Development of a Hybrid Power Supply and RF Transmission Line for SANAEM RFQ Accelerator

Abstract

SANAEM Project Prometheus (SPP) has been building a proton beamline at MeV range. Its proton source, two solenoids, and a low energy diagnostic box have been already manufactured and installed. These are going to be followed by a 4-vane RFQ to be powered by two stage PSU. The first stage is a custom-built solid state amplifier providing 6 kW at 352.2 MHz operating frequency. The second stage, employing TH 595 tetrodes from Thales, will amplify this input to 160 kW in a short pulsed mode. The power transfer to the RFQ will be achieved by the means of a number of WR2300 full and half heightwaveguides, 3 1/8″ rigid coaxial cables, joined by appropriate adapters and converters and by a custom design circulator. This paper summarizes the experience acquired during the design and the production of these components.

Overview

SANAEM Project Prometheus(SPP) is Turkey’s first locally built proton accelerator, currently under construction. SPP’s proton source with 20 keV extraction potential has been installed, and it is going to feed a 4-vane Radio Frequency Quadrupole which will accelerate at least 1 mA of current from 20 keV to 1.3 MeV. The assembled LEBT consists of two solenoids and a compact beam diagnostics box capable of measuring beam current, profile and emittance. SPP RF Transmission Line is to provide power to operate low-beta acceleration cavity-RFQ. SPP operation frequency is determined as 352.2 MHz, and required power for the RFQ is 120 kW continuous mode but SPP will operate with the duty factor below 3%. To provide this power, a two stage amplification is considered. A transmission line and a circulator to transport the created power are designed and the assembly of manufactured parts is ongoing.

Solid State Preamplification

This custom designed and built circuit contains BLF-578XR high power transistors. This circuit amplifies RF signal at the order of 10 W to 1.7 kW with a pulse shorter than half of a second. We combine 8 of such circuits resulting in 6 kW in continuous mode or 10 kW in pulsed mode.

Tetrode

Homebuilt amplification board is followed by Thales’ TH595 tetrode. TH595 with its acceleration cavity TH 18595A is fed with 6 kW power to amplify the RF power to ~160 kW in a pulsed wave of a few ms.

Circulator

H-plane waveguide junction type of circulator has been designed by SPP-team to manage power flow and possible reflection. CST MWS based design is represented below and scattering parameters are calculated to be -55, -0.26, and -30 dB corresponding respectively to S11, S21, and S31. Two NG1601 ferrite disks has been ordered from Magnetics Group, USA, and these will be held by two aluminium disks inside the HH WR2300 circulator.

Waveguides, Converters

Depending upon SPP frequency of 352.2 MHz, WR2300 with full-half heights are used. Therefore, 3 1/8” coaxial rigid cables are also needed to bridge between the PSU, the HH circulator and the RFQ. Also, RF load, H and E-bends are produced. CST MWS is used for design and mostly local industry is asked for the production. They are assembled and tested, they operate with low loss of below -60 dB. Besides, insertion loss is better than -0.2 dB.

Outlook

SPP Power supply will be delivered in the second quarter 2015 and the transmission line is will be subjected to high power RF tests in the third quarter of 2015. The entire RF line is supposed to be tested in the end of 2015, and SPP is going to be fully operated in early 2016.