An Optimal Procedure for RF Conditionning at the FREIA Laboratory 26th Oct. 2017 Han Li, Behalf of FREIA team Uppsala University 2/22/2019

A Conditioning System Acquisition system, control system and feedback can help to adjust and control the testing parameters with respect to the conditions. Condition: defined by experts ( interlock trig threshold and auto conditioning threshold) Acquisition system: RF power, vacuum levels and all the interlocked signals. Control system : software controlling (duty and peak power of pulse, switching on and off the RF power, and resetting system)

RF-Vacuum Feedback system Fig. Layout of a simple RF-Vacuum Feedback system The main idea of a RF-vacuum feedback system is to regulate RF power as a function of vacuum pressure around the coupler. All unexpected phenomenon on the coupler cause a bad vacuum. The change of the coupler vacuum is easier, fast enough and change significantly when harmful activities happen. Not highly depend on the installation position.

Hardware list The main devices for the RF conditioning process are: Signal Generator Power Meter Vacuum Gauge Arc Detector Electron Detector Fast RF Interlock Switch

Conditioning program An automatic conditioning system, which consists of an acquisition system, a control system based on LabView software and feedback was developed at FREIA. Key parameters are primarily set. This system has been verified on ESS spoke package. The overall FREIA system worked as expected. The FREIA automatic RF conditioning mainly collaborates with EPICS system. A new conditioning program based on EPICS is undergoing. The whole program consists of several modules, to make debugging easier and future upgrading more flexible.

Main Parameters of Spoke Cavity Conditioning For different cavity, parameter would varied. This depend on the highly likely outgassing region. Parameter value Loop interval time(s) 1 Pulse repeat rate (Hz) 14 Power increase increment (dB) 0.1 Power TB increment (dB) Vacuum upper limit (mbar) 1e-6 Vacuum lower limit (mbar) 5e-7 RF Lower limit (dBm) -23.3 (generator) 100 W (coupler) RF Upper limit (dBm) -3.2 (generator) 120 kW (coupler) Initial pulse length (µs) 20 pulse length step 20 µs, 50 µs, 100µs, 200 µs, 500 µs, 1ms, 1.5 ms, 2 ms, 2.5ms, 2.86ms

Software logic

Stats The FREIA automatic RF conditioning control program is based on LabView platform, with functions reading or publishing data from/into EPICS system. The whole program consists of several modules, to make debugging easier and future upgrading more flexible. Initialize state Increase state Hold state Decrease state Vacuum upper limit state Fault state Ramp after fault state End state

Conditioning procedure 1. RF Calibration • Time Domain Reflectometer (TDR) cables check • Directional Couplers/ Circulators: get calibration data • Calibrate RF power measurement cables/devices at 352.21MHz/704.42MHz • Make RF calibration summary table 2. Technical Interlock/Sensors •Check the sensors (vacuum, arc detector, electron detector ,water flow, temperature, etc) • Validation of RF switch • Set the hardware interlock thresholds • Set the forward power hardware limite /interlock if need 3. RF source/Waveguides/LLRF • RF station (Klystron)/LLRF check on the load • Waveguides visual check • System check check at low power 4. Conditioning software • Validation of software arithmetic • Validation of the communication between EPICS and Labview • Set conditioning initial parameters • Validation of data aquisition

Conditioning procedure (cnt.) 5. Coupler conditioning at warm • Start with low pulse duration • Start with lowRF amplitude • Auto cycle at the nominal power length and amplitude • Monitor the field in the cavity 6. Cooldown to 2 K 7. Cryo check • Check and monitor the helium flow for the coupler cooling 8. Coupler conditioning at cold (on/off resonance) • Tune/detune the cavity. Frequncy sweeping around the resonant frequency at low power first ( only for ”on resonance conditioning”). • Start with low RF amplitude • Continiuelly running on the nominal pulse length and amplitude for several hours.