G.P. Saraph

Publications (15)10.34 Total impact

• Conference Proceeding: ADM reduction in SONET-WDM rings for stochastically varying traffic

  Gaurav Bhati, G.P. Saraph
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  ABSTRACT: Optimal grooming in SONET-WDM ring networks corresponds to minimization of add-drop multiplexers under given constraints. The general grooming problem is NP-complete. We present an approach towards reduction in the number of ADMs under stochastically varying traffic. First, a model of blocking probability is presented. Then we present the complete mathematical formulation (ILP) of the problem. Lastly, we discuss the type of solution which is required for this problem.
  Broadband Networks, 2005. BroadNets 2005. 2nd International Conference on; 11/2005
• Source

  Available from: iitb.ac.in

  Conference Proceeding: Traffic engineering using new VS routing scheme

  G.P. Saraph, P. Singh
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  ABSTRACT: Goal of traffic engineering in packet networks is to improve the network performance by providing support for congestion management, higher bandwidth utilization (or throughput), and QoS or priority-based services. Open shortest path first with traffic engineering extensions (OSPF-TE) (J. Moy, April 1998) and multiprotocol label switching (MPLS) protocols are commonly viewed as possible solutions. Both, the OSPF-TE with optimized link weights or MPLS with explicit optimal path set-ups, work ideally under static network conditions with a known demand-matrix. However, these methods do not provide scalability and flexibility to adapt to arbitrary, dynamic demand patterns in large networks. A novel traffic engineering scheme based on the virtual space (VS) routing (G. P. Saraph and P. Singh) is proposed here, which has the scalability, flexibility, and robustness to rapidly adapt to arbitrary, dynamic load conditions in large networks. Simulations are carried out on randomly constructed 40, 80, and 200-node networks with arbitrary demand matrices, which demonstrate excellent capability of the VS routing in terms of load balancing, packet throughput, and congestion avoidance. The proposed VS scheme is used for path selection in MPLS and integrated with the signaling protocols for path establishment, such as the constraint based routing (CR-LDP) (J. Ash et al., Jan. 2002) or resource reservation (RSVP-TE) (D. Awduche et. al., Jan 2002) protocols.
  Communications, 2004 IEEE International Conference on; 07/2004
• Source

  Available from: iitb.ac.in

  Conference Proceeding: New scheme for IP routing and traffic engineering

  G.P. Saraph, P. Singh
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  ABSTRACT: A novel scheme for routing data packets in high-speed communication networks is presented and described in detail. Simulations have been performed on randomly constructed 25 and 100 node networks, which demonstrate excellent IP throughput and the capability to adapt to dynamic network conditions. The most important benefit of this scheme is to simplify the route look-up tasks and save on resources required for route processing, routing updates, data storage, memory access, and information exchange. The scheme can be used as a stand-alone IP routing protocol or used with the conventional IP, ATM, or MPLS for path selection, QoS support, and traffic engineering. It can quickly adapt to the dynamic load conditions of traffic congestion or link breakage to enable QoS support or priority-based differential services. The scheme may be implemented in software or hardware to give a simple, fast, and cheap solution. The simulations show that the solution is robust and highly scalable for large high-speed networks.
  High Performance Switching and Routing, 2003, HPSR. Workshop on; 07/2003
• Article: A comparative study of three single-stage, depressed-collector designs for a 1-MW, CW gyrotron

  G.P. Saraph, K.L. Felch, J. Feinstein, P. Borchard, S.R. Cauffman, S. Chu
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  ABSTRACT: 1-MW continuous-wave (CW) gyrotrons operating at 140 GHz are being developed for heating fusion plasmas. Energy recovery using a depressed collector is employed to improve total efficiency and reduce power supply voltage and voltage regulation requirements for various electron beam devices. This paper describes and compares three different types of single-stage, depressed collector designs. The first design is a magnetically shielded, coaxial collector with fixed-current collector coils. The second and third designs use cylindrical collectors with an outer magnetic shield and collector coils with time-varying current values. The time-varying magnetic field produced by the collector coils sweeps the beam trajectories on the collector surface lowering the average power density. The second design employs axial beam sweeping using axisymmetric collector coils, whereas the third design employs transverse beam sweeping, making the instantaneous fields and electron trajectories nonaxisymmetric and three-dimensional (3-D). Relative advantages and disadvantages of these three schemes are discussed.
  IEEE Transactions on Plasma Science 07/2000; · 1.17 Impact Factor
• Source

