H - ion source at the pre-acc R&D lab Update HINS Meson meeting January 20 th, 2011 L. Prost, C. Schmidt, D. Bollinger, R. Tomlin

2 Source specifications for HINS at Meson  From Beams-doc-3056-v1 “H - Ion Source Spec for HINS and Considerations for Project X H - Ion Source” (B. Webber)  50 kV  ±5% energy variation  10 mA  ≤ 0.25  mm mrad, rms, normalized  1 ms pulse length  Repetition rate: 10 Hz (max) 1 Hz preferred ?  Beam current variation: ≤ 15% droop; ≤ 5% rms in any 10  sec  Duty cycle: 0.1% (max)

3 Test stand for H - source  Was used by the Linac Dpt personnel to study their own version of the source  Different anode-to-extraction electrode gap 35 kV instead of 50 kV  Different aperture  Pulsed einzel lens (preliminary tests to be used as a chopper)  ‘LINAC-type’ source taken off the test stand and reconfigured for HINS purposes (and cleaned)  Anode-to-extraction electrode gap => 0.076”  Aperture => 0.08” diameter  Pumped down (12/25/10)  Arc formed & extractor PS operational (12/29/10)  Beam extracted and accelerated to 50 kV (1/5/11)  Not stable at this point; lots of sparking Conditioning

4 Operation at ~200  s pulse width  Default pulse width was ~200  s at 15 Hz  Easier than for a long pulse and at a lower rate  Beam current: mA with 10 kV on the extraction electrode Some discrepancy between the toroid measurement and the Faraday cup (FC) measurement  Still not very stable operation (1/7/11)

5 Operation at 1 ms pulse width (I)  After reasonable conditioning, switched to 1 ms pulse width  Rep rate: between 1 Hz and 3 Hz Trying to get a handle on the effects that the source/cathode temperatures have on the arc current and beam stability  Example: Several parameters tweaked throughout a day  Source heater temperature  Arc current  Gas pulse  Gas pulse – Arc pulse delays  … Extractor voltage [kV] Cathode temperature [°C] Source temperature [°C] Arc current [A]

6 Operation at 1 ms pulse width (II) Extractor voltage [kV] Cathode temperature [°C] Arc current [A] Source temperature [°C]  Achieved stable operation at 1 ms pulse width and 1 Hz on Friday (1/14/11)  Extractor voltage at 10 kV One discharge over 1h30: Seems to be more or less typical at this stage  Beam current: mA Line voltage [V] Beam current – toroid [mA] 1.5 hour span

7 Operation at 1 ms pulse width (III) Same nomenclature as for the previous slide  Increased extractor voltage to 15 kV  Did not find quite satisfactory settings for good stability over long periods of time… yet  Beam current: 28 mA (tor) - 36 mA (FC) 17 hours span

8 High voltage droop – HV measurements calibration  U acc = 50 kV, U extr = 15 kV, 1 ms, 1 Hz, U foc = 35 kV  Two measurements with different devices Resistive divider (permanent) HV probe (temporary) Resistive divider calibration (readback * 1.176) FC Toroid 16 traces average HV probe Resistive divider ~2.2 kV (~4.5%) Initial step down ~1.9 kV 50 kV power supply calibration < 1% w.r.t. HV probe Normal behavior for a toroid Correction can/will be applied offline Probably want to increase one capacitor 2-4×

9 Issues - Plan  Faraday cup and toroid give different current value  ~30% discrepancy (for V ext = 15 kV; FC > toroid ) Biases on FC checked  May be not an important problem for future use of the source  Plan (kinda)  Improve stability at V ext = 15 kV Not absolutely necessary since V ext = 10 kV already gives mA  More tuning for better understanding of important parameters  Some source characterization curves In particular I vs V ext  Phase-space measurements Different currents Several time slices –Beginning, middle and end of the pulse  Test new power supplies (Hays) and modulator (Saewert) End of February time frame ?

10 More details ?  HINS LogBook  HINS PD Ion Source/Hminus Ion Source/Test Stand Start up  INS PD Ion Source/Hminus Ion Source/Test Stand Startup INS PD Ion Source/Hminus Ion Source/Test Stand Startup