Wolfgang Anders, BESSY, Berlin CW Tests of TESLA cavities and RF-sources at the HoBiCaT Test facility at BESSY Wolfgang Anders, BESSY, Berlin BESSY FEL Layout HoBiCaT test facility CW Modules HOM problems Microphonics CW coupler tests CW transmitter

BESSY FEL Layout Full Energy 2.3 GeV Duty Factor CW BC1 (200 A) RF Photoinjector (65 A) BC2 (2 kA) L2 753 MeV EXT1 L3 1020 MeV FEL1 Arc (240 A) 2300 MeV L4 FEL2 FEL3 EXT2 Collimators L1 + Booster (L0) 3rd harmonic cavity 219 MeV Full Energy 2.3 GeV Duty Factor CW Number of cavities per module 8 Number of modules 18 Accelerating field 16 MV/m (< 20 MV/m) Operating temperature 1.8 K Cavity quality (Q0) > 1.3 x 1010 or higher Dynamic losses at 1.8 K per cavity < 30 W Dynamic losses at 1.8 K per module < 151 W Total dynamic losses at 1.8 K < 3 kW

HoBiCaT Cavity Test Facility The HoBiCaT Test facility include all things you need for measurements of cw-related topics of TESLA type cavities: Cryogenics 80 W @ 1.8 K Cryostat for two cavities Cavities Tuner CW Transmitter Low level electronics

Cw Bottelnecks in LHe tank Bottelnecks in the LHe tank ca. 80 cm DT(0.5 W/cm2) = 8.8 mK T = 1.802 K, Tsat = 1.824 K 0.5 W/cm2 DT = 2 mK 1.8 K, 16.38 mbar Want to avoid boiling in He-II, otherwise danger of microphonics Rule of thumb: Heat flux in 1.8 K He-II must be less than 1 W/cm2 to avoid boiling To be verified experimentally in HoBiCaT

Microphonics vs. Heater power Microphonic detuning (sigma Hz) versus heater power of a foil heater on the Cavity vessel O. Kugeler

Cryogenics versus heater power

TESLA  CW Modul TESLA: 10 modules (string) form one string All supply and return lines span the entire string Supply by one JT valve Total dissipated power per string = 150 W ~ 1 CW Module  Should have one supply per CW module TESLA: One conn. between 2-phase line and GRT / module (15 W)  Flow in 2-phase line more „relaxed“ than in CW Module  2-phase line should be as big as possible  Add connections TESLA: GRT handles gas from 16 strings = 2.4 kW  Size of GRT should be OK for CW operation

BESSY CW-Module Layout Enlarged chimney to 90 mm ID Reservoir with heater and level meter. Heater likely to be distributed along module Enlarged 2-phase supply line to 100 mm ID No connection between modules Additional connection GRP unchanged

Pressure Drop Helium plant in the middle of the linac  pressure drop on GRP low and vapor velocity well below 4 m/s Section 4 Section 3 Section 2 Section 1 EXT1 Arc+BC2 BC1 Helium plant VB DB Modules 1-8 9-18

HOM damper problems  We are working on the problem !!! Slight heating of HOM Q-switches seen 10-14 MV/m Test with saphire feedthrough from DESY/JLab Measurements extremely preliminary  show no data Next steps: Instrumentation Improve cooling Determine source of heat Without cable cold intercept in cable More ideas ???  We are working on the problem !!!

Microphonics measurements at HoBiCaT Microphonics compensation for 9-cell superconducting TESLA cavities using a Piezo-tuning system: PLL based measurement setup Piezo-tuning system included into the TTF-Saclay-I tuner design O. Kugeler, J. Knobloch, A. Neumann

Microphonics measurements at HoBiCaT Microphonics spectrum: LHe pressure fluctuations, mechanical resonances Mech. resonance <1Hz due to LHe pressure Example of integrated microphonics measured at 1.8 K f1/2=21.6 Hz Microphonics spectrum at 1.8 K without compensation O. Kugeler, J. Knobloch, A. Neumann

Microphonics compensation Feedforward and feedback compensation tested: W. Anders, O. Kugeler, J. Knobloch, A. Neumann

Warm coupler mounted on HoBiCaT flange CW TTF III coupler test Inner conductor bellows Test the coupler at room temperature on test stand while measuring the temperature of ceramic windows (IR sensor) and inner conductor (PT 1000) Critical component is the inner-conductor bellow test under cryogenic (standard operating) conditions Mount coupler test stand in HoBiCaT Test Facility and operate at LN2 temperature Standing wave and travelling wave tests Test with and without (normal) air cooling of inner conductor Example of the temperature rise as a function of time as RF power is applied. Warm coupler mounted on HoBiCaT flange

CW coupler test Thermal time constant is very long (50 mins) Results and Conclusions Temperature rise per kW of applied power at the PT1000 sensor in the inner conductor All tests in HoBiCaT except the one marked „on the test stand.“ Thermal time constant is very long (50 mins) Inner conductor bellows region becomes very hot. We imposed a limit of 300 C, but outgasing limits to about 180 C. Interlock trips due to vacuum and reflected power limited the tests (but these are not a fundamental limit). Extrapolation: 10 kW TW and 5 kW SW operation with existing coupler should be possible. No significant difference seen between warm and cold tests  Cold window ceramic is not the limiting item for heat conduction Tests up to 10 kW (klystron limited) were also done with the inner conductor air cooled. If the results are extrapolated, 25 kW SW operation is feasible

Klystron IOT The Efficiency of a klystron and IOT at peak power is comparable, but in the typical operating range the IOT has much better efficiency due to the class B operation mode.

Installed RF Transmitters at HoBiCaT CW Transmitter Development for the BESSY FEL Development steps for 1.3 GHz tranmitter IOT Prototype Power supply 10 kW Klystron 10 kW klystron transmitter 10/2004 Stability tests of power supply with IOT protoype at reduced power level 04/2005 Optimized IOT transmitter at full power 12/2006 Price optimized prototype for series production 8/2007 High precision low level electronics using FPGA micro processor technique in test phase Installed RF Transmitters at HoBiCaT

Conclusion HoBiCaT is running producing many results on cw-operation mode related issues of TESLA cavities. Measurements are ongoing. We are open for questions on cw-related issues. Suggestions are welcome! Please contact our team: knobloch@bessy.de anders@bessy.de kugeler@bessy.de neumann@bessy.de