  Available from: umd.edu

  Article: An overmoded coaxial buncher cavity for a 100-MW gyroklystron

  M. Castle, J. Anderson, W. Lawson, G.P. Saraph
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  ABSTRACT: An overmoded abrupt transition coaxial buncher cavity has been designed and experimentally cold tested for use in a second-harmonic 17.136-GHz three-cavity 100-MW gyroklystron. Circuit efficiencies of 41% can be achieved with a buncher cavity that has a quality factor of 389 in the TE₀₂₁ mode. Scattering matrix and finite-element codes were used to design and model the cavity theoretically and to determine that the cavity would be stable to oscillation. The experimental cold testing confirmed these results and refined the final dimensions from the theoretical models
  IEEE Microwave and Guided Wave Letters 10/1998;
• Source

  Available from: umd.edu

  Article: Design of a single-stage depressed collector for high-power, pulsed gyroklystron amplifiers

  G.P. Saraph, V.L. Granatstein, W. Lawson
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  ABSTRACT: Net efficiency of microwave devices can be enhanced by recovering energy from the spent electron beam. Depressed collectors are commonly used for low to medium voltage (<100 kV), CW microwave tubes to achieve this objective. Designs of single-stage depressed collectors for high-power, high-voltage, pulsed gyroklystron amplifiers are presented here. Theoretical velocity distributions of the spent beams from 17.14 and 35.0 GHz relativistic gyroklystron designs are used as input to the particle trajectory simulations. The entire spent beam is collected at the cylindrical collector held at a depressed potential with respect to the interaction cavities. The magnetic field profile is adjusted to achieve collection of electrons at the maximum depressed value of the collector potential. A significant improvement in the device efficiency is estimated for both designs. A possible implementation scheme for the energy recovery using a double anode electron gun is described in detail
  IEEE Transactions on Electron Devices 05/1998; · 2.32 Impact Factor
• Article: A novel hybrid slow-wave/fast-wave traveling-wave amplifier

  W. Lawson, A. Fernandez, T. Hutchings, G.P. Saraph
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  ABSTRACT: We introduce a new broad-band amplifier configuration which contains elements of both linear and cyclotron resonance maser microwave tubes. A helix slow-wave structure is used to bunch a linearly streaming annular electron beam. A nonadiabatic magnetic transition, which is placed after a drift region at the point where the ac beam current is nearly maximized, converts much of the beam's axial momentum to rotational momentum. The beam then travels through a tapered right-circular waveguide, where microwave energy is extracted via the gyrotron interaction. The design of a proof-of-principle X-band amplifier is given, and the codes that are used in the simulation are described. The nominal beam voltage and current are 45 kV and 8 A, respectively. The tube is predicted to be stable, to possess a peak efficiency above 43%, and to have an instantaneous bandwidth of over 9%
  IEEE Transactions on Plasma Science 11/1997; · 1.17 Impact Factor
• Source

  Available from: kek.jp

  Conference Proceeding: Initial operation of the Maryland coaxial gyroklystron experiment

  W. Lawson, M. Castle, J. Cheng, B. Hogan, G.P. Saraph, V.L. Granatstein, M. Reiser
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  ABSTRACT: We describe results from the initial operation of our coaxial gyroklystron experiment, which is being evaluated as a potential driver for future linear colliders. The interaction is designed to occur between a 500 kV, 500-700 A beam and a series of coaxial TE₀₀₁ microwave cavities. Output powers in excess of 100 MW at 8.568 GHz are expected with an efficiency of about 40%. We detail performance of our single anode magnetron injection gun in addition to the stability and amplification properties of our preliminary microwave circuit. We also discuss our designs of near-term future tubes which are expected to have comparable performance at 17.136 GHz
  Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
• Article: Gyroklystrons for driving linear colliders at 35 GHz

  V. L. Granatstein, G. P. Saraph, G. S. Nusinovich, A. Singh, W. Lawson
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  ABSTRACT: Abstract unavailable.
  AIP Conference Proceedings. 03/1997; 398(1):874-886.
• Article: High power gyroklystron development for advanced accelerator applications

  W. Lawson, J. Anderson, J. P. Calame, J. Cheng, M. Castle, V. L. Granatstein, B. Hogan, M. Reiser, G. P. Saraph
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  ABSTRACT: In this paper we present the design details and report on the current status of both a first harmonic two-cavity coaxial gyroklystron and a second harmonic three-cavity amplifier tube, each of which is designed to produce over 100 MW of output power. Both tubes utilize a fundamental mode TE011 input cavity which is driven by a 150 kW magnetron at 8.56 GHz. The former tube also has an 8.56 GHz TE011 output cavity while the latter system has a buncher cavity and an output cavity that resonate at twice the drive frequency in the TE021 mode. We present details of all system aspects, including the test bed modifications required to produce the enhanced beam characteristics, simulated beam properties, and simulated circuit interactions. Cold test results of both tubes are detailed and our preliminary HFSS modeling efforts are described. Results to date indicate that both systems should be at least 40% efficient. © 1997 American Institute of Physics.
  AIP Conference Proceedings. 03/1997; 398(1):865-873.
• Source

