1. 1 Potential Hardware Improvements, Related R&D Wieman RNC LBNL TPC Review Friday 6 October 2006

2. 2 Issues, prioritized? list  Inner field cage, single gap fluctuating resistance  Outer field cage, single gap fluctuating resistance  Grid Leak, space charge distortion  Reduction of space charge distortion, increase drift field  Use corrected pad response function to improve tracking precision

3. 3 Inner field cage, single gap fluctuating resistance  The problem: A short developed in the inner field cage that unlike others could not be found and removed. Solution was to lock down the short and increase neighbor resistors to restore undistorted drift field. Later developed reduced resistance with humidity dependence. It was assumed that epoxy used was bad and bridged a gap. Inner field cage outside of drift volume Resistor chain cover

4. 4 Field cage currents in IFCW (blue) and IFCE (brown) showing excess current and noise in IFCE. IFC East variable resistance  Distortion now being minimized by adjusting current to hold most of the cage to the proper boundary condition uPossible because flaw is very close to the sector  Proposed solution: clean up epoxy  Risk: low  Effort: relatively low – remove SVT with cones to access uWill be done when TPC rolls out and SVT is removed For scale one resistor error 420 nA B. Stringfellow

5. 5 Field cage currents in OFC west (blue) and OFC east (brown) showing the bi- stable excess current in OFC west Outer field cage West bi-stable problem  Distortion small, but can be detected  Cause unknown, concern if becomes worse  Action being considered: uDevelop small contact probe to insert into insulating gap to locate z position uDevelop clean techniques with outward air flow when opening the gap uKnowing z position allows precise correction  Risk: could introduce dust or relocate existing dust and cause a corona leak For scale one resistor error 420 nA B. Stringfellow

6. 6 Outer field cage West bi-stable problem  To replace resistor in the outer field cage uRequires putting people inside TPC uOpening of resistor chain cover uDifficult and very risky

7. 7 Ground stripes Fix grid leak to reduce positive ion distortions? A. Lebedev

8. 8 Inner sector A. Lebedev

9. 9 Outer sector A. Lebedev

10. 10 Fix grid leak to reduce space charge distortion  Tasks (if work done outside TPC) uRework sector tool uConstruct clean rooms uDevelop and fab barrier electrodes uStrip sectors uRemove inner sectors and add electrode uReinstall sectors uReinstall cooling manifolds uReinstall electronics and test  Effort: 44 man months  TPC down time: 6 months  Cost (if sector and electronics handling labor free) : 424 k$  Risk significant, need to redevelop lost skills and know-how  Alternative approach – work inside – very risky, but could save effort

11. 11 Increased drift field to reduce space charge distortion  Double field and reduce distortion by ~4 uDouble positive ion velocity reduces space charge by two uIncrease drift E field component relative to space charge E field  Requires C 2 F 6 gas in the 5 cm outer field gas insulator gap uPresent gas – nitrogen uPresent voltage – 27 kV  One problem – a leak between drift volume and the insulator volume which prevents use of C 2 F 6 uWe observer rapid onset of CH 4 in the insulator gap when TPC pressurized to 2 mBar operating pressure E drift E space charge Distorted path

12. 12 Increased drift field to reduce space charge distortion  Alexei Lebedev would like to try to find the leak using gas transit times – an interesting approach, but one would have to be lucky to find the leak. There is a lot of surface. Only if it is at the end joint could one ever hope to solve the problem.  Other risks uInner field cage hold off uCorona leaks uMore shorts between equipotential rings

13. 13 Additional improvements that have been considered  Correction for non-Gaussian pad response function – possible tracking improvements on 200 micron scale (A. Lebedev ) uMostly a software issue  Low frequency laser shots during particle runs to dynamically monitor space charge ( A. Lebedev ) uCould be done using a laser shutter  CF 4 -Ar TPC gas for modest improvement in transverse diffusion ( N. Smirnov ) uRequires higher drift voltage

14. 14 MAGBOLTZ result for Ar+CF4 gas mixture ( 2.5, 5., 7.5, 10. %) in 0.5 T magnetic field, and data for P10. N. Smirnov

15. 15 END  No easy or free lunch