gradient. Another new feature of the circuit is an enlarged downstream drift tube to improve on beam clearance. This paper discusses the considerations involved in designing a multi-gap output cavity and presents the cold test measurements on the three-gap circuit. The experimental data is compared with numerical results from the 3-D simulation code ARGUS

Strongly interacting Higgs sector without technicolor

Simulation results are presented on Higgs mass calculations in the spontaneously broken phase of the Higgs sector in the minimal Standard Model with a higher derviative regulator. A heavy Higgs particle is found in the TeV mass range in the presence of a complex conjugate ghost pair at higher energies. The ghost pair evades easy experimental detection. As a finite and unitary theory in the continuum, this model serves as an explicit and simple example of a strong interacting Higgs sector without technicolor. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(94-233) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekUSDOE, Washington, DC (United States)DEGerman

Cosmological lepton asymmetry, primordial nucleosynthesis and sterile neutrinos

We study post weak decoupling coherent active-sterile and active-active matter-enhanced neutrino flavor conversion in the early universe. We find that under some circumstances sterile neutrino production via these processes can leave the active neutrinos with non-thermal energy spectra. In turn, these distorted energy spectra can affect primordial nucleosynthesis by altering the neutron-to-proton ratio. Inclusion of this effect changes the relationship between the cosmological lepton numbers and the primordial "4He yield and reduces the range of lepton numbers that could reconcile the observationally-inferred primordial helium abundance with active-sterile vacuum neutrino mixing in the mass-squared difference range 0.2 eV"2 < #delta#m"2 < 10eV"2. This #delta#m"2 regime currently is being probed by accelerator-based experiments (mini-BooNE). (orig.)SIGLEAvailable from TIB Hannover: RA 2999(04-202) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Massive quark production in electron positron annihilation to order #alpha#"2_s

Recent analytical and numerical results for the three-loop polarization function allow to present a phenomenological analysis of the cross section for massive quark production in electron positron annihilation to order #alpha#_s"2. Numerical predictions based on fixed order perturbation theory are presented for charm and bottom production above 5 and 11.5 GeV, respectively. The contribution from these energy regions to #alpha#(M_Z"2), the running QED coupling constant at scale M_Z, are given. The dominant terms close to threshold, i.e. in an expansion for small quark velocity #beta#, are presented. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-220) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Deutsche Forschungsgemeinschaft (DFG), Bonn (Germany); International Association for the Promotion of Co-Operation with Scientists from the Independent States of the Former Soviet Union (INTAS)DEGerman