MKDV upgrade LIU-SPS ABT meeting V. Senaj, L. Ducimetiere, P. Faure November 4 th 2014

MKDV up-grade Motivation Proposed solution Present status Risks Cost estimation

Extraction and dilution of the beam

Present configuration Two 2 Ohm magnets driven by 3 composite switches from three 3 Ohm PFNs PFN nominal voltage of 60 kV; magnet current 15 kA with ±15% ripples In case of sparking energy of all 3 PFNs goes into spark and results in a total loss of kick

Magnet damage due to sparking Serious damage to magnet in case of sparking due to high energy stored in PFNs (5 50 kV) Machine down time to re-condition or repair magnet Irradiation of downstream equipment

Proposed solution Complete separation of 2 magnets: PFN – Switch – Magnet – TMR: Safer operation: keeping at least ½ of kick in case of sparking in one magnet Less energy in spark and hence less damage to magnet Possibility of individual PFN voltage adjustment in case of magnet weakness Replacement of gas switches by semiconductors: due to I.t product (+50 % compared to 3 switches) more robust thyratron would be necessary - risk of obsolescence; semiconductor switches preferred Reduction of complexity of supporting electronics (PS for heaters, reservoirs) Reduction of restart time (no heat-up time); Elimination of mercury hazard (ignitrons)

Present status Self healing capacitors for new PFN developed, produced and tested (AVX) Prototype of 2 Ohm PFN with adjustable coils built and tested Test of single ring gate GTO with PFN prototype and real magnet done Design of GTO stack ongoing (2 stacks of 10 GTOs in series; 2 branches of 2 series stacks in parallel); 40 GTO per PFN Design of fast triggering transformer with reduced stray inductance (topology similar to MKD one) ongoing Preliminary measurements shows magnet field rise time (2% - 85%) of ~ 1.2 – 1.3 µs (~ ns longer compared to composite switch) Test of current compression with saturation ferrite under preparation with the goal to gain ~ 50 ns of field rise time

New PFN with self-healing capacitors Use of self-healing capacitors (higher energy density) allowed to store 50% more energy in 30% less space (still many of old capacitors) Possibility to incorporate semiconductor switches into PFN

Adjustable coil with reduced stray field Original design with possibility to adjust coil inductance within +-5% Reduced stay field and hence coils mutual coupling and PFN cover influence Simplifies PFN adjustment

Solid state switch development

Measurement setup Magnetic field measurement with a pickup coil inside magnet and integration of the induced voltage by scope T_rise measured between 2% and 85% of the kick

GTO triggering current influence to Trise Trise = Itrig = 500 A & Vpfn = 2500 VTrise = Itrig = 1000 A & Vpfn = 2500 V Strong influence of the GTO trigger current on T_rise observed Very slow initial field build-up due to low GTO commutation speed

T_rise dependence on GTO voltage UPFN [V] T_rise [µs] Umag [V] GTO commutation starts very slowly compared to thyratron resulting in slower field rise around lower threshold of the T_rise measurement (2% level) In order to keep the rise time below 1.2 µs, the PFN output cell was modified compared to optimised simulation (output cell more capacitive) resulting in a field distortion and a peak voltage at the magnet entry ~ 13% higher than simulated one

In progress/ to be done Triggering transformers + semiconductor switchesdesign in progress Triggering system: depending on test of MKD type PTM - design of higher voltage/current triggering might be necessary Surveillance – discussion ongoing Control system: upgrade done during LS1; heavy modifications not expected GTO ~ 150 pcs to be acquired (50 GTO already delivered) Mechanical modification of existing 3 PFN tanks (1 done)

Provisionnal Budget

Conclusion Preliminary test shows magnetic field Trise (2% - 85%) < 1.2 µs within the range 100 V – 3 kV per GTO Full scale measurement to be done Importance of GTO triggering (>1 kA needed) Compromise between Trise and magnet entry voltage to be done Abort gap duration will need to be increased by ~ ns Some T_rise reduction expected with saturation coil (~ 50 ns)