  Available from: umd.edu

  Article: 100-150 MW designs of two- and three-cavity gyroklystron amplifiers operating at the fundamental and second harmonics in X- and Ku-bands

  G.P. Saraph, W. Lawson, M. Castle, J. Cheng, J.P. Calame, G.S. Nusinovich
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  ABSTRACT: Efficient 100-150 MW X- and Ku-band microwave sources with pulselengths of 1 μs are being developed for driving future linear colliders. Two- and three-cavity co-axial designs of relativistic gyroklystron amplifiers are presented here which fulfill these requirements. Numerical simulations predict over 40% efficiency, 45-50 dB gain, and 100-160 MW power level for the gyroklystron designs operating at fundamental (8.568 GHz) and second harmonic (17.136 GHz). It is shown that introducing a penultimate (buncher) cavity significantly improves efficiency and gain of the second-harmonic amplifier
  IEEE Transactions on Plasma Science 07/1996; · 1.17 Impact Factor
• Source

  Available from: rit.edu

  Article: Design of a high-efficiency low-voltage axially modulated cusp-injected second-harmonic X-band gyrotron amplifier

  W. Lawson, A. Grigoropoulos, A. Liu, G.P. Saraph, J. Rodgers, W.W. Destler
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  ABSTRACT: We present the theoretical design of a second-harmonic small-orbit gyrotron amplifier which utilizes the interactions between a 35-kV 4-A beam and a TE₀₁₁ cavity to produce over 70 kW of amplified power at 9.9 GHz in a 1.83-kG magnetic field. One of the novel features of this device is that the electron gun produces an axially streaming annular beam which is velocity modulated by a short TM_0n0 input cavity. Perpendicular energy is imparted to the beam via a nonadiabatic magnetic transition at the end of a 13-cm drift region. An electronic efficiency of 53% is predicted with a large signal gain near 20 dB by a single particle code which takes into account nonideal effects associated with finite beam thickness and finite magnetic field transition widths
  IEEE Transactions on Plasma Science 07/1996; · 1.17 Impact Factor
• Article: A study of parametric instability in a harmonic gyrotron: Designs of third harmonic gyrotrons at 94 GHz and 210 GHz

  G. P. Saraph, T. M. Antonsen, G. S. Nusinovich, B. Levush
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  ABSTRACT: Mode competition can present a major hurdle in achieving stable, efficient operation of a gyrotron at the cyclotron harmonics. A type of mode interaction in which three modes at different cyclotron harmonics are parametrically coupled together is analyzed here. This coupling can lead to parametric excitation or suppression of a mode; cyclic mode hopping; or the coexistence of three modes. Simulation results are presented for the parametric instability involving modes at the fundamental, second harmonic, and third harmonic of the cyclotron frequency. It is shown that the parametric excitation can lead to stable, efficient operation of a high‐power gyrotron at the third harmonic. Based on this phenomenon, two practical designs are presented here for the third harmonic operation at 94 and 210 GHz. © 1995 American Institute of Physics.
  Physics of Plasmas 06/1995; 2(7):2839-2846. · 2.15 Impact Factor
• Conference Proceeding: Modeling of mode purity in high power gyrotrons

  S.Y. Cai, T.M. Antonsen Jr, G.P. Saraph, B. Levush
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  ABSTRACT: Summary form only given. Spurious mode generation at the frequency of the operational mode in a high-power gyrotron can significantly reduce the power handling capability and the stability of a gyrotron oscillator because these modes are usually not matched at the output window and thus have high absorption and reflection rates. To study the generation of this kind of mode, the authors have developed a numerical model based on an existing multimode self-consistent time-dependent computer code. This model includes both TE and TM modes and accounts for mode transformations due to the waveguide inhomogeneity. This tool has been used to study the mode transformation in the gyrotron and the possibility of excitation of parasitic TE and TM modes in the up-taper section due to the gyroklystron mechanism. Preliminary results show moderate excitation of both TE and TM modes at the same frequency as the main operating mode at locations near their cut-off
  Plasma Science, 1993. IEEE Conference Record - Abstracts., 1993 IEEE International Conference on; 07/1993
• Article: Regions of stability of high-power gyrotron oscillators

  G.P. Saraph, T.M. Antonsen Jr, B. Levush, G.I. Lin
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  ABSTRACT: The problem of mode competition in a high-power gyrotron oscillator is considered. The regions of parameter space in which a preexisting large-amplitude mode is able to suppress competing satellites are determined for cases in which the coupling coefficients and cavity quality factors for the operating and satellite modes are different. In addition, the effect of beam quality on the regimes of stable single-mode operation is investigated. Generally speaking, the requirement of stable operation favors devices whose interaction length measured by the parameter μ is not too large. It is found that for μ near 10 the operation is relatively stable and μ near 17 is not
  IEEE Transactions on Plasma Science 07/1992; · 1.17 Impact Factor