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Solid State RF System for SCRF Cavity Characterization in VTS at RRCAT

This paper discusses the advancements in the development and testing of solid state RF systems for the characterization of superconducting cavities in the Variable Temperature Superconducting (VTS) facility at the Raja Ramanna Centre for Advanced Technology (RRCAT) in Indore, India.

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Solid State RF System for SCRF Cavity Characterization in VTS at RRCAT

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  1. Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015 Solid State RF System for SCRF Cavity Characterization in VTS at RRCAT Purushottam Shrivastava, P. Mohania, D. Baxy, V. Rajput, A. Mahawar, K. A. P. Singh Pulsed High Power Microwave Section Raja Ramanna Centre for Advanced Technology Indore, India 1

  2. Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015 Status of Solid State RF Systems for VTS at RRCAT • The design details for the 1.3 GHz LLRF system, control and data acquisition software were provided by Fermilab, USA, based on which the first version of 1.3 GHz LLRF circuits were developed by RRCAT. • Value addition was done in order to incorporate provisions for latest instruments, with several enhancements, for performance improvement and reduce the test run time. • VTS RF system at 1.3 GHz was thus successfully developed, commissioned and put to use for testing the superconducting cavities in the VTS at RRCAT. (three tests on 1.3 GHz single-cell cavities performed). • Subsequently a 650 MHz RF system has been designed and developed by RRCAT which does not use frequency up/down conversion thus avoiding the difficulties associated with image frequencies. (one test on 650 MHz single-cell cavity performed). • Solid state RF amplifiers with output power of 500 W have been designed and developed in-house at 325 MHz, 650 MHz and 1.3 GHz to cater to these tests. 2 2

  3. Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015 Improvements made in VTS LLRF System • Use of Peak Power analyser, in place of diode detectors, to measure decay time of cavity. This reduces the errors associated with the nonlinearity of the diodes. • Use of RF signal generator as reference oscillator to allow the cable calibration at both 650 MHz & 1.3 GHz, at various power levels. • Optimum phase identification routine : • A software routine is developed to identify the optimum phase for locking the SRF cavity for quick identification of phase and optimum locking of PLL loop to the SRF cavity resonance frequency. • Two separate LLRF system cater for 650 MHz and 1.3 GHz, which allow quick changeover between these frequencies depending upon the cavity. 3 3 3

  4. Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015 Typical steps for RF tests in VTS at RRCAT • Sealed cavity is mounted on insert assembly & RF connections are made. • Insert assembly is lowered in VTS pit. Connections of top flange and RF cable connections are done and connections and resonance frequency is checked by VNA with adequate amplifiers, before cool down. • VNA tests are repeated with/without amplifier after filling liquid helium but before pumping at 4.2 K, followed by cable calibration and complete cavity characterization at 4.2 K. • VNA is used to identify resonance frequency, cable calibration and RF characterization is done at 2 K & 1.8K. • Decay measurement is performed using power meter and Qext2 is calculated. • Calculated value of Qext2 is inserted in VTS software and CW measurement is performed. • Graph between E and Q is displayed. 4 4 4

  5. Solid-state RF systems developed for VTS at RRCAT • Inhouse developed 500 W solid state RF power amplifiers at325 MHz,650MHz & 1.3 GHz. • The performance of the 650 MHz and 1.3 GHz solid state RF amplifiers has been found satisfactory during the test run of respective SCRF cavities. 1.3GHz & 650MHz LLRF systems in VTS control room 650 MHz LLRF system designed and developed at RRCAT 1.3 GHz, 500W SSPA 650 MHz, 500W SSPA installed at RRCAT VTS site Preparations of cavity in VTS insert 5 5 5 5 Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015

  6. Results of 1.3 GHz single-cell Nb SRF cavity at 2 K & 1.8 K performed on JAN 31, 2014 at RRCAT VTS Quench @36.7MV/m Mp Quench @36.2MV/m Quench @36.2MV/m 6 6 6 6 Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015

  7. Results of first 650 MHz single-cell cavity test performed on Jan 16, 2015 at RRCAT VTS 7 Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015

  8. Initial information needed from FNAL • Information about latest status of Fermilab VTS RF system at 650 MHz and 1.3 GHz. • Upgrade plans, if any, for Fermilab VTS RF system. 8 Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015

  9. Thank You 9 Raja Ramanna Centre for Advanced Technology IIFC Meeting Feb 24-25, 2015